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Sputter, hesitation and frustration!


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Firstly, I've been watching these pages for a number of months and this topic has been touched on but I still haven't figured it out. Thought I'd start with a new post with all the info.

1989 4.0 4X4. Motor is from a Cherokee (same year). I did not do the swap, but the problem has been present from that time. Truck starts and idles fine, but stumbles and backfires under acceleration so bad that it barely moves the truck. Here's what I've done so far;

-Started with fuel filter. Plugged!

-Inspected tank. Terrible. Bought new one from RockAuto and installed with clean, working pump/hanger from a running parts truck.

-Blew out fuel rail and supply/return lines.

-Installed new fuel injectors.

-New quick connect fuel line couplers.

-Replaced fuel pressure regulator from the same running parts truck.

-New EGR valve, used EGR solenoid from parts truck.

-New oxygen sensor.

-New front and rear vacuum harness from RockAuto.

-New PCV valve/crankcase vent hose.

 

So with all that I'm thinking it's not the fuel or vacuum. Dristributor cap is not fouled but it almost seems like the timing is not advancing under acceleration.

As stated, this is a 4.0L from a same year Cherokee. Under my inexperienced inspection all electrical seems to be connected. I've just about wore the pages of my Haynes manual out trying to find the problem. I became a member on this site when I got the truck late last fall, and really admire the knowledge packed through these pages. I'm hoping someone can point me in the right direction. Thanks in advance,,,,

comanche.gif :dunno:

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Check timing with a timing light on #1 plug wire and look at the timing marks on the harmonic balancer and timing cover. The marks should line up at around 10*-14* advanced @ 2000 RPM or so. They should also be steady and not jumping around. You can't adjust it, but this will tell you if the distributor is installed correctly and the shaft gear teeth are okay.

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I had my suspicions about timing, but because of my total lack of any experience I had to go the trial and error route. Had no idea the truck could idle fine with the distributor installed incorrectly. The other parts needed to be replaced regardless, so it wasn't a waste.

Haven't played with a timing light before, but I'll borrow one and am sure Mr. Google will help me out there. Thanks a ton and I'll keep you posted.

:clapping:

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I have played with this thing all day and still the same problem!

Instead of going the timing light route, I have been turning the motor to TDC and then playing with the distributor. When pointing at #1, (which is where it was) - same problem. I have tried installing the distributor on either side of #1 and it's worse.

However I am not sure if I'm only moving the distributor one tooth at a time. How much movement in the rotor between teeth once seated? 4 to 5 o'clock or less?

I've even tried another distributor out of the parts truck.

 

:fs1:

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