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Chevrolet 1990 C1500 TBI Back Firing
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ledopmi
New User
May 25, 2014, 12:10 AM
Post #1 of 6
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Chevrolet 1990 C1500 TBI Back Firing
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I'm looking at a friends 1990 Chevrolet C1500 with a TBI 305. I don't know the history of the truck. I'll have to find out the mileage but I'm sure it has a lot. He just bought in and it initially wouldn't start due to no fire. He replaced the distributor and it is running now but it has a back fire problem. When accelerating, it feels like the engine will cut out completely then come back with a single huge backfire through the exhaust. It seems to want to do it a lot of times right before shifting to second gear but not always during a shift. He told me it would backfire around 50 mph but when I drove the truck it happened around 30. It does it under light throttle or full throttle. A few times it would start 'popping' a lot without completely cutting out then upon shifting it would run OK again. The engine idles relatively smooth with no miss, the firing order is correct, the timing looks OK and I could not find any vacuum leaks. I checked the codes after I adjusted the timing and it had 42, 43, and 44. I thought they may have been set when I adjusted the timing so I cleared the ECM. After a short drive, no codes have reappeared so far. He took the truck back home last night so I'll check it later today for codes.
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Hammer Time
Ultimate Carjunky
/ Moderator
May 25, 2014, 12:56 AM
Post #2 of 6
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Re: Chevrolet 1990 C1500 TBI Back Firing
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You need to determine if the spark is dropping out when this happens but I am suspecting a bad coil.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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ledopmi
New User
May 25, 2014, 1:12 AM
Post #3 of 6
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Re: Chevrolet 1990 C1500 TBI Back Firing
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How can I check this?
(This post was edited by ledopmi on May 25, 2014, 1:12 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
May 25, 2014, 1:14 AM
Post #4 of 6
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Re: Chevrolet 1990 C1500 TBI Back Firing
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You would have to be observing an inline spark tester at the moment the problem occurs.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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kev2
Veteran
May 25, 2014, 7:48 AM
Post #5 of 6
(1582 views)
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Re: Chevrolet 1990 C1500 TBI Back Firing
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did you unplug set timing connector when setting BASE timing?
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ledopmi
New User
May 25, 2014, 9:07 AM
Post #6 of 6
(1580 views)
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Re: Chevrolet 1990 C1500 TBI Back Firing
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Yes and I set the timing to zero.
(This post was edited by ledopmi on May 25, 2014, 9:53 AM)
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