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Jeep question 4.0L inline 6


BoostedAce

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I recently just bought a 2001 jeep grand cherokee 4.0L inline 6 as a daily beater. It has 128,000 miles, it has a extended startup/hard start. Vehicle also misfires on 4 & 5 at idle or in gear stopped but drives fine. I ran engine cleaner threw the intake and put plugs in it and seemed to change nothing. Any help would be appreciated. Thanks
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I recently just bought a 2001 jeep grand cherokee 4.0L inline 6 as a daily beater. It has 128,000 miles, it has a extended startup/hard start. Vehicle also misfires on 4 & 5 at idle or in gear stopped but drives fine. I ran engine cleaner threw the intake and put plugs in it and seemed to change nothing. Any help would be appreciated. Thanks

 

My bet would be a weak pump. I believe the regulator is located within the pump assembly on those, but I am not positive. The best thing to do would be to verify you have the correct fuel pressure.

 

It's possible the fuel filter is just that clogged (which I'd replace when I replaced the pump anyways) so maybe throw a new filter on first and see what happens. If your fuel pressure doesn't improve then it's a failing pump assembly.

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I have a fuel pressure tester if you want to check it. Come by and I will hook it up.

 

Misfires on old jeeps tend to be one of four things:

1) bad cam sensor inside the distributor

2) bad throttle position sensor

3) bad coil

4) clogged injectors.

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Good article on possible issues:

http://www.jeepforum.com/forum/f11/4-0-check-engine-light-cylinder-2-3-6-misfire-894762/

 

His was a problem that Chrysler had a TSB for on the manifold (overheating or bypassing - unsure).

 

I was going to bring that up to. The intake manifold overheats and boils the fuel in the #4 and 5 injectors causing a misfire.

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Engine running was 60lbs engine off was around 50

 

that sounds fine. I don't think it is a pump issue but you may have a small weep bleeding the line down in static.

 

The problem is that it is now cool enough that if you were having thermal failure on the electrical components you wouldn't know it - thermal failure in the ignition system is usually responsible for long hot starts or no starts.

 

do you have a spark tester? put it on each of the plugs and see if your misfire is limited to one cylinder or if it is all of them. If one trace it back and see if you have an interruption in the wire or something causing arc-ing.

 

You can test the crank position sensor with a continuity tester. I just realized above where I wrote Throttle position sensor I meant crank position sensor. my mistake. There should be no continuity between the b and C pins. Test hot and cold. http://www.cherokeeforum.com/f51/testing-cps-5563/

 

The cam sensor inside the distributor is a common fail point. I have put two or three in my jeep over the years to the point where I sometimes forget to check it when diagnosing ignition problems.

 

Check your coil for cracks. Jegs had an accel coil replacement that I just bought and it is awesome. my coil was still functional but cracked to hell.

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