aerocorey Posted February 19, 2008 Share Posted February 19, 2008 Hi folks, picked up another MJ. I had an '89 a few years back and I was on the old Yahoo forum. The current one is a '90. I'm in the middle of a big move and pretty much have no time to troubleshoot this. Done some searching but can't find what I'm looking for. The truck starts and runs well enough...when it wants to. When it doesn't start I can smell fuel, not too much, just smelling that it's getting fuel so I suspect it's a spark issue. More than likely I'll throw a new cap, rotor, plugs, wires, etc. at it and see if it goes away. In the meantime, I've been out of the 4.0 for a few years and can't recall off the top of my head if there's anything obvious I'm overlooking. I've been pretty heavy into FSJs for the last 2 years. If this was a stock Grand Wagoneer from the same year I would suspect the ignition module but I can't recall if the Renix modules are prone to failure or not. This is how a GW acts when the module is on the way out. Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 19, 2008 Share Posted February 19, 2008 Crank position sensor is a likely culprit. They typically are not an intermittent problem, but I have seen them do it. Check the wiring going to the CPS as well because it tends to get a little close to the exhaust sometimes and get damaged. Link to comment Share on other sites More sharing options...
Eagle Posted February 19, 2008 Share Posted February 19, 2008 Crank position sensor is a likely culprit. They typically are not an intermittent problem, but I have seen them do it. Check the wiring going to the CPS as well because it tends to get a little close to the exhaust sometimes and get damaged. x2 - Crank Position Sensor (CPS) Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted February 19, 2008 Share Posted February 19, 2008 Cory, glad you made it over. I was beginning to wonder :brows: acting like a parrot, a CPS would do it, its not a favoured piece to replace Link to comment Share on other sites More sharing options...
aerocorey Posted February 19, 2008 Author Share Posted February 19, 2008 Thanks for the replies. I do recall now from the last time I had an MJ that the CPS is a known weak link. Changing it in a hotel parking lot was the least fun I've ever had in a hotel parking lot. It also didn't fix the problem. :wall: I'm probably not going to mess with it anymore this week. I'm towing the MJ from UT to VT behind my Grand Wag. We're rolling out tomorrow morning. If I can get this problem licked we're planning to ship this truck overseas next month with us. I still haven't done the plugs and wires and crap, so I'm not freaking out just yet. Guess I now have a spare CPS. Any other suggestions are welcome. What's wierd is that when it's running it never dies. It waits until I shut it off, then it just won't start. Seems like if I give it an hour or so it's ready to start again. Vacuum stuff all looks good. Maybe a bad coil? Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 19, 2008 Share Posted February 19, 2008 Maybe a bad coil?That was going to be my next guess at it. I can't imagine changing that CPS in a parking lot :eek: KUDOS to you... :cheers: Link to comment Share on other sites More sharing options...
aerocorey Posted February 20, 2008 Author Share Posted February 20, 2008 Pulled the coil to put a multimeter on it. I have a Haynes book. The picture in the book doesn't match the plug on my coil. Can anyone talk me through what each terminal is? Link to comment Share on other sites More sharing options...
Oizarod115 Posted February 20, 2008 Share Posted February 20, 2008 Maybe a bad coil?That was going to be my next guess at it. I can't imagine changing that CPS in a parking lot :eek: KUDOS to you... :cheers: they aren't THAT bad... a 1/4" drive wobble socket and a few foot long extension its a 20 minute job. (of course working above your head is always better than working on your back) Link to comment Share on other sites More sharing options...
aerocorey Posted February 20, 2008 Author Share Posted February 20, 2008 Maybe a bad coil?That was going to be my next guess at it. I can't imagine changing that CPS in a parking lot :eek: KUDOS to you... :cheers: they aren't THAT bad... a 1/4" drive wobble socket and a few foot long extension its a 20 minute job. (of course working above your head is always better than working on your back) Sooo, you're telling me that when you're at a hotel you have enough 1/4" extensions on you to get the ratchet clear of the transmission. Wow, you are prepared. Seriously, it wasn't that bad. I'd rather have done it on a lift, not in february, and not with a glovebox toolkit, but it wasn't that bad. Like 3 seconds after I asked for help figuring out the coil connector I realized I was looking at the coil mount and that the coil pops out of it. I ran the tests in the book, it checks good. Maybe I should start the truck for a few minutes and test it again. Link to comment Share on other sites More sharing options...
BLHTAZ Posted February 20, 2008 Share Posted February 20, 2008 I tried it laying on the ground with about an 18" extension on a 3/8 drive wobble... :headpop: gave up after a little over an hour and I am taking it to the dealership tomorrow to have it done. ;) Link to comment Share on other sites More sharing options...
aerocorey Posted February 25, 2008 Author Share Posted February 25, 2008 Replaced the coil today. Haven't had it happen since I replaced it. Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted February 25, 2008 Share Posted February 25, 2008 Replaced the coil today. Haven't had it happen since I replaced it. I was just going to suggest this. GOOD JOB!! If you look underneath you coil. You will see the epoxy the factory pours in to seal the electronics. I am going to bet there is cracks in it!!! I didn't have the NO START..but mine was running funny with poor mileage. I swapped out the coil and presto chango my problem is all FIXED!!! I am glad you got it fixed as well!! ;) CW Link to comment Share on other sites More sharing options...
aerocorey Posted February 25, 2008 Author Share Posted February 25, 2008 No cracks in it, in fact it looks pretty good. It never really failed the tests with a multimeter that my Haynes book says to run either, but it just made sense that the coil would cause the problem. I've only run it for a day since replacing it. Watch it die on me again later today just to be spiteful because I think I've got it fixed... Link to comment Share on other sites More sharing options...
aerocorey Posted February 25, 2008 Author Share Posted February 25, 2008 $#!&!!! I just started it and shut it off a few times to mess with the heater. Now it won't start. :headpop: Link to comment Share on other sites More sharing options...
aerocorey Posted February 26, 2008 Author Share Posted February 26, 2008 Replaced the air filter, fuel filter, cap, and rotor. Much better starting. We'll see if it fails me again... Link to comment Share on other sites More sharing options...
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