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-   -   4.0l stumbling above 1700rpms (http://www.jeepforum.com/forum/f13/4-0l-stumbling-above-1700rpms-1548980/)

bigb229 07-14-2013 06:36 PM

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..:confused::confused::confused:

gearheadnick 07-14-2013 06:52 PM

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?

bigb229 07-14-2013 06:55 PM

Checked for gear slop and its solid. The 4.0l distributor is uber simple....pick up coil checks out as well too...

ZeeJay1997 07-14-2013 08:48 PM

did you put a stock cam in it?

bigb229 07-14-2013 08:51 PM

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...

ZeeJay1997 07-14-2013 08:56 PM

rotor at 5 oclock with timing mark on zero and #1 on tdc intake stroke?

bigb229 07-14-2013 08:59 PM

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

ZeeJay1997 07-14-2013 09:03 PM

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.

bigb229 07-14-2013 09:05 PM

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

ZeeJay1997 07-14-2013 09:12 PM

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.

ZeeJay1997 07-14-2013 09:16 PM

one more thing... how does the intake vacuum look on a gauge?

bigb229 07-14-2013 09:19 PM

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.

bigb229 07-17-2013 07:37 PM

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.

ZeeJay1997 07-17-2013 08:09 PM

What kind of Bosch injectors? What is ohm reading across the contacts?

dellis 07-17-2013 08:50 PM

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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