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

[tblazerdude]

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.

Wait, you use 10 quarts of engine oil? Do you have any oil modifications?

 

[CaptainXL]

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??

There is a flow diagram/tshoot proceedure on Alldatadiy.com and thats what I am going by. Not assuming anything here. And yes.. I am testing with the exhaust connected. This is just taking extra long to complete because we just had a baby and as you can expect things are being done piecemeal.

 

[DenaliHD66]

IF you are trying ot mash the pedal to the floor as fast and hard as you can, I dont think the PCM tune will let the engine rev like that. Remember our trucks are drie by wire .. there is not cable from the pedal to the throttle body. Try a gradual but steady pess of the pedal and see how that works. At least that is what I have to do. Just my 2 cents

I have a PCM tune on mine, and I notice that when I totally mash it, as opposed to gradually getting into it, it doesn't accelerate as fast when I mash it. So it does, as you say, sorta compensate and doesn't let the engine rev up as fast if it notices the sudden stomp of the gas pedal. I think the difference is barely noticeable, but you'd certainly expect it to launch a bit more if you mash it down, as opposed to pressing it firmly.

 

[Chickenhawk]

You want exhaust backpressure numbers at idle, and at 2500 RPM.

The numbers should read 0 PSI at idle and no more than 3 or 4 PSI at 2500 RPM.

Let us know what your numbers read.

 

[CaptainXL]

You want exhaust backpressure numbers at idle, and at 2500 RPM.

The numbers should read 0 PSI at idle and no more than 3 or 4 PSI at 2500 RPM.

Let us know what your numbers read.

I looked up the Alldata proceedure and it says the following.

1.25 PSI at idle warmed up.
3 PSI at 2000 RPM warmed up.

 

[Chickenhawk]

Sounds about right.

There is enough variation in cat sizes over the years that there are no hard and fast numbers. On the other hand, I would guess that a cat clogged bad enough to affect performance would be giving significantly higher numbers than these.

I would also record the number at 2500 RPM as well as 2000 RPM, for the simple reason that so many manuals and techs use 2500 RPM numbers.

 

[gmcman]

Would the ECM ever need to regulate airflow in the event of clogged injectors to maintain AF ratio?

 

[CaptainXL]

Sounds about right.

There is enough variation in cat sizes over the years that there are no hard and fast numbers. On the other hand, I would guess that a cat clogged bad enough to affect performance would be giving significantly higher numbers than these.

I would also record the number at 2500 RPM as well as 2000 RPM, for the simple reason that so many manuals and techs use 2500 RPM numbers.

Finally did the exhaust pressure test! I got 0 psi at idle, 2K and 2.5K rpms.

The gauge never moved. I blew slightly into the end of the gauge just to verify and it works.

I'm starting to lean towards fuel now. Suggestions welcome.

 

[gmcman]

I've been searching around and it may not pertain to our platforms, but the consensus is that the throttle plate openings never really register 100% and mid to high 80% is the norm.

Someone mentioned that when the plate is inline with the shaft it doesn't matter how much more it opens since there will be a restriction (shaft) anyway.......dunno but makes sense.

You could have someone stand outside and watch the throttle plate while power-braking it to see if it fully opens. Worth a try.

If that were my vehicle I would run a can of BG 44K through it and see what happens after a tank. Did the vehicle sit for a long period of time without driving...maybe a few months?

 

[McGMT]

I've been searching around and it may not pertain to our platforms, but the consensus is that the throttle plate openings never really register 100% and mid to high 80% is the norm.

Someone mentioned that when the plate is inline with the shaft it doesn't matter how much more it opens since there will be a restriction (shaft) anyway.......dunno but makes sense.

You could have someone stand outside and watch the throttle plate while power-braking it to see if it fully opens. Worth a try.

If that were my vehicle I would run a can of BG 44K through it and see what happens after a tank. Did the vehicle sit for a long period of time without driving...maybe a few months?

On my 06 WOT = 88% . With key on engine off I get 20% to 88% at idle KOEO the minimum depends on the RPM the PCM asks for as the throttle blade IS the IAC which is why when the gunk builds up around the throttle blade they wont idle as there is no space for the air to pass thru. Normal idle on mine at ~700 RPM is 16% But even that is variable as the injector pulse dictates idle.

 

[fadyasha]

I know exactly what you're going through. Unfortunately my suggestion already applied in your case which was the Coil check. For what it's worth couple of weeks ago I cleaned the throttle body, cleaned out the air filter (K&N) and acceleration improved a bit. I then checked my exhaust system and apparently there was a leak which of course leads to losing pressure. You've already done that though soo hmm..

Wish could help more. My TB does act up though, sometimes would accelerate just great and other times as if something is holding it back. Mostly happens if I floor it

 

[CaptainXL]

I noticed something the morning that I didn't before and maybe someone can back up my observation.

I took the Envoy out for a drive this morning and usually when getting on the highway the VVT kicks in at around 3000 rpm. Now it won't kick in until 5000 RPM. I don't know how long this has been going on. Perhaps now I am getting closer to the root cause?

Now I am starting to think oil pressure, CPAS (which I already changed), or the actuator itself.

But damn. If the actuator wasn't working right I would think I would have a code or something. Huh...

 

[The_Roadie]

A Tech II tool can command the CPAS through its range. Is it out of the question to find a competent independent mechanic with a Tech II?

 

[gmcman]

I took the Envoy out for a drive this morning and usually when getting on the highway the VVT kicks in at around 3000 rpm. Now it won't kick in until 5000 RPM.

I think mine kicks in around 5K also but almost sounds like it starts working earlier near 4300 ish. I don't know for sure it the CPAS is gradual or just on/off though.

Could also be the fact our throttle bodies open very slowly under torque management and you are hearing the full intake growl at 3000 when fully opened. For example, it takes about 2-3 sec for the throttle to open if you mash the gas under stock tune.

 

[gmcman]

Get some of this and fill the tank, even if it doesn't cure the problem you will only benefit from it. If it helps you will notice prob before the tank is empty.

After the tank is empty then you can chase your fuel issues further.
I use this religiously roughly every 25K.

 

[CaptainXL]

A Tech II tool can command the CPAS through its range. Is it out of the question to find a competent independent mechanic with a Tech II?

Yes its out of the question for now money being tight and having new kids and all. Just trying to do the most I can myself without buying all these tech toys.

Given I don't have any codes I think it's best to take a step back and rethink. I think I should be looking at some other classical (non emission control) causes of poor performance.

I was just thinking outloud about the cpas.

 

[CaptainXL]

Get some of this and fill the tank, even if it doesn't cure the problem you will only benefit from it. If it helps you will notice prob before the tank is empty.

After the tank is empty then you can chase your fuel issues further.
I use this religiously roughly every 25K.

I would rather not. I have spent enough money throwing parts and cleaners into this truck. I've probably spent close to $100 on fuel system cleaners over the past year. Redline sl1, techron, gumout, Lucas,etc...

 

[gmcman]

Can you take a ride again and let me know what the spark advance is at WOT?

It will jump around but when you are cruising along, push on the gas for a strong accel, try to avoid a downshift first and see where the advance tends to settle at.

 

[gmcman]

Now that I'm away from the cell phone.....I agree we need to take a basic aproach at this.

For normal operation, we need:

Air
Fuel
Spark
Compression

We have spark and air coming in, we have also verified air is flowing out by the backpressure test.

We haven't confirmed: fuel, compression and spark advance.

There are alot of variables here especially with the ECM controlling most everything, but we do need to cover the basics. Providing we have fresh fuel, at optimum pressure, unrestricted, then we need proper spark advance and compression. After that we can start probing deeper but if you can, finding out the comprerssion in each cyl will aid greatly in this quest.

One way to somewhat get a ballpark figure is to probe each exhaust port with an infrared temp gun. once warmed up see if you can get a reading from each cylinder. The readings wont be highly accurate since heat will dissipate between the manifold but there will be a difference if something is drastically amiss.


PM me your address and I will send you a can, consider it a baby shower gift. Congrats on the new edition BTW.

 

[CaptainXL]

Now that I'm away from the cell phone.....I agree we need to take a basic aproach at this.

I appreciate your support. I will endeavor to get a compression test done next and get some timing advance numbers. You are too kind. Will let you know if there is any difference with the BG.

Edit: It would help if someone had a timing map sheet from using a programmer like EFI Live or HP Tuners. Otherwise we don't really know what the base timing is at different rpm's.

 

[gmcman]

we don't really know what the base timing is at different rpm's.

It will be all over the place, when warm it will stabilize more but when accelerating it will peak out at certain values and after driving around looking at the values for 10 min or so you will get an idea where they are maxing out. They will never be the same but you will see a pattern. It will be somewhat normal or way off, not a real definite way to diagnose the problem but may or not tell a story.

 

[CaptainXL]

It will be all over the place, when warm it will stabilize more but when accelerating it will peak out at certain values and after driving around looking at the values for 10 min or so you will get an idea where they are maxing out. They will never be the same but you will see a pattern. It will be somewhat normal or way off, not a real definite way to diagnose the problem but may or not tell a story.

Ok, I will just use my Torque app and record a log and then we will see what we can see.

 

[WarGawd]

Hey Captain -

I've been lurking this thread a bit to see if there have been any developments. From what I gather you've done the backpressure test and satisfied yourself that a clogged cat is not an issue. I suspected this would be the case given the previous test run with the exhaust disconnected with no performance change.

I see you and gmcman are still of the mindset that it's a power production/ouput type issue, this despite a previously mentioned result with your torque app (showed 267HP IIRC?). As far as the engine making power is concerned, did you ever get around to testing fuel flow (presssure was ok IIRC)? And what about the misfire on #6 mentioned in another thread - any change in that situation?

What scanner do you use with Torque? Would it help if I did a few runs and datalogged a pile of parameters using my scantool? Lemme know which ones are of interest, I'd be happy to go driving. FYI, I have the OBDLink SX Scan Tool with the basic OBDWiz software that supports these PIDs, if that helps you decide what you want me to look at. May03LT also has a youtube video on the subject of scan tool values:

[video=youtube;KcEf_-wXaR8]http://www.youtube.com/watch?v=KcEf_-wXaR8&feature=channel&list=UL[/video]

At about 5:10 he mentions there would be a link to a thread somewhere here on GMTN, but my searches haven't turned that up (or maybe I suck at searching). Anyway, a PM to him to see if he ever started that thread may give you another angle of attack for comparing scan results/expected values.

Oh BTW, I found this article that you may find informative as it regards your previous line of questioning about whether a wonky PCM might be at the heart of this. It's not definitive by any means, but may be helpful.

Lastly:

I noticed something the morning that I didn't before and maybe someone can back up my observation.

I took the Envoy out for a drive this morning and usually when getting on the highway the VVT kicks in at around 3000 rpm. Now it won't kick in until 5000 RPM. I don't know how long this has been going on. Perhaps now I am getting closer to the root cause?

Now I am starting to think oil pressure, CPAS (which I already changed), or the actuator itself.

But damn. If the actuator wasn't working right I would think I would have a code or something. Huh...

I think mine kicks in around 5K also but almost sounds like it starts working earlier near 4300 ish. I don't know for sure it the CPAS is gradual or just on/off though.

Could also be the fact our throttle bodies open very slowly under torque management and you are hearing the full intake growl at 3000 when fully opened. For example, it takes about 2-3 sec for the throttle to open if you mash the gas under stock tune.

Can you guys tell me how you are observing this...it doesn't seem to be something that is noticeable for me. Lemme know and I'll see if I can offer up anything for comparison.

Cheers

 

[CaptainXL]

I see you and gmcman are still of the mindset that it's a power production/ouput type issue, this despite a previously mentioned result with your torque app (showed 267HP IIRC?).

It was something I noticed once. I can't remember where I saw it using Torque. I will try to find it again.

As far as the engine making power is concerned, did you ever get around to testing fuel flow (presssure was ok IIRC)? And what about the misfire on #6 mentioned in another thread - any change in that situation?

Fuel pressure was Ok but I would like to test volume at some point. I will need to hotwire the relay connection to run the pump continuously to find out. The #6 misfires I used to see were only at idle and are within spec as far as GM is concerned. Thier TSB explains away this behavior.

What scanner do you use with Torque?

FWIW I use a generic ELM 327 bluetooth scan tool.

Lastly:

Can you guys tell me how you are observing this...it doesn't seem to be something that is noticeable for me. Lemme know and I'll see if I can offer up anything for comparison.
Cheers

I just look at my tach and can feel the boost the VVT gives me. I used to notice the boost around 3K but now it's later around 5K.

 

[gmcman]

What throttle setting do you feel the "kick" at 3K?

Reason I ask is I feel it also at about 1/2 throttle but you can hear the intake growl a little at 5K.

Here's a great demonstration of the lag in throttle opening when the gas pedal is depressed....May explain the surge at 3K a little more.
[video=youtube;VLsY7dYjenY]http://www.youtube.com/watch?v=VLsY7dYjenY&feature=youtube_gdata_player[/video]

 

[C-ya]

result with your torque app (showed 267HP IIRC?).

Can someone post the HP PID for Torque that they are using and getting believable numbers for? I tried it on mine, and it showed a max of 46 hp, I think, which is not right.

 

[CaptainXL]

Can someone post the HP PID for Torque that they are using and getting believable numbers for? I tried it on mine, and it showed a max of 46 hp, I think, which is not right.

It's not a PID. Its a calculation done by Torque using weight and I think a few more variables when you set up your vehicle profile

 

[C-ya]

My profile is complete. It never gave believable numbers for my GMC truck either.

 

[CaptainXL]

What throttle setting do you feel the "kick" at 3K?

I've always been at WOT with all my tests when i feel it kick in. This demonstration of the throttle does not relate to my tests because the throttle would be fully open after at most three seconds as seen in the video. It's interesting but unrelated.

 

[CaptainXL]

My profile is complete. It never gave believable numbers for my GMC truck either.

Well hold on there. That is one of the things I am trying to find out. I wouldn't dismiss saying Torque doesn't work at calculating HP semi accurately.

 

[WarGawd]

Hmmmm

It was something I noticed once. I can't remember where I saw it using Torque. I will try to find it again.

My point was if you are still choosing to investigate power production type issues, I assumed you would have some reason for distrusting or disregarding the the reported result. I was hoping your reply would offer that feedback on your thinking there. Otherwise, and perhaps C-ya has a valid point, the 267hp seems like it's at least pretty close to expectation, and should send you looking in other directions...your thoughts? I don't have Torque, so I can't comment on how accurate the calculated result is.

I just look at my tach and can feel the boost the VVT gives me. I used to notice the boost around 3K but now it's later around 5K.

I'm still unclear whether we are talking about the same thing. It adds to the (my?) confusion a bit when there are 2 similar acronyms. The Cam Angle Sensor (that you already changed) is (my understanding only, someone correct me if I'm wrong) involved with the PCM being able to command the correct ignition timing, in conjunction with the Crank Angle Sensor. This allows for the limp home mode in the event that one of the two sensors goes bad.

OTOH the Camshaft Position Actuator Solenoid, is what the PCM uses via engine oil pressure to effect the Variable Valve Timing. From the Vortec 4200 technical paper I downloaded elswhere on GMT (Mooseman maybe?) VVT is intended for "...linear delivery of torque, with near-peak levels over a broad rpm range..." (from page 10 of that doc): {Aside @ gmcman...given the 25 degree range that the PCM can adjust the exhaust cam timing, I suspect it must not be on/off, but rather progressive depending on conditions}

View attachment 23007

So to me that sort of fits my experience with my truck...no noticeable "boost" at least not in the way I understand you to mean it. I DO however get a "flat spot" where there seems to be a slight/brief lag lasting for about a second from ~2300-2400 rpm, after which the pickup seems to increase...this may be the "boost" you are referring to. I did a plot of some of the data from my scan tool run which shows this a bit better:

View attachment 23008

Here's a great demonstration of the lag in throttle opening when the gas pedal is depressed....May explain the surge at 3K a little more.

I've always been at WOT with all my tests when i feel it kick in. This demonstration of the throttle does not relate to my tests because the throttle would be fully open after at most three seconds as seen in the video. It's interesting but unrelated.

Furthermore, since I have a stock PCM, CaptainXL and I have the almost identical vehicles, and mine does NOT seem to exhibit the throttle lag behavior, I don't think that video has much bearing on his problem comparatively speaking.

Cap'n, you never did say if you want me to collect a bunch more logged data for you to compare with?

 

[gmcman]

Capt.....I can't write a big long post right now but do me a favor... take a piece of paper and hold it against the exhaust outlet with the motor running and let me know if at any point it gets sucked back into the tailpipe.

 

[gmcman]

I drove to work with my scantool and I was getting 22 deg. advance at full throttle, yours should be similar but if its down near 15 deg I would suspect a problem.....conditions vary but I'm. curious to what yours is.

Something else is I also had 100% on my TPS at WOT.

 

[bravad'oh]

Perhaps you could try a torque converter stall test. This will help rule out some stuff. If your engine won't make enough HP it will not reach the spec. If it exceeds the spec. rpm it points toward a transmission problem. I found this test. It's for a Hyundai but the procedure is always the same.






CONVERTER STALL TEST

 

[Chickenhawk]

Good suggestion.

Just one modification to their test. I would apply chocks to the FRONT wheels on our platform. Wouldn't want the driving wheels to spit out the chocks!

Keep in mind that GM does not recommend a stall test, nor do they publish stall RPM specs. They are concerned about the hazards in performing the test and extreme strain on the transmission.

 

[Wooluf1952]

Something else is I also had 100% on my TPS at WOT.

Sorry if I missed it,but do you have a tune with 100% of the torque management removed?

 

[CaptainXL]

Hey guys. I've been listening to all of you but I wanted to give an update. Today I did some more 0-60 runs and now I get 10 -11 second runs. The only difference was the outside temp. It was about 65 deg.

[video=youtube;WFch0ymH7aM]https://www.youtube.com/watch?v=WFch0ymH7aM&feature=youtube_gdata_player[/video]

 

[gmcman]

Sorry if I missed it,but do you have a tune with 100% of the torque management removed?

No, Mine is stock.

 

[WarGawd]

Hey guys. I've been listening to all of you but I wanted to give an update. Today I did some more 0-60 runs and now I get 10 -11 second runs. The only difference was the outside temp. It was about 65 deg.

Wow! I know you said earlier that you felt performance was better in cooler temperatures but WOW!!! This CAN'T be the the complete explanation for what's happening. Essentially you would be saying that a 30-40ish degree temperature change equates to a 3+ second difference in your 0-60 times?!?! The air density doesn't change THAT much over that temperature range and even then I think the PCM is actively managing the air-fuel mixtures based on the IAT data.

I mean consider all the people that went to an aftermarket CAI...even though ours are already considered to be somewhat of a cold air intake system, even if the aftermarket ones gained someone a 10 degree intake air temp difference, your result would suggest that they should also experience significant performance improvents, which isn't really consistent with all the feedback that I've read (some impreovement yes, but nowhere near this much).

Temp change may be a factor, but I suspect it would have to be a secondary one...maybe along the lines of a bad IAT sensor feeding the PCM bad data?? I know there's concern sometimes about damaging the MAF sensors when people clean their throttle bodies, I can't say I've seen anything about the IAT's though...is it possible for one to go bad, be damaged or dysfunctional in a way that doesn't throw codes for the longer term?

You've suspected a lack of performance from when you first got the vehicle, you've had it now over 1-1/2 years, so did you notice a similar massive perfomance gain last fall when temperatures started getting cooler?

 

[WarGawd]

Something else is I also had 100% on my TPS at WOT.

No, Mine is stock.

I'm curious about that result...can you reply with the PID that the number actually references? Any of my previous throttle position references (eg 87.5% @ WOT) have been PID 0x11 Absolute Throttle Position. I do notice that there are other absolute and relative throttle position PIDs (0x45, 0x47, 0x48)but I haven't used or logged any of those so far. Maybe we're comparing apples and oranges?