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Discussion Starter #1 (Edited)
Hello everyone my name is Chris and I am new around here. I am glad I found this place because I can really use some help from people who know what they are talking about. I've taken to trying to repair an issue myself rather than the usual trip to the mechanic because they have failed to solve or find the issue. I have a stalling and hesitation issue and I will put the details in bullets below because I know that makes it easier for everyone to read rather than pulling details out of an essay.

2002 Trailblazer LTZ 4.2 6 cyl

Conditions for stalling/hesitation
1. Must have sat for more than 12 hours
2. Must be cold
3. Once fully warm runs like a dream
4. Runs great from the get go if cold but has sat for 11 hours or less
5. No codes or lights


What I have done so far
1. Fully removed and cleaned throttle body spotless
2. Replace all 6 coil packs and plugs
3. Replaced cam position sensor
4. Ran 1 1/2 tanks of fuel system cleaner with 93 fuel

So my next thought is water in the tank? It has never sat long enough for that to be a likely issue.

So next I want to change the Camshaft Position Actuator Solenoid. This is where I am looking for advice. This job is outside my skill level and will have to pay a mechanic. So before I go and tell him to change it, is this a possible cause of my issue??

Thanks all!
 

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2004 gmc envoy_slt
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Do not change parts just by guessing. I think the only way to diagnose this issue is to monitor the live data on the OBDII port with a scan tool when the engine is cold. I believe that the intake air temperature sensor may be giving incorrect data to the PCM. Another possibility is a malfunctioning MAF sensor. These can be confirmed by a technician using a scan tool.
 

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The fact that it's something happening at cold start means it's an open loop issue - ie. the O2s haven't warmed enough, so it's relying on "default" parameters based on the MAP/MAF. My 2007 uses a MAF, but I THINK back then they used a MAP/IAT?

That may point you in the right direction.
 

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2002 chevy trailblazer_ls
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Is this a recent issue? There was a stalling update I had done to mine years ago when it was still under warranty. Hasn't stalled or died sitting at a red light since.

I doubt the cam position solenoid is the problem, plus if you've done 1 thru 3 replacing it would be a piece of cake. I replaced mine because it was leaking oil.
 

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2002 chevy trailblazer_lt
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What state are you in....if your close drive over....if you cleaned the throttle body then replacing the cam sensor and vvt sensor is easy both are 10mm screws, pull the belt release the three 13mm from behind the power steering sprocket the one down below you can loosen enough sometimes to get out of the way to remove the vvt....use only ACDelco parts!!

Typically when the VVT is old and the micro screen clogged you get funckanosis big time especially upon start up after sitting and cold. Once installed pull fuse 10 and 28....the chart is on the underside of the plastic fuse box cover....say 30 min or longer....reset the fuses go have fun....the relearn for the throttle body is 3min turn on and run at idle....turn off for 60 seconds....them turn on and run for 3 mins....then shut car down....next drive make it round trip 40 miles come back home get up next am and you should be good to go....have him look at your bearings and pulley on front they are easy and inexpensive to replace too.
 

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Discussion Starter #9 (Edited)
The fact that it's something happening at cold start means it's an open loop issue - ie. the O2s haven't warmed enough, so it's relying on "default" parameters based on the MAP/MAF. My 2007 uses a MAF, but I THINK back then they used a MAP/IAT?

That may point you in the right direction.
Thanks!! Here is something else its not just a cold start but it has to be a cold start after an extended sit. It can be ice cold but if I drove it to work it will start up and drive fine on my way home. Next morning, its up to its shenanigans again...
 

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Discussion Starter #10
Is this a recent issue? There was a stalling update I had done to mine years ago when it was still under warranty. Hasn't stalled or died sitting at a red light since.

I doubt the cam position solenoid is the problem, plus if you've done 1 thru 3 replacing it would be a piece of cake. I replaced mine because it was leaking oil.
Yes only started a few months ago. The second part requires removing the belt and moving the water pump out of the way. I could do it but you might say I mechanically inclined but not inclined to be a mechanic :dielaugh:
 

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Discussion Starter #11 (Edited)
What state are you in....if your close drive over....if you cleaned the throttle body then replacing the cam sensor and vvt sensor is easy both are 10mm screws, pull the belt release the three 13mm from behind the power steering sprocket the one down below you can loosen enough sometimes to get out of the way to remove the vvt....use only ACDelco parts!!

Typically when the VVT is old and the micro screen clogged you get funckanosis big time especially upon start up after sitting and cold. Once installed pull fuse 10 and 28....the chart is on the underside of the plastic fuse box cover....say 30 min or longer....reset the fuses go have fun....the relearn for the throttle body is 3min turn on and run at idle....turn off for 60 seconds....them turn on and run for 3 mins....then shut car down....next drive make it round trip 40 miles come back home get up next am and you should be good to go....have him look at your bearings and pulley on front they are easy and inexpensive to replace too.
Thanks I appreciate the info I am on Long Island. I am going to put it in the shop at some point. It is my 3rd/snow vehicle and its mid summer so I am not in a rush but I will report back once I get it figured out.
 

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Thanks!! Here is something else its not just a cold start but it has to be a cold start after an extended sit. It can be ice cold but if I drove it to work it will start up and drive fine on my way home. Next morning, its up to its shenanigans again...
hmmm...if it's happening after a long sit (regardless of temp), have to checked into the fuel pressure? I believe back then they used a standard fuel pressure regulator (attached to the fuel rail)? If so, those are prone to fail over time, not holding the pressure. It may be a slow leak, such that a few minutes/hours doesn't bleed off enough pressure, but over a prolonged period, there is enough pressure loss to have a no/poor start. Have you checked the fuel pressure over time? Don't rely on an OBD reading of pressure (if it's available) - use a "real" pressure gauge hooked into the system and see if there is a "resting" pressure drop after however many hours.
 

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2008 chevy trailblazer_lt
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Besides possibly old O2 sensors, and I think there is no MAF sensor for that year, I'd wonder if there are any vacuum leaks like loose intake manifold bolts or cracks in runners, etc. I saw you can buy an aftermarket intake manifold, but I don't know where they may "typically" fail, that the aftermarket decided to make a manifold for them. If you pulled all spark plugs after a normal drive, any one that looks different than the others might tell you if it's any one cylinder running lean, etc. I definitely second the idea of checking fuel pressure, but usually it's a problem of pressure dropping when the pump is hot, I'd guess, or maybe it is low all the time, but not compensated for in open loop.

Rob in AZ
 

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Besides possibly old O2 sensors, and I think there is no MAF sensor for that year, I'd wonder if there are any vacuum leaks like loose intake manifold bolts or cracks in runners, etc. I saw you can buy an aftermarket intake manifold, but I don't know where they may "typically" fail, that the aftermarket decided to make a manifold for them. If you pulled all spark plugs after a normal drive, any one that looks different than the others might tell you if it's any one cylinder running lean, etc. I definitely second the idea of checking fuel pressure, but usually it's a problem of pressure dropping when the pump is hot, I'd guess, or maybe it is low all the time, but not compensated for in open loop.

Rob in AZ
I looked up parts, and it looks like that year IS a MAP (not MAF), oddly, I did not see an IAT (intake air temp) sensor, and usually if it's a MAP system (pressure), there's an IAT for air temp. Perhaps it relies on engine temp? In a MAF system, usually the MAF handles both.

Either way, at startup the engine runs "open loop" because the O2 sensors would not be warmed up to spec yet. Because of open loop, the engine has to use default parameters based on the volume and temperature of the air.

So if it's stalling/running rough at startup, it could be an old/faulty MAP and/or IAT (or engine temp sensor if it's the case) sending bad info to the ECU, which in turn feeds too little/much fuel.

The fact that it DOESN'T happen if only sitting a few hours, points LESS to this type of problem, since it would still start in open loop and he isn't experiencing the problem in such case.

That's why I suggested fuel pressure leak down at rest. If the FP regulator (I checked, and that year DOES use one - versus the later year's in-tank system), does not hold pressure properly, the pressure would draw down so when he tries to start their may be enough residual pressure to FIRE, but the fuel pressure immediately drops (stalling or inadequately fueling the car) until the pump can "catch up."

If you google "fuel pressure regulator" and "stalling," you'll likely see a lot of info on exactly what happens. I also think if you add "Trailblazer" to the search you'd likely see that it's a fairly common problem with the FP regulated Trailblazers.

IF it is the FP regulator, it's likely a VERY slow/small leak for now, given the amount of hours it takes to happen, but will get worse over time.

I THINK the older ones that use an external regulator make it easy to check the pressure - there should be a port to attach a gauge that looks like a tire pressure gauge at/near the rail.

But the problem is why you have to check with a gauge (not OBD), since as soon as you turn the ignition, the fuel pump starts going and you can't see if there was a pressure drop - unless it was so severe that you can see the pressure rise in the first few seconds. It doesn't seem like his is dropping THAT much - IF it's a fuel pressure problem.
 

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Hello everyone my name is Chris and I am new around here. I am glad I found this place because I can really use some help from people who know what they are talking about. I've taken to trying to repair an issue myself rather than the usual trip to the mechanic because they have failed to solve or find the issue. I have a stalling and hesitation issue and I will put the details in bullets below because I know that makes it easier for everyone to read rather than pulling details out of an essay.

2002 Trailblazer LTZ 4.2 6 cyl

Conditions for stalling/hesitation
1. Must have sat for more than 12 hours
2. Must be cold
3. Once fully warm runs like a dream
4. Runs great from the get go if cold but has sat for 11 hours or less
5. No codes or lights


What I have done so far
1. Fully removed and cleaned throttle body spotless
2. Replace all 6 coil packs and plugs
3. Replaced cam position sensor
4. Ran 1 1/2 tanks of fuel system cleaner with 93 fuel

So my next thought is water in the tank? It has never sat long enough for that to be a likely issue.

So next I want to change the Camshaft Position Actuator Solenoid. This is where I am looking for advice. This job is outside my skill level and will have to pay a mechanic. So before I go and tell him to change it, is this a possible cause of my issue??

Thanks all!
I’ve got a 2002 as well doing same thing except it runs fine when engine is up to temp or sometimes I’ll push it in neutral and shut the car off going down the road and restart it and it’s perfect . But only when the engine is not operating temp . I’m at a loss
 
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