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Discussion Starter · #1 · (Edited)
2002 Trailblazer LTZ 4.2 throttle body only partially opens. At full throttle scanner shows APP at 100% but TPS at 30% and is not in reduced power mode and there are no codes. Suspected throttle body. Removed it, put it on my 2005 LS 4.2 and it works fine. ECM? - Wiring? Has anyone had this problem?
 

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2002 chevy trailblazer_lt
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Is this with engine running? Driving or in Park? Remember that these are drive by wire amd the throttle is not going to match the accelerator pedal position.
 

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Discussion Starter · #3 ·
Key on, engine off or running, parked or driving, all the same. removed air inlet to inspect visually, throttle plate barely opens about 1/4 inch. My other trailblazer opens all the way.
 

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2002 Chevrolet TrailBlazer LTZ 4.2L
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How clean is it? Check your wiring and harness plugs at the pedal as well as the throttle for corrosion or issues in the wires.
 

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Key on, engine off or running, parked or driving, all the same. removed air inlet to inspect visually, throttle plate barely opens about 1/4 inch. My other trailblazer opens all the way.
Curious. My 2002 with key on engine off has always shown both throttle sensors at 30-35% with APP sensors at 100%.

Engine running I don't think I have ever had my accelerator pedal to 100% in the 12 years and 140,000 miles I have had it so cannot comment on that.

I can say under normal operation my 2 throttle sensors and 2 accelerator pedal sensors pretty much never match.
 

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'05 Chevy TB EXT
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2002 Trailblazer LTZ 4.2 throttle body only partially opens. At full throttle scanner shows APP at 100% but TPS at 30% and is not in reduced power mode and there are no codes. Suspected throttle body. Removed it, put it on my 2005 LS 4.2 and it works fine. ECM? - Wiring? Has anyone had this problem?
OK --- everyone done guessing by now? Good ... here's the real answer ....

The throttle body will not open far enough to allow the plenum vacuum to fall below a programmed-in value.

It does this by either computing the air flow through the MAF (if it has one) or the values acting upon the MAP or BMAP --- to make sure that there is always some vacuum to pull fumes through the CV side of the PCV. This vacuum must be substantial enough to promote flow of those fumes collected in the crankcase, and ultimately, the CV and KV emission control devices.

You will get progressive throttle as that values rises when/if the RPM and swept volume in the cylindrical airflow increases .... and that keeps crankcase vapors from escaping the engine and getting out to the atmosphere.

I made a video --- <yeah, I dood!> .... LISTEN to it all and get the idea behind HOW it works .....

 

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Discussion Starter · #7 ·
I have 2 trailblazers 2002 and 2005 same engine and drivetrain 4.2 / 4L60E. The 2005 runs and drives perfect and throttle plate opens all the way, APP and TPS readings match 100% at full throttle. The 2002 (which is not in reduced power mode) barely accelerates to a max speed of 20 MPH, throttle plate only opens 1/4 inch, APP at 100% = TPS at 30% (parked or driving). All wires from APP to ECM and ECM to TB / TPS have been tested good. Swapped throttle bodies and both vehicles run the same no change so throttle body is not the problem. APP 1 and 2 agree, TPS 1 and 2 agree.
 

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No. You're wrong here --- the 2002 and the 2005 are NOT "the same" and the ECMs and the whole programmed-in code is different.

That your 2005 can go WOT in neutral, standing still --- is wrong! It is not supposed to work that way .... unless ....

<here's the Crazy Ivan> if you have a tune'd ECM - you MIGHT be able to wing the throttle to 100% - but remember that you might be talking the throttle pedal values and not the actual throttle body opening factor.

I never supposed that the throttle body was defective --- it can only move as the ECM tells it and that's that. You've already proved that this "problem" is in the 2002 TB, solely.

You're urinating on the wrong pants-leg here --- you most likely have a sensor problem ... perhaps <like I said> it could be a sluggish MAF or BMAP or MAP or anything that tells the ECM the quality of the vacuum behind the throttle plate.

If the ECM "sees" that the vacuum is too low - as in going to swap over to pressure from a bonified vacuum value --- then the throttle plates are commanded to NOT open so far as to ruin that vacuum and stall the PCV action.

"Too far" & "too low" is best explained as the value at which vacuum in the plenum, will no longer pull blowby products of combustion <CO, H2SO4, hydrocarbons, condensation - which is water - which destroys the VVT and the cam lobes and main & rod bearings, etc., etc.> --- is sensed and the ECM will not allow the throttle plate to open too far.

I know you're getting tired of blaming me for this problem, and I won't disappoint you 'cause this is kicking a dead cat in my opinion.

I'm gonna say this one more time ... make SURE that the PCV system works correctly --- not like YOU want it to.

By federal law, there must never be any way for the PV to n ot work correctly.

But here's what I'll finally say --- this may also come down to the Federal or CONUS or Canadian or CalEPA standards that affected the way one of your vehicles was manufactured and for which AQMD Zone it would be originally sold in, since The Feds overrule any emissions qualifications for every state --- this included the ICC rules and FTC dictates and then there's always California and New Jersey and Massachusetts, etc.

I'm not gonna waste my free time with arguing with you --- you can do YOU, because by now I have done ME - no matter how your repair turns out.

IDC. 6's and 8s.
 

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Discussion Starter · #9 ·
I only said the engine and trans are the same, never said programming was. But 05 does physically open 100% (stock ECM). Sorry, forgot to mention I've already checked the PCV system. And have already checked all other components. Scanner readings are all normal, and no codes. I'm not arguing with you, nor am I blaming you for anything. I only asked for advice and IDC for YOUR RUDENESS. I will not waste any more of YOUR free time! GFY
 

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'05 Chevy TB EXT
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I only said the engine and trans are the same, never said programming was. But 05 does physically open 100% (stock ECM). Sorry, forgot to mention I've already checked the PCV system. And have already checked all other components. Scanner readings are all normal, and no codes. I'm not arguing with you, nor am I blaming you for anything. I only asked for advice and IDC for YOUR RUDENESS. I will not waste any more of YOUR free time! GFY
If only that were so.

I'm not rude --- you're argumentative and don't want to listen to someone who has better insight into something which you have been in contention.

What proof do you present that the PCV system is working properly --- or even at all?

Stick with it here and learn something and quit trying to impress me with your claims/counterclaims
Can you back them up?
I can, mine.
If you think I'm rude --- I have only just begun - if rude means telling the truth.
 
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