Backfiring
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Backfiring
I need some help here before i completely strip out my engine to ground zero.... I been having a spuddering and popping backfire sound since i tuned my truck up. Not gunshot loud, but backfiring. I replaced my wires again, my plugs, adjusted mt carb, larger fuel filter, timed it and everything.... Well one of my plugs a wet look to it of which smelt like fuel, but the distributor cap wasnt damaged or worn or anything? Basically anyone have any ideas? Also i was told it could possibly my timing chain???? PLease HELP!!!
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77mud, NO on the firing order.... i quadrupled checked that before anything else. ALSO i didnt mention in my first post also, after changing the plugs and wires again after my first tune up and adjusting the carb..... NOW its backfiring through the carb?
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
What engine is this, and what firing order did you use? If it's a 351, the firing order listed for a "351" in a lot of shop manuals is actually for a 351W, but a 351M is different. You need to tell us more about the vehicle and engine.
What do you mean by "adjusted the carb?" What specifically did you do? Help us help you.
What do you mean by "adjusted the carb?" What specifically did you do? Help us help you.
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77mud, no pun intended! ;-)....... customrich, before i try my timing chain i want to change the cap and rotor as to i heard it could be cracked or even warped therefore not getting enough connnectivity and causing to fire improperly...... fmc400, im runnning a 360 v8, 74 ford f-100 sitting on a 75 frame, also as far as crossed wired and such ive checked everything from online to whats in my book........ so im just narrowing down the unwrechable ideas first, AND YOU ALL HAVE BEEN VERY HELPFUL!!!!
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First, let's understand what causes a backfire: It's the result of fuel being lit off when it's not supposed to. Sometimes it happens and lites off through the carb or out the exhaust, but at the wrong time. I'd be suspicious of that one wet plug. I say pull that side's valve cover and inspect the valve train -wiggle the push rod, check for a loose rocker, and a lazy or broken valve spring.
Other possibilities:
Double check the vacuum hose from the dizzy to the carb. Ya got it on the correct port???
Some plug wires will work themselves loose from the cap - especially ones made without a 90-degree lug. Ya sure they're all seated?
Remove the cap and look at the contacts. All of them should show an indication of making contact with the rotor. Rotor - is if firmly seated on the dizzy shaft?
Also, don't rely on factory-gapped spark plugs. They bounce around during shipping and could have gotten crimped causing a weak spark.
Other possibilities:
Double check the vacuum hose from the dizzy to the carb. Ya got it on the correct port???
Some plug wires will work themselves loose from the cap - especially ones made without a 90-degree lug. Ya sure they're all seated?
Remove the cap and look at the contacts. All of them should show an indication of making contact with the rotor. Rotor - is if firmly seated on the dizzy shaft?
Also, don't rely on factory-gapped spark plugs. They bounce around during shipping and could have gotten crimped causing a weak spark.
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From: Denver Metro Area, CO
Since this problem began as soon as you tuned it up, the chances are pretty good that something in your tune-up changes are causing this (as opposed to a sudden & coincidental mechanical failure).
A good possibility in my opinion is the front dampener being separated and you're therefore using incorrect indications for setting the ignition timing.
A backfire is as described above - instead of combustion happening inside the combustion chamber, it's instead happening in the exhaust or intake.
If it were mine, I would futz with the timing by turning the distributor irrespective of what the timing light tells you - you might use a vacuum gauge to set the timing.
A good possibility in my opinion is the front dampener being separated and you're therefore using incorrect indications for setting the ignition timing.
A backfire is as described above - instead of combustion happening inside the combustion chamber, it's instead happening in the exhaust or intake.
If it were mine, I would futz with the timing by turning the distributor irrespective of what the timing light tells you - you might use a vacuum gauge to set the timing.
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From: Sioux Falls Area
(fighting this problem on a non-ford-POS right now)
thanks!
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