Chevrolet Repair: Chevy K2500 engine stumble, fuel pressure regulator, haynes manual

Question
Robert,
 I hope you had a great vacation. Here is my question:  I have a 1990 K2500 pickup with a 5.7L TBI engine.  It has run great for years but has recently had the CEL light come on when driving on the highway or under heavy load (towing).  After further diagnosis, I found it runs great at idle either hot or cold and when the throttle is "eased" up.  During a snap throttle test the engine will stumble continously. During normal driving, the engine will hesistate mid-rpm in all gears (Auto-Trans).  OBD-I codes (if I am reading the flashes correctly) are 32 (EGR), 43 (ESC-Knock) & 44 (Lean exhaust).  Given the above codes, I have checked the O2 sensor (voltage looks appropiate according to Haynes manual), checked the timing (pretty sure it is correct, markings on my sawtooth reference plate are worn away) and then sequentially replaced the fuel filter, fuel pump, fuel pressure regulator, plugs, cap and rotor.  Symptoms still remain as before.  I can put a scope on the knock sensor but would need clarification on what type of signal to expect. Online details suggest it is difficult to tell a "good" sensor from a "bad" sensor without a side by side comparison.  Anything else I should be looking at?  It has been a great truck for so long but I am at wits end with this problem.

Thanks in advance,

Lorin

Answer
Hi Lorin... i had a great holiday, thank you.... eat lots of lobster... here are a couple of things you can try... when ever i see a problem with a stall/ stumble i check the temp sensor. they can read from -40 to + 40 and if it is reading too hot or cold or it is flashing or roaming it can cause the engine to stumble because the pcm is not getting a proper referance. also check the 02 sensors, if you haven't chenged them in the last 50 or 60 thousand klms they are due...they only work good for approx that long, even if they are reading right the voltage from them may change under differant load conditions. also make sure that EGR code is really an egr problem, not a high nox reading from bad temp/o2 sensor. also i have ran into a problem in the older chevs where the dist pick up, shorts to ground, you may want to check that as well, also check bushings in the dist as excessive run out in the dist can cause that same problem... hope this helps

Bob