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92 4.0 accel studder and intake backfire

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Old 05-09-2011, 12:01 AM   #1
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Default 92 4.0 accel studder and intake backfire

Hi all, I have a 92 Cherokee sport 200k mi 5 speed. Recently I have noticed a slight studder under acceleration anywhere from 25 mph all the way to 75 mph. It happens most around 45 mph. Also sometimes when the studder occurs I get a backfire through the intake. I have replaced my fuel pump and filter. I have under 5k miles on new plugs and wires. I just cleaned up the cap an rotor as well. I have good fuel pressure. Anyone know what could be causing this problem? As an added note...the jeep feels very sluggish and does not feel like it has the power it use to have.
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Old 05-09-2011, 12:09 AM   #2
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Quote:
Originally Posted by 92jeepxj
Hi all, I have a 92 Cherokee sport 200k mi 5 speed. Recently I have noticed a slight studder under acceleration anywhere from 25 mph all the way to 75 mph. It happens most around 45 mph. Also sometimes when the studder occurs I get a backfire through the intake. I have replaced my fuel pump and filter. I have under 5k miles on new plugs and wires. I just cleaned up the cap an rotor as well. I have good fuel pressure. Anyone know what could be causing this problem? As an added note...the jeep feels very sluggish and does not feel like it has the power it use to have.
Also forgot to mention that the studder happens only under 3k rpm. Most prominent right under 2k
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Old 05-09-2011, 12:14 AM   #3
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Set your timing. It's off.
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Old 05-09-2011, 12:24 AM   #4
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Isn't the 91 Cherokee timing not adjustable?
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Old 05-09-2011, 12:24 AM   #5
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Woops 92 I mean
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Old 05-09-2011, 12:33 AM   #6
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It can definitely jump timing via the chain.
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Old 05-09-2011, 12:35 AM   #7
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Saw someone saying a lean condition can cause an intake backfire. Not sure how though.
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Old 05-09-2011, 12:39 AM   #8
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Related to this?
http://www.cherokeeforum.com/f2/putt...ackfire-56846/
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Old 05-09-2011, 12:55 AM   #9
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I'll check my timing tomorrow at work. Also will try the deadpan and see how that does
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Old 05-09-2011, 12:56 AM   #10
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I'll check my timing tomorrow at work. Also will try the seafoam and see how that does.
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Old 05-09-2011, 12:57 AM   #11
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That doesn't really sound like the problem I'm having but the seafoam is worth a shot
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Old 05-09-2011, 01:15 AM   #12
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You may have a plug wire or boot letting the spark leak out, could have carbon tracking inside the dist cap, or could have a couple wires cross firing. The timing should be ok if you never dinked with the distrbutor, and a jumped chain would cause a problem at any RPM if the engine even started.
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Old 05-09-2011, 01:22 AM   #13
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I went out at 1 this morning to the darkest back road I could find. Turned my lights off and opened the hood...no spark jumping at all. I also pulled the plugs one at a time to check engine idle and speed...all were good. Also I just cleaned out the distributor and rotor (cleaned the wear off the points). Could this be an O2 sensor problem?
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Old 05-09-2011, 06:24 AM   #14
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A backfire occurs when there is an imbalance in the air to fuel ratio required for your vehicle to operate properly. Yes, a lean condition can cause backfires in the intake.

Unless you have verified fuel pressure with a gauge, you're guessing if you have proper fuel delivery. Regulator still in play here. Be sure that your pressure is within factory SPEC. A gauge is the only way to be sure you're not chasing your tail here.

The backfire solution usually involves checking for vacuum leaks, and ensuring the fuel system is functioning properly.

Other things to consider if you have no vacuum leaks and fuel delivery is within spec: Ensure that your ignition is solid. You mention new plugs and wires and that you cleaned the cap and rotor. I would replace the cap and rotor. They aren't designed to be cleaned, and aren't expensive to replace. They can have cracks in them that you can't possibly see. Oxygen sensor can be responsible as well if they fail in a certain way. They have a finite lifespan between 100k and 150k, depending on the efficiency of the engine.
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Old 05-09-2011, 10:19 PM   #15
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Well I unplugged my o2 sensor for the drives today and it actually drove fine! No sluggishness and no stuttering at all. So should I automatically point my finger at the o2 sensor?
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