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Discussion Starter #1
1988 Nissan Sentra. I belive it is TBI.
The car runs rough and backfires very loudly on decel when cold, it cuts in and out on hard acceleration. There are points on the RPM range where it runs great then cuts out. After having it run for 20-30 minutes it magically runs super smooth and stops backfiring. Ive done cap, rotor, plugs, wires.

My thoughts at the moment are:
1: A gakset leak somewhere and when everything warms up it seals
2: A temp driven choke/mixture setting that isnt set right
3: Weak fuel pump
 

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Sup Mod keeping the peace
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An exhaust tail pipe backfire is caused by an excessive amount of un-burnt fuel remaining in the exhaust system or fresh air being allowed to enter the system which ignites a small amount of un-burnt fuel. When the engine is cold, the ECU rich-ens the mixture for easier startup and smoother running. There may be an exhaust leak in the pipe running from the exhaust manifold to the CAT; if fresh air is allowed to leak into the exhaust system it will ignite the un-burnt fuel inside the system creating the backfire.

The problem could also be the TBI dumping an excess amount of fuel during cold running.
 

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Discussion Starter #3
The car had no exhaust at all when I got it. It's got a generic muffler on it currently, no CAT.

I'm thinking it's a ECU/ temp related issue because once it's warmed up it runs pretty good and dosent backfire at all. I'm going to test fuel pressure next.
 
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