Weird Starting Issue After Truck Sits More Than A Few Hours

[hagar]

Cylinders have no fuel in them. Injectors are not leaking. Plugs are clean and dry. Even tested the injectors with noid lights. After the truck has warmed up it'll fire back up with no issues whatsoever. That is until it sits again for a few hours or more. Also, when the truck is running and you disconnect the MAF, it doesn't die or change or anything. I've owned tons of cars and fixed tons of cars and every car I've had if I've disconnected the maf while running it will die immediately. No I don't have any codes for the maf though. Today it also threw the P0172 and P0175 codes on top of the P0178 and P0443. Both purge valves were replaced with OEM. Didn't change a thing. I was considering it being an ecm because it has some other weird electrical things that have made me think it could be the ecm. I know it is a common thing on GM trucks and cars of the 00's.

Seems like you have gone over everything, sounds like you know what you have left to try. Could be an internal ground in the ecm causing issues. When you read about the ground issues on the frame and head and such causing these issues, the same can happen with internal grounds on ecms. I have successfully fixed internal ecm ground issues in the past by running various sensor grounds to actual grounds, but you kinda need to go over the wiring diagrams to figure out the reasoning of the problem. I have had a couple throttle position sensor problems for example that wouldn't solve its issue by replacing the sensor, but splicing into the ground wire feeding the sensor, and putting it to direct ground fixed the issue because the computer itself was responsible for supplying the ground internally and couldn't. The computer itself didn't even care I was grounding externally.

The problem is you need to still realize the problem to solve it. I wouldn't even try to start the truck unless the scanner is hooked up and logging, you need to be able to catch the flaw in real time. If you see the coolant temp showing negative 50 degrees for example when you turn the key on before starting, you know your problem.

There is no such thing as voodoo and witches with vehicles, it just feels like it sometimes. It's just data that needs to be figured out, it is there to interpret if you treat it as a circuit and don't just jump around.

If i had the truck, i would pull it in my shop and shut it off. I would then wait the 6 plus hours required to get a no start, then i would hook my computer up to it with key on power only, without trying to start it.

I would then look at my coolant temp, air intake temp, map and maf, source of fuel commanded, fuel commanded, injector pulse width both banks, then I would attempt a crank and see what happens. If it doesn't Start after 2 seconds, I would leave the key on and don't touch the throttle, then look at all the data. The reason the truck isn't starting will be somewhere in that data alone, since you know you have proper fuel and spark.

 

[TylerHagerdorn]

Seems like you have gone over everything, sounds like you know what you have left to try. Could be an internal ground in the ecm causing issues. When you read about the ground issues on the frame and head and such causing these issues, the same can happen with internal grounds on ecms. I have successfully fixed internal ecm ground issues in the past by running various sensor grounds to actual grounds, but you kinda need to go over the wiring diagrams to figure out the reasoning of the problem. I have had a couple throttle position sensor problems for example that wouldn't solve its issue by replacing the sensor, but splicing into the ground wire feeding the sensor, and putting it to direct ground fixed the issue because the computer itself was responsible for supplying the ground internally and couldn't. The computer itself didn't even care I was grounding externally.

The problem is you need to still realize the problem to solve it. I wouldn't even try to start the truck unless the scanner is hooked up and logging, you need to be able to catch the flaw in real time. If you see the coolant temp showing negative 50 degrees for example when you turn the key on before starting, you know your problem.

There is no such thing as voodoo and witches with vehicles, it just feels like it sometimes. It's just data that needs to be figured out, it is there to interpret if you treat it as a circuit and don't just jump around.

If i had the truck, i would pull it in my shop and shut it off. I would then wait the 6 plus hours required to get a no start, then i would hook my computer up to it with key on power only, without trying to start it.

I would then look at my coolant temp, air intake temp, map and maf, source of fuel commanded, fuel commanded, injector pulse width both banks, then I would attempt a crank and see what happens. If it doesn't Start after 2 seconds, I would leave the key on and don't touch the throttle, then look at all the data. The reason the truck isn't starting will be somewhere in that data alone, since you know you have proper fuel and spark.

Coolant temp has been reading normally since replacing the sensor. If you look back in this thread I posted the readings from yesterday. Dead cold, key on engine off. Here it is again. Truck sat for 12 hours. The readings where it's running were only a couple minutes into it running. I've replaced all the infamous grounds with good solid grounds and even added a couple. But I may pick up an ecm from the junkyard because they are only 20$. I'm leaning towards the ecm quite honestly. If the readings look okay to you then I'll grab an ecm. My scanner isn't crazy advanced but does show fuel trims and the normal live data stuff. I can get fuel trims with it dead cold and not running if that makes a difference. They looked in spec to me.
Alright so here's the readings-
Cold readings Not Running:
MAP-29(inHg)
ECT-32 degrees
IAT-32 degrees

With Truck Running:
MAP-10(inHg)
ECT-60 degrees
IAT-32 degrees
MAF-1.37(lb/min)

 

[hagar]

Coolant temp has been reading normally since replacing the sensor. If you look back in this thread I posted the readings from yesterday. Dead cold, key on engine off. Here it is again. Truck sat for 12 hours. The readings where it's running were only a couple minutes into it running. I've replaced all the infamous grounds with good solid grounds and even added a couple. But I may pick up an ecm from the junkyard because they are only 20$. I'm leaning towards the ecm quite honestly. If the readings look okay to you then I'll grab an ecm. My scanner isn't crazy advanced but does show fuel trims and the normal live data stuff. I can get fuel trims with it dead cold and not running if that makes a difference. They looked in spec to me.
Alright so here's the readings-
Cold readings Not Running:
MAP-29(inHg)
ECT-32 degrees
IAT-32 degrees

With Truck Running:
MAP-10(inHg)
ECT-60 degrees
IAT-32 degrees
MAF-1.37(lb/min)

The only thing out of that info that is unusual to me is that your air intake temp stays the same as key off ambient temp after 12 hours.

If your starting problem was after a short amount of time not running, I would say we have your answer.. if your operating system is running with the air intake temp as a start up fuel input, it would make perfect sense that you have an over fuel situation on a warm engine with your ait reporting cold when the air charge is warm, but you are saying it only happens after the engine cools.

Warm that sucker right up and see if your ait still shows 32.

 

[hagar]

The science behind the ait theory is that you inject certain amounts of fuel vs temp because of not only the air density, but the intake wall temperature impact of the injection. If you have a warm engine and inject the same amount of fuel as a cold engine when starting, the engine will flood and not start.

This is not a small deal on starting an engine. If I am even a few percentage points off on a tunes cranking fuel, it makes the difference between a vehicle that cranks and stalls, or one that fires right up and idles.

 

[TylerHagerdorn]

The only thing out of that info that is unusual to me is that your air intake temp stays the same as key off ambient temp after 12 hours.

If your starting problem was after a short amount of time not running, I would say we have your answer.. if your operating system is running with the air intake temp as a start up fuel input, it would make perfect sense that you have an over fuel situation on a warm engine with your ait reporting cold when the air charge is warm, but you are saying it only happens after the engine cools.

Warm that sucker right up and see if your ait still shows 32.

The other day it stayed the same. And I let the truck run for 30 minutes. I haven't checked today. But it still really struggles and sometimes doesn't start even after sitting for an hour or two. Once it's fully warmed up, it'll start right up after you shut it off and say go into the store. But after an hour or two of sitting or longer it has that issue.

 

[TylerHagerdorn]

The science behind the ait theory is that you inject certain amounts of fuel vs temp because of not only the air density, but the intake wall temperature impact of the injection. If you have a warm engine and inject the same amount of fuel as a cold engine when starting, the engine will flood and not start.

This is not a small deal on starting an engine. If I am even a few percentage points off on a tunes cranking fuel, it makes the difference between a vehicle that cranks and stalls, or one that fires right up and idles.

The IAT is in the MAF from what I'm reading...is that correct? And again if you disconnect the MAF while the truck is running nothing changes or happens and it doesn't die. It appears it's the OEM maf as well. I did take it out and use CRC MAF cleaner and cleaned it well but it didn't change

 

[TylerHagerdorn]

The science behind the ait theory is that you inject certain amounts of fuel vs temp because of not only the air density, but the intake wall temperature impact of the injection. If you have a warm engine and inject the same amount of fuel as a cold engine when starting, the engine will flood and not start.

This is not a small deal on starting an engine. If I am even a few percentage points off on a tunes cranking fuel, it makes the difference between a vehicle that cranks and stalls, or one that fires right up and idles.

Hagar,
It's been getting worse and what I mean is even just an hour or two will cause this issue now. If you drive it and get it warmed up, run in the store and come back it'll start up. But now it's to the point where it acts up after an hour or two. Now I'm wondering if it's the maf since it has the iat in it. It is the original one with 243k miles and 18 years old. I will get you an iat reading in a bit after I drive it for awhile and get it fully warmed up

 

[TylerHagerdorn]

Hagar,
Fully warmed up and I drove it around for 3 hours the IAT was reading 32 degrees and the MAF was reading 0.76 LB/MIN.

 

[George B]

deleted stupid comment.

 

[TylerHagerdorn]

Can’t remember if I asked this.

Can you post a video of a failed start for us? I have a theory…

My previous “2003 Burb” had an issue restarting when it was luke warm. When I would turn the key it almost start and kick the starter back. It would do that several times and then be flooded and require holding the pedal to the floor. I suspect it may have actually been the starter but traded it in before fixing it.

If you've read my thread, you will see that it's not the starter and it starts fine when it's warmed up and been running. It only has the issue when it's dead cold. Thanks for your comment but the above member Hagar is onto something. It's computer or sensor related.

 

[Fless]

The intake air temp should be changing as the truck warms up. I'd say that it's time to swap in a known good MAF to see if that makes a difference.

 

[George B]

If you've read my thread, you will see that it's not the starter and it starts fine when it's warmed up and been running. It only has the issue when it's dead cold. Thanks for your comment but the above member Hagar is onto something. It's computer or sensor related.

I have been following your thread all along but I forget stuff. Just thought I would throw it out there… I will go ahead and delete my stupid comment.
Good luck.

 

[TylerHagerdorn]

This morning the iat was reading 21 degrees. Yesterday it was 18 degrees outside and this morning it was 13 degrees. It didn't seem to struggle to start this morning but as soon as it caught I gave it gas to make sure it stayed running. I'm definitely doing to pick up a couple used ecms but I'm just waiting to hear from you on if you think the iat is bad Hagar. Let me know. Thank you

 

[TylerHagerdorn]

The intake air temp should be changing as the truck warms up. I'd say that it's time to swap in a known good MAF to see if that makes a difference.

Isn't the iat supposed to be somewhat close to ambient temperature? I haven't messed with an iat since my cavalier some 5 years ago

 

[Fless]

Isn't the iat supposed to be somewhat close to ambient temperature? I haven't messed with an iat since my cavalier some 5 years ago

Yes, close to ambient. The engine compartment temps can affect the IAT. On mine the IAT goes up somewhat from what's shown at a cold start.

 

[TylerHagerdorn]

Yes, close to ambient. The engine compartment temps can affect the IAT. On mine the IAT goes up somewhat from what's shown at a cold start.

It's 20 degrees outside here right now. We are about to head out so I will get a cold reading and then a warm reading again. If I unplug the maf nothing happens. Truck doesn't die or change at all. Every car I've ever worked on if you unplugged the maf it would die immediately if it was good. With these trucks having the iat and MAF in one unit is different for me but I'm not sure if it's actually bad or not. I'm waiting for Hagar to give me his input as well. I'm leaning towards the ECM being bad because I have weird shit going on besides this. I know ecms are common to act up on these GMT800 trucks.

 

[Fless]

A MAF issue is much more common than a ECM issue; however, before replacing the ECM I would recommend removing and inspecting both ECM connectors. The gaskets can go bad, leading to water migration, especially in the lower part of the connector. This has been know to cause parasitic draw and all sorts of sensor issues. Costs nothing but some time and a little work.

 

[TylerHagerdorn]

A MAF issue is much more common than a ECM issue; however, before replacing the ECM I would recommend removing and inspecting both ECM connectors. The gaskets can go bad, leading to water migration, especially in the lower part of the connector. This has been know to cause parasitic draw and all sorts of sensor issues. Costs nothing but some time and a little work.

Yeah you're right on that for sure. But I know the computers have issues on these trucks too. The IAT readings fluctuated while driving earlier but was still within 10 degrees of ambient temp. Now, I got home and I went to unplug the maf and nothing happened, and then when I tapped on the MAF and connector then unplugged it the rpms dropped significantly but it didn't die. I plugged it back in, then tried unplugging the MAP sensor and that made it die immediately.

 

[TylerHagerdorn]

A MAF issue is much more common than a ECM issue; however, before replacing the ECM I would recommend removing and inspecting both ECM connectors. The gaskets can go bad, leading to water migration, especially in the lower part of the connector. This has been know to cause parasitic draw and all sorts of sensor issues. Costs nothing but some time and a little work.

I know it's a little different but I had an issue with a 2002 Cavalier I owned a few years ago. It was a weird ass fuel issue. We replaced the pump and filter and harness with an OEM Delphi unit and it was still acting up. Turned out the main harness connector under the drivers side kickpanel the wire for the fuel pump had melted at the connector and it was common. I cut the wire at each end and spliced in a wire bypassing the connector for that wire and it fixed it. I haven't pulled the connectors at the ecm yet but I have heard the gaskets go bad. It's such a dumb location to mount the ecm in these trucks among other gm cars.

 

[TylerHagerdorn]

Hey all. Figured I'd post here and update what I've found since the last time. Fuel pressure should be 48-54 since mines a flex. Hit the key and the pressure is about 45. Even when running. After it sits for more than a couple hours it's back down 0 psi. Suspected an internal fault on the FPR. Replaced with an ac Delco and no change. Still loses all pressure fast. Pulled all plugs again and dry. I beat on the bottom of the tank and it started right up but I also had the throttle body unplugged at the same time and forgot. Not really much else besides the fuel pump right?