Weird Starting Issue After Truck Sits More Than A Few Hours

[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?