Muddz

I'm helping a friend with a 1992 Laredo 4.0L automatic that was running ok. After jumping another vehicle it now starts and then shuts off.

We checked the fuel pressure where the engine ran a bit before shutting down the fuel pressure is maintained at ~40 psi, and doesn't drop below 30 psi with the engine off.

I also tried connecting the two wires to the ballast resister, but he same thing occurs , engine starts then shuts off.


If the key is held to start the engine seems to keep running until the key is release, however I didn't want to hold the key too long as to ruin the starter and possibly the flywheel.

The distributor cap appears to be ok and I removed a coil from my 98 XJ to test if his coil is bad or weak, however the 92 uses a different connector for round pin so we could not test to see if the coil is the problem.

So he ordered a new coil, distributor rotor and ballast resistor. I have additional dist. caps and plug wires.

I did test the spark from the coil and it's yellow and not blue.

I had a similar problem with my 98 XJ 4.0L where it had problems starting and running. The spark from the coil was yellow so I swapped in a new coil and the problems vanished.

Perhaps this problem isn't with the coil and spark and it's a circuit related to the fuel pump?

Before getting into sensors what else should we be trying to diagnose?

I do have a Snap-On MT-2500 scanner but since the engine isn't running not much in the way of live data and diagnostics is provided.

gat

I read many problems on here about the neutral safety switch going bad and causing trouble starting. There is also an auto-shutdown relay to test.
When you tested the ballast by by-passing it, did you also checked hat the voltage was across it and to the wire to it?

Muddz

I removed the two wires to the ballast resistor, connected only 12 volt a test light individually to each, key on both blinked, key to start both the were on steady.

After connecting the two wires to the ballast resistor together the same thing happened tries to start then the engine shuts off, the engine never actually runs, tries to run but shuts off.

Yes I also thought about the neutral safety switch which we will need to test if engine doesn't start with new coil.

I've had problems with a nss in my 98 XJ. Would drive to a store, shop, then to and try and start the engine and nothing, no engine turn over. Eventually the engine started after messing with the gear shift lever. Didn't want to become stuck somewhere so replaced with a Mopar oem re-manufactured.

So if the NSS the starting I think would behave differently, Bad NSS usually prevents the starter and solenoid from engaging. His 92 Laredo the engine turns over, tries to run and then shuts off.

Possibly a bad sensor such as a CPS. A bad coil sometimes produces difficult starts where the engine won't actually normal start and keep running.

Besides the coil he also ordered a new ignition switch.

cruiser54

Ignition switch is probably bad in the Run position.

DFlintstone

I've got a rusty memory of something about one of the miny fuses can blow and cause that, maybe something to do with the ASD relay. Not even sure if 92 has those baby fuses but not a bad Idea to check all the fuses anyway. (maybe the jump popped one)

Muddz

Problem turned out to be the ignition switch. Replaced and now starts and runs ok.

I don't know if you want to know it's history to present and what repairs were done. The person I'm helping I believe this is his first Jeep. He picked up the 92 Laredo running for $175.00. He has so far spent another ~$200.00 on body (JY fender and rear door) , headlight chrome rim, corner light, tail lights and ignition repairs.

Have only ridden in it but the engine and transmission appears to be running good and hasn't exhibited any problems.

Perhaps I should drive it and see if I can feel anything different, abnormal with the engine and transmission?

Eventually wants to tow a motorbike and trailer over long distances. Suggested he may want to replaced the current diff oil with 75W-145?

Told him I have a set of rear helper springs, installed for a while on my XJ before upgrading to OME, that I would give him.

Tires and brakes appear to be ok. (told him if he removes the wheels I'd give the brakes a closer inspection) Cooling system is only a single row alum. I suggested for extensive towing he will want a transmission cooler.

I'm uncertain if he wants or needs to spend money for a heavy duty radiator?

Also told him about renewing the grounds and inspecting the wiring harnesses and plug-ins. He has worked on commercial fishing boats and currently works as a farm hand. Uncertain how much patience he has for electrical. Sorta explained some of what I've learned working on my 98 XJ for more than 10 years. I have a Snap-On MT-2500 I told him will provide live readout and some diags.

DFlintstone

Cruiser gets the star again! Wonder why a jump toasted the ign switch? Anyway, the 4-W4 tranny full of pink DexIII/Merc fluid, and a reasonably well maintained 4.0 are not likely to be much of an issue, both are nearly bulletproof. Just the stuff trying to keep up it is an issue, U joints, belt, mounts, hoses, steering. One of mine, the uni-body is cracking all over! (after 1000's of miles being tugged around by that 4.0)