backfiring through exhaust

backfiring through exhaust

Postby markmitch [OP] » January 6th 2013, 10:18pm

OK my Astro is a 1989 RS with 4.3 and 700R4 it had 189,000 miles on it when I bought it and it was burning oil badly and the trans shifted slow. So after I owned it a couple months I pulled the stock engine and trans out and installed a 80,000 mile 95 astro 4.3 and a rebuilt 700r4 trans. I reused the TBI system but rebuilt the TBI unit and had the injectors cleaned and flow tested by witchdoctor. plugs, wires, cap, rotor, air cleaner, pcv valve,oil & fuel filter&oil filter were all replaced new. I also replaced the water pump. Other then the intake swap the insides were never touched. Now the problems. It starts great and idles fine but as soon as you touch the gas it backfires and has very little power. The timing is on the money. It backfires through the exhaust only and there is no smell of raw fuel. Feel free to send me your thoughts on what to check.
By the way I drove it `18 miles home like this and it got worse as it warmed up. Sometimes if I shut it off and attempt to restart it does not like to start.
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markmitch
250k+ Miles
250k+ Miles
Firing on 8 Cylinders (L1)
Firing on 8 Cylinders (L1)
Years of Membership: markmitch has been a member for 6 full yearsmarkmitch has been a member for 6 full yearsmarkmitch has been a member for 6 full yearsmarkmitch has been a member for 6 full yearsmarkmitch has been a member for 6 full yearsmarkmitch has been a member for 6 full years
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Year: 1989
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Extra Info: RS

Re: backfiring through exhaust

Postby chevymaherchevymaher is online! » January 6th 2013, 11:15pm

If the engine ran fine before the switch, it isnt a valve or timing chain issue.
The EGR was working on your engine so it probably okay. I would check to see if it getting proper vacuum signal, and not a metered or delayed vacuum.
I would look and see if the injectors are spraying a mist. Rebuilt or not. It always what you don't check.
It sounds like the timing to far retarded. It only takes a second. Loosen it and move it around see if that improves things. It a gen 1 OBD1 it don't got to be where it supposed to, to work at all. Mine miles off from factory and a screamer. It sure isnt at factory settings.
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Re: backfiring through exhaust

Postby chevymaherchevymaher is online! » January 7th 2013, 2:23am

90 starter
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