I Have a 1999 Chevy S10 4.3 Vortec. I am having a problem starting the truck when it sits for a while. It will crank over for several minutes. Once it starts and i run it, it will start all day with no issues. It only happens when it sits over night or for a long time.I can hear the fuel pump turn on, and it has been replaced. The plugs, wires, and cap all have been done. Tried a new battery. Had hours of diagnostics done and have gotten nowhere. I just dont get why it is only when it sits. Its driving me crazy.

Any Ideas?

 

Howdy, jrod332.Was the fule filter also changed? try some fule injector cleaner/octaine boost, and a free code scan from the parts store. it might read out somthingintermittint, also check your ground wires to the chassy.

 

Howdy, Update on cold start or sitting a while,The Haynes manual pg 6-8 (IAT) Intake Air Temperature sensor, Inside the air duct in the filter housing acts like a cold air thermostat. I suggest the manual from a parts store for the rest of the details.
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Definately could be a air thermo sensorproblem as stated by sickvortec.

 

There is a sensor at the back of the engine, it is on the driver side behind the valve cover, this sensor was not on the 1995 engine block i used to rebuild my jimmy. i think it is called the ambient oil temp sensor, regardless i changed that and it was just about impossible because you really need the engine out to do stuff like that, anyway with some work you can change it and some cars don't have a clip, so you will need to splice the replacement back to the harness, anyway i had a similar problem, it wouldn't start and would kill the battery or at least almost drain it before it started running, hope this helps someone.

 

98 4.3 sonoma. Going down a steep hill, I downshifted the auto to 3. It gets to bottom of hill and stalls. I roll into side lot and try to restart it. It won't start and the battery dies. I tow it home and begin restoration process. I first diagnosed a weak spark situation. May have been like that a long time. I pull a used coil that tested in limits, $3. I also pulled a used ICM $10. I went ahead and took the cap as it looked better than mine $3. I get it all put on and it sputters. I figured its flooded. I cranked it on and off for a day and finally it fires off and runs great. I will most likely need a starter next.

Continued issues are a faulty fuel regulator. Short term solution is to unplug the vacuum sensor. Only an issue on hot days. Also could use new plugs and wires but on the 4.3 Sonoma, its a "b".

 

So what solved the problem?