87 MJ wont start

Hi all, new to the boards and the whole jeep scene. Looking for some help on the following vehicle.

1987 Jeep Commanche
2.5L engine
5 Speed Manual transmission

I bought the truck running only on 3 cylinders, found a replacement motor out of a 97' Wrangler, but wanted to have it run on all 4 cylinders until i could do the swap. Pulled plug #4 (dead cylinder) it was covered in oil, cleaned plug threw it back in, and started it up, it ran better that in had in the two weeks before, that i had been driving it on 3 cylinders. Pulled out of the parking lot, got about 40 feet down the road from the shop i work at, and it died. Towed it back to work the next day, threw in new plugs, still nothing. Check for spark, and getting nothing. put in:

Brand new coil
Brand new CPS sensor, metered 235 resistence old one was 150

Tried to get it to start, and still no fire, with the key on, I have 11.9 volts on one of the wires the leads to the coil, one other is ground and the thrid has small amount a millivolts.

I cleaned all my grounds,
Checked the connection at the computer, its in there tight.
Fuel pump cycles when you turn the key on
Switched the two blue relays on the passenger side around


What should i check next? Any suggestion appreciated! Glad to be a member, thanks in advance for the help!

Have you checked the cap and rotor button to make sure they are not corroded or burned?

Not real familar with the 4cylinders, but the 6cylinder renix system releys on the sync signal or pickup in the distributor to identify cylinder #1 or #6, then the ecu signals the Ignition Control Module to fire the coil. So you might want to check to see if it is within specs, and have continuity between the distributor connector and the corrisponding ecm connector pins.

Again, not familar with the 4cyls but hope any of this helps.

Justin

Cap is barnd new also, the guy i bought it from replaced it thinking that was causing #4 to be dead when it was oil. Havent checked the rotor though. Can anyone vouch for the distributer sync thing on the 2.5 i though it was only on the 6's or for MPI and i have TBI.

Any way of testing the computer to see if its taken a crap?

someone suggested testing the Ignition Module, what the procedure for that?

Went out and pulled some voltage readings of the Control Module. The orange wire that feeds into the module is the "trigger wire" That the computer sends the signal to fire the coil, thus giving ignition. I probed into the back of that connector to get these readings:

With the ignition off it dances around.1-.5 millivolts.
Key on in run position 50.xx mili-volts.
Turn key to crank motor over, and voltage drops to zero.

Is this normal? What should the voltage on this wire be doing?

Do you have a Chiltons or Haynes shop manual? They aren't quite as good as a factory shop manual in most respects, but they should conver stuff like that. Good luck!
Jeep on!
--Pete

ComancheClub.com

not sure if this helps, i had a similar problem on my MJ. Wouldnt start or stay running. I replaced the ignition switch undr the dash on the colunm. Thought I had it.. Than same thing happened. Did some more digging and found the fuel pump relay was taking a dump. replaced it and no more problems.

If you have a bad ring in the one cylinder, you can end up pressurizing the crank case causing oil into the distributor and coating the inside of the cap. It wouldn't hurt to check. If you are getting no spark a the plugs, pull the coil wire and check there.

The 2.5L does have a camshaft position sensor.

I have no spark at the coil. Does the 2.5 TBI use a Cam Position Sensor? I was under the impression that it was only after 90 that they did. I got a spare ECU from a friend, tried that, no difference