I have a 95 Jimmy with a 4.3l that I’ve been having intermittent long starts on and a slightly shaky idle. I got a P0340 code for the camshaft position sensor yesterday and through a new sensor in it. Sensor wires looked good. I’m still having long start times and a shaky idle. Fuel pressure and leakdown look good. The long starts occur after getting the car hot and parking it for several hours. If I start it after a long start and don’t let it get hot and start it again after several hours it starts fine. Could it be a bad PCM? Does anyone having experience with PCMs going bad on these?

 

A bad PCM is a rare occurrence and I don't think your there yet. Your P0340 code is a bad camshaft sensor circuit problem. Its the wiring, grounds, power, reference voltage, etc at least half the time when a sensor circuit has problems. If a sensor is cheap and easy to get to then throwing a new sensor at it with the parts cannon is OK but its better to check those other things first. You need to test power, ground at the sensor and the integrity of the signal wire.

On your long start, check the fuel pressure during a quick start and compare that to the same measurement during a long start. Same with spark at a couple of plugs. 1" of strong blue spark with a regular cadence. :Look under your distr cap for carbon tracing or arcing. Mist the electrics in the dark during a long start and look for external arching.

George

 

If I had to guess (and I do), I would say it sounds like fuel is leaking somewhere into the intake manifold (leaky injector or fuel pressure regulator, maybe) and causing it to flood when hot. You can check with a fuel pressure gauge to see if it leaks down after you shut it off, or maybe try holding the gas pedal all the way down while you try to start it.