Help with '89 RENIX, I can't afford to loose any more hair!

'89 XJ 4.0 auto with 166K miles

I have been lurking here for a while and have done many searches on this and have tried the following to solve this intermittent stalling problem. It may run for a couple days with no problems and then it may only run a couple minutes before stalling. Sometimes it will crank right back up and sometimes it won't crank for days. Anyway here is what has been checked or replaced so far:

Fuel pressure is steady between 32 and 37 psi

Cleaned fuel pump ballast resistor connectors

CPS has been changed 3 times (last time only took 15 minutes) and the last one was genuine MOPAR sensor.

Cleaned MAP sensor.

Replaced O2 sensor.

Replaced temp gauge and computer temp sensors.

Replaced cap and rotor.

Replaced coil.

Adjusted TPS.

What am I missing? I also had to replace a badly leaking rear main seal. Is it possible that the flex plate in the bell housing is so covered in "gunk" that the cps can't read it? I tried looking at it without actually removing the inspection plate and it didn't look that bad at all. This is the first XJ I have owned and it is driving me nuts.

Sorry so long and thanks for any help!

Dave

Might be the ECU since you have hit all the common problems. There is one other thing that has been known to cause your issues. C101 the connector above the brake booster. There was even a TSB issued on it. Pull it apart and check for corrosion. Also unplug and replug the connectors on the ECU.

I have a spare ECU for a manual tranny you can borrow to troubleshoot with if you need it.

Do check the C101 IF you have it - if you are looking around and can't quite figure out what is it you don't have it, it sticks out like a sore thumb If you do have it you want to split it and clean the hell out of it. Another thing you can do (if you have the C101) is get a CPS from the dealer for a 1988 XJ, that will come with a C101 bypass wire for the crank sensor. Alternatively you can hard wire a bypass for the whole thing, that is a more permanent fix. 1989 was a transition year for the C101, early '89's had a C101 while later ones didn't (luckily mine is later!).

As for your problems here is how I would attack it (in this order):

Check the underhood wiring. Pay particular attention to the CPS wiring harness and the lower engine wiring harness (Goes to the Oxygen, Knock, and Coolant Tempature sensors); these harness like to get eaten by the exhaust manifold. When my lower engine harness was bad it would cause an intermittent no-start and stalling condition.

When the Jeep is acting up take a multimeter and probe the diagnostics port on the passenger fender wall; you'll need a Factory Service Manual for this to tell you which ports should have positive or negative power. If you do not have an FSM I should be able to get you that information.

Check the distributor. Is there slop in the shaft? Also take a look at the stator (also known as the pickup coil and camshaft sensor); I've had one of these guys go bad on me once before.

Of course the usual suspects also apply; spark plugs and wires. Even if they're new suspect them anyway, particularly the coil wire.

In my personal experience Renix ECU's hardly ever go bad; I've battled with a supposedly bad ECU before, to the point of purchasing another one from a bone yard..well..I have a spare now! The thing to know though is that the connectors to the ECU do get dirty, you should take them off and clean them up well as preventative maintenance. When I did this I took the whole unit out so that I could clean it up on the computer side as well. Getting a Renix ECU out isn't an easy task, the human hand is too large and doesn't have enough joints on it to make it comfortable however it is possible to do without dissembling anything on the dash board, you merely move a few wires out of the way (by pushing them) and you can get it with a short nut driver.

One last thing: Is there anything else associated with this? When it stalls does it just cut out immediately or does it stumble to a stop? Also, when you have a no-start situation will holding the throttle to the floor while attempting to start make any difference? What about disconnecting the MAP sensor wiring and/or vacuum hose; try doing this when it is not starting.

I can't think of anything else at the moment...

Sequoia

Nobody has mentioned anything about BAD GROUNDS! There are grounding points all over the engine compartment and they all need to be removed, cleaned, coated with something and reinstalled. Maybe even new battery cables are in order.

JoBo

Second on the bad grounds !!! SPECIFICLALY THE GROUND FROM THE FIREWALL TO THE ENGINE BY THE INTAKE MANIFOLD CHECK IT FIX IT THATS IT I KNOW IT GO ME GO ME