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Old 06-21-2018, 02:47 PM   #1
dylanborns
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4.0 misfire and running rough

'96 4.0/ AX15, unknown miles, but I know there's not many on it, installed in my CJ7. (I'm putting in the cherokee forum due to it coming out of a Cherokee).



This started a couple weeks ago. It had been driving smooth, until I got in it to run around. It was running really rough, stuttering, and sounded like it was going to backfire. I read codes and got speed sensor, multiple cylinder misfire, and cylinder 1 misfire. I changed the plugs, which the old ones looked good, and checked that the plug wires were working. That didn't change anything, and I still had the cylinder 1 misfire, and multiple cylinder misfire.

I sprayed the intake area with brake cleaner to see if I had any vacuum leaks, and I didn't find any. I put in a new crankshaft position sensor. I put in a new coil, and tried a new distributor cap and rotor. I checked fuel pressure at the rail, and got 55psi. I reread it and it was showing misfire cylinders 1,2,3.

I checked all cylinders for compression, and all were in range.

If it stops raining today, I'll take it up and have it reread. I drove it, and it's better, but it's still not running smooth.



Any other suggestions?
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Old 06-28-2018, 06:39 AM   #2
rhandwor
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Re: 4.0 misfire and running rough

If it's a 3.7L like mine looking at the engine with the hood open. 1-3-5 are on the right. 2-4-6 are on the left. I would use an ohm meter and ohm the plug wires from the 3 coils to the plugs. They should be somewhere in the middle. Where the boots on the 3-coils good. A bad injector will cause a misfire. Use your ohm meter and ohm all injectors if one or two readings a way different I would replace these injectors.
Advance or Auto Zone has loaner tools. Get a set of noid lights plug into the injector and they should blink mwhen cranking the engine.
It's possible you crossed a plug wire when doing the job.
Auto Zone or Advanced will scan the engine free.
A crankshaft sensor code will also cause problems.
It's under the air cleaner on my 3.7L either do from the bottom or remove the air cleaner.
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Old 06-28-2018, 06:41 AM   #3
vietqb
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Greetings

Hi all. My name is James. Nice to make friend with all of you
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Old 06-28-2018, 08:44 AM   #4
Mode01
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Re: 4.0 misfire and running rough

Another thing to check is the crank sensor trigger wheel. Had 1 one time that got bent a little during an engine installation. A labscope on the crank signal would show it, but I found it by visually looking at it while rotating the engine.
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Old 06-30-2018, 12:16 PM   #5
12Ounce
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Re: 4.0 misfire and running rough

I'm a newbie when it comes to Jeeps, but it just so happens this week I helped a friend get his 97 4.0 running again. After miles of faithful running, and his beginning to do maintenance to it, it suddenly it would not restart after a trip to local store and he had it towed to his carport. Enter Me.

He, earlier, had already replaced plugs, distributor cap, and crankshaft sensor... to get rid of "occasional misfire". I found the camshaft position pickup coil (under distributor cap) damaged (Did he damage installing cap?) and we replaced. I went through the ignition set-up using markings on crankshaft pulley damper and block ... would not run!

I decided the crankshaft pulley had become too old to use for reference, and removed plugs, cranked shaft over and marked TDC using piston crown as indicator. Made temporary crankwheel markings with Witeout : followed set-up as outlined in Haynes and now it runs well. The rubber must have slipped in the crank shaft pulley .... but then, the Jeep has over 200K miles.
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