[Flatspin]

Anyone help please?

Sorry for the long description, but I am trying to include all relevant information.

I have a 94 5.7L k-1500 with 170K miles on it. It started hesitating on acceleration, and I tracked the problem to low fuel pressure. Rather than just replace the pump I opted for an Edelbrock Multi-point conversion with new pump, filter and the chip for the ECM. Since then I am getting a rough idle and stalling on deceleration. I have replaced the O2 sensor and back-probed the TPS, MAP and EGR, getting results within the parameters from Haynes. Compression test is happy at +/- 150 PSI. Pulling a vacuum directly on the EGR causes the motor to stumble, so I assume that the EGR valve is working? Ditto the MAP sensor. My local auto-parts guy lent me an ICM which did not solve the issue. I have tried new rotor, cap, wires and plugs. I am getting no codes except a sporadic 33 (High MAP at idle) caused by the stumble/stall (I think) The timing is set at zero per the manual, if I advance the timing to 4 degrees BTDC static the problem is better, but not fixed. I have not been able to find any vacuum leaks, although I did remove the throttle body and install another gasket just for grins. At highway speed the truck goes like stink and I am highly impressed but the sudden loss of power steering and brakes when it stalls is getting old really fast. Edelbrock says that the Multi-point conversion is not as tolerant of faults as the TBI system, and the problem was probably there all along.

Any ideas where to look? Thank you in advance.



***** Turns out the EGR Solenoid, which held a vacuum and back-probed OK when tested was actually at fault. Don't know exactly what was wrong but I suspect that the solenoid was sporadically opening at idle (vibration maybe?) and causing all kinds of vacuum problems for the computer when the EGR valve unexpectedly dumped exhaust gas into the intake. I changed the solenoid 2 days ago and have not had any of the symptoms since.