Please HELP!!!!

[redneck_rollercoaster]

I have an 87 MJ long bed with the 4.0, 5 speed and it is a 4x4 with 128,000 miles on it. oh pic coming soon. any way here is the problem, when I puchased this MJ it was cuting out while driving like it was a fuel problem so I replaced the fuel pump, filter and pressure regulator to no avail. and I had the injectors checked they were good. so I replaced the plugs, wires, cap, rotor, distributor, coil, ignition module, and oxygen sensor. still didnt work so I replaced the entire eghaust system and that didnt work. if anyone knows what may be causing this PLEASE HELP! :mad:

[CEThomas]

Check the MAP sensor.

 

Charles

[whowey]

Check the CPS, many a bizarre ignition problem can be traced to it.

 

Also check the C101 connector. Thats the big plug above the master cylinder.

[redneck_rollercoaster]

thanks guys for the input. I'll give it a try and I'll let you know how it turns out. 8)

[bdjr]

could be vapor lock. does it run fine for a a bit then start cutting out. just a thought. mine did it when whenmy tank slid and pinched a return hose.

 

bill

[redneck_rollercoaster]

I don't think I have a pinched fuel line, when I replaced the pump and filter I checked my lines for leaks and any thing else that looked abnormal. all I know is that I'm frusturated, I really love this little truck and it's starting to cost me a lot of money. which is very upseting do to the fact that these outfits are usally known for there reliability, and the fact that even my local jeep stealership can't tell me what the problem is. Oh well I guess I'll just keep trying until I find the problem. thanks for the input. :cheers:

[aemsee]

Don't take this wrong, but don't blame the vehicle for having someone throw a lot of parts at it to fix one problem. You need to try and find a competent mechanic that is willing to take the time to drive your vehicle around until it dies on him or her, then diagnose the actual problem.

How do you get the truck to restart after it dies? Does it just crank right up, or do you have to let it sit for a period of time? Is there any visible smoke when restarted? Does it run good right away, or spit and sputter for a bit. When it is dead, does it try and run when you crank it, or turn over with no sounds of life? Does it just conk out while driving, or when coming to a stop, hitting a bump, turning a corner, braking hard?

All engines need basically air, fuel and spark to run. You have addressed the fuel delivery aspect with the pump and filter, air with the new exhaust. You need to figure out what is being lost. A bad crank sensor will lose you both fuel and spark, a bad coil module will lose you just spark.

Carry around a can of carb cleaner in your truck. When it dies, spray a bunch in the TB and see if it fires up. That will tell you lack of fuel. Get yourself a spark tester from a parts store, and a long plug wire that will hook on to the coil terminal so that you can see the tester from the drivers side, and a jumper wire to ground the tester well. Hook it up when the truck does run and see how it works, then when it dies you can check for spark yourself. Keep this in your truck as well.

Chances are that most guys at your dealership are young and don't have a clue about your truck, and if it is a newer dealership then they won't even have the diagnostic equipment to hook up to your truck. A dead vehicle is one of the easiest things to diagnose, one that is intermittant and doesn't act up is just a crap shoot and usually ends up costing way more that it should to fix, as you are finding out.

[bdjr]

WOW! yeah what he said! :bowdown:

[jeepdoggydogB]

I don't think I have a pinched fuel line, when I replaced the pump and filter I checked my lines for leaks and any thing else that looked abnormal. all I know is that I'm frusturated, I really love this little truck and it's starting to cost me a lot of money. which is very upseting do to the fact that these outfits are usally known for there reliability, and the fact that even my local jeep stealership can't tell me what the problem is. Oh well I guess I'll just keep trying until I find the problem. thanks for the input. :cheers:

 

Fiatslug87 had a similar issue, I believe it was a short. This is what he wrote.

 

By Fiatslug87

"I think I've found my problem. I put the fuel pump back in and was able to start the truck (remember the intermittent voltage issue), but when I released the parking brake it died and this repeated a couple of times (my wife was present to witness it so I'm not delusional). It also died when I slammed the door shut; apparently the wiring harness to the fuel pump runs inside the cab near the E-brake and the connection must have been loose. A couple of months ago I replaced the weather stripping and had to remove all the interior panels and I must have jiggled the connection loose. I should have looked for the simple solution first- Occam’s razor correct again. It’s been running fine for a couple of days now so that must have been it. Thanks for all your help."

[redneck_rollercoaster]

ok first of all please understand that the little guy dosen't die it just spits and sputters, cuts out while it's idleing or driving, and if it starts to act up while at a stop light for instance it starts to idle very rough for a few seconds and then revs for just a moment ( like it would at start up) and proceeds to run smooth. there is no smoke, the compression is good across the board, and if you read my first entry you will see what I have replaced which is more than the fuel pump and filter. there seems to be no rhime or reason to the problem I've tried to figure out if there are certain times when it does this. at start up, braking, turning, shifting, lugging the engine, warm or cold outside, racing the engine thru the gears,ect... the one thing that I can say however is if I let it warm up until its at running temp and then drive it, sometimes it doesn't do it at all but if I run all over town like this, shut it off and restart it after only a couple of minutes it starts doing it again! and sometimes when I start it in the morning after sitting all night it does cough and stutter like its missing ever so slightly and when it warms up there seems to be no miss? but the timing index it accurate according the the dealer. urgh... Oh I checked the C101 connector and it seems fine, I unpluged the plugs and checked for corosion and loose wires spayed some W-D on it and pluged them back in. also my stealership, which is well established said that the MAP sensor is good. but I will definently ask about the crank sensor. because the third shop I took it to for this problem YES THE THIRD!!! said at a certain point in the rpm's I was loosing spark, thus all the electricial components I replaced. Also I can't agree more with finding a compatent mechanic and there is one in this area his name is rick nakyha and he owns rick's off road center here in Idaho Falls and I highly recommend him if any of you are in the area he is outstanding! a true jeep guru. Now with that said he is out of town for a few months on family buisness so I'm told, and this bieng my daily commuter I just can't wait that long. as I'm sure most of you can relate. plus it's hunting season so I need my little guy. Thanks for everything guys I really do appriciate it and please leave more input. I promise I will let you know what fixes it when I find out. Sincerly, Derek Austin :cheers:

[aemsee]

Here are a couple of ideas that are free or cheap to try.

There was a bulletin out for hard start / driveway die out that involved replacing the crank sensor, cutting off the connector and slicing wires in to the crank sensor and running them through the firewall and splicing them directly to the ECM under the dash. You could try this with out replacing the sensor to see if it makes a difference. Be sure to twist the replacement wires that you run to the ECM to eliminate induced voltage. I believe that is what the original issue was. If you want to try this I can probably find the old bulletin and send you a copy.

Make sure your throttle body is clean, including removing the idle air control motor and cleaning the pintle and bore with carb cleaner and a NYLON brush

I also recommend checking the TPS and eliminating the connector off of it as well, directly splicing the wires together if it is one with the pigtail off of it.

Any wire splicing needs to be done by soldering together clean wires, no butt connectors or scotch locks. If the wires are a bit dark or burnished, just scrape then with a knife blade or razor blade until you see shiny copper.

As for the timing, with the miles on your rig, I imagine the timing chain as a bit of stretch to it. If you kept your old distributor cap, locate #1 terminal, and carefully use a dremel tool or something like that and cut a window out of the plastic that will allow you to see the #1 electrode through the window you will make. Now turn the engine over by hand until you have the timing marks on the crank pulley lined up at TDC for #1 cyl, turning only clockwise as you look at the front of the engine. This is important as you don't want any slack in the drive side of the chain. Now put the modified cap on your distributor and look to see where the rotor lines up on the terminal. You want the tail, or trailing edge, of the rotor terminal to line up with the #1 terminal on the cap. If it isn't, adjust your dist so it lines up. If you have the ears on your dist that keeps it from moving, you will need to remove it and cut them off, being sure to mark everything so it goes back in the correct spot.

Does your engine run a EGR valve? They switched back and forth so much I can't remember which years did or didn't. Make sure that is working properly. It will need to be removed to be fully checked for bleed by. I can give you more instructions on this if you want to check it.

 

Another thing I have seen for erratic driveability issues with the 4.0, especially the older ones for some reason, is a heavy build up of carbon deposits on the back of the intake valves. Unfortunately this means pulling the head and cleaning or replacing the valves at this point.

Good luck and keep us posted. :cheers:

[redneck_rollercoaster]

aemsee I will definently try the things that you have posted and let you guys know how it turns out. once again I GREATLY THANK all of you!!! your insight has been a god send. Derek

 

[aemsee]

Do you want me to try and find that CRK sensor bulletin?

[Eagle]

Do you want me to try and find that CRK sensor bulletin?

Did the TSB actually talk about modifying the stock wiring harness?

 

I ask because you can buy replacement CPS's that come WITH the replacement two-wire harness to run straight from the CPS through the firewall to the ECU. The problem (as it was explained to me by the gurus at Bradshaw Jeep) was (is) that the run in the stock harness is too long, causing a voltage drop. The CPS doesn't generate all that much voltage anyway, so it doesn't require much drop to cause problems. The replacement harness, being a short and direct run, is intended to eliminate this problem.

 

I haven't priced them recently, but the last time I bought one the CPS with the replacement harness actually cost less than a replacement CPS without the harness. If you need the part number, I can probably find the spare I bought and get the number off the box. It just might take a little while.

[aemsee]

Do you want me to try and find that CRK sensor bulletin?

Did the TSB actually talk about modifying the stock wiring harness?

 

.

 

Yes, it did (does?). It had us drilling a hole throught he bulk head , cutting and splicing the CRK wires at the ECM and even said how many twists per foot of wire to put in. Took care of alot of intermittant stalling issues.

[redneck_rollercoaster]

ok guys I've got bad news and even more bad news,

My MJ just spent the last two days at the dealership and while they were running a battery of test which involved testing all electrical sensors, ohm test on the wiring harness, cps test, and ecm test. all of which passed with flying colors. However while running the tests my MJ started to heat up (not redline) but it got hot and the oil pressure dropped to less than ten pounds! and while the heart attack started to comence the top end started to chatter not bad but like a heavy lifter tick. and the only thing that the dealer could think of is that I have floating valves. so all and all it's time for an overhaul. the reasons that they came to this is the obvious sounds but also they said that while the truck is rev'd to about 1200 rmps and held there it starts to cut out every 18sec's, revs and then runs smooth. if this doesn't sound accurate to any one please let me know. Thanks again guys. Derek

:cry:

[redneck_rollercoaster]

here's a new development I have just encountered, in the course of the last day ( and mabye it's just a fluke ) every time I let my MJ warm up to running temp, about ten to fifteen minutes it runs fine? Man I'm confused.

:headpop:

[aemsee]

So, as long as it is up to full operating temp, it runs OK?

[Pete M]

while running the tests my MJ started to heat up (not redline)

Specifically what temp? 220 is perfectly normal for a 4.0L. Does it have an electric fan? What condition is the radiator in?

 

 

but it got hot and the oil pressure dropped to less than ten pounds!

What grade oil do you use? You wouldn't happen to have a Fram filter would you?

 

 

I'm no mechanic, so I haven't a clue about floating valves. Is this something that could be caused by gunk build up under the valve cover? Maybe a good cleaning is in order?

[mjeff87]

Valve float is typical of higher revving engines. Because the valves are opening/closing so rapidly, the valve springs (weak) cannot fully close the valve on the seat inbetween bumps from the cam, which causes compression loss in the cylinders.

 

Unless your valve springs are completely hosed, they wouldn't float the valves @ such low RPM's. I'd suspect that the loss of oil pressure is causing the lifters to partially collapse, and the clacking you're hearing is from the slack in the valvetrain (pushrod to rocker clearance). I'd do what Pete suggests....clean everything, run fresh dino oil, and a good quality filter and see if it clears up.

 

Jeff

[redneck_rollercoaster]

Hey aemsee, good to here from you again. and yea it's the strangest thing once it's warm it runs fine... a little doggy (like it's tired) but fine. well running temp for my MJ seems to be about 175 to 185 farenhieght and the radiator seems to be fine theres no leaks, I'm not losing any coolant and the fins look clean, oddly enough the only time it got hot which according to you Pete isnt hot at all (and I was not aware of the normal running temps so thank you) was at the dealer when they held the rpms at about 1200 for roughly ten minutes the temp went up to about 215 farenhieght. and yes I am running a fram filter on the oil and air. oh also it runs a good ol' fashion clutch fan. my oil grade is 10-30 valvoline. I'm with you mjeff, I think that was just a stab from the dealer because they don't know whats wrong and they even said there not sure what the deal is.and I was under the impression that if you have a valve problem like floating or dropped, the engine would make sounds almost all of the time and mine just makes a lifter tick sound sometimes? One thing I am concerned about outside of the obvious is my oil pressure over all. when it's cold outside, at initial start up my oil pressure is about 40 pounds but after warm up at idle its 10 pounds and running down the road it's only about 25 pounds? Thanks again guys.

:cheers:

[aemsee]

10 psi is actually acceptable for a hot engine at idle. If you had an idiot light instead of a guage you would never know it. And it may just be the sender and not the actual pressure at all. Would need to hook up a mechanical guage to check if you are really concerned.

One of the symptoms that were listed with the crank sensor TSB was rough cold idle and stalling. Was the dealer able to monitor the coolant temp sensor for the ECU? Could be that it is not sending the correct reading causing the mixture to be off when cold. Takes alot more fuel to keep a cold engine running.

[Pete M]

The Fram filters have a history of internal failuress that cause a sudden loss in oil pressure. I had it happen to me on my way to The Badlands offroad park a couple years back. Lost all pressure at idle and had to do the "dance of the pedals" to keep the rpms up at all times during the entire trip. I thought it was a bad pump and found that the pressure came back slightly after I swapped in some thicker oil (in the parts store parking lot), but I didn't learn about the filter until I got back home. Sure enough, a new filter solved it.

Oh, and 210* is technically the normal operating temp for the 4.0L, what I should of said is that 220 is fairly common and not a huge deal. Anything approaching 230 should be looked into. But even then, there are Jeeps out there that have perpetually hot engines where the owner insists that it still runs just fine. The 4.0L is just so friggin' bulletproof that sometimes it's hard to tell what constitutes a legitimate concern. :D My 88's engine has twice survived 0 oil pressure (that fram filter and then later on when the rear main blew wide open and drained it almost dry), various overheating episodes (that one time on the dunes the needle was pegged all the way over and coolant was spewing out of the radiator), a water pump whose impeller disintegrated and spread tiny aluminum bits throughout the cooling system (I think I've flushed them all out), at least 5 different owners, and years of my abusive right foot. :D And I'm sure I'm forgetting something. Someday I'll replace it with a stroker 4.7, but in the mean time, it's still alive and kickin'. :D

[Oizarod115]

The 4.0L is just so friggin' bulletproof that sometimes it's hard to tell what constitutes a legitimate concern. :D

 

i have a friend whos dad gave her a 2dr 4.0 XJ on 35s (bushwackers and a 2" BB.. ?? it was ghetto-lifted.)

 

anyways, she ran it OUT OF OIL... completely dead engine cut off. NO OIL.

my buddy went up there to help her out, dumps 6 qts in... lets it drain down. fires it right up... she's still driving it... (6months later)

 

talk about bulletproof :eek:

[redneck_rollercoaster]

once again I let it warm up and it runs fine? anyway thanks Pete, I am going to run a system cleaner thru the engine and change to a different oil filter. aemsee I'm not sure if the dealer tested that so I called them and they said they tested so much stuff on it there not sure if they tested that or not? sounds kind of funny to me but whatever. when I run the motor flush thru it and change the filter I will let you guys know how it turns out. also I think that I may change the CPS to. for some reason I think that it's just not working properly?