New XJ in the family need some help
Printed From: TheAMCForum.com
Category: Competition
Forum Name: Jeeps and Eagle 4x4 fun.
Forum Description: Rock crawling events or results, Muddin' it through the riverbed with your Eagle
URL: https://theamcforum.com/forum/forum_posts.asp?TID=93799
Printed Date: Apr/16/2024 at 1:54pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com
Topic: New XJ in the family need some help
Posted By: WesternRed
Subject: New XJ in the family need some help
Date Posted: Apr/25/2018 at 6:41am
So I sold my SJ Cherokee a while ago and have just bought an XJ to fill the need for a Jeep in the family. The idea is that it be a first car for my young bloke, who is now old enough to drive and it is probably a bit more sensible than a 360 powered SJ. I know it's a bit late model for die hard AMCers , but not straying too far and I'm sure there are some knowledgeable people on here. The issue is it has a pretty severe missfire, basically rough idle and under any sort of load. At light throttle cruise and free revving, it seems to run ok. Came with a few spare sensors, so previous owner has been fiddling to try and solve it, but has given up and hence it was a cheap purchase for me. Just got it home, so haven't had much of a chance to tinker, but looking for some ides and diagnostic tips if anybody has some?
|
Replies:
Posted By: jpnjim
Date Posted: Apr/25/2018 at 7:54am
|
What year and engine? I know they used Diesels in other parts of the world after they stopped using them here, not sure if you guys got the gas 4.0L in the majority of them like we did in the US. ------------- 71 P-code 4spd Javelin/AMX some Jeeps and some Fords |
Posted By: WesternRed
Date Posted: Apr/25/2018 at 5:39pm
| Sorry, 1995 4.0 petrol engine with 4WD and auto transmission (gas means LPG down here). |
Posted By: JeeperJolene
Date Posted: Apr/25/2018 at 5:46pm
|
Is it a random misfire or is it the same cylinder?Is it after the Jeep warms up, cold or both? |
Posted By: jpnjim
Date Posted: Apr/25/2018 at 6:07pm
|
Yeah, those 91-95 4.0L's will pretty much run great no matter how bad they are neglected. Crank Position Sensor usually makes itself known by randomly not starting, injectors can get dirty like anything else, and a bad Throttle Position Sensor can hurt acceleration, or make the trans not want to kick down, but it's really one of the most simple MPI systems around. The distributor is supposed to be locked, I wonder if someone tried to "adjust" is sometime in the last 23 years (?). A weak coil is possible, but I've had them all either work great, or completely fail with nothing in between. I'm guessing you looked at the plugs, fuel filter, wires, etc? Sometimes the throttle body can need a cleaning, the little idle step motor in the TB (I forget the name right now) can clog and give it a bad idle and the thin CCV tube at the back of the valve cover clogs so the air filter fills with engine oil, but the CCV shouldn't hurt the idle much. If that stuffs all good I think I'd peek to see no one messed with the distributor, then try a compression test to see what you're working with. I guess a flat cam is a possibility too, but I've never run into that either. Great vehicles tho, good luck ------------- 71 P-code 4spd Javelin/AMX some Jeeps and some Fords |
Posted By: jpnjim
Date Posted: Apr/25/2018 at 6:14pm
|
I'll add one more thing, the simple plugs/wires/cap & rotor is the main thing with these, I had one run poorly for a while, after a tune up. I couldn't understand why, till I pulled the distributor cap and saw that the rotor was 50% missing  I have no idea how it even ran with half a rotor, but that's how reliable these engines really are, they just *want* to run, no matter what  ------------- 71 P-code 4spd Javelin/AMX some Jeeps and some Fords |
Posted By: amxdreamer
Date Posted: Apr/25/2018 at 6:49pm
Great vehicle for a new driver. A little higher up so better visibility and collissions and can take a bit of a beating! This is my 16 year old sons that he has been slowly fixing up! ------------- Tony Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
Posted By: AMXRWB
Date Posted: Apr/25/2018 at 9:43pm
| Cracked head could be the problem. |
Posted By: WesternRed
Date Posted: Apr/25/2018 at 10:32pm
| Lets hope not. |
Posted By: WesternRed
Date Posted: Apr/26/2018 at 6:06am
| Just did the key dance and the only OBD code to come up was 55, which pretty much means nothing wrong there. |
Posted By: THE MENACE
Date Posted: Apr/26/2018 at 11:49am
|
Seems like a lot of people overlook the fuel filter on XJ's for some reason. It's above the rear diff. Injectors get clogged. A great upgrade for 91 up 4.0L XJ's are Dodge Neon injectors. They are a simple direct replacement (no mods) for the OE injectors and are pretty common to find at the bone yards, at least around here. Get them ultra sonic cleaned and they work like new. My 91 XJ ended with better acceleration and slightly improved fuel mileage with the Dodge Neon injectors. ------------- Former Owner of: The Craig Breedlove "AERO AMX" Still Owner: SS/AMX #9 replica (THE BIG MENACE) 70 AMX 416, EFI, Nash 5 speed 70 Javelin 401, 727 (Wife's car) 72 Gremlin Autocross Project. |
Posted By: Pdok
Date Posted: Apr/26/2018 at 7:01pm
|
This link is useful for MPFI troubleshooting: http://www.4wdmechanix.com/Jeep-Multi-Point-Injection-Operation-and-Troubleshooting?r=1" rel="nofollow - http://www.4wdmechanix.com/Jeep-Multi-Point-Injection-Operation-and-Troubleshooting?r=1 Symptoms could conceivably be caused by: erratic fuel pressure or regulator Erratic fuel delivery (as mentioned, injector clogged), or more rarely, injector wiring faulty ground injector problems will usually throw an OBD code, however, even if intermittent. I've found that to be true anyway. Ignition coil issue O2 sensor (engine never gets past open loop warmup) We're sure no valves are sticking? No vac leaks, intake/exhaust tight and gaskets good? Best of luck, wish I could fly down and drink a beer while you fix it... ------------- 76 Grem X 258/904,4.0 head/MPFI, Comp X250H cam, Hughes springs, Clifford header, serpentine swap. |
Posted By: WesternRed
Date Posted: Apr/26/2018 at 7:05pm
I think I will start with this stuff and a compression test, then move onto the electronic stuff. |
Pdok wrote:Posted By: 70 Donohue 390
Date Posted: Apr/26/2018 at 9:50pm
  It's currently for sale on The Medford Craiglist  I bought my 172k mile 96 from the original owner after she totaled it. I rebuilt it and have put 12k miles on it the last 18 months. It was running rough, when I first bought it. so I ran a can of Marvel Mystery Oil down the carb and 90% of the miss was gone. Then I wanted a smoother idle and better gas mileage so I changed my cap, rotor & wires. Get the better heavier cap (I think that may have been my main problem) My E3 type plugs are very clean but the wires were showing their age. Keep an eye out for a leaking oil pressure sending unit. They blow the back off and oil on hot pipes is ugly. ------------- 67 Rogue 290 Convert 70 BBO 390 5 Speed Javelin-under construction |
Posted By: WesternRed
Date Posted: Oct/11/2018 at 10:15pm
|
I should update this, replaced the rear main seal and oil filter adapter O-rings, fixed a small vacuum leak in the PCV system and the thing has been running fine ever since. ------------- I've finally given up drinking for good...........now I only drink for evil. |
Posted By: 73Gremlin401
Date Posted: Oct/15/2018 at 1:23pm
Sometimes it is the simplest of things that makes them run right! AMC 6s in general are super sensitive to vacuum leaks, so this repair makes sense. Glad it's doing well. ------------- 73 Gremlin 401/5-spd. 77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto  |