long starting when warm

[Sebaz]

I have an issue with my 96 sonoma 4.3 with 177,000 miles. When it's cold it starts great, it turns over a bit longer when the engine is warm or hot. It will seem to idle a little rougher afterwards. I have checked for vacuum leaks manually and with a scanner and couldn't find any. What could be causing this?

Things I have done so far.
Replaced fuel filter, spark plugs and wires(got the good ones), cap and rotor(ac delco), coil, air filter, engine temperature sensor, replaced the fuel pump 8 months ago because the old one failed, had the fuel injection cleaned. I have checked the pressure on the fuel pump, when you turn the ignition on the pressure goes to 60 psi then drops to 55psi while idle. I watched the pressure after I turned the engine off and it dropped to about 30psi after 15 minutes, but quickly jumped back to 60 once the ignition was on. I don't figure that's too much bleed off, it will take longer to start after 1 minute and the pressure is still up. I don't have any engine codes coming up. I have changed the TPS and AIC also. I also checked the sensor at the air intake. I think that's it.

we scanned the engine and only found cylinder 2 misfiring a little. I pulled the spark plug and it wasn't white or ashy ( I was wondering if the fuel injector was clogged maybe) It always eventually starts, just very annoying.

any ideas?
thanks

 

[Molson02536]

I have an issue with my 96 sonoma 4.3 with 177,000 miles. When it's cold it starts great, it turns over a bit longer when the engine is warm or hot. It will seem to idle a little rougher afterwards. I have checked for vacuum leaks manually and with a scanner and couldn't find any. What could be causing this?

Things I have done so far.
Replaced fuel filter, spark plugs and wires(got the good ones), cap and rotor(ac delco), coil, air filter, engine temperature sensor, replaced the fuel pump 8 months ago because the old one failed, had the fuel injection cleaned. I have checked the pressure on the fuel pump, when you turn the ignition on the pressure goes to 60 psi then drops to 55psi while idle. I watched the pressure after I turned the engine off and it dropped to about 30psi after 15 minutes, but quickly jumped back to 60 once the ignition was on. I don't figure that's too much bleed off, it will take longer to start after 1 minute and the pressure is still up. I don't have any engine codes coming up. I have changed the TPS and AIC also. I also checked the sensor at the air intake. I think that's it.

we scanned the engine and only found cylinder 2 misfiring a little. I pulled the spark plug and it wasn't white or ashy ( I was wondering if the fuel injector was clogged maybe) It always eventually starts, just very annoying.

any ideas?
thanks

Try replacing your map sensor and inspecting you ICM, very first sign of a failing ICM (ignition control module) is hard starts when they start to warm up and get hot. After it cools off again, the engine starts great. The MAP sensor can also do this but you would of had a code for a faulty MAP sensor reading. Try those two area's for now and keep us posted eh.

Keep up the great work on keeping your Sonoma running like new.

 

[Sebaz]

will try the ICM. the scan said the MAP was reading right.
thanks

 

[Sebaz]

changed to ICM and the MAP sensor (this one because it broke when i was trying to check it), still having the same issue.

 

[Molson02536]

changed to ICM and the MAP sensor (this one because it broke when i was trying to check it), still having the same issue.

The only other thing that can cause your issue would be a bad CSFI system and it's going to need to be replaced. You might get lucky with trying to clean the fuel system out with fuel injector cleaner and see if that will clear up your idling issues. You mentioned you only get 60 PSI, you should be getting 62-65 PSI during your starts.

You may be weak on fuel pressure, even a couple of lbs low on a cold start will cause a no start. Double check cold start cranking fuel pressure. If under 63-62 lbs you have problems. Run the full fuel pressure test and post back pressures.

Here is the guide lines on testing.
Hard to start cold. If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Check cold start fuel pressure. Cold start should be 64-65 lbs of pressure.
Check engine running fuel pressure. Later V6 and V8 gm engines should have 60-66 fuel pressure.
Check engine running on the road fuel pressure. Engine running should be 60-66 lbs pressure depending on engine load.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure. Full pressure with return pinched off should be 75-85 or more, and if it has a fast leak down after shut off you have a leak.

Post back fuel pressure readings. Oh also take note that the ground lead wire to the fuel sending unit is separate and is grounded on the frame and has been know for that wire to corrode and give a bad ground.

Here is a TSB about the issues your describing.

http://members.shaw.ca/betterthanyoutoo/Sticking Poppet.htm

Keep me posted.