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4 litre stuck at 4000 rpm's, any ideas???


 
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dirtydeez
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Joined: 06 Nov 2004
Location: Portland, OR

PostPosted: Thu Jan 24, 2008 2:10 pm    Post subject: 4 litre stuck at 4000 rpm's, any ideas??? Reply with quote

I recently replaced the head gasket on my 91 xj. Took off and re installed all the fun stuff along with..... fuel injectors, throttle body, manifold, etc. When I fire the Jeep now its stuck at 4k rpm's. Tried jamming it into gear and still doesnt calm down. Checked all the vacuum lines and hoses. No problems with the throttle body. Double checked to make sure no ground wires were pinched. Any suggestions on what I may be missing??
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adamzski
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Joined: 29 Oct 2007
Location: massachusetts

PostPosted: Thu Jan 24, 2008 6:52 pm    Post subject: Reply with quote

double check your IAC and all the wiring for it. theres a connector at it as well as another harness further down the wiring that is easy to forget. also, check to be sure your throttle body gasket is intact. also, if your "fun stuff" included a throttle body spacer, this could be the problem cause the 4.0L's don't react well to them and will idle high like you described. while ur at just be sure all your other sensors and in good working order, tps, map, etc. o, and if you like your tranny, i wouldn't slam it into gear, try pumping the throttle quick if anything.
_________________
99 Cherokee XJ
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Toliver09
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Joined: 16 Oct 2007
Location: Central Illinois

PostPosted: Thu Jan 24, 2008 8:11 pm    Post subject: Reply with quote

sounds to me like a vacuum line... normally thats the only part besides the throttle body itself that would make it idle high, if your brake booster is run off vacuum it will definately cause that. double check all your vacuum lines and check your intake for places where lines need to be hooked up (brake booster is often run to the intake since it runs off of a pretty large vacuum)
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DavidXJ
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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Fri Jan 25, 2008 8:04 am    Post subject: Reply with quote

I know you said that your throttle body checks out, but your symptoms sound exactly like what happens when the ISA motor or "throttle body motor" gets stuck. When this was happening to the '87 I used to own, taking it off and cleaning it well with carb cleaner would temprorarily solve the problem. But when it reoccured a couple of times, I ended up replacing it. After that, I didn't have any problems.
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dirtydeez
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Joined: 06 Nov 2004
Location: Portland, OR

PostPosted: Fri Jan 25, 2008 2:08 pm    Post subject: Reply with quote

Thanks guys for all the input, ill re check everything and the additional stuff you added. As for the throttle body spacer, tried that on my 97 xj and it ran like crap. I'm thinking the only thing to counteract the problem wouldve been larger injectors, but the money spent then wouldnt be worth the minimal gains.
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Fri Jan 25, 2008 5:59 pm    Post subject: Reply with quote

i don't think larger injectors would make a throttle body spacer work , they just don't do anything .

at the most like 1/2 a horse power .
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dirtydeez
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Joined: 06 Nov 2004
Location: Portland, OR

PostPosted: Sat Jan 26, 2008 8:02 pm    Post subject: Reply with quote

figured out the problem with the high revving, a portion of the exhaust manifold wasnt snug against the head. Rookie move. thanks for all the input.
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DavidXJ
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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Wed Jan 30, 2008 8:20 am    Post subject: Reply with quote

dirtydeez...

I have a Banks header sitting in my garage because my stock one is cracked more than 1/2 way around one of the collector tubes. But I've been reluctant to start because it seems like a ton of work. My biggest concern was getting the new header and intake manifold secure when I install it. Any tips you learned so I can avoid making a rookie mistake too?
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rockjock
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Joined: 03 Feb 2008
Location: KY

PostPosted: Sun Feb 03, 2008 6:16 am    Post subject: Reply with quote

Hey Deez,

I don't know what your electronics are like on the 91 but I installed the header on my 99 and re into a similar problem (it idled at 3200rpm). Come to find out the idle control module had gone bad (I forget the actual name of the part, look in a Haines Manual). It's located on the fuel injector body. I relplaced mine and all has been well for 30,000+
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