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Backfire through intake when cold
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hutchhash
New User
Jan 5, 2009, 4:10 AM
Post #1 of 2
(2021 views)
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Backfire through intake when cold
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1999 Jeep Wrangler 4.0L with 120,000 miles. Never had a tune up until last year (because it was running rough). Replaced all the ignition stuff (plugs, cap, rotor, wires). Runs much better now, but backfires through the intakake only when cold and only when accelerating. I assume it is a fuel mixture problem probably not related to the engine control chip. I'm thinking O2 sensor(s). Thoughts???
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Loren Champlain Sr
Veteran
/ Moderator
Jan 5, 2009, 4:58 PM
Post #2 of 2
(2012 views)
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Re: Backfire through intake when cold
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Hutch; You are more than likely correct, that it is a fuel related issue. Backfiring, up through the intake, is 99% of the time due to a lean condition. The O2 sensors don't come into play on cold start up. Check the coolant temp sensor as it may not be telling the PCM that the engine is cold. Sometimes, it's just a poor connection at the sensor. Also note that a cold engine requires more fuel than a warm one. It could be due to partially plugged injectors..If you haven't had the injectors cleaned in the past 40K, I'd recommend you have that done, also.
Loren
SW Washington
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