Throttle Position %?

[PLAT515]

This screenshot was taken when vehicle was completely up to operating temp. Just curious really on my TP% being so low at 2.75%, ive got an 02 TB aswell that reads somewhere around 10% give or take 2% cant remember exactly and feel i've seen other posts with theirs higher aswell. Something to be concerned about? No codes, but my 02 with 272k takes off and gets up to speed very quick and comfortably. My 03 with 183k i feel im using more effort to accelerate to the same speed. Thought that might be the reason the 03 feels the way it does. I plan on swapping my 02's pedal into the 03 see if that does anything, or my other two hunches were Throttle body or maybe the VVT thing. Just a guess. CAT is cut out aswell, on both trucks actually.

 

[budwich]

which PID are you using? Based on my monitoring of my 2008, at warm idle, I see higher values. I would say that the system is trying to "lean out" your fueling... meaning it is trying to reduce the air to improve the overall mixture (at idle) for it to maintain the idle speed (not shown). Check your trims to see what they look like at this point to potential confirm or not other fueling adjustments.

Not sure which pids are involved but note that there is the "request pedal" by operator "push" and the "system commanded" (throttle body / motor)... they should be within a certain range of each other otherwise a code will be set.

 

[TJBaker57]

I initially thought to compare my readings to yours but while looking at your vacuum readings (both in/hg and psi) it occurred to me that mine may be not be a good comparison due my home elevation of 8200 feet. While Torque Pro is likely using a standard 14.7 psi atmospheric pressure at sea level for its' calculaions my atmospheric pressure is only 10.8 psi. This may cause my readings to be substantially different.

That said, it doesn't explain why you have two different reading on your 2 similar vehicles. Just speculation here but could a small vacuum leak allow just enough unmetered air into the intake to cause the throttle to close down more? I don't know.

 

[PLAT515]

which PID are you using? Based on my monitoring of my 2008, at warm idle, I see higher values. I would say that the system is trying to "lean out" your fueling... meaning it is trying to reduce the air to improve the overall mixture (at idle) for it to maintain the idle speed (not shown). Check your trims to see what they look like at this point to potential confirm or not other fueling adjustments.

Not sure which pids are involved but note that there is the "request pedal" by operator "push" and the "system commanded" (throttle body / motor)... they should be within a certain range of each other otherwise a code will be set.

Sorry not really sure what you mean by PID, this is using the Torque Pro app with BAFX $25 scanner. Not shown here i have the fuel trims long and short term readings and as far as ive learned long term trim should be near 0 and on both of my Traiblazers 02 and 03 are identical sitting -1 at most. Top right corner of screenshot shows my idle speed at 602rpm. I will screen record later today for a live video of BOTH trailblazers to compare.

 

[PLAT515]

I initially thought to compare my readings to yours but while looking at your vacuum readings (both in/hg and psi) it occurred to me that mine may be not be a good comparison due my home elevation of 8200 feet. While Torque Pro is likely using a standard 14.7 psi atmospheric pressure at sea level for its' calculaions my atmospheric pressure is only 10.8 psi. This may cause my readings to be substantially different.

That said, it doesn't explain why you have two different reading on your 2 similar vehicles. Just speculation here but could a small vacuum leak allow just enough unmetered air into the intake to cause the throttle to close down more? I don't know.

After you and budwich put that into perspective it totally makes sense to me. Unfortunately i have limited live data and zero codes at all so im wondering if i could get my hands on a smoker or something and force a leak to show itself ? Never done such a test just a thought, hopefully someone else can chime in on that.

 

[PLAT515]

Here is my 03 sitting idle in my driveway after some errands. Video shows fuel trims aswell

 

[azswiss]

Vacuum looks good. Both short & long term fuel trims are negative meaning the PCM is trying to cut back on fuel feed. What do the O2 sensors look like? Any fuel smell?

A shot in the dark here: clogged air filter? Faulty MAF?

 

[PLAT515]

Vacuum looks good. Both short & long term fuel trims are negative meaning the PCM is trying to cut back on fuel feed. What do the O2 sensors look like? Any fuel smell?

A shot in the dark here: clogged air filter? Faulty MAF?

There is a quick 2 - 3 second clip of my 02 sensors at the end of the video. I have rear 02 sensor tuned out as my CAT is gutted. No fuel smell, new air filter and dont believe 03's have a MAF not positive though

 

[PLAT515]

Small update, swapped throttle pedals. No change, still 3ish % at idle. Got more data recorded i can upload aswell that includes Fuel Trims, and 02 sensor readings for an extended period of time

 

[budwich]

Sorry not really sure what you mean by PID, this is using the Torque Pro app with BAFX $25 scanner. Not shown here i have the fuel trims long and short term readings and as far as ive learned long term trim should be near 0 and on both of my Traiblazers 02 and 03 are identical sitting -1 at most. Top right corner of screenshot shows my idle speed at 602rpm. I will screen record later today for a live video of BOTH trailblazers to compare.

the pids are the parameters that a given display is showing.... in torque, you point at a specific pid in the table of manageable pids to cause the dial / display to show.... which one did you choose? Its too bad that torque does not directly show that... :-(

I am probably wrong about which pids there are but I thought there was at least two... one absolute. and the other?

Your trims are relatively OK and not "extreme" so it would appear that "base fueling" controls are OK. IF the number is correct, it would appear that your system is almost "choked" to some degree with such a small percentage (very low air intake)... at least my read on what its telling you. My feeling is some form of intake air leak resulting in "adequate" air getting to the engine to ensure reasonable running.

Not sure what "vacuum pid" you are using. I think TJbaker has played in this area and indicated that there is a vacuum pid that is "manufactured" in some form by torque.... I am confused as to what it references versus "manifold pressure".... basically am expecting something provided by the MAP which I think is the only "air metering" that is done for your years.... 2006 and on have a MAF also to help the cause.

Maybe a temperature sensor is "asking for choke conditions" which the system seems to be trying to carry out.... maybe...

 

[PLAT515]

the pids are the parameters that a given display is showing.... in torque, you point at a specific pid in the table of manageable pids to cause the dial / display to show.... which one did you choose? Its too bad that torque does not directly show that... :-(

I am probably wrong about which pids there are but I thought there was at least two... one absolute. and the other?

Your trims are relatively OK and not "extreme" so it would appear that "base fueling" controls are OK. IF the number is correct, it would appear that your system is almost "choked" to some degree with such a small percentage (very low air intake)... at least my read on what its telling you. My feeling is some form of intake air leak resulting in "adequate" air getting to the engine to ensure reasonable running.

Not sure what "vacuum pid" you are using. I think TJbaker has played in this area and indicated that there is a vacuum pid that is "manufactured" in some form by torque.... I am confused as to what it references versus "manifold pressure".... basically am expecting something provided by the MAP which I think is the only "air metering" that is done for your years.... 2006 and on have a MAF also to help the cause.

Maybe a temperature sensor is "asking for choke conditions" which the system seems to be trying to carry out.... maybe...

Engine Coolant Temperature
Engine RPM
Fuel Trim Bank 1 Short Term
Fuel Trim Bank 1 Long Term
Fuel Trim Bank 1 Sensor 1 (Did not realize this one was here and showed a given value until now)
Intake Air Temperature
o2 Bank 1 Sensor 1 Voltage
o2 Bank 1 Sensor 2 Voltage
Throttle Position(manifold)
Timing Advance
Turbo Boost & Vacuum Gauge

I hope this is what you mean.. when i hit add display, and then select sensor thats what i chose. No other PID show up as green and with a reading. Just black, no reading. Going to go get another recording now.

 

[Mooseman]

Engine temp seems to be OK so I don't think it's in open loop or running in cold mode.

Have you tried cleaning the throttle body and disconnecting the battery for 30 minutes? You could also do a quick check for vacuum leaks using brake or carb cleaner. While it's idling, spray some lines and spots around the intake manifold and injectors while listening for changes in RPM. Wouldn't be surprised if the intake manifold bolts are loose.

 

[azswiss]

Negative fuel trims means either not enough air or too much fuel (??). Building on @budwich's comment above, the system is either choking for air or gagging on fuel. Since the air cleaner is new the question becomes how could too much fuel become a problem. Excessive fuel pressure due to a faulty regulator?

Edit: I have never seen the STFT vary uniformly like that (bears a strong resemblance to upstream O2 sensor variation). Is this typical for this year/engine?

 

[PLAT515]

Engine temp seems to be OK so I don't think it's in open loop or running in cold mode.

Have you tried cleaning the throttle body and disconnecting the battery for 30 minutes? You could also do a quick check for vacuum leaks using brake or carb cleaner. While it's idling, spray some lines and spots around the intake manifold and injectors while listening for changes in RPM. Wouldn't be surprised if the intake manifold bolts are loose.

I cleaned the throttle body when i did valve cover/intake manifold, and yes followed proper torquing procedure. Also Yes disconnected battery to relearn when i did that aswell. Ill give that idea a shot on spray around the intake.

 

[PLAT515]

Negative fuel trims means either not enough air or too much fuel (??). Building on @budwich's comment above, the system is either choking for air or gagging on fuel. Since the air cleaner is new the question becomes how could too much fuel become a problem. Excessive fuel pressure due to a faulty regulator?

Edit: I have never seen the STFT vary uniformly like that (bears a strong resemblance to upstream O2 sensor variation). Is this typical for this year/engine?

Fuel Pressure regulator is new aswell ACdelco. Old one was squirting gas out the vacuum nipple!
New videos uploaded soon with more info

 

[PLAT515]

Another Live Data run, Idling at start and end of video. This one is quite long, id double the video speed while you skim through it. I notice Long Term fuel trim isnt actually in the negatives. It seems to hover over in the positives. My 02 TB's video to compare probably tomorrow or monday.

 

[azswiss]

STFT and LTFT look to be centered around 0% in this run. Will be interesting to see the comparable logs from your other vehice

 

[budwich]

Edit: I have never seen the STFT vary uniformly like that (bears a strong resemblance to upstream O2 sensor variation). Is this typical for this year/engine?

that is how it is supposed to work. The upstream O2 "waggle" which results in the system "waggling" the fueling. The system is operating in "closed loop" which is kind of in "feedback" mode... o2 provides feedback to the system which then adjusts which then moves in a direction and the feedback continues, continually "correcting". At idle the "frequency" is usually a "nice wave"... at speed, it is harder to capture as the data transfer "reads" for the obd might not be sufficient to accurately graph.

 

[azswiss]

Understood the cyclic upstream O2 variation, just had not seen the same pattern in the STFT.

 

[budwich]

Understood the cyclic upstream O2 variation, just had not seen the same pattern in the STFT.

had not seen the pattern in stft? how else do you think the o2 would result in a fluctuation. That can only be caused by a changing fuel input or valve issue.
Anyway, IF your stft is not fluctuating, you have an issue.... only the ltft is relatively stable / flat.

 

[PLAT515]

Very interesting results here guys, couple red flags here on my 2002 Trailblazer even though she runs like a top, easily gets 16+ minimum and if its highway 21mpg no problem.

First noticed coolant stays between 186 - 192 on the 02 truck, nov 2017 i replaced with ACdelco thermostat. 5 years old. - My 2003 stays between 206 - 210. Thermostat is new, but it isn't ACdelco

Second thing i notice if you watch my LTFT when im off throttle say from cruising at 65mph to coasting to a stop it drops significantly and immediately as i get off throttle. This does not happen on my 2003, LTFT holds a steady line.

Aswell with the LTFT i notice im sitting in the negatives cruising at about -5 with my 2002, compared to my 2003 at about +3.

 

[PLAT515]

The 02 Idling in driveway

 

[budwich]

Very interesting results here guys, couple red flags here on my 2002 Trailblazer even though she runs like a top, easily gets 16+ minimum and if its highway 21mpg no problem.

First noticed coolant stays between 186 - 192 on the 02 truck, nov 2017 i replaced with ACdelco thermostat. 5 years old. - My 2003 stays between 206 - 210. Thermostat is new, but it isn't ACdelco

Second thing i notice if you watch my LTFT when im off throttle say from cruising at 65mph to coasting to a stop it drops significantly and immediately as i get off throttle. This does not happen on my 2003, LTFT holds a steady line.

Aswell with the LTFT i notice im sitting in the negatives cruising at about -5 with my 2002, compared to my 2003 at about +3.

Interesting capture.
I figure it must be cold in Min. at this time. Quite likely then, that an "unloaded" vehicle running at highway speed may not see "normal operating temp" (192) for much / any of the time. The other one (2003) maybe having a bit of a "stuck" although if it was totally stuck closed it would probably still run higher even on cold days.

The difference might not even be anything to do with cooling... Leaner mixtures run hotter.

I haven't ever graphed / watched / captured a run on mine outside of just watching "gages". The drop in ltft with pedal off / coasting seems "unusual". Somewhat related, is the timing. On mine and others, I see it drop to near 0 when the pedal is off. I don't think yours did that but maybe the data (torque) isn't able to capture that much data... you have a lot going on in the screen for data collection.

not sure if your 2002 and 2003 share the same MAP... I can't remember if you tried a swap to see if things change... you could try that.

 

[PLAT515]

Interesting capture.
I figure it must be cold in Min. at this time. Quite likely then, that an "unloaded" vehicle running at highway speed may not see "normal operating temp" (192) for much / any of the time. The other one (2003) maybe having a bit of a "stuck" although if it was totally stuck closed it would probably still run higher even on cold days.

The difference might not even be anything to do with cooling... Leaner mixtures run hotter.

I haven't ever graphed / watched / captured a run on mine outside of just watching "gages". The drop in ltft with pedal off / coasting seems "unusual". Somewhat related, is the timing. On mine and others, I see it drop to near 0 when the pedal is off. I don't think yours did that but maybe the data (torque) isn't able to capture that much data... you have a lot going on in the screen for data collection.

not sure if your 2002 and 2003 share the same MAP... I can't remember if you tried a swap to see if things change... you could try that.

So far i've only swapped my Accelerator Position Pedal Sensor, with zero change. As far as rockauto shows, the MAP sensor is the same part number between the 2 years. Ill forsure swap that out see if there is a notable change.

 

[PLAT515]

Well think i figured it out... The most recent time i can remember relearning the system was when i cleaned TB and did valve/intake gaskets. My CAT plugged up some time after i did that maintenance - which i speculated was already damaged due to the cracked manifold and bad upstream o2 sensor when i bought the truck. First thing i did was that on this truck, ran the CAT until i convinced myself it was plugged up by downstream o2 sensor readings and lack of highway power etc... i cut the CAT out, replaced with pipe and gained some of my power back and i think i might have just left it since then, i should've let the system relearn after cutting the CAT out...if i didnt, really cant remember.

So with that being said after the relearn, Throttle Position(Manifold) still sits around 3%, LTFT sits at 0 in case your interested. - I still plan on spraying around intake like Mooseman suggested

Only follow up question i have is my temp. My 2002 sits avg 190 seems kinda low, My 2003 sits avg 208 seems a bit warm, with a brand new thermostat from Napa. Any thoughts?

 

[Mooseman]

I think your 03 is kinda on the high side, especially if it's cool out and not running the A/C. I haven't checked mine in a while but IIRC, it's usually sits around 190-195. I know that below 190 I look at replacing the thermostat. My 02 was running in the 180's after a new aftermarket thermostat and after replacing it with an ACDelco, was back up over 190.

On both, check that your EV fan clutches are working. If it isn't, that could explain running a little warmer than normal.

How to test the electro-viscous fan clutch

 

[TJBaker57]

My own 2002 has always run right at 206.6 °F.

 

[PLAT515]

I think your 03 is kinda on the high side, especially if it's cool out and not running the A/C. I haven't checked mine in a while but IIRC, it's usually sits around 190-195. I know that below 190 I look at replacing the thermostat. My 02 was running in the 180's after a new aftermarket thermostat and after replacing it with an ACDelco, was back up over 190.

On both, check that your EV fan clutches are working. If it isn't, that could explain running a little warmer than normal.

How to test the electro-viscous fan clutch

Oops, forgot to mention my 2003 has a regular thermal fan clutch with codes tuned out