Engine Performance problem
1995 Chevy Truck V8 Two Wheel Drive Manual 150K miles
Bone stock code H (305) engine mated to a 5 spd. Manual trans.
About 6 months ago, during a severe thunderstorm here, the truck suddenly and un-expectedly starting running badly, no power off of idle, increasing throttle opening further would cause it to stall.
This truck is used infrequently so I just ignored the problem.
Now the problem has progressed to the point where I need to manually prime the TBI bores with carb. Cleaner just to start it Once it does run, I need to feather the throttle just to keep it running. Also, a huge amount of air bypasses the IAC, creating a massive vacumn leak.
So far I have checked fuel pump pressure (12 psi)
Read codes from ECM, besides the normal code 12 a code 33 was displayed. This points to the MAP sensor, which I have replaced, I even cleaned out the vacumn source for this sensor, it's attaching hose is intact.
I do not usually replace engine management sensors at will, but the IAC, coolant, MAP and TP sensors are new also, I am desperate.
Evidently there is an issue now with the injectors not firing during startup, can anyone give insight as how to diagnose this? Perhaps no signal from distributor?
Also. What would cause the IAC to allow a huge amount of air bypassed?
Getting back to the TP, I believe I have installed it properly, just to verify resistance varies from.5 volt to 4.5 at WOT, what should resistance readings be for idle to WOT?
Hope someone can help !
Friday, June 5th, 2009 AT 5:43 AM