Mechanics

CHEVY ENGINE BACKFIRES/ MISSES/ NOW IT WONT R

1992 Chevrolet Spectrum

Engine Performance problem
1992 Chevy Spectrum V8 Four Wheel Drive Automatic 257000 miles

Yes sir, I have a 92 GMC Suburban- I've never looked to help till now and I have a problem that could be as simple as a knock sensor as hard as finding a broken wire.
possibly unrelated but a year ago the ign. Module went bad, shut down on the highway towed home, new ignition module fixed it. 6 months later started missing and running rough, idle would drop way low at coasting to stoping speeds and computer would catch it from stalling. Guy at Checker said and I did Re-built throttle body, changed fuel filter. Not a changed at all. Feul pump was changed 6 years ago. Now its still missing and runs bad when under part load, can get it to clean up when full throttled. Will run fine upon some start ups for a one way trip. Then it just got worse and worse with the backfiring and missing. Mainly off the line it would pull then completly loose a ign. Signal and rpm gauge would fall as the sound of would engine with loud exhaust would become silent, and it would fire back up and run again then again stall but pick up and run agian then a lil back firing action as I triy to accl. With a trailer and load on truck. Tried a new coil just enchanced the missing problem it was an msd it might not have enchanced it could just be a mental noise enhance you know since its the end all be all " MSD". The cap and plugs and rotor and coil wire were replaced b 4 problem started. Dad took truck with car to race track, he said it was real bad, he changed the distributor b 4 the drive home. Not a fix at all. Then he ran new wires from dist. To computer. Time passed it would still work with out a problem for me sometimes mainly under full load seemed to clean up. Next Drove to a friend who had a snap on scanner, it said it was electronic spark advance change ecm or something else, my dad did the diegnosing and said to change the ecm, changed that with a re man ecm and installed old PROM in re man comp, no change in the funny loud backfire missing truck it was becming to be, kind of like a rodeo in a truck feel. Back and forth as it cuts in and out then goes but it misses when it goes. Its like it has no advance under load, when you floor it you can feel power coming in and out as its going through missing and an ocaasianal backfire. So 3 months goes by still nt running good at all! Drove it 6 hours from minneapolis to milwaukee. Works fine at 75-80 mph then misses or more so cuts out when you go 60 mh a sharp cut out and right back in to same rpm. Make it back my tranny rear u joint was toast absent of needle bearings, changed that. I've just kept on driving it with it running like junk, it would stall sometimes when comming off throttle starting around a corner or when your taking off from a stop light and it cuts in and out like a rodeo it will sometimes stall if you change the throttle position to compensate it. Finally a few days ago I was idleing in a parking lot and it stalled, ok I knew it wasnt uncommon, tried starting it, wouldnt start sounded like it wanted to but sounded way ruff and battery went dead didnt take much battery didnt have a full charge from previous day when I left an amp on. So we tried jumping it. Truck didnt really want to fire up. Sounded like the ign would kick in at the end of letting off the started, and it would fire as your let off the starter or key, you would have best luck tapping the starter, got it running once it was souding way ruff like a carb car that was way rich after it being flooded and you haveing t clean it out. Well tried to give it some gas when it was running rough and it didnt take it, it stalled. Took a few more trys after battery charged to get it to fire up and run now my dad said just let it idle when it starts- it started sounding like a flooded v-8 with a carb, it didnt clean up and stalled after like 30 mins. We had been thinking it was the PROM in the computer since he changed just the ecm before. Went and got a junk yard ecm with prom pugged that in no change at all would not start at all, towed it to my place or working on cars. Tried old coil that worked fine, no change tried new coil wire played with coil wire connections, checked spark plugs looked ok 160 psi in one cylinder, thats probably ok. Was thinking bad gas, stoped feul flw gt new gas dumped that down sounded the same tried that and some starting fluid and no change. Checked timing to see if time chain jumped up or down, nope timing at zero and computer dose the rest, well seems like the comp dont do the rest. So now tonight I heard knock sensor can change timing up to 90* degrees? I will check that next, have one I could swap in there for a check. And also its the third tranny thats been in it, so the TSI around our place were a few trucks have been, do poor intallation work of the tranny themselves, know for putting metric bolts half in tranny to engine holes and skipping a hole and on mine the last time here was missing 3 tranny to engine bolts, so a possible set of wires could be pinched or broke somewhere? And also the speedo jumps rapidly coming to a slow stop and now sometimes when your not moving, but were moving So we could put a carb manifold and an hei dist in it but thats to easy I would like to figure this out. So hope this is a good jog for your memory as it has been for me, and whatever your thinking a knock sensor some pinched wires a ign module and why would the speedo jump around. And for your time and knowledge thank you
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Mark1142
March 14, 2008.




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