Backfire and Lag

joejeep92 · Jun 9, 2010

I bought a 1987 XJ that had 202k on it originally. New rear end, new front end, and 5-speed tranny. There is a newer (52k on it) motor from a tj in it. The problem is that when getting into higher rpms on each gear but especially fifth it backfires A LOT. I put new injectors in it as soon as I got it as well as new plugs, wires and distributor cap and rotor. With the backfiring it runs great at an idle but as soon as I get on it the motor runs real rough. Any ideas?

joe_peters · Jun 9, 2010

4.0?

Was the EGR system retained?

Backfiring is usually a symptom of air entering the exhaust allowing the unburnt fuel to detonate.

joejeep92 · Jun 9, 2010

It is a 4.0. I do think the EGR was retained yes.

joe_peters · Jun 10, 2010

Ok, I would start with a test of the EGR system.

See my post in this thread for the EGR test procedures: http://www.naxja.org/forum/showthread.php?t=984274

Ignore all of the parts about the Vacuum Transducer Valve--87 doesn't have it, only 88-90.

You will need a vacuum gauge and vacuum pump, rent them if you don't have them already.

joejeep92 · Jun 10, 2010

Gotcha. Will do this evening.

joejeep92 · Jun 10, 2010

Another note. The motor is out of a 1991 tj

bowzone_mikey · Jun 14, 2010

joejeep92 said:
Another note. The motor is out of a 1991 tj

YJ???

JJacobs · Jun 14, 2010

Remove the distributor cap, grab the rotor and give it a wiggle. Does it only have a couple of degrees of play or a LOT of play? It should be tight. The distributor roll pins are known to break apart causing this problem.

Backfire and Lag

joejeep92

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joe_peters

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joejeep92

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joe_peters

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joejeep92

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joejeep92

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bowzone_mikey

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JJacobs

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