87 MJ won't fire

[billyboyxoxox]

I recently had started having problems with my 1987 Comanche 4.0 refusing to start after being warmed up. I realized quickly that it wasn't firing and would pop the hood and shake the wiring harness going into the ignition control module while shorting across the starter relay and it would start but it continued to happen. I even loosened the coil and worked it up and down and it would always start. I did replace the coil and ignition control module but the problem continued although it would still start and never failed to get me to my next destination. A week ago, it wouldn't start from cold and I checked the coil for fire and it was firing hot to the distributor but not to the plugs. I learned that the CPS was likely the problem and replaced both that and the distributor with new. Then it wouldn't even fire from the coil although the coil was getting power so I replaced the ECU just today and it's the same problem. There is power to the coil on both terminals but no spark from the coil at all now. I've gone over all the fuses and fuse links and they are all good. I've also checked continuity across the plug connectors at the distributor and CPS and they are fine. I've spent a small fortune I probably didn't need to but it is a 29 year old truck so once it runs again, those parts will be good for the rest of its time with me. 

My first question is: is there ever a time when the CPS needs to be loosened and moved whatever tiny bit it will actually move? I can't imagine it the way it mounts but I don't know. What else am I missing? Is there a relay I don't know about that controls anything with the ignition? This problem has given me fits. I did get it to fire up for a couple of seconds after the CPS was replaced but it lost all fire after that and hasn't shown any fire since although the coil still has 12 volts going to it. I'm expert at installing distributors and top dead center on the compression stroke has been redetermined a couple of extra times in my frustration. I'm at a complete loss.

This is my daily driver and needs to run again soon. It has 153,000 miles and actually runs very good and I've babied the BA-10/5 most of the 22 years I've owned this truck. It's a rust bomb but it has worked so hard for me with an extra leaf added to both sides in back to make the 3" Rancho suspension lift look fine. It will carry as much firewood as any full size half ton pickup and I've had it stacked to 7 feet off the ground. I was only going a short distance mind you but it rocked the load for me. Any help for an idea to my firing problem will be greatly appreciated and I thank you in advance for any help you can give.

billyboyxoxox

[billyboyxoxox]

I've just been looking around this site and found Cruiser54's excellent help with Renix problems and I've already learned a lot. I'm going to follow his suggestions for CPS testing and possibly the adjustment mod, drilling out the upper mounting hole. I did buy an O'Reilly's after market CPS because they were the only ones that had it in stock. I admit that I didn't bother testing the voltage on the new one while cranking and I see now how that was a mistake. I hope to not have to get rid of the C101 connector yet but that might be in my near future too. All of my grounds have checked out so far. I hope to be back later this weekend with the news that my problem has been solved and I'm sorry that I didn't get around to looking at Cruiser's posts before crying the blues here. Bless you all!

billyboyxoxox

[cruiser54]

I've just been looking around this site and found Cruiser54's excellent help with Renix problems and I've already learned a lot. I'm going to follow his suggestions for CPS testing and possibly the adjustment mod, drilling out the upper mounting hole. I did buy an O'Reilly's after market CPS because they were the only ones that had it in stock. I admit that I didn't bother testing the voltage on the new one while cranking and I see now how that was a mistake. I hope to not have to get rid of the C101 connector yet but that might be in my near future too. All of my grounds have checked out so far. I hope to be back later this weekend with the news that my problem has been solved and I'm sorry that I didn't get around to looking at Cruiser's posts before crying the blues here. Bless you all!

billyboyxoxox

You're on the right track and beat me to the punch. 

 

Do 1 through 5 for sure, and 27 is actually the preferred option for 2. 

[billyboyxoxox]

Cruiser, I bought the Napa CPS and installed it. It only put out .3 volts so I did the drill out to 3/8's and now it goes to .5 but drops right back to .4 after a few revolutions. Is it possible to drill the upper mounting hole out one more size without the sensor getting into the flywheel? I got a couple of hot sparks from the coil but they weren't constant at all and of course the motor didn't start. I did solder the brown/tracer ground wires together and cleaned the C101 connnector up as good as I could but I don't think there is a problem with that at this point. Any ideas about drilling that CPS mounting bracket out a little more would be greatly appreciated and I thank you in advance for your help.

I did manage to reach in and wipe the flywheel with a cloth while turning it over but there is no way I can reach with a feeler gauge to check that clearance. I assume it must be pretty close to the flywheel already.

[cruiser54]

Cruiser, I bought the Napa CPS and installed it. It only put out .3 volts so I did the drill out to 3/8's and now it goes to .5 but drops right back to .4 after a few revolutions. Is it possible to drill the upper mounting hole out one more size without the sensor getting into the flywheel? I got a couple of hot sparks from the coil but they weren't constant at all and of course the motor didn't start. I did solder the brown/tracer ground wires together and cleaned the C101 connnector up as good as I could but I don't think there is a problem with that at this point. Any ideas about drilling that CPS mounting bracket out a little more would be greatly appreciated and I thank you in advance for your help.

I did manage to reach in and wipe the flywheel with a cloth while turning it over but there is no way I can reach with a feeler gauge to check that clearance. I assume it must be pretty close to the flywheel already.

It's not really that close to the flywheel. 

[billyboyxoxox]

Hello again Cruiser54. I thank you so much!, for your website which is of course bookmarked for future reference. I went ahead and drilled the CPS upper mounting hole out one more size and got .5vac and even .6 for a revolution or two. I went ahead and got rid of the C101 while I was at it and the battery was charging. It finally started after a good few extra attempts! Here's what's happening now. It wants to run okay but will still die and there's the sound of a backfire when it does. It has done this about every time it's started even though that's only half a dozen times so far. The distributor only has a couple of degrees of play when loosened and I tried moving it that much with the same results. Surely it won't start at all if the distributor is even one gear key off will it? I'm overly confident that the distributor is in correctly but I could be mistaken. Surely the Renix ECU isn't smart enough to run it with the distributor out is it? I've reset the distributor half a dozen times while monkeying with it and every time I feel the rotor is as close to the no.1 terminal as it can be at top dead center on the compression stroke. I've been checking that with my finger over the no.1 spark plug hole and a wooden dowel for a feeler. It is a remanufactured ECU and this is the first time it has run with it. Does it take a few starts to settle in? It's so darn close to being right and I'm thankful I took your advice and got rid of that C101. I didn't think that was the problem in my last post but it very well could have been contributing to it. I thank you again for any extra help you can give with ideas for what is wrong now. Bless you! I owe you a few beers already or whatever your drink of choice is. I advise people I care about to avoid sugary drinks...

By the way, I just rechecked the voltage on the new CPS and it read .7.  Is there such a thing as too much voltage from that device? It's not starting consistently but it wants to. It runs really rough when it does start. My poor battery has about had it and is charging again and again.

Another odd thing, in the 'tell tale' panel lights on the far left just under the emergency brake light, there's a upward arrow that lights and when it did run, another one flashed to its left that I've never seen before. That one didn't stay lit long enough for me to even see what it was. Neither stays on but the downward arrow sometimes comes on when the key is put in ignition. Neither is explained in my Chiltons manual.

[cruiser54]

Have you seen Tip 13? 

[billyboyxoxox]

I will admit, tip 13 scared me with cutting the aligning tabs off of a new distributor so I thought I might cut the ones off of the old one. That still scared me so I simply put the old distributor back in this morning and the damn thing started right up and is running about as good as ever. I can't believe what I've gone through to get to this point. 

I want to thank Cruiser54 again for his fantastic Renix tips because I wouldn't have made it without his help. Your experience with old Jeeps like mine really paid off for me even if it took me a week longer than it should have. Thank you so much!!

I guess I have a new distributor for a backup now. I'm guessing the wear on the old one was just that little bump in timing that it needed this time. Praise the Mother!

[billyboyxoxox]

I want to thank Cruiser54 for his excellent 'Renix tips' because I don't know what I would have done without his help with that page.

 

This morning, I was perusing tip 13 about cutting off the aligning tabs on the new distributor and then thought, 'no, that's crazy on a new distributor', so I thought that I would do it to the old distributor but even that scared me. I ended up putting the old distributor back in without cutting the tabs off and the truck started right up and ran as smooth as ever! Who would have thought it? I sure didn't.

 

There went $90 down the drain for a new distributor I probably didn't need but I have it just in case now. The CPS tips for modifying the upper mounting hole to get the correct voltage were invaluable as were the instructions for eliminating the C101 connector. If I had found Cruisers tips earlier, I may have saved myself from the distributor purchase but I won't be sorry about the new coil and ICU. The old MJ lives again!

 

After all the schmidt I've been through these past 10 days or so, I'm thanking the Holy Mother with a smudge in the old Jeep and heading into town for groceries and to pay a bill or two here in a short while. I can't believe what I've just been through to get to this point but I am so very thankful. Thank you again Cruiser!

[cruiser54]

You're welcome!! Enjoy your MJ.