My 05 Envoy has no ballz. 0-60 times horrible!

[jrSS]

Also if I my add....temp. and elevation can decrease ur performance.

 

[Boricua SS]

Also if I my add....temp. and elevation can decrease ur performance.

^^ what we call DA (density altitude) in the racing world...

its just like all us SS folks that go racing... stock to stock in 1/4 mile times... some run 13.8's, 13.9's, 14.0's, all the way to 15's in the AWD SS'... why are we all different, when its 2WD against 2WD, and AWD against AWD??? just too many factors... air, outside temps, weight (meaning driver, passengers, cargo, gas, etc...) tires,.. all the way to a possible mechanical defect...

and to the OP, if your Voy has been this way since the day you bought it... then i think its safe to say that what ever is going on, is not harming anything.. but i can understand your frustrations...

 

[WarGawd]

First I just want to say that I am not calling you a liar, or assuming that you didn't hit 90mph in 23 seconds, but from the sounds of this and your vehicle gear ratio being 3.42 and mine being a 3.73, I should be hitting 0-60 in like 7-8 seconds and I am running 10-11 second times.

No offense taken..I am new to these too. And it was the fact that the higher geared trucks weren't hitting 0-60 times as fast as mine that troubled me. I agree they should be a tad faster than the 3.42 geared vehicles, ALL ELSE BEING EQUAL.

On the upper speed limit I reached, I'm not gonna stick to it hard n fast. I was clipping along pretty good, may have gotten nervous about how fast I was going in a 60 zone, and let up a touch on the gas a bit (ie letting it shift a bit sooner than it would have at WOT) and my attempt at a quick glance at the tach/speedo at the shift point may give me a bit of a flawed memory - maybe it was 85mph /140ish km/h. The point of my post was to support OP in his belief that his vehicle should be capable of more. It is worthy of a proper test.

However let me say the 6100rpm 53mph 86kph shift point at 6.875s is something I would be prepared to defend in court. THAT was the one I deliberately set out to pay attention to, having done that specific test sevearl times earlier in response to a thread on the TV site where it was a method suggested for checking a possible blocked cat. In the several previous runs using the (somewhat coarse) DIC timer, my WOT runs always reached 6100rpm shift at 86+/-1kph just before the timer hits the 7s mark.

And it should actually be easy for someone with a slight bit more knowledge than I to tie the vehicle speed to the engine rpm knowing the rear end ratio and the tranny drive ratios in various gears. My Envoy has fairly new stock sized P245/65/R17 Toyo Open country tires. GPS cross references suggest my speedo is accurate to +/- 1kph. With all that info, and with someone who knows what the standard shift rpm is for the 4.2L I6 going from 2nd to 3rd, we could calculate what the speed actually was. Too bad the video above stops where it does, I kinda feel like he's still picking up speed before the 2nd shift.

Cheers
WarGawd

 

[CaptainXL]

Also if I my add....temp. and elevation can decrease ur performance.

Yeah however as voymom indicated some days the performance feels better than others so this can't be elevation. I do notice that the truck is much more sporty in cooler < 75 degree days. I am thinking that there is a component on our trucks that is temperature sensitive that I have not replaced. About the only sensor I haven't replaced is a bad wheel sensor and my crankshaft position sensor. Due to the fact that I know my abs needs a new part yet I don't have any codes concerns me a bit. The fact that a catalytic converter can be partially clogged and reduce performance to that of a 2 cylinder lawn mower yet not show a cel is disconcerting to say the least.

 

[Sparky]

I notice the temperature and humidity effect too. Dry air at 75 is pretty good. Get it humid though and not as good. Make it 90+ and really humid, then kick the AC on, and it is really slow and grumpy

 

[jrSS]

I notice the temperature and humidity effect too. Dry air at 75 is pretty good. Get it humid though and not as good. Make it 90+ and really humid, then kick the AC on, and it is really slow and grumpy

I agree. 110%

 

[Voymom]

I notice the temperature and humidity effect too. Dry air at 75 is pretty good. Get it humid though and not as good. Make it 90+ and really humid, then kick the AC on, and it is really slow and grumpy

I agree also....The days that I can't seem to pass a Ford escort are on the days when it is 80+ with a high percentage of humidity in the air.

I guess now the question still remains as to what is "normal" for each gear ratio assuming the truck is 100% stock in every way? Or how would you determine that the lack of power is environmental or a performance issue? How would the stealership/shop even test a truck if there are so many factors such as climate involved? Would you just start playing the elimination game? Check certain things like the cat, fuel pump etc...and eliminate those as possible source? And if everything else is fine and in tip top shape, blame it on the weather and of course GM

I'm a woman....I read way to much into things but it is a very interesting topic to say the least.

 

[WarGawd]

On the upper speed limit I reached, I'm not gonna stick to it hard n fast.

You'll see in a moment that I was actually quite accurate with that observation.

However let me say the 6100rpm 53mph 86kph shift point at 6.875s is something I would be prepared to defend in court.

OTOH, I'm sorta glad nobody took me up on that in court, I was a little bit off (but not horribly), and I kinda know now what happened.

Lemme explain it all in detail:

First, I did look into the info required to calculate speed from engine rpm. From the VIN comparisons thread at the old site I looked up what my tranny actually is:

RPO code M30 = 4L60E 4 spd automatic with electronic shift. According to Wikipedia the tranny gear ratios are as follows (and I believe this applies to a huge majority of all of our TrailVoys):

Gear ratios:

1 2 3 4 R
3.059 1.625 1.000 0.696 2.29


From a little research at TireRack, the stock sized (on XL anyway) P245/65/R17 tires range from 702 to 708 revolutions per mile (My Toyo's show at 703). I averaged that out to 705 (+/- 3) which introduces at most a 0.4% error, or about 1/4 mph at 60mph.

The formula for finding speed in mph from engine rpm is:

Engine RPM x 60 min/hr x 1/Tranny Ratio x 1/Rear end ratio x 1/Tire revolutions per mile. An example:

In an earlier post I said the 1-2 shift at WOT was at 6100rpm, which I believed occurred at 86kph/53mph. The calculation shows

6100rpm x 60 min/hr x 1/3.059 x 1/3.42 x 1/705 = 49.62mph (80kph). What I think happened in my earlier tests is that by focusing on the shift, by the time I refocused on the speedo (while making sure I stayed on the road), I had gained a bit more speed. I may have also had a slight downhill grade, but that would only have improved the TIME it took to reach that point, not altered the speed of travel at which the shift occurs (the PCM doesn't know you're going downhill). Keep in mind also that I was reading off the tach, and the shift point may not be EXACTLY 6100. If it were +/- 50rpm that would result in a difference of about 1/3mph, relatiively small for our purposes here.

2nd example: Assuming I really did keep it WOT in the audio test above, and assuming that it shifted at 6100rpm again (cuz I never really got to watch that), what should I expect the speed to be at that point?

6100rpm x 60 min/hr x 1/1.625 x 1/3.42 x 1/705 = 93.41mph (150kph)

So this morning I went out and videoed 2 runs at WOT over the same section of flat road, where run #2 was the reverse direction of run #1 to avg out any possible road incline/descent. I also decided to use the Trip B tripmeter on the DIC to approximate the 1/4 mile runtimes / speeds. (1/4 mile = 402.3m or just a shade past the point where the tripmeter hits 0.4km in my case). Here is a summary of the results, videos to be posted somewhere later when I figure out where to host them:

Run #1:
(Times mentioned below were obtained by watching the video in 0.03x slow motion , using VLC media player...they're pretty damn close but a proper video editor would allow someone to pin it down more accurately)

{aside - my Nokia N8 records 720p video @30fps, so this way realtime playback is very close to 1 fps, so I can physically COUNT the number of frame updates past an even second marker to an event of interest}

Mashed the throttle a shade past the 0:41s mark of the video.
1-2shift occurs at 6100 rpm as expected, a shade past the 0:48s mark of the video. With the video it's easier to see this really does occur at 80kph (50mph)

Watching as close as I can, I pegged the 96/97 km/h (60mph) point just a bit past the 0:51s mark of the video, making my 0-60 time about 10s. Working backwards with the formula, I can get the expected tach reading: 60mph*705*3.42*1.625/60min/hr = 3918rpm - I would say the video shows it to be a little over 4k in this run, still probably close enough for the girls I go out with!

Tripmeter hit 0.4km right at the 0:59s mark of the video, tach is a bit blurry but looks pretty close to 5400rpm & speedo shows 130kph almost bang on. Result is 1/4 mile time of ~18 - 18.5s at 81mph. Double check using above formula says 5400rpm x 60 min/hr x 1/1.625 x 1/3.42 x 1/705 = 82.69 mph (133 kph), so both are in pretty good agreement.

Finally, the 2-3 shift does indeed occur at 6100 rpm, and from the result above I expected that to be at a speed around 93mph (150 kph). The shift occurs just a bit past the 1:04 point of the video ( a few frames got wiped out by sun shining thru the trees, but if you watch close you can catch it. So it was right aroud 23s in very close agreement with my previously mentioned audio test. The speedo indicated 146-147 kph (91mph) as close as I can tell, again in very close agreement with what I calculated above.

Run #2 (reverse direction):
(Times mentioned below were again obtained by watching the video in 0.03x slow motion, using VLC media player)

Floored the throttle almost exactly at the 0:27s mark of the video.
1-2shift occurs at 6100 rpm as before, a shade past the 0:34s mark of the video. Speedo indicates ~79kph (49mph)

Tripmeter hit 0.4km right at the 0:45s mark of the video, tach again looks pretty close to 5400rpm & speedo shows ~131kph almost bang on. Result is 1/4 mile time of ~18 - 18.5s at 81mph.

Watching closely for the 60mph mark, I would put it right around the 0:37s mark, tach again showing a bit over 4k, 0-60 ~ 10s again

The 2-3 shift hits 6100 rpm again just past the 0:50s mark of the video. The speedo indicated right around 147 kph (91mph).

These were recorded while carrying all the same junk as my audio test above, plus I don't mention in the video but yes the guage is correct and I really do have a full tank of gas.

So CaptainXL, since we have the same truck I really would say you are justified in expecting more. Hope this helps you and others looking for baseline comparisons. I'll find a spot for the videos and U/L them after work tonight.

Cheers all,
WarGawd

 

[SAR85]

I sense a scientist or engineer in our midst! That's a great evaluation, hopefully it will be helpful to others.

I would imagine if you lost 2-3 hundred pounds in cargo/fuel you time would be closer to 9 sec.

 

[Sputnik312]

You'll see in a moment that I was actually quite accurate with that observation.



OTOH, I'm sorta glad nobody took me up on that in court, I was a little bit off (but not horribly), and I kinda know now what happened.

Lemme explain it all in detail:

First, I did look into the info required to calculate speed from engine rpm. From the VIN comparisons thread at the old site I looked up what my tranny actually is:

RPO code M30 = 4L60E 4 spd automatic with electronic shift. According to Wikipedia the tranny gear ratios are as follows (and I believe this applies to a huge majority of all of our TrailVoys):

Gear ratios:

1 2 3 4 R
3.059 1.625 1.000 0.696 2.29


From a little research at TireRack, the stock sized (on XL anyway) P245/65/R17 tires range from 702 to 708 revolutions per mile (My Toyo's show at 703). I averaged that out to 705 (+/- 3) which introduces at most a 0.4% error, or about 1/4 mph at 60mph.

The formula for finding speed in mph from engine rpm is:

Engine RPM x 60 min/hr x 1/Tranny Ratio x 1/Rear end ratio x 1/Tire revolutions per mile. An example:

In an earlier post I said the 1-2 shift at WOT was at 6100rpm, which I believed occurred at 86kph/53mph. The calculation shows

6100rpm x 60 min/hr x 1/3.059 x 1/3.42 x 1/705 = 49.62mph (80kph). What I think happened in my earlier tests is that by focusing on the shift, by the time I refocused on the speedo (while making sure I stayed on the road), I had gained a bit more speed. I may have also had a slight downhill grade, but that would only have improved the TIME it took to reach that point, not altered the speed of travel at which the shift occurs (the PCM doesn't know you're going downhill). Keep in mind also that I was reading off the tach, and the shift point may not be EXACTLY 6100. If it were +/- 50rpm that would result in a difference of about 1/3mph, relatiively small for our purposes here.

2nd example: Assuming I really did keep it WOT in the audio test above, and assuming that it shifted at 6100rpm again (cuz I never really got to watch that), what should I expect the speed to be at that point?

6100rpm x 60 min/hr x 1/1.625 x 1/3.42 x 1/705 = 93.41mph (150kph)

So this morning I went out and videoed 2 runs at WOT over the same section of flat road, where run #2 was the reverse direction of run #1 to avg out any possible road incline/descent. I also decided to use the Trip B tripmeter on the DIC to approximate the 1/4 mile runtimes / speeds. (1/4 mile = 402.3m or just a shade past the point where the tripmeter hits 0.4km in my case). Here is a summary of the results, videos to be posted somewhere later when I figure out where to host them:

Run #1:
(Times mentioned below were obtained by watching the video in 0.03x slow motion , using VLC media player...they're pretty damn close but a proper video editor would allow someone to pin it down more accurately)

{aside - my Nokia N8 records 720p video @30fps, so this way realtime playback is very close to 1 fps, so I can physically COUNT the number of frame updates past an even second marker to an event of interest}

Mashed the throttle a shade past the 0:41s mark of the video.
1-2shift occurs at 6100 rpm as expected, a shade past the 0:48s mark of the video. With the video it's easier to see this really does occur at 80kph (50mph)

Watching as close as I can, I pegged the 96/97 km/h (60mph) point just a bit past the 0:51s mark of the video, making my 0-60 time about 10s. Working backwards with the formula, I can get the expected tach reading: 60mph*705*3.42*1.625/60min/hr = 3918rpm - I would say the video shows it to be a little over 4k in this run, still probably close enough for the girls I go out with!

Tripmeter hit 0.4km right at the 0:59s mark of the video, tach is a bit blurry but looks pretty close to 5400rpm & speedo shows 130kph almost bang on. Result is 1/4 mile time of ~18 - 18.5s at 81mph. Double check using above formula says 5400rpm x 60 min/hr x 1/1.625 x 1/3.42 x 1/705 = 82.69 mph (133 kph), so both are in pretty good agreement.

Finally, the 2-3 shift does indeed occur at 6100 rpm, and from the result above I expected that to be at a speed around 93mph (150 kph). The shift occurs just a bit past the 1:04 point of the video ( a few frames got wiped out by sun shining thru the trees, but if you watch close you can catch it. So it was right aroud 23s in very close agreement with my previously mentioned audio test. The speedo indicated 146-147 kph (91mph) as close as I can tell, again in very close agreement with what I calculated above.

Run #2 (reverse direction):
(Times mentioned below were again obtained by watching the video in 0.03x slow motion, using VLC media player)

Floored the throttle almost exactly at the 0:27s mark of the video.
1-2shift occurs at 6100 rpm as before, a shade past the 0:34s mark of the video. Speedo indicates ~79kph (49mph)

Tripmeter hit 0.4km right at the 0:45s mark of the video, tach again looks pretty close to 5400rpm & speedo shows ~131kph almost bang on. Result is 1/4 mile time of ~18 - 18.5s at 81mph.

Watching closely for the 60mph mark, I would put it right around the 0:37s mark, tach again showing a bit over 4k, 0-60 ~ 10s again

The 2-3 shift hits 6100 rpm again just past the 0:50s mark of the video. The speedo indicated right around 147 kph (91mph).

These were recorded while carrying all the same junk as my audio test above, plus I don't mention in the video but yes the guage is correct and I really do have a full tank of gas.

So CaptainXL, since we have the same truck I really would say you are justified in expecting more. Hope this helps you and others looking for baseline comparisons. I'll find a spot for the videos and U/L them after work tonight.

Cheers all,
WarGawd

^^ we got ourselves a Stephen Hawkins lol damn nice work bro

 

[CaptainXL]

So CaptainXL, since we have the same truck I really would say you are justified in expecting more. Hope this helps you and others looking for baseline comparisons. I'll find a spot for the videos and U/L them after work tonight.

Cheers all,
WarGawd

Ok. Thanks for that.

 

[WarGawd]

I sense a scientist or engineer in our midst!

Given the jabs taken at the engineers for some of the really dumb design ideas on these trucks I was kinda hoping to hide a bit. Guess that kind of anal retentive attention to detail doesn't go unoticed though.

^^ we got ourselves a Stephen Hawkins lol damn nice work bro

Kind of funny/ironic that your screenname is sputnik...I'm an aerospace engineer, but Hawkings still has an IQ I can't calculate!! Thanx though.

Ok. Thanks for that.

Not so fast Cap'n....I SAW the pre-edit tongue-in-cheek comment (something about positronic collision speeds or something?!?!) No worries, I laughed.

And lastly, here's the videos I promised:

[video=youtube;obsNLG7wcyo]http://www.youtube.com/watch?v=obsNLG7wcyo&feature=channel&list=UL[/video]

[video=youtube;d9jRkqSgilA]http://www.youtube.com/watch?v=d9jRkqSgilA&feature=channel&list=UL[/video]

Enjoy

 

[mubai]

Looks like 9 sec for me (0:26-0:35). Ehh...not bad for 187K miles.

[video=youtube;RC7ad3yh-bE]http://www.youtube.com/watch?v=RC7ad3yh-bE[/video]

 

[WarGawd]

Looks like 9 sec for me (0:26-0:35). Ehh...not bad for 187K miles.

TBH it looked to me like 10 (25 -35) but it'll be hard to pin down exactly without really looking at the video closer. And I believe yours is a SWB so just the weight diff alone should make for some improvement over the LWB models....it may help OP to know what your rear end gears are so he can see where he fits in the grand scheme of things.

 

[mubai]

TBH it looked to me like 10 (25 -35) but it'll be hard to pin down exactly without really looking at the video closer. And I believe yours is a SWB so just the weight diff alone should make for some improvement over the LWB models....it may help OP to know what your rear end gears are so he can see where he fits in the grand scheme of things.

If you scroll the video time bar to the right to 0:26, you'll see the needle just starts to move. Either way 9 or 10 seconds, it will get me enough power to get on the on the ramp.

REAR AXLE - 3.42 RATIO

 

[Jkust]

If you scroll the video time bar to the right to 0:26, you'll see the needle just starts to move. Either way 9 or 10 seconds, it will get me enough power to get on the on the ramp.

REAR AXLE - 3.42 RATIO

Wasn't the difference between the XL and the swb less than 300lbs?

 

[WarGawd]

Wasn't the difference between the XL and the swb less than 300lbs?

A quick search with Google got me these results:

2005 Envoy XL SLT 4x4: 4954lbs curb weight

2005 Envoy SLE 2WD: 4417lb curb weight

A difference of 537 lbs in that example...I guess YMMV, so you may be correct at 300 lb difference for any 2 particular vehicle configurations. Other variables (full / empty tank, passengers or not, tools and gear or not) may make the difference more pronounced too.

In any event all I was suggesting was that some weight savings for vehicles with same engine/rear end should translate to slighly better times.

 

[Jkust]

A quick search with Google got me these results:

2005 Envoy XL SLT 4x4: 4954lbs curb weight

2005 Envoy SLE 2WD: 4417lb curb weight

A difference of 537 lbs in that example...I guess YMMV, so you may be correct at 300 lb difference for any 2 particular vehicle configurations. Other variables (full / empty tank, passengers or not, tools and gear or not) may make the difference more pronounced too.

In any event all I was suggesting was that some weight savings for vehicles with same engine/rear end should translate to slighly better times.

I get different numbers depending on where I look so I can't be sure. I get a 360 lb difference on when both are 4x4's which I suppose is like an empty xl compared to a swb with a couple passengers. Also intersting then is when you compare some of the other in the lineup the swb, I6 is over 2700lbs and of course then it adds 60lbs additional lbs for the v8.

 

[gmcman]

Capt....I cannot view your 0-60 vid but 14 sec is way off, needless to say.

Have you checked your air filter or performed an exhaust pressure test? I would think 9-10 sec, maybe 11 at the most.

How old is the fuel and have you replaced or checked the operation of the CPAS actuator?

Has your MPG dropped recently and/or do you have any brakes dragging?

Is this vid on YouTube or can you repost it?

 

[CaptainXL]

Capt....I cannot view your 0-60 vid but 14 sec is way off, needless to say.

Have you checked your air filter or performed an exhaust pressure test? I would think 9-10 sec, maybe 11 at the most.

How old is the fuel and have you replaced or checked the operation of the CPAS actuator?

Has your MPG dropped recently and/or do you have any brakes dragging?

Is this vid on YouTube or can you repost it?

I am running a few more tests including checking all of what you said again. The truck feels heavy off the line. My neighboor had his throttle changed out for something similar and I am looking into that. Will get back to you all in a few days or over weekend.

 

[gmcman]

This would generally throw a code if there was a problem with continuity but try removing your TB harness and replacing it about 5 times or more....in case there may be a hint of corrosion on the terminals.

Likely not the cause but I have cured a few electrical issues like that in the past....even a couple gas HVAC components.

 

[C-ya]

Capt....I cannot view your 0-60 vid but 14 sec is way off, needless to say.

Is this vid on YouTube or can you repost it?

I had trouble viewing it, too, so I searched for his username and found the vid. Here ya go.

[video=youtube;3KnQkr0aFhA]http://www.youtube.com/watch?v=3KnQkr0aFhA&feature=plcp[/video]

 

[gmcman]

Thanks, I tried searching but didn't find it.

Capt.....can you post another vid, from a stop...without the music?

What does the air filter look like, when was the fuel filter and the plugs changed?

 

[CaptainXL]

Thanks, I tried searching but didn't find it.

Capt.....can you post another vid, from a stop...without the music?

What does the air filter look like, when was the fuel filter and the plugs changed?

Air filter new. There is no fuel filter on 05 +. Factory Plugs changed at 110K. Found a nasty coil the other day. No CEL on and not misfiring yet but the corrosion was due to me not putting the gasket on right and water got in the spark plug well. Different coil was installed but no difference in performance.

View attachment 22794

Will post another vid soon.

 

[WarGawd]

Hello everyone. I've been having an issue with my 05 envoy xl I guess since the day I got it. When I hook my scantool up and use torque to see my throttle position it max's out at about 80%. If you have any ideas please let me know. Just about at my limits troubleshooting this thing! Thanks.

It may be written elsewhere, but remind us how long you've owned it, how many miles you've driven it, and total mileage now??

It's a long shot but here's where I'm going with this...my old Montana developed a problem once where the o-ring in both calipers developed a ridge that would on occasion give rise to some pretty serious pad drag on the rotors. It wasn't as consistent as your issue seems to be, but since we're grasping at straws...

My scan tool should show up in the next week or so and I'll be looking for excuses to play with it, so I'll see what I can do to give you a cross reference on the throttle body plate position.

 

[CaptainXL]

From my experience its definitely not my brakes because I just rebuilt the calipers and the wheels spin freely with no drag noise. The truck just feels heavy as if there isn't enough torque. About the only thing I can think of that wouldn't throw a CEL is a clogged exhaust or a fubar ecu/pcm. Possibly leaking exhaust valves of bad compression but I am checking that this weekend. We will see. Again I have calculated my horsepower and its about 130. Almost like my engine is being governed but with absolutely no reason to be so.

I have noticed that I have at least one bad wheel sensor because the abs activates at slow speed. I'm wondering if the vehicle goes into some type of limp mode if an underlying subsystem such h as the abs goes wonky. I know it sounds like a wacky conspiracy but I would piss on a spark plug if I thought it would do any good.

 

[NJTB]

From my experience its definitely not my brakes because I just rebuilt the calipers and the wheels spin freely with no drag noise. The truck just feels heavy as if there isn't enough torque. About the only thing I can think of that wouldn't throw a CEL is a clogged exhaust or a fubar ecu/pcm. Possibly leaking exhaust valves of bad compression but I am checking that this weekend. We will see. Again I have calculated my horsepower and its about 130. Almost like my engine is being governed but with absolutely no reason to be so.

I have noticed that I have at least one bad wheel sensor because the abs activates at slow speed. I'm wondering if the vehicle goes into some type of limp mode if an underlying subsystem such h as the abs goes wonky. I know it sounds like a wacky conspiracy but I would piss on a spark plug if I thought it would do any good.

Damn, thats dedication.

 

[Jkust]

Again I have calculated my horsepower and its about 130.

Hold on there, I didn't see where you mentioned you calculated your HP. How would you go about doing that without a dyno to measure the actual HP?

 

[CaptainXL]

Hold on there, I didn't see where you mentioned you calculated your HP. How would you go about doing that without a dyno to measure the actual HP?

If I use the Available 0-60 calculators on the web and put in a 9 second 0-60 time given the curb weight of an XL or ext then it comes out to roughly 275 HP. I just adjust the HP variable to get my 0-60 time. The calculator uses an average of multiple vehicle profiles to come up with the 0-60 times.

 

[WarGawd]

From my experience its definitely not my brakes because I just rebuilt the calipers and the wheels spin freely with no drag noise. The truck just feels heavy as if there isn't enough torque. About the only thing I can think of that wouldn't throw a CEL is a clogged exhaust or a fubar ecu/pcm. Possibly leaking exhaust valves of bad compression but I am checking that this weekend. We will see. Again I have calculated my horsepower and its about 130. Almost like my engine is being governed but with absolutely no reason to be so.

I have noticed that I have at least one bad wheel sensor because the abs activates at slow speed. I'm wondering if the vehicle goes into some type of limp mode if an underlying subsystem such h as the abs goes wonky. I know it sounds like a wacky conspiracy but I would piss on a spark plug if I thought it would do any good.

Sorry Cap'n, I was a little lazy with my post - I wasn't necessarily suggesting brake caliper drag (but it's good to know that variable is eliminated), only trying to use that example to inspire some outside the box thinking that also accounts for the evidence you have put forth so far.

You seem to have been thorough with the maintenance, and checked the most likely candidates, so you have to start looking at more bizarre explanations IMO.

I know you have a scantool, so even if the actual dash light for the CEL or other MIL was burnt out, or otherwise failing to illuminate, you still would have noticed with the scanner.

It seems you've done a decent job investigating airflow related stuff (air cleaner, cat etc) leaving the ~85% throttle plate position as the last remaining possibility on that side of the equation. Hopefully in a few days my scanner will get here and I can add some input for comparison with mine. Is it possible for you to temporaily swap pcms with someone else, or use your scanner and Torque app on another LWB with an I6 to see how it compares?

Part of the reason I (& someone else earlier in the thread) asked for a refresher on how long you've owned it and how many miles you have put on it plus how many miles are on it total, is to be able to start speculating about some of the other weirder possibilities. IE if you've only had it a short time, and only driven it a couple hundred miles, it's possible you may not have noticed some behavior that might be relevant, whereas on the other hand if you've had it a long time, and driven it a lot, you would have noticed something if it had changed. You say that the performance has been sub-par since you first got it, I just thought it might help people to come up with other angles for you to check if they knew all the variables.

I'm hoping you can see the concept I'm digging at with the rambling that's about to follow:

In the context of Newton's F=ma and comparing yourself, me and seanpooh, there's only so many variables that go into making the power. Seanpooh has the same truck as we do (essentially, I will consider model year differences and minor weight & air density/temperature differences to be of minimal influence) so I will say all the masses are the same and don't enter into consideration (unless you both have a boat trailer still hooked up and both forgot to mention it)

He has the same 0-60 time as you, WITH a PCM tune. For that reason, in comparison with mine I think you both have an issue. Both of you seem to be of the opinion that you're not experiencing any performance issues otherwise, and neither of you seems to have any codes alerting you to problems. Seanpooh didn't post a video to see the 1-2 shift timing, but I will assume it's similar to yours at ~10s. For comparison, mine is right around 7s. I think it simplifies things if we limit the comparisons there for the moment, as we can probably disregard any tranny related shifting issues (it's still in first, at WOT).

Now because seanpooh has the PCM tune which really only professes to gain a few HP, and maybe a few ft-lbs torque, I really can't see that equating to a nearly 4 second difference in 0-60 times. Furthermore because he has the tune and is still getting very similar performance, I would go out on a limb and guess that this excludes your own PCM/programming/spark advance/timing etc etc as the issue. And I also think that it diminishes the likelihood of you both having clogged fuel filters, especially given a roadie post that I can't find ATM. where he's adamant that the pump will fail long before the filter ever becomes a problem.

So with equal masses, roughly equal engine power (BTW if you have valves or rings so bad that compression ratios are affected to THIS extent, I think you would have seen definite evidence of that at the tailpipe by now), same rear end gears, no serious drag factors to account for, in my mind the only thing that can be left is something tranny related that can exist without throwing codes after being present for the longer term. You say yours feels heavy off the line, low on torque...what about the possibility of a clogged tranny filter, or an improperly installed one that somehow prevents full flow to the TC under heavy load. Maybe a kinked cooler line restricts flow somehow. Have you ever dropped the pan and changed the fluid and filter? If not have you ever had it to a shop for a "flush"? Is your scanner/Torque app capable of monitoring any transmission related parameters that you could look at that might be relevant. You get the idea....

 

[Phantom]

Now just a question to throw out there, and I don't know if everybody's is the same or not, but did GM happen to put different size gears in the trannys??? I know mine said 2.69 on the housing the other day and i don't know if that has anything to do with it or not. but after reading WarGawds last post i didn't know if that was a variable that might be overlooked?
View attachment 22871
On the bottom it says ratio with the 2.69 above it.

 

[McGMT]

Now just a question to throw out there, and I don't know if everybody's is the same or not, but did GM happen to put different size gears in the trannys??? I know mine said 2.69 on the housing the other day and i don't know if that has anything to do with it or not. but after reading WarGawds last post i didn't know if that was a variable that might be overlooked?
View attachment 9329
On the bottom it says ratio with the 2.69 above it.

That's just the transfer case ratio....

 

[gmcman]

Air filter new. There is no fuel filter on 05 +. Factory Plugs changed at 110K. Found a nasty coil the other day. No CEL on and not misfiring yet but the corrosion was due to me not putting the gasket on right and water got in the spark plug well. Different coil was installed but no difference in performance.

View attachment 9239

Will post another vid soon.

I forgot about the filters on the 05+, my bad.

Just a hunch....was that the #4 coil just under the hood cowling? If so, that one is prone to corrosion due to the 1/2" opening near the weatherstripping allowing water to drain down directly on top the coil. That was the one coil I had go bad on me as well, good preventive maint on your part.


Were you able to perform an exhaust pressure test yet?

 

[seanpooh]

Hmm, I think I should post up a video of my 0-60. I don't think my cat is clogged, no symptoms of such. Oh, and also my tranny was rebuilt, flushed ~25K miles ago. I have a straight pipe muffler and no resonator. I also have 10 quarts of oil instead of the conventional 7.

I think my shift from 1-2 happens at 55mph @6K rpm. The video will clear things up (hopefully). I really hope nothing is wrong with my truck.

 

[WarGawd]

Now just a question to throw out there, and I don't know if everybody's is the same or not, but did GM happen to put different size gears in the trannys??? I know mine said 2.69 <snip> didn't know if that was a variable that might be overlooked?

That's just the transfer case ratio....

Correct...specifically the 4LO ratio. I had come across that before when doing up the calcs for rpm vs speed, but the 4HI ratio was 1:1 so I ignored it in the formula. If we had all been dealing with 4WD time to speed, then that would be another factor to enter in the calcs.

I forgot about the filters on the 05+, my bad.

Yes apparently on '05 & later the (not regularly serviceable) filters are in the tank as part of the regulator/pump assembly. In the context of CaptainXL's issue my comment earlier was to suggest that it's unlikely given what roadie had said...I neglected to consider that seanpooh's '02 still has the external filter. Nevertheless, I still tend to think it's unlikely that seanpooh and Cap'n have two different problems that manifest themselves in what seems to be exactly the same way.

Hmm, I think I should post up a video of my 0-60. I don't think my cat is clogged, no symptoms of such. Oh, and also my tranny was rebuilt, flushed ~25K miles ago.

That seems to be some interesting info...that would seem to mean the filter is pretty new, and if the rebuild was done by comptetent people, not likely installed incorrectly...which would then suggest if you and Cap'n really do have the same root cause my earlier idea goes out the window. I know next to nothing about automatic transmissions, so I can't really put forth other similar ideas. But if we 3 believe our engines are running good (IE same power o/p within a few %), and we have the same rear ends, no major drag losses etc, the answer seems like it can only lie in how the power is being transferred...something tranny related.

Out of curiosity seanpooh, did the rebuild use the old TC or was it changed/inspected/replaced?

I think my shift from 1-2 happens at 55mph @6K rpm. The video will clear things up (hopefully). I really hope nothing is wrong with my truck.

Yeah that's what I thought too until I did my videos...it's a bit hard to catch all the action at once. From my previous post I bet you'll find it's 50 +/-1 mph at 6100 rpm, but the time it takes to happen is what will have more relevance here now.

 

[bravad'oh]

I have noticed that I have at least one bad wheel sensor because the abs activates at slow speed. I'm wondering if the vehicle goes into some type of limp mode if an underlying subsystem such h as the abs goes wonky. I know it sounds like a wacky conspiracy but I would piss on a spark plug if I thought it would do any good.

The abs sensors get dirty with particles and cause your abs system to think one wheel is slipping. I had acces to a scan tool where I could see the sensors outputs in realtime. When driving around 5mph one sensor was showing a different speed than the others. I was able to pull it out and clean it that fixed it. I have cleaned abs sensors a dozen times since on other gm trucks. The hardest part is getting the sensor out. If you don't have tool to scan the ABS, I think you can test Voltage output from the sensor while spining the wheel by hand and the one that has less output is the one that needs to be serviced.

I think I need to do this WOT test when I get a chance as well cuz I don't think my Bravada is a s snappy as it should be. This is great to have lots of reference to compare to. Stock truck AWD( not currently working ) with 3.73 gearing.

 

[WarGawd]

It seems you've done a decent job investigating airflow related stuff (air cleaner, cat etc) leaving the ~85% throttle plate position as the last remaining possibility on that side of the equation.

I got my scanner a couple days ago. I used it to replicate my previously posted video results, WOT 1-2 shift at 7s / 6040rpm, 0-60 @ 10.2s, {didn't track distance parameters to verify 1/4 mile times} and 0-90 @ 22.72s.

For those interested, I was carrying same full tank of gas, a slight bit more "crap", and the ambient air temp was about 15 deg C cooler than in the videos. Other than that all I had changed was oil and plugs prior to these runs.

All of the above occcurred while the WOT position indicated was 87.5% and only one data point ever went above that to 88.23%....so this seems to nullify throttle plate position as a factor in the limitations you and seanpooh seem to have.

Seanpooh...how's the video coming?

 

[Jkust]

If I use the Available 0-60 calculators on the web and put in a 9 second 0-60 time given the curb weight of an XL or ext then it comes out to roughly 275 HP. I just adjust the HP variable to get my 0-60 time. The calculator uses an average of multiple vehicle profiles to come up with the 0-60 times.

Ok got it. It reminded me of the Top Gear episode where they each bought super cars from the 70's and dyno'd them and literally some had under 100hp left.

 

[CaptainXL]

Well I think my last line of troubleshooting with this thing is to get some real numbers for you guys. Therefore I bought a relatively cheap exhaust pressure tester and I want to see first hand if I have any problems. As I discussed earlier I disconnected the exhaust at the catalytic converter but I failed to get the third bolt completely undone so the pipe was separated by about 1/2 inch. I was hoping that would be enough to relieve some of the pressure.

So just bear with me and I am going to hook up this bad boy and see if its the problem. I already have the heat shield removed and such so all I need to do is remove the O2 sensor. If all goes well then I will post the pressure numbers.

 

[gmcman]

Well I think my last line of troubleshooting with this thing is to get some real numbers for you guys. Therefore I bought a relatively cheap exhaust pressure tester and I want to see first hand if I have any problems. As I discussed earlier I disconnected the exhaust at the catalytic converter but I failed to get the third bolt completely undone so the pipe was separated by about 1/2 inch. I was hoping that would be enough to relieve some of the pressure.

So just bear with me and I am going to hook up this bad boy and see if its the problem. I already have the heat shield removed and such so all I need to do is remove the O2 sensor. If all goes well then I will post the pressure numbers.

I don't want to sound like you are going about this the wrong way but I assume you are taking measurements with the exhaust connected and also disconnected?

I don't know what the numbers should be but if I remember correctly I believe the max pressure should be 1.5 lbs??