Backfiring

Question

'94 Southwind 454 TBI. When climbing hills just before downshift from overdrive when the engine starts "lugging" it sometimes backfires. After downshift it runs "OK". Engine has 41,000 miles and ran fine from IL to FL. Started doing this half way through the first day heading from FL to TX. Usually doesn't start doing this until several hours of driving. Am I correct in thinking plugs, plug wires. distributor cap, or coil as possible problem? Going to be in TX for a week to ten days so going start working on the problem.

Besides this and the other leveler problem I posted we also lost an AC cover in the wind in Louisiana.

lynnmor · Answer

haydoracin wrote:'94 Southwind 454 TBI.  When climbing hills just before downshift from overdrive when the engine starts "lugging" it sometimes backfires.  After downshift it runs "OK".  Engine has 41,000 miles and ran fine from IL to FL.  Started doing this half way through the first day heading from FL to TX.  Usually doesn't start doing this until several hours of driving.  Am I correct in thinking plugs, plug wires. distributor cap, or coil as possible problem?  Going to be in TX for a week to ten days so going start working on the problem.Besides this and the other leveler problem I posted we also lost an AC cover in the wind in Louisiana.Wild guess:  maybe the injectors need cleaned, it sounds like the mixture is going lean.  Try a good dose of fuel injection cleaner.

paul_g_ · Answer

Don't forget about the ignition module, it's located inside the distributor cap. I had one go bad, had it tested and showed good, replaced it and no more problems. The symptom was intermittent backfiring.

Hope this helps.

Paul...

cpthester · Answer

I once had a Dodge 440 engine and it started backfiring when a load was put on the engine. Practically rebuilt the engine and it still back fired. Traded it off. The new owner said he replaced the fuel line which was rotten and was letting air into the fuel system.

Been there, done that.

donn0128 · Answer

Check the timing.  Backfire is generally caused by one of two things.  Burned valves or timing.  Big blocks are hard on timing chain sets.  GM in particular should be done pretty regular.

scottg · Answer

Along with what others have said, it's been my experience that bad spark plugs (or wires) can cause backfiring under heavy load like heavy throttle just before it down shifts.

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Backfiring

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