View Full Version : End of my flippin' rope! Help!

September 4th, 2010, 08:48
Hi all,
I'm relatively new here, got a lot of good help and info, still learning so I haven't been much help to others.
I have a 96 Cherokee Sport I6, auto tranny and demons running all through the thing. Here's where the problem started - I had to pull my engine because the passenger side motor mount bolts sheared off. This was my biggest project ever. I managed to tap out 2 bolts and had to rethread one (here's hoping it holds). I dropped the engine back in and figured I would do a little work on it.
Here's the list
oil change and filter
tranny fluid change and filter
new distributor, rotor, cap, wires, plugs
Now it starts great but after 30 secs the idle starts to jump between 500 and 1000 rpm. It will do this for a few minutes then stalls. It runs fine up to about 20 mph and about 1700 rpm then starts to bog down - more pedal equals less power. If you run it below that it will slowly accelerate. After about 50 mph it seems fine, you can goose the pedal all you want...unless it has been running for about 45 min to an hour then it starts losing power the same way.
So far I have replaced: IAC, MAP sensor, TPS, canister purge valve and upstream 02 sensor. Nothing changed.
One thing I have found out is that if you unplug the vacuum line under the MAP sensor (not the little elbow hose on it) it revs up to about 1200 rpm and stays there.
Fuel pressure is around 49 PSI, which is supposed to be normal.
Compression is fine according to the mechanic.
I cant find any bad relays, fuses or connections. The only thing I can think of is the computer control module died, but thats another 200$ I can't dump in it. I know this is probably very long winded but if anyone can help me out I would really appreciate it.

September 4th, 2010, 09:08
Tie another rope onto the end. :D

injectors?fuel filter?

September 4th, 2010, 10:25
Is the computer setting any codes?

Trace the wiring harness back from the crank position sensor and make sure it hasn't been burned/heat damaged.

Does the lock of power/slow rev. happen while sitting in neutral? 'Curious if the fuel pressure stays the same at higher RPM, or if a weak pump/blockage won't allow enough fuel above idle.

The high idle caused by a vac. leak is normal. The idle on the 4.0 is set by a stepper motor(the IAC/Idle Air Controller)that is just a fancy adjustable vacuum leak.

September 4th, 2010, 12:29
Well, one thing part of your symptoms indicates to me that the distributor is not quite indexed correctly, possibly one tooth off.

I would try moving one tooth counter clockwise, if no improvement or worse then take it one tooth clockwise from the original position.

Try that and post up what you get.

Matthew Currie
September 4th, 2010, 12:35
I was about to suggest the same thing as Joe P., since that is one of the few tuneup items involved that really changes any settings. The only other thing I can think to do is to go over the wiring very carefully, and make sure that all plugs are together right, and all grounds properly established.

September 6th, 2010, 11:34
Thanks for all the quick replies. Turns out it was the distributor. I must have had it just far enough out of whack to make it act all crazy. Thanks again!

September 6th, 2010, 11:48
Glad you got it.

Now, go have fun.