4.0 Problems

[Kkilmer87]

89 4.0 column shift auto .....bought it as my first Manche paid to much and spent to much .....the engine was not running well when purchased and I have little background info on it besides it came from ct and was hit from behind and parked for about a year.....I have done a major tune up on it replaced all vac lines, manifold gasket , rod bearing, oil pump, distributor, plugs, wires rotor , cap, cleaned grounds, cleaned idle air control, etc etc etc i have thrown every part at it and replaced many things I'm in of 2500 and have no chance of making money back,.........to get to the point it stumbles and hesitates when driving or revving the engine....idles just fine.......alittle history of my ownership.....I drove it and ran fine a few times one day I was pulling stuff in yard and the engine overheated because cooling fan relay failed to work and I knew nothing about jeeps at the time so it got so hot that the oil pressure dummy light began to flicker this is where the problems began .....never ran right after that day so the guy how sold it to me went to fix it put in the wrong distributor and it got loose and messed up the oil pimp drive distributor and the rod bearings so today we started it after long months of working on it and it runs fine but when revved it still skips it is timed correctly and my friend a good jeep mechanic did it......still can't figure out stumbling I have swapped fuel rail and injectors out of a working engine, fuel filter , checked fuel pressure and compression, he thinks it may be a computer issue .......any input would be awesome sorry for the long story

[Kkilmer87]

Bump I'm all out of ideas. !!!!

[Oyaji]

You mentioned it was hit from behind a year or so ago.

 

Did you check and refurbish the fuel pump ground behind the left tailight?

[Kkilmer87]

wow ive heard of that but never thought of it thanks man ill keep u posted appreciate all the ideas i have almost every part new on this thing lol

[Bornindesert]

Had a simiilar stumbling issue with my first 2WD Sport Truck. It had been parked for about a year too before I noticed the problem. Engine would start but no power, stumble and stall. Called Buddy back in NJ and he told me it sounded like the Catalytic converter had broken apart internally, and the slug slid back blocking the exhaust. I hate muffler work, but went ahead and removed the Cat and sure enough, it was loose and sitting at the back of the casing. Installed a new one and it fixed the stumble, completely.

 

As mentioned, check fuel rail pressure...should be something like 38psi with key on, 28-29psi once it's started and running. Going from memory so might not be 100%, but close enough to pinpoint a fuel pump or fuel filter issue.

[Kkilmer87]

Refreshed all grounds and the cat and muffler were replaced off my cherokee its a flow master and the cat and muffler worked fine on that and it didn't sit long but I'm gonna look into it keep the ideas coming I drove it today and the stumble seems to come and go at least the severity of it does.......I still would like to think its electrical but can't find a thing I have multiple running 4.0 s and I have switched parts and tested a lot of things......thanks for the help guys bring on some more ideas

[Bornindesert]

Dirty terminal connections on the ballest resistor, drivers inner fender. Cracked vacumm line, the one that goes to the IAC thingy on the firewall. Stale fuel, or no gas :)

[misfitmechanic]

X 2 on the fuel pump resistor. I had a hard to find hesitation and it turned out to be a bad resistor. It was dropping over nine volts when the truck warmed up.

[Kkilmer87]

so i figured out the resistor was affecting it so i changed it and the connections........now it revs fine in park or neutral but when driving it as soon as i put on the gas it starts to stumble bad again.....i also swapped out fuel pump and cleaned the filter which was new.....had some debris in it for sure but pump screen looked okay.......need more ideas running out of money and options........

[cruiser54]

Bypass the fuel pump resistor and see what happens.

[bradseals]

id try replacing the ignition coil and rotor in the distributor again to be sure

[Bornindesert]

Sounds like you dropped the tank or maybe just left it in and changed out the pump. Almost sounds like bad gas, or water in the fuel. Are you sure you have fresh fuel in the tank?

[djdr1988]

Had a similar issue with my xj. Check the crankshaft position sensor as it is a major part of the ignition timing

[Kkilmer87]

Fuel is fresh and ill try the cps

[sloride]

O2 sensor been changed recently?

[Kkilmer87]

Nope will def swap one in soon its been on my list but I have 4 other Comanches in front of that lol

[cz777]

the ground taps for redix .....old wiring is one the biggest head aches i have run into -by flexing for years etc things break ...other is corrosion at the plug/sockets ....  

[92tanMJ]

Have you checked your engine codes? I know it sounds dumb but the CEL doesn't come on in these unless it's a more serious issue.

[Kkilmer87]

Ok guys I may have figured it out but in a bad way.......need ur guys help to determine if this is a possible problem........so when working on my problems I discovered that my distributor was loose and that was causing my problems to which I replaced and still had the same problems........well my mechanics mint eliminator just started to act the same way and while tuning it up the distributor was also really loose.... One local xj guy I talked to said the cam gear being messed up could cause this type of stumble that we are both experiencing and when I replaced my distributor the teeth were def messed up and so was the cam gear when I replaced the rod bearings........sound like a possibility .? My buddy with the eliminator is ready to flip it or swap in a ho for no reason cause he convinced its that.......any input

[Kkilmer87]

It only stumbles around 2500 to 3000 he says on his no stumble at idle or casual driving

[deziped1]

Bad plug wires show up under load, like accelerating  from a stop or pulling an incline.  Had several rigs that would start up hills fine but by the time you get to the top they have slowed to half their speed and sputtering to keep moving. Hit the flats and no load they run fine again.  Cure, new plug wires.  Just saying--------------

[Kkilmer87]

Have new everything except wires ill try that but seriously doubt it's that easy I've been over them before and my buddy Manche he just put brand new everything in no real change

[Kkilmer87]

Thanks though I will try on mine

[Kkilmer87]

Well he snapped a tooth off his distributor and prolly cam gear so his eliminator is now eliminated .....:( I feel mine has the same fate