Jeep running rough...

I have changed plugs, wires, cap, rotor, and fuel filter...still chugs/seems to have lost power. Could it be the catalytic converter? Any other ideas?

Year? Mileage?

Especially if it's a Renix era XJ the first thing I'd do is go over every single electrical connection in the engine bay. Open the connection, spray with contact cleaner, plug and replug several times. If it's an older one with the dreaded "C-101" connector on the firewall, don't neglect that one.

Check vacuum, including while it is running and chugging. Vacuum is a useful diagnostic, often neglected these days. Problems with fuel injection will probably not show on a gauge, whereas internal and ignition problems will. Scout out all vacuum lines, and check for cracks and rot, including the line under the battery and the canister behind the bumper.

Other suspects might be O2 sensor, and MAP sensor. Some early Chrysler era (91-up) models have been said to have bad coils. A few 93's seem to have bad fuel injection wiring harnesses. My 95 chugged and spat when the MAP sensor went bad, but sent no failure codes.

Better information may come when you provide more complete information.

edit: For vacuum, get a vacuum gauge and a very long piece of hose, tee it off from the intake manifold wherever you can (you can temporarily steal the heater/axle disco connection if you must), and tape the gauge to the side-view mirror. You can then monitor vacuum while you drive. this may be the only way to catch an intermittent problem that you can't make appear at will.

87 with 337,000 miles

With that kind of mileage, you should also check compression.

Does it run rough all the time? Only at idle?

Is is fuel injected?

Yes, fuel injected. Idle isn't bad. Seems to be worse under a load.

I'll bet its a vacuum leak. Check all vacuum lines. Get some carburetor cleaner (spray can) and spray it around suspicious areas. If the engine changes its idle RPM, you've found your problem.
Recently got rid of my '85 after 17 years. My leak was found at the base of the carburetor. It'll take some looking, but you'll find it.
Since yours is injected, maybe one of your injectors is giving up the ghost. Take the plug off each cylinder in turn & see if you can isolate the bad injector.
regards,
jlex.

jlex said:

I'll bet its a vacuum leak. Check all vacuum lines. Get some carburetor cleaner (spray can) and spray it around suspicious areas. If the engine changes its idle RPM, you've found your problem.
Recently got rid of my '85 after 17 years. My leak was found at the base of the carburetor. It'll take some looking, but you'll find it.
Since yours is injected, maybe one of your injectors is giving up the ghost. Take the plug off each cylinder in turn & see if you can isolate the bad injector.
regards,
jlex.

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I pulled the plugs. They all look the same. Looks like it is running a little on the rich side....

One day while bleeding the air out of the head, I accidentaly broke the MAP hose (apprx 0.125" black hard plastic pipe that connects the MAP on the firewall to the pass-side of the throttle body) and it instantly began running rough/rich, and MPGs dropped from apprx 20 to apprx 10.

If this is it, you can splice it with some vac. hose, but the OEM dealer part isn't too high... I swapped mine out when I replaced all the CCV harness.

At that mileage, if you haven't tested/replaced the injectors it might be time. Good idle probably rules out the EGR valve, but not vacuum. Might be a good idea to check the cat for clogging. That's a LOT of miles! But definitely if it's an 87 you need to go over all those connectors. My 87 was really sensitive to poor connections. Even a tiny variation of voltage at the TPS and other sensors can make a big difference.

Is there any good way to test the injectors at home? I'd love to do this with mine - no real reason other than 13mpg and 200,000 miles...

If it's running rough at load, is the engine getting enough fuel when it needs it? Next step would be to check the gas pressure at the fuel rail to make sure it's getting enough.
jlex.

Had a tester hooked up today. It said all is well. Vacuum check said the timing is off. Unplugged the connector at the bottom of the distrubutor and it had no effect good or bad. What next?

How do I tell if it is the distrubutor?

extankerguy said:

How do I tell if it is the distrubutor?

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The timing is not set by the dist, sounds like a vacuum leak to me.

All the guys have given good advice. Connectors, I spray the pins with contact cleaner and then scrub them the best I can, with one of those tooth brushes for between your teeth. More often than not, the motor runs better.
Vacuum, either the vacuum connections or the intake manifold (check the bolts, I've found mine loose before). You end up with some cylinders slightly rich and some slightly lean. Which can't be good for a smooth running motor. How is the idle RPM?
Distributor, if you can move the shaft sideways, more than very little, like a thousandths or 2, it´s gonna run bad and often the rotor will strike the cap high voltage studs. Up and down play on the shaft, doesn't seem to make much difference.
I've had an O2 sensor make mine buck at around 2000 RPM and then the replacement made it idle like chit. Took two tries to find one that worked well. The one that idled bad was OEM.
Some sensors make it run bad from the get go, some when it gets up to operating temp. Helps narrow it down some.
Check under the ignition coil, separate the coil from the ignition control module and clean the contacts. I went to remove a spark plug cable from my cap (a month old) and the whole stud came out of the cap. All sort of strange things can go wrong. Spark plug cable are always suspect, even new ones, I've had new ones, separate the end from the wire inside the boot (hard to see).
A stuck IAC will make it run rough till you get the RPM´s up, it does more than just idle.
Do you have a bottom end knock of any sort? My motor was running well, but did the shimmy shake at idle. A new set of connecting rod bearings sure did smooth things out. I get the feeling the rough idle was messing with my CPS sensor and the inputs to the ICU, can´t prove it, but the motor smoothed out a lot more than a marginal set of connecting rod bearings can account for. I also scrubbed the engine temp. sender, knock sensor and O2 sensor plugs while I was under the motor. That could also be part of the improvement.
At 337,000 yours almost has to need connecting rod and main bearings. I've seen numerous 4.0's that had enough crank gyration from worn main bearings to wear out a rear main seal twice a year. Which pretty much has to mess up the CPS pulses, somewhat.

langer1 said:

The timing is not set by the dist, sounds like a vacuum leak to me.

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HMMMMM.......

I just replaced the Distributor and now it runs great...

Thanks for all of the input!