NEED HELP Doesn’t stay running when cold

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
I have an 07 gmc envoy 4.2 I6 4wd with 165k miles. No codes showing when scanned.
So on cold mornings it will start up immediately then rpms jump around for a few seconds then dies. It does this whether I give it gas or not until it gets a little warmth to it. I have replaced the MAF, MAP, and temperature sensors, intake manifold gasket, and throttle body. It has recently also had air filter, spark plugs, and battery replaced. I have tested fuel pressure, the fuel injectors and vacuum pressure. The O2 sensors are reading within tolerance.
I am rather lost on what else the problem could be. Any advice at this point would be greatly appreciated.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Only because it is easy to do.... I would try cycling the ignition key a few times before starting the engine just to see what happens. Cycling the key should cause the fuel pump to run its prime routine each time. If it behaves differently then you could concentrate efforts on the fuel system.
 
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mrrsm

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Check the MAF and EFI Ignition and Other Harnesses over very closely with a Bright Flashlight while looking for signs of "Rodent Over-Night Stays" under the hoods of any vehicles with invitingly Warm Engines at Nightfall.

They have this Nasty Habit of Chewing on the Wiring and Plastic Electrical Connectors enough to wear down their Incisors and this condition can leave us all confused about Sketchy Running SUVs & Trucks ...if the damage goes overlooked.
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
Only because it is easy to do.... I would try cycling the ignition key a few times before starting the engine just to see what happens. Cycling the key should cause the fuel pump to run its prime routine each time. If it behaves differently then you could concentrate efforts on the fuel system.
Funny you said that. I did that this morning after a couple of failed starts and it started and ran perfectly fine. I’ll start check more into the fuel system.


Check the MAF and EFI Ignition and Other Harnesses over very closely with a Bright Flashlight while looking for signs of "Rodent Over-Night Stays" under the hoods of any vehicles with invitingly Warm Engines at Nightfall.

They have this Nasty Habit of Chewing on the Wiring and Plastic Electrical Connectors enough to wear down their Incisors and this condition can leave us all confused about Sketchy Running SUVs & Trucks ...if the damage goes overlooked.

i have thought about something chewing on wiring but once it starts and stays running it’s fine all day. Once it gets a little warmth to it it’s fine.
The MAF is new and been rechecked.
When you say the EFI ignition are you talking about the ignition switch or something else?
Forgive me as I’m not a mechanic by trade so there’s a lot I don’t know.
 

mrrsm

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NP... There is still so much that I too have yet to learn... The EFI (Electronic Fuel Injectors) use a Wire Harness to communicate to and from the PCM. It runs along the Top Left Side of the Engine Block adjacent the Black Plastic Intake Manifold connecting to each of the (6) EFIs in turn.
Small Deer Mice can crawl along in that narrow area and Chew on the Harness ....out of Plain View.

Rising Temperatures can serve to seal up temporary Vacuum Leaks around the gaps in the three Oval Paired Gaskets of the Intake Manifold that when Ice Cold... shrink down enough to allow un-metered air to get ingested into the Engine. Those gaskets can be snugged up using ONLY 87 Inch Pounds of tightening torque along the Intake Manifold Flange

This action of having un-metered leaks sidesteps the means for Weighing the amount Air being ingested (Gram By Gram) as the Incoming Air Stream normally should be passing through The Air Filter Box, The Mass Air Flow Sensor, The Inlet Air Temperature Sensor while sending signals to the PCM with enough information for it to Gauge, "How Much Fuel Does This Motor Need to Run Right at THIS Present RPM?".

Unmetered Air can "Throw a Monkey In The Wrench" with all of those Computer Controlled Steps and ruin the chance for the Engine to function properly. Also... If the Rodents Feast on the Wiring Insulation and Plastic EFI Connectors... Random Short Circuits may occur in the Wiring Harness as the Engine operates and confuse things for the PCM and cause poor or failed engine performance.
 
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Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
NP... There is still so much that I too have yet to learn... The EFI (Electronic Fuel Injectors) use a Wire Harness to communicate to and from the PCM. It runs along the Top Left Side of the Engine Block adjacent the Black Plastic Intake Manifold connecting to each of the (6) EFIs in turn.
Small Deer Mice can crawl along in that narrow area and Chew on the Harness ....out of Plain View.

Rising Temperatures can serve to seal up temporary Vacuum Leaks around the gaps in the three Oval Paired Gaskets of the Intake Manifold that when Ice Cold... shrink down enough to allow un-metered air to get ingested into the Engine. Those gaskets can be snugged up using ONLY 87 Inch Pounds of tightening torque along the Intake Manifold Flange

This action of having un-metered leaks sidesteps the means for Weighing the amount Air being ingested (Gram By Gram) as the Incoming Air Stream normally should be passing through The Air Filter Box, The Mass Air Flow Sensor, The Inlet Air Temperature Sensor while sending signals to the PCM with enough information for it to Gauge, "How Much Fuel Does This Motor Need to Run Right at THIS Present RPM?".

Unmetered Air can "Throw a Monkey In The Wrench" with all of those Computer Controlled Steps and ruin the chance for the Engine to function properly. Also... If the Rodents Feast on the Wiring Insulation and Plastic EFI Connectors... Random Short Circuits may occur in the Wiring Harness as the Engine operates and confuse things for the PCM and cause poor or failed engine performance.
I made sure to get it properly torqued when I replaced it but I will double check it. And I will look at the harness to see if I can find anything. Would it be possible the little O rings on the injectors are allowing air in when it’s cold?
 
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mrrsm

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Those Viton (Teflon) PTFE (Poly-Tetra-Fluorine-Ehtyline) "O" Rings are usually VERY Snug inside of the Aluminum Engine Head Intake Ports, so I would doubt they'd be expanding or shrinking enough to allow any ambient air to slip by. The normal induction of Fresh Air from the Intake Manifold helps to carry in and mix with the fuel misting from them deeper inside each cylinder, so normal outside air pressure has no affect upon them.

Besides... They are so low and intimately placed along the intake side of the engine block that with the rapid, rising heat from combustion... they warm up so rapidly that even under the Coldest Conditions, they all rapidly seal up inside of their six smooth tubes leading just above the where the intake valves leading to the combustion chambers open and close. Those seals are meant more for keeping fuel spray inside of the engine head rather than keeping any ambient air out.
 
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gmcman

Member
Dec 12, 2011
4,656
You could try a new fuel pump relay, hope for the best. What plugs did you use? Not likely the plugs, but the colder dense air being harder to light off if maybe a severly incompatible set of plugs were used.

I'm also going with a possible fuel pressure issue as more fuel is required when cold.
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
You could try a new fuel pump relay, hope for the best. What plugs did you use? Not likely the plugs, but the colder dense air being harder to light off if maybe a severly incompatible set of plugs were used.

I'm also going with a possible fuel pressure issue as more fuel is required when cold.

I used ac delco iridiums. Not 100% of the code off the top of my head but I know they were highly recommended on another forum for the I6. We tested the pressure and injectors but that was after it started for the day. May have to try again when it’s messing up and see what we get. as for the relay I actually tried swapping it out and had the same result. I appreciate you guys throwing ideas out because I was completely out!
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
ACDelco 41-103 Iridium are the only ones this engine likes.
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
Just curious, how cold is cold? To me that means below 0 degrees F. To someone in Florida or Arizona it could be 40!! :wink:
So around 32F is when it’s acting up.
it’s currently 25F with gusts of wind up to 40mph. And it died on me but once it reached its normal temperature it’s been fine.
ACDelco 41-103 Iridium are the only ones this engine likes.
yes those are the ones! I couldn’t remember the number on them, thank you
 

gmcman

Member
Dec 12, 2011
4,656
What was replaced before you had the issue with the cold operation? Focusing on the throttle body and the idle speed. Recently a member had an issue with a broken tooth on the plastic gear.

Being in open loop, the PCM relies on stored data, so you may have a lean condition or just a lack of airflow.

I would try to reset everything, pull the PCM fuse or remove the NEG cable for 15 min.

Upon re-connection, turn the key to ON but don't start it, let it sit there for about 2 min, then start the engine but don't touch the gas.

If it runs, let it fully warm up. If it stalls, let it crank without touching the gas a few times.

Maybe it can relearn the cold idle. I'm thinking it has old values stored on an old throttle body, and this much colder air is not playing well with the stored tune.

Worth a try.
 
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Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
What was replaced before you had the issue with the cold operation? Focusing on the throttle body and the idle speed. Recently a member had an issue with a broken tooth on the plastic gear.

Being in open loop, the PCM relies on stored data, so you may have a lean condition or just a lack of airflow.

I would try to reset everything, pull the PCM fuse or remove the NEG cable for 15 min.

Upon re-connection, turn the key to ON but don't start it, let it sit there for about 2 min, then start the engine but don't touch the gas.

If it runs, let it fully warm up. If it stalls, let it crank without touching the gas a few times.

Maybe it can relearn the cold idle. I'm thinking it has old values stored on an old throttle body, and this much colder air is not playing well with the stored tune.

Worth a try.
Nothing had been replaced before the problem started. Just basic maintenance (oil change, air filter) it acting up is what lead to all the other items being replaced.
I will give that relearn a try and see what happens.
thank you!
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
What was replaced before you had the issue with the cold operation? Focusing on the throttle body and the idle speed. Recently a member had an issue with a broken tooth on the plastic gear.

Being in open loop, the PCM relies on stored data, so you may have a lean condition or just a lack of airflow.

I would try to reset everything, pull the PCM fuse or remove the NEG cable for 15 min.

Upon re-connection, turn the key to ON but don't start it, let it sit there for about 2 min, then start the engine but don't touch the gas.

If it runs, let it fully warm up. If it stalls, let it crank without touching the gas a few times.

Maybe it can relearn the cold idle. I'm thinking it has old values stored on an old throttle body, and this much colder air is not playing well with the stored tune.

Worth a try.
Didn’t help. It did the same thing. I noticed it seems to be bouncing between normal idle and the cold idle when it does it.
 

mrrsm

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Oct 22, 2015
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Given the issues of the Deep Winter Cold conditions you have to deal with right now... I'm loathe to suggest doing this, but it might be time to R&R the Coil Packs and Test them ALL using a DMM,

This entire R&R procedure is nicely covered and explained in this linked Video; but in particular from around 1:30 into it, the VOP (Video Original Poster) Demonstrates How to DO this specific procedure and explains what you should be looking for.

Just know that Failing Coil Packs can sometimes present with the symptoms of having Difficult Starts and Inexplicable Stalls. Even though your situation is somewhere in-between, looking into this possibility may give you a new direction for solving the problem.

The only GOOD aspect of this is that the entire procedure happens right on top of the Engine. Please... Be Very Careful when Unbolting and Re-Tightening these COP Fasteners to avoid snapping them off. As with Spark Plug R&Rs ... Do NOT attempt to remove them when the Engine is HOT:


At 3:40 into THIS Video... The VOP uses a Digital Multi-Meter to perform a Generic COP OHMS or Resistance Test that you can also follow and emulate with your GM 4.2L Coil On Plugs and likewise test them in this manner:

 
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budwich

Member
Jun 16, 2013
2,027
kanata
Post some data (running warm at idle and constant medium throttle)... things like trims, vacuum, rpm, upstream o2 sensor readings. They may provide some direction.

Having said that... your post 4 indicated you would "work with a fuelling area" more... have you done anything there in to investigate further. You could try jumpering (bypassing) the fuel pump relay on a "cold start attempt" and see if that changes the reaction... go from the result.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Also post the cold and running coolant temps. Is your temp gauge working correctly? Where am I headed with this? Maybe it's not reading the correct temp and is going into closed loop when it shouldn't.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
Funny you said that. I did that this morning after a couple of failed starts and it started and ran perfectly fine. I’ll start check more into the fuel system..

If it ran "perfectly fine" when you did this key cycle test, have you repeated this procedure? Not only after failed start attempts but right from the start? If it runs "perfectly fine" when you do this why then chase other squirrels through the forest?
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
If it ran "perfectly fine" when you did this key cycle test, have you repeated this procedure? Not only after failed start attempts but right from the start? If it runs "perfectly fine" when you do this why then chase other squirrels through the forest?
Because the last few days were warmer and the issue went away again. Now that the temperature has dropped again it’s back. I think cycling the key was a fluke because I have repeated the test with no success.

Also post the cold and running coolant temps. Is your temp gauge working correctly? Where am I headed with this? Maybe it's not reading the correct temp and is going into closed loop when it shouldn't.
I currently can’t post any numbers as I’m not at the shop and my scanner doesn’t show live data. If I get a chance to I will.
 

Voy07

Original poster
Member
Dec 20, 2020
9
Belton Missouri
Well here’s to fingers crossed! I got ANOTHER throttle body and swapped it out. Turned it over once and no change. Did the relearn suggested by GMCMAN except I gave it a half hour instead of 15 minutes...fired right up nice and smooth. It’s almost to normal operating temperature. Once it gets there I will let it sit. The outside temperature is supposed to be in the teens again this evening(27F now) and I will test it again to see if I really have fixed it.
whether it’s fixed or not I want to thank ALL of you. I was at my wits end with it and little suggestions and tweaks helped me keep at it as much as the big ones. Couldn’t have done it without you all!
 

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