91 z28 conv. started loosing power over a few months, now it's very hard to start, it backfires occasionally through the tpi intake. have replaced fuel pump, filters, injectors, egr, plugs, checked plug wires, checked the distributer, tried a new computer, checked the timing chain and timing, checked for a plug exhaust, and all vacuum lines and volume. had a tech check for any problems and he said that the car should run. if i get it started it has no power, like it's starving for fuel or is out of time. the timing is ok and the fuel pressure is where it needs to be. have check the lift of the valves and they appear to be opening far enough via visual inspection.
any ideas????

frankc

 

is the cat plugged?

 

Check your air filter and your cat. Is your check engine light on?

 

no i disconnected the exhaust ahead of the cat, no difference.

 

air filters are new the cat is not plugged and no engine light. the gm tech said there is no reason it shouldn't run.

 

replace them and afterward, properly set the timing.

 

I RECHECKED THE DISTRIBUTER, ALL PARTS CHECKED OUT OK. REPLACED THE PLUG WIRES, AND RESET THE TIMING. IT STARTS EASIER AND RUNS BETTER THEN IT DID BEFORE, BUT IT STILL DIES OUT, BUT DOESN'T STALL, AND STILL POPS BACK THROUGH THE INTAKE. WHY THE BIG HESITATION AND POPPING BACK??? NO CHECK ENGINE LIGHTS... AND THANKS FOR THE INFO, EVEN TOUGH THE OLD WIRES CHECKED OUT OK I CAN BELIEVE THE BIG DIFFERENCE IN THE IDLING AND REVVING. HOPE YOU HAVE THE OTHER ANSWERS I NEED, THANKS AGAIN.
FRANKC

 

does it backfire as you describe in the first 60 seconds of the first startup of the day? If not, replace the O2 sensor

 

IT POP BACK AND HESITATES WHETHER HOT OR COLD. QUESTION I'M GOING OVER THE CHILTON'S BOOK, AGAIN, AND IT MENTIONS A MEM-CAL., WHAT IS IT AND WHERE IS IT? PG 2-27.

 

has anyone had any troubles with the MEMCAL in there (91) camaro? if so what kind of trouble has it caused you?

 

backfire through the intake sounds like a timing issue to me. I would take the dizzy out bring the engine to TDC then put the dizzy back in pointing towards the #1 and set the timing from there. Every car I have worked on that involved backfire through the intake was timing issues.

 

The GM Tech that looked at it. Did he check Block Learn for signs of a lean condition? Did he compare ECM timing to actual timing? These are things that a GM drivability tech would check and they will most certainly reveal your trouble whether it's in a controlled device, such as injectors, a mechanical device such as the timing chain or distributor drive gear, or the Memcal.