Random, intermittent engine failure on 2.5

[armyofchuckness]

Hey, guys. I'm a bit perplexed on this one. Two days in a row now my 86 MJ has done the same thing. Cruising at around 30MPH the engine cuts off. Just dies. Nothing else changes. No flickering lights. No other signs of failure. Just the engine cutting out. Both times I coasted to a stop and started cranking the engine. After two minutes of just cranking (no catch, no sputter, just the starter spinning), I'll hit it again and it immediately turns over and runs like a champ the rest of the commute home. Both times were in the evening. Both times the headlights were on. I have a full cluster and nothing on the instruments indicates any problems. I'm completely stumped. Anyone run across something like this?

 

I've checked everything on the electrical and nothing seems to be out of place. I can't replicate it in the driveway. I've left it running in the driveway for 20 minutes. Nothing. I've driven it five times in the last two days and it's only failed twice.

 

Any help you could offer would be greatly appreciated.

 

Thanks!

[88whitemanche]

Double check if your cps wires aren't touching the exhaust...or even close to it it can lose its connection

When this was happening to me...I had a series of stuff go out....ignition coil, ignition switch, and cps

[armyofchuckness]

Thanks for the tip! I've got a new CPS and I'm going to swap it out and reroute the wires away from the exhaust. We'll see what happens.

[Jeep Driver]

Since you have a CPS on an '86, I assume you have a 2.5?

 

 

Last time that similar thing happened to me it was the fuel pump relay.

[armyofchuckness]

Thanks for the tip, JD. Yes, it's a 2.5. I mentioned it in the post title, but I should've been more clear in the body of the post. Here's what I've established so far:

 

A proper CPS should display .5 VAC while cranking. The replacement I got (which didn't solve the problem) pulled. .3 before I tried a mod I found on another forum and broke it. I put the old one in and it's pulling .2 VAC, so something is definitely not right there.

 

Someone has suggested to me that it's the ECU, which I'd really rather not replace if I can help it. I don't think it's that anyway. (That's what I'll keep telling myself.)

 

The relay is definitely a possibility. I'm sure it's a much cheaper fix than a new ECU. That would be a very difficult thing to test for failures, as it only fails for a matter of seconds. I've gotten it to repeat the scenario in three different drives. It always only happens once per drive, and it only fails for about 60 seconds at the most. Tonight, I got it started again after about ten seconds. 

 

Thanks again for the advice!

[cruiser54]

It's not the ECU. Your CPS signal is low.

 

Can't for sure remember if the 86s had the C101 connector, so click on my link below and view Tips 2 and 27.

[armyofchuckness]

Yeah. I think the CPS still needs to be replaced. I'm ordering another one that will hopefully be better quality. Jeep Driver wins the diagnosis award though. I replaced the fuel injection relay and it hasn't stalled since. Thank you all for the help. I'd have been stumped otherwise, and probably spent big bucks with a mechanic trying to fix a $10 part.