car started running poorly,no power, wouldn't rev past 2500 rpm under load or not. 5 speed manual transmission, error codes popped up p0108, p0172,p0300. spark plugs black and sooty.seemed to idle okay after warming up. fuel pressure at 55-60 psi. fuel regulator was replaced(new) since i thought that was high,since found out thats norm. map sensor replaced (new) this resulted in no change. coilpack and spark module exchanged (no change) since i planned on keeping car i purchased a reflashed pcm off ebay, car wouldn't even start with that pcm, returned to original pcm car ran as before. fuel filter was then changed car seems to have worsened as now idle isn't as smooth and rpms unable to exceed 1500.pcm was exchanged per shop manual, battery un hooked etc... almost ready for dealer. any help appreciated,

is there anything knocking

1st off change the spark plugs and 2nd check all your vacuum lines. By just looking up the codes online P0108 and P0172 both can be thrown due to vacuum leaks and P0300 can be thrown due to faulty spark plugs. New spark plugs should take care of P0300 and for the other 2 im betting that you have a vacuum leak. Check ALL you vacuum lines and off the top of my head im thinking it might be the vacuum line to the fuel pressure regulator. I hope this helps.

Have you done a compression check? If something's gone wrong with the valvetrain, or valve timing, nothing else will compensate for it. I'm not sure what is typical for the Ecotec, but on my LN2 my compression is around 180 PSI.
I was trying to chase a misfire code last year at this time - it was a burnt exhaust valve. At least doing this will verify that your main mechanicals are intact. I wish I had started there, instead of throwing new parts at it first.
John

because all four plugs are the same its an across the board issue. engine didn't miss or skip just wouldn't generate any power and started relatively easily. didn;t seem like timing or valvetrain. but will put compession check on to do list. since plugs were dry and not wet i was starting to wonder about fuel pump even though pressure was within spec. misfire code only shows sporadically

if the misfire code shows sporadically, generally means that there is a problem with ONE of the coils/spark plugs. i would 1.) do a compression test 2.) replace spark plugs 3.) see where you are from there.


one other thing, did you check to see if maybe your injectors are clogged and/or leaking?

and also, you would be surprised as to what a vacuum leak will do to your motor

compression test revealed: 205,200,205,210 and p0300 is a random misfire meaning its not confined to any one cylinder. p0301,p0302,p0303 etc. is specific to 1rst,2nd cylinder etc..i know its not a plug issue, when you can actually hear engine it's way better than any attempt to describe symptoms. but i do intend to try new plugs (to eliminate any possibility) just not leave them in, i believe random misfire is generated by fuel mixture. vacuum leak i haven't found as of now. after clearing codes and running engine, first pending code is always p0108

This sure sounds like an ignition or EGR problem to me....

and ya... it's amazing what a vaccum leak can do.... my brake booster line started leaking just a little bit once.... and the car thre a code and my Cruis control wouldn't work.

didn't see much of an egr system when i was under the hood,have not found a vacuum leak,and cat isn't plugged.

P0108 is a high MAP reading, P0172 is a rich condition, P0300 is random misfire.

the strange thing about this is that P0172 won't set unless P0108 has not set. that says that you had a rich condition before you had a high map reading. (this is based on information from alldata) you said the plugs were black and sooty, so i would start with replacing them. your fuel pressure is normal and with it being a random miss, it doesn't sound like there's a leaky injector or something like that. a vacuum leak could definitely be at least part of the problem. check your igniton system. it doesn't sound like there's any issue with the fuel system. there was something else i was going to say but i forgot