95 xj driving us crazy

My friend has a 95 XJ that has us stumped. Once in every 10 or 12 starts, it runs like a clock from idle to redline. The rest of the time, it stumbles, shudders, lopes, back fires, and runs like crap.

We have replaced every sensor at least twice, the computer 3 times, the distributor and cam sensor 3 times, installed a new alternator and a new coil. cleaned all grounds. Unhooked and re-connected every sensor with the engine running and if they did not kill the engine, they made no difference in the symptoms.

We have metered every wire and found no discrepancies. The CPS and cam sensor are getting a 7.45V feed and they are putting out 4.36V.

I'm thinking that it is a corroded ground splice somewhere in the harness, or a connector socket that has been spread and is making intermittent contact with its mating pin.

Does anyone know if there is a ground splice in the main harness that runs along the firewall? We are having trouble finding a complete schematic for a 95 so we have been using one from a 94. I know the 96's were different.

My friend has been a mechanic for 40 years, so i don't feel so bad about being stumped, but i would like to see this thing run.

Any suggestions would be appreciated.

Have you verified fuel pressure?

I think go1lum is on the right track. The fuel pump
assembly has rubber connector lines that tend to split
and crack over time. This allows fuel pressure to bleed
off and also air to enter the fuel lines.

The fuel pump on a 95 can be accessed with the tank
left in place.

A post awhile back a guy had a similar problem and it turned out to be a splice in the injector harness. The injectors are hot on the dark green and orange wire when the ASD relay is activated. Same circuit (and wire color) as the coil and alternator power in. The injectors fire on the negative side.

Never heard of it on anything but a Renic but possible later models may have the same issue eventually. Where the injector harness bends at the firewall, possible the copper core of the dark green and range wire has cracked. Hard to see when it is under the insulation.

Kind of a reach, but when all else fails you grasp at straws.

I'd hook a volt meter up to the number one injector with the motor running, check my voltage and maybe wiggle the harness some. Open up that neat harness box over the injectors. A bunch of splices in there.

And like mentioned check your fuel pressure, could be a failing pump, could be electrical, could be rotting in tank hoses.

The last time I had something similar it was the O2 sensor.

Check the O2 sensor harness where it runs up through (or behind) the power steering pump bracket and make sure it isn't cooking on the exhaust manifold. A cursory check isn't going to do it, where it burns is hard to see, you need a flashlight, a mirror and look carefully.

A couple of things i should have mentioned, fuel pressure is 31 with regulator connected and 39 with regulator disconnected. No codes show up on an OBD1 scanner. Cleaned and polished the dipstick and chassis grounds.

8Mud, you are thinking along the same lines i am. We will check the injector harnesses, but we have tugged and pulled on every wire in the engine bay.

Thanks for the repiies, keep em coming.

91Heep,
I typed "95 cherokee wiring diagram" in the yahoo search box and then when it came up went to the "images" tab. it brought up dozens of them, lots of 94 images but no 95.

I'm with 8Mud - check the upstream O2 sensor wires - from the sensor connector, all
along to where the harness exits the end of the hard black plastic protective squarish
tube that is above the intake manifold.

It is not uncommon for that part of the wire harness to get burned or heat damaged
because it is routed so near to the top of the #1 exhaust port header tube.

In my case ('98 XJ), that part of the wire harness looked all good externally. There
were no external nicks, no burn marks, etc. BUT - that part of the O2 wire harness
was actually damaged and repaired (well … sort of) by a PO who had used those
damn butt crimp connectors. New tape wrap and a new section of split convoluted
plastic harness cover was then used to make everything look nice and professional
after the “repair”.

Unplug the upstream O2 sensor, and gently pull up the wire harness, and lay it across
the upper radiator support. Open the split convoluted plastic harness cover and
unravel the wire harness tape and carefully check all along the (4) wires for any sort of
splices or previous repairs, or breaks, nicks, or burns. There shouldn’t be any splices
there because the factory didn’t put any splices in that part of the harness when the
car was designed.

Correct any bad sections using solder and heat-shrink tubing. Do not use any
crimp splices.

Check and clean the O2 connector socket and pins. It is not difficult to disassemble
the O2 connector to get to everything in there.

Loose Vac line from the throttle body to the MAP sensor is major possibility for those symptoms. Easy to fix.

O2 sensor issue, wiring, heater power relay to the O2 sensor if the 95 has one?

Busted cat that is loose and one minute it blocks exhaust the next minute it does not. It will come and go like you mentioned.

Is the Dizzy off by one tooth? Try reinstalling it. See Cruiser54 's write up on it.

We thought the dizzy off a tooth might be the problem, but no luck.

We even removed the dizzy hold-down bolt and held the dizzy down by hand, then we turned it slowly with the engine running. We could turn it quite a way and the computer kept compensating, up until we got some significant pinging, but it made no difference in the symptoms.

We have unplugged the O2 sensor with no change in symptoms, but we will definitely check out the wiring as suggested.

The intermittent nature of this problem is sho nuff aggravating..............

thinking of looking for a complete JY harness

Time to run a compression test on each cylinder and a vacuum diagnostic test. They will tell you a lot and save time if you have engine problems. Also need to test the O2 wires and signal itself, live, and the MAP sensor vac hose and signal and the MAP sensor signals with a volt meter. And test the sensor ground wires in the harness. Don't forget the problem can be a busted cat with a loose honeycomb in it that randomly blocks the exhaust and then moves and unblocks it.

Have you checked for codes using the ignition key- on-off-on.... cycle trick yet?

tugalo said:

My friend has a 95 XJ that has us stumped. Once in every 10 or 12 starts, it runs like a clock from idle to redline. The rest of the time, it stumbles, shudders, lopes, back fires, and runs like crap.

We have replaced every sensor at least twice, the computer 3 times, the distributor and cam sensor 3 times, installed a new alternator and a new coil. cleaned all grounds. Unhooked and re-connected every sensor with the engine running and if they did not kill the engine, they made no difference in the symptoms.

We have metered every wire and found no discrepancies. The CPS and cam sensor are getting a 7.45V feed and they are putting out 4.36V.

I'm thinking that it is a corroded ground splice somewhere in the harness, or a connector socket that has been spread and is making intermittent contact with its mating pin.

Does anyone know if there is a ground splice in the main harness that runs along the firewall? We are having trouble finding a complete schematic for a 95 so we have been using one from a 94. I know the 96's were different.

My friend has been a mechanic for 40 years, so i don't feel so bad about being stumped, but i would like to see this thing run.

Any suggestions would be appreciated.

Click to expand...

This will be interesting to see if you find your issue.
I have been strugling with the same problem ever since I rebuilt mine into a stroker.

+1 on o2 sensor wiring. mine was not great and a Re-do of these wires made a difference for me.

+2 All the vacuum lines. Tape them up. see if it makes a difference.

This may seem stupid.
But 99% of the ignition diagrams for the xj on the internet are wrong.
Check the Firing order.