View Full Version : Need help diagnosing rough running 89

October 4th, 2017, 15:19
Ran into some trouble with my 89 XJ and hoping to get some tips to diagnose it. Finally had the car on the road and now its back in the driveway.

Everything was running ok (didn't seem perfect) and I took it on the freeway to run an errand. On the way (downhill) I started noticing hesitation when coming on throttle. Got to the destination, started it up and took the streets home. As I made my way it got worse and I'd have to floor it to get it to come back on power.

Got almost home when temps started to creep up (I live up a pretty big hill) and I parked it to avoid severely overheating. After it cooled completely down I went back and drove it the remaining few blocks home. Found low fuel pressure and replaced the pump and filter. Starts up much better after this.

The problem now is it runs extremely rough and sounds like terrible. I drove it up my driveway but when trying to get up to speed on the streets the car struggles terribly. Noticeable lack of power as well.

Just wondering where to start given the backstory. The following have all been replaced in within the last year and done under 2000 miles:
- Injectors
- Plug wires
- Cap & rotor
- Vacuum lines (almost all of them - picked up the full replacements)
- O2 Sensor

October 4th, 2017, 15:20
Will also post video of how it's running ASAP. Tried to go record it now but the battery has gone flat since I last started it. Will record and post as soon as I get it charged back up.

October 4th, 2017, 17:00
A low battery will cause exactly what your are describing on a Renix. The low fuel pressure would have made it run lean and overheat as well and the low battery voltage could have contributed to your low fuel pressure. I would check to make sure your alternator is putting out.

October 4th, 2017, 17:30
Map sensor vacuum line to the throttle body can cause exactly what you're describing if it's leaking or disconnected

October 4th, 2017, 20:45
Also, you can bypass the ballast resistor for the fuel pump,
located near the driver's side front. That will increase voltage
to the fuel pump.

October 5th, 2017, 09:25
Thanks everyone! The battery is charging now, so I'll report back after it's charged up and add a video of how it's running then if it isn't resolved.

I checked the vacuum to the MAP and it looks like it's good. Will investigate further once it can be started.

I think the fuel pump is fine now. There was a noticeable difference when starting it up after the recent replacement. I'll check pressure and if it's not in range will bypass the blast to see if it improves the situation.

October 5th, 2017, 10:36
Ok - got it started and the alternator looks good. Battery was up over 12v when I started it and read over 14 when running.

I was able to drive it briefly and it drives ok (not great) other than the noise. I did notice it gets worse as RPMs rise, but dies off above 4k.

Links below include a video of it running in the driveway and another one capturing the noise while driving it. I could probably stick a go pro to it and record more driving footage if it would help?



I'm also wondering if maybe this is the flexplate bolt issue? Will probably get under there and give those a look today just in case that is the issue.

October 5th, 2017, 11:49
Flexplate bolts are all good. Just confirmed.

October 6th, 2017, 05:55
Go to www.cruiser54.com and do Tips 1, 3, 4, and 5.

Triple check the tB to MAP hose. all it takes is a pinhole.

October 6th, 2017, 07:51
Thanks Cruiser! I'll look those over and make sure all is good with those. Your site was a massive help when I originally got this Jeep back on the road last year!

October 6th, 2017, 16:01
Collapsed lift, broken valve spring, stuck valve. Sounds top end and not a rod knock but if the valve train is good you may need to drop the oil pan. I would start by pulling the valve over and see if it is anything obvious.

October 6th, 2017, 17:48
When trying to pin down a sound like that, a piece of plastic tubing held to your ear can really help. I've chased down odd sounds that way, now I have a mechanics stethoscope. I actually chased down a connecting rod bearing issue to single cylinder using plastic tubing, if I can do it you can do it.

I don't know the answer but my first impression was a dead cylinder, maybe from a valve train issue. A compression test should show something like that quick and/or a vacuum gauge. It sure sounds like you are firing a cylinder or two short.

But it is even harder to pin down direction from a video. Check your distributor shaft and the inside of your distributor cap. Up down movement in the shaft doesn't usually mean a lot, side to side play does.

Check the obvious first, a timing light will tell you quick if a cylinder has a high voltage issue (spark), just move the pickup from cylinder to cylinder and point the light at something dark.

Double check your firing order. Both the cap and the plugs.

October 12th, 2017, 17:52
Some updates since I had some time to work with it today.

Put new plugs in just on a whim. No difference.

Disconnected exhaust to check for clogged cat. Much louder, no better.

Did a compression test. All came back around 120 per cylinder. Battery had gone flat and it was just coming back up when cranking, so suspect it would read a little higher with a fully charged battery.

Pulled cap and no play in the distributer shaft. Contacts on rotor and pins in the cap looked good.

My hunch is ignition, but everything but the coil was replaced within the last year?

October 12th, 2017, 18:17
Compression test on each cyli

October 12th, 2017, 18:21
Sounds like a rod

October 19th, 2017, 10:37
Well this got interesting. Pulled the valve cover this morning and found this special treat...


Put it back in place, put everything back together and it runs like it used to but is still ticking.

October 19th, 2017, 12:45
Did you pull it out to see if it is bent or anything?

October 20th, 2017, 16:01
Cant see the pic. Was anything loose on the valve train. The rockers? Could you spin the push rods with your fingers?

October 21st, 2017, 10:09
The picture showed a rocker that had moved over off of the push rod. Not sure why the picture is gone. I saw it the other day

October 22nd, 2017, 16:09
do you have a video of it ticking now? its possible that rocker or rod is damaged or bent.