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Unread 07-14-2013, 07:36 PM   #1
bigb229
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1998 ZJ 
 
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Location: ga
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4.0l stumbling above 1700rpms

Alright fellow gear heads. Did a recent build on the 4.0l comp cam lifters, head work, msd ignition, Bosch 4hole injectors, and fresh ckps. Jeep is hard to start but idles fine until 1700 rpm then it starts to stumble. Timing is jumping all over the place when you put the light on it. We're stumped. All sensors have been checked and or changed. Timing is set properly as well....verified but multiple shops. Suggestions? New ECM as well.....well reman..

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Unread 07-14-2013, 07:52 PM   #2
gearheadnick
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I haven't gotten too much into the distributor, but that's where I would start looking for problems. Loose drive gear maybe? I don't know if it has mechanical advance weights like a v8 does, but perhaps a problem there?
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Unread 07-14-2013, 07:55 PM   #3
bigb229
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Checked for gear slop and its solid. The 4.0l distributor is uber simple....pick up coil checks out as well too...
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Unread 07-14-2013, 09:48 PM   #4
ZeeJay1997
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did you put a stock cam in it?
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Unread 07-14-2013, 09:51 PM   #5
bigb229
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I had the stock cam and lifters in and it did the same thing. Thought I might have gotten a bad set of lifters. Dropped their high energy cam for fuel injected 4.0l in it and their lifters. Same thing still...
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Unread 07-14-2013, 09:56 PM   #6
ZeeJay1997
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rotor at 5 oclock with timing mark on zero and #1 on tdc intake stroke?
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Unread 07-14-2013, 09:59 PM   #7
bigb229
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Yeah and I've tried a tooth advanced and a toothe retarded just to make surei was in the sweet spot. It's almost like the system isn't getting the correct voltage
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Unread 07-14-2013, 10:03 PM   #8
ZeeJay1997
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unplug the tps, turn switch on and see it it has 5v between the black and white wires. this same 5v is also fed to the crank and cam sensors. it's just easier to check there.
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Unread 07-14-2013, 10:05 PM   #9
bigb229
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I'll check that in the morning for sure.....say I don't find the 5v there.....we checked the asd today and it was functioning
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Unread 07-14-2013, 10:12 PM   #10
ZeeJay1997
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did you reconnect the two grounds on the right side on the engine? those are critical for the sensors and pcm and can cause the reference voltages to be out.

also, do you know what shape the cat is in?

try disconnecting the o2 sensors

that all i've got for tonight.
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Unread 07-14-2013, 10:16 PM   #11
ZeeJay1997
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one more thing... how does the intake vacuum look on a gauge?
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Unread 07-14-2013, 10:19 PM   #12
bigb229
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Haven't gauged the vacuum but its strong it'll die out if you smoother it. Cat is a manga flow. Fairly new., I did reconnect but might try cleaning them again. I did run a ground straight from the battery to the engine with no improvement.
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Unread 07-17-2013, 08:37 PM   #13
bigb229
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Bump. Come on guys.....where are the techs at? I've pinned out all the grounds and signal wires and have found no problems.....checked the tone ring and its fine as well.....just before taking it to the dealership.
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Unread 07-17-2013, 09:09 PM   #14
ZeeJay1997
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What kind of Bosch injectors? What is ohm reading across the contacts?
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Unread 07-17-2013, 09:50 PM   #15
dellis
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My only thought is that your crankcase position sensor (CKPS) is too far away from the flywheel (it wasn't properly seated during installation). If a CKPS is positioned too far away from the flywheel, it will cause problems at higher RPMs. What are the symptoms? I'm not sure because I've never personally encountered this problem. I've just read that a CKPS that is too far from the flywheel will cause timing issues (including backfires and misfires) at higher RPMs.

So, perhaps you should remove it, put on a new spacer (or check to ensure the old spacer is still good), and reinstall.
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