back fire?

Old 04-23-02, 11:03 PM
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Question back fire?

hello everyone I have a big problem please help me Ihave a ford f150 79' 400engine two weeks ago I was driving my truck and suddenly start to back fire and since that day still back fire I change spark-plugs plug-wires rotor and rotor-cap but still doing the same thing I all ready check the timing and is ok can some one tell me what it the problem please and sorry for the misspelling
Old 04-24-02, 06:34 AM
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Either a plug wire is on wrong, or the timing is still off. The chain may have skipped a tooth on the gear or it's worn.

Does it backfire at idle when it's running?

How many miles on this thing?
Old 04-24-02, 07:40 PM
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Just started

When your engine started to back fire what were you doing just before it started? Did you pass a car? Come off a Hiway onto an off ramp? What did you do just before it backfired?

How many miles do have on the 400? Have you ever had your timing chain & gear set replaced?
Old 04-25-02, 09:33 PM
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If it backfires when you let off of the gas and the truck has a air pump (smog). Could be the air diveiter valve. Had this problem on
my 84 chevy.
Old 04-26-02, 05:47 AM
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That is usually an exhaust leak or a timing problem.

Fords of this vintage are emission winners and have a gazillion unnecessary parts compared to a GM of that same vintage.

Make sure there are no exhaust leaks or misrouted vacuum lines for starters.

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