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engine sputtering

meathead40

NAXJA Forum User
Location
snyder texas
Perhaps someone else has had this experience. I'm about ready to throw my hands up.
90 xj, 4.0, aw4, 231. The engine sputters pretty bad right about 2000 rpms. It goes away when giving it gas or letting off the gas. does't matter what gear it's in, just feels worse on the freeway. probably because it's in overdrive. goes away over 2100 rpms. no problems under 2000 rpms. i've check every thing I could think of. Finaly I took it to a shop for a ignition and conponant test. they had it for several days and could not find it. they gave it a good going over. didn't even charge me. they said everything checks out that they could test. I was advised that it could be a conponant that is going out that the testing could read or read as a good conponant. I was told the next step was to just start replacing parts to find it. starting with the ignition module. they figure its an electrical or ignition problem. A new ignition module cost about $140 and it might or might not fix it so this could get pretty expensive. I'm hoping someone else had this problem and can point me to the right direction. by the way the motor only has about 500 miles on a complete rebuild so it has a new cap, rotor, sending unit, filters, rv cam, etc. checked to make sure all the vaccum lines are were they are supposed to be. switched out the coil no fix
 
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I cant offer advise but I can say that my 90' XJ has 156k with the automatic and does the same exact thing so I think we can rule out all that you replaced including the engine. I have been reading and researching on this for two weeks now and dont have an answer. I want a positive direction to go and dont want to just throw money at it. I called the Jeep dealer today and the guy played dumb and quoted me 1-2-hrs labor at $88 per hour to diagnose the problem. This is a common problem so I know somebody has the answer. Just have to find that somebody.
 
Any chance the sputtering is not the engine, but the transmission? When it happens did you look at the RPM gauge? Did the indicator jump around or move while holding the engine at 2000 RPM? Does it happen when you park the Jeep and rev up to 2000 RPM? Did the shop pull up any fault codes?

If you know without a doubt it's the engine, then I suspect, as did the shop, that it's an electrical issue. Perhaps at 2000 RPM it's creating a resonant frequency vibe that's messing with a wire or connection that's creating an intermittent open or ground. You may need to perform a very detailed inspection of all wires, looking for chaffing, especially around stress points, junctions, and factory splices. Also check the wires where they enter connectors.

If you can replicate the problem reving the engine while in park, have the shop analyze it at that time. Sorry, I know this type of problem is frustrating. Best of luck.

Tom
 
One way you can try to narrow down the problem is to get a vacuum gauge on it. You can put the gauge on a long line and tape it to your side-view mirror so you can see it as you drive. If it's an internal engine problem, or (usually) if it's ignition related, you should see the vacuum needle react. If it's a fuel injector, the needle will not react, though. This can be very informative, especially if you can find (often packaged with the gauge) good instructions on reading a vacuum gauge.

I (actually my stepson) had a similar problem with a 93 which turned out to be a flaw in the wiring harness that caused an injector not to fire when it warmed up. The vacuum gauge finally caught it.

I'd definitely also check the egr valve on this one. Try just crimping off the vacuum line to it, and see if that changes anything.
 
Thanks guys for the replies. Tom R It's possible it could be (could have been) the transmission it was rebuilt also.

I went out drove it again. Once it warmed up, I floored it several times, letting the engine down shift and up shift. got it up to 4500 to 5000 rpms. I did this several times. the problem seems to be almost gone. I've been babying it because it's only got about 500 miles on the engine & trans. maybe something was stuck or clogged up. I'll know for sure when I go to work. Lots of freeway. (the egr valve seems to be working)
 
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