Seanmcarter62

Hey Friends
I'm new to the forum but have searched and poked around and still haven't been able to figure out my problem.

Context:
I was given a 1988 XJ with the 4.0 in it last summer. It sat since 1998 in a gravel parking lot. She had 215k on her last summer and is now up to 221k and her name is Trixie. It's a cool story.

I've done a bunch of work over the last year or so and she has been my daily driver. Two days ago after an oil change (I don't think that's related but who knows?) I randomly got what felt like a miss driving into town doing about 60 miles per hour. Power dropped off, I drove it home and have been diagnosing since.

Symptoms: It starts fine and idles at what should be a normal RPM, no high idle. It feels like a miss at idle and reving but seems to clear up reved way up holding idle. However, when driving no matter the RPM I believe its still there. I think I smell more rich exhaust than normal but thats hard to say because I have exhaust leaks.

Below is some history of what I've done - I'll organize pre and post
Pre issue - things I don't think are related as I have drivin the jeep more than 1k miles since these:
New rad
New thermostat
Cooling system flushed and all hoses replaced
New distributor cap, rotor, wires, plugs
New IAC valve
New CPS
Oil changes at 3k miles with one rear main seal in a bottle, and I run the silver 'restore' can every oil change
Slowly plugging away at oil leaks - Oil filter housing seal, valve cover gasket, etc
New vaccum line kit from rock auto and all grommets replaced - I believe these are all back in the correct spot
New air cleaner
Trans filter and fluid changed
Front and Rear dif fluid changed
Brake and power steering fluid changed
New front rotors and pads
new wheel cylinders in the back
New fuel pump and filter x2 Most recent a month ago
Grounds - i haven't done the crazy ground kit, bit I have verified all grounds and updated some.
Fresh battery cables
I forget the jeep guru on this forum but he has a post about cleaning all the electrical connectors - I did that too.
4 port injectors and fresh seals
fuel pressure regulator


After the issue - in the last 48 hours as of 7/30:
Throttle body cleaned
TPS adjusted
A can of seafoam high mileage down the yap
Verified I have power to all injectors
Did the screwdriver stethoscopetrick to listen to the injectors - I believe they are all firing as they should
I have spark from the coil pack
I measured the resistance of all plug wires and they are all in spec
Compression test:
1 - 110
2 - 90
3 - 110
4 - 100
5 - 100
6 - 110
While running pulled each plug wire from the plug and rpm noticeably dropped each time - this is how I checked each plug was firing
Removed plugs and checked all of them. They were not exactly pretty, but none looked fouled - at most a little hot.
Tightened intake manifold bolts - they were hella loose.

Without starting to throw parts at it I feel like I'm left with:
MAP - I believe this is working I did buy a new one, swapped for a previous issue a month ago, and there was no change. BUT it could have broken between now and then?
O2 Sensor - I have run it with the sensor plugged in and without - there is no change. I was hoping if I unplugged it, the ECM would revert back to a 'standard' of some sort.
Distributor - There is a little oil in the bottom, but I know I'm getting spark.
ECM - Could be I guess since it was so sudden?
I used a small amount of antiseize on the spark plugs upon install could this be preventing ground? Maybe not because when I pull each wire off the plug it gets worse.

So I'm lost. Any suggestions? I'm trying to not just throw parts at it if it doesn't need it but it is my daily and I plan on continuing to drive it. Up to this point I averaged 20 mpg. I have a lifted tacoma but it literally gets 13 mpg. The money I've spent on Trixie I've saved by not driving the jeep. I can take pics and video as needed.

Thanks

Saudade

Well, a couple of things.

First go to https://cruiser54.com/?page_id=75 for all tips Renix (that's the fuel management system your XJ has) and do/redo tips 1-5. (I know you said you already did some of these.)

Next go to https://cruiser54.com/?page_id=365 and get the 1988 FSM to help further diagnose your issues.

The ECM does not store any data or codes so unplugging things doesn't make any difference other that hopefully freshen the contacts.

Your compression is very low. Spec is 120-150psi with a max 30psi spread. None of yours is within specs and #2 is very low.

Run the engine, then grab the harness along the valve cover and give it a few good shakes. Not like your tearing it off, just some good motion and see if it hiccups. The injectors get power from the ECU but all share a common ground. All the grounds go into a single splice inside that harness. I had an intermittent misfire and it turned out to be corrosion of that splice would break the connection to my #3 injector. Sometimes the slightest touch or vibration would make it connect again and mine would run fine. Then a bump or something would break it and misfire.

RIP Cruiser54

Seanmcarter62

Thanks for the response!

I went back through and followed your suggestion of redoing 1-5.
Im confident grounds are good by the dipstick tube. I also added a ground from the firewall to the fuel rail bolt as suggested in Cruiser54s post.
Checked the C101 connector - I already cleaned out the tar and filled it with electrical grease but just made sure everything looked good.
Rechecked any connectors and made sure I had good clean connections
Rechecked coil contacts - those are good.
Soldered the 6 grounds together - this made my voltmeter gauge work better, but didn't solve the issue.
For the sensor grounds, I have 0 ohms no matter what I do when I follow the check procedure.

I also wondered if the old plastic line from the throttle body to the map sensor was cracked. I verified it was not, and just for good measure, ran some fresh vacuum line from the map sensor to another vacuum port and covered the holes in the throttle body - no change there. I replaced the original equipment.

Thanks for the info on the ECM. That's one more thing I don't have to mess with - I did refresh those contacts a few weeks ago FYI.

I also shook the harness there was no change that I could tell in the running. I also ran it cold and hot to see if there was any difference at different RPS and it is a consistent stutter/miss/shake/whatever.

I keep calling it a miss, but I've checked spark and fuel and they are both there at this point. So that leads me to what I think you are referencing with the compression.

I don't have milk shake in the oil, nor do I have oil in the coolant. Those are my initial tests for a headgasket - any others I should think of before I rule that out?
That leaves just rings and me accepting Trixie is tired and needs some work. Is it possible there is a stuck valve or something? Is it worth pulling the valve cover and going down that path? Checking valves, making sure pushrods spin like they should, etc?

I'll start working through the service manual to see if I catch anything.


IF it is rings, I know its always better to have the block worked by a machine shop, but is it realistic for me to replace the crank bearings, pistons, rings, and the stuff that goes with that and get another couple years out of it?

dmoe69

I think the compression check numbers are suspect. They are very low, as said, but also for an engine with 200K miles. Did you pull all the plugs out and test one cylinder at a time? Also, two tests per cylinder, one dry and one with a squirt of oil in the cylinder will give you a better idea of where the failure is. It is good you have updated the grounds some, but the only way to check them is with a multimeter. I personally think the best way to check your ground is by back probing the "B" terminal of the TPS connector and checking resistance to the negative post of the battery - and agitate the wiring harness while you are doing this check to see if there is any variation in Ohms reading.

Seanmcarter62

Thanks for the reply.
When I did the compression check, all plugs were out and fuel pump relay was pulled and I did it one at a time. I didn't do it wet. I'll try that again today and see if that makes a difference.

I did the ground test as you suggested at I have 0 ohms with lots of jiggling.

When I first got this running last summer, it overheated really badly until I fixed and basically replaced the entire cooling system, so I don't know if the previous owner drove it hot? It is an 88 and I know for sure it was parked in 98 and didn't move until the summer of 23. So it was driven hard, I'm assuming highway, for 10 years then left up.

dmoe69

Excellent grounds, that is not your worry. As for the compression test, it just seems abnormally, but consistently low. How confident are you in the compression tester you are using? At those values, even doing the compression test wet won't relieve you of the fact the compression is low. Does it seem to burn oil or have excessive blow by?

That Jeep Guy XJMJ

Anyone else curious about the injectors? We're these brand new or used/refurbished.

Honestly I tried the "X" holes injectors once and didnt have a good time with it and went back to factory ones. Perhaps toss the old ones or even just another factory set in and see if theres any difference?

You could also remove the fuel rail and try a wet test by letting it do it's first prime cycle into the environment, if all injectors aren't spraying in uniform then you would have a culprit

dmoe69

Very good point on the injectors. Refurb (from reputable vendor) is far more preferable than "new". The Volve -746 4 holes are the closest match to the factory injectors. Test data on the fuel rail would be good. Should see 31 PSI at idle and 39 PSI at idle with the vacuum disconnected.

Seanmcarter62

It's the compression tester that has been in my box for probably 15 years but I've only used it probably 3 times in that time. I can go rent one from the auto parts store and do it again for a comparison. I don't have blue smoke out the back and it doesn't usually stink, but I'm sure there is some amount of blow by. There is vacuum in the valve cover and as far as I can tell the PCV system is working as it should but I don't really have a reference for what is excessive.

The injectors I purchased were from K Suspension - https://www.ksuspensionfab.com/store...XJ%2FMJ.html#/
Upon instillation, they made a big improvement in driveability and power with no impact on gas mileage.
I'll pull the fuel rail today and try to let it prime and observe for anything weird. And try to not catch the Jeep on fire.

I'll get the data on the injectors itself. About a month ago, when I replaced the pump and filter for the second time, I tested the fuel pressure. I forget exactly what it was but it was as it should be. I'll get the gauge back out and get the data to share here for diagnosis.


Thanks again for the responses and time on this - I REALLY don't want to have to buy another car or drop any serious money onto something unless I have to.
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dmoe69

If it ran good for a fair amount of time/miles with the new injectors before you started having this drivability issue, I don't think I would be concerned about those injectors.

SimpleDad

Checked the local news for any 'gas station sells gas with water in it' stories? Did you happen to fill up that day? Have you reseated your gas cap since this started? Have you ever replaced the gas cap? Don't know on XJs but I had a WRX that acted like that, turned out it was the gas cap.

Seanmcarter62

Alright issue resolved - spoiler: it was an intermittent fuel injector. I spent the better part of a week and a half going back through everything. The way I found it was after replacing the plugs and wires, just to rule it out for sure. I ran it, it still missed. Then I pulled the plugs to read them and #1 didn't look like there was any combustion. I verified it had spark then rechecked my injector connector - both of which were fine. So - it was my #1 injector. I called K Suspension, the folks I got the rebuilt 4 port injectors from in the first place, told him all I had done, and he shipped my a new injector no problem and free of charge.

Highly recommend the people at K Suspension and issue resolved. Thanks everyone for the help and input!

That Jeep Guy XJMJ

Thanks for the update on the resolution!

makros

sounds like a similar problem except mine is stuck open