2007 GMC Sierra C1500 Classic 4.3L

[thx1138v2]

I'm having a problem with this truck. Once it gets warmed up and I come to a stop light or stop sign the engine dies. It won't restart unless I wait for 20-30 minutes. Then it restarts fine but will die again unless I put it in neutral and keep the RPM's at about1200 at the next stop. I can get it home that way.

 

Does anyone know how to raise the idle on a 4.3L Classic throttle body engine or have any other advice for curing this problem?

 

BTW, it doesn't throw any codes. It just dies.

Edited August 23, 2024 by thx1138v2

[thx1138v2]

******

Edited August 23, 2024 by thx1138v2

[richard wysong]

Fuel filter, ignition control module, clogged injectors , vacuum leak are all possibilities. A scan tool that does live data may be needed to determine the fault. Do not try to adjust the idle. Try cleaning the idle air control valve, it may be stuck or if it is running so poorly that it can't raise the idle enough. Look down the venturi on the throttle body and see if both injectors are spraying evenly, shining a timing light on the spray may help you see the pattern. what does the scanner read for coolant and ambient temperature?

[thx1138v2]

22 hours ago, richard wysong said:

Fuel filter, ignition control module, clogged injectors , vacuum leak are all possibilities. A scan tool that does live data may be needed to determine the fault. Do not try to adjust the idle. Try cleaning the idle air control valve, it may be stuck or if it is running so poorly that it can't raise the idle enough. Look down the venturi on the throttle body and see if both injectors are spraying evenly, shining a timing light on the spray may help you see the pattern. what does the scanner read for coolant and ambient temperature?

It doesn't have a fuel filter. The ignition control module is new and I renewed the temperature grease on the back between the module and the heat sink and the heat sink and the steel bracket.

 

It runs fine when it runs so that rules out clogged injectors and vacuum leaks. It is a 2007 model so it has OBDII but throws no codes.

 

Do not try to adjust the idle. OK.

 

IAC is new so that's not the problem. It is an LU3 engine so I can't see the injectors but it has 6, not 2.

 

 Coolant temperature shows on interior gauge and is acceptable. Ambient is about 90F but it doesn't matter if I'm driving in early AM or late afternoon, I have the same problem.

 

I tried to bench test an O2 sensor this morning but couldn't get it above ~375F with my propane bottle. I'll have to get some oxygen for my oxy/acetylene rig.

 

At this point I'm thinking it is running fine while in open loop but stumbles and dies when I come to a stop and it has switched over to closed loop. I can go a couple of miles but when I come to a stop it dies. If I let it cool off for ~30 minutes or so it will start and run fine until the next time.

 

Edited August 24, 2024 by thx1138v2
Added more info

[richard wysong]

Yeah you need a scan tool that does live data to see what the problem is. The temp gauge and actual outside temp have nothing to do with what the sensors are reporting to the PCM . I would check the fuel pressure AND volume. There is a filter in the tank that may be clogging and then the debris washes off enough to restart

[thx1138v2]

How would a temporary clog of the in-tank filter show up on a pressure test?

[richard wysong]

The pressure should drop off