1992 Jeep, Crank but no SPARK!

New owner of a 1992 Jeep Cherokee 4.0 Auto that I bought for my son as his first vehicle. I’m going to add unnecessary details just in case something stands out to one of you guys because I’m at a standstill. Sorry if this is long! 1 month after purchase my son blew the motor (230k miles) it blew from a bad! overheat condition, he knows now that 290 degrees is a smidge too warm. We towed him home in neutral (neutral safety switch problem??). I picked up a re-manned from AutoZone, all numbers match, head, block etc. Swapped everything over and threw it in. Replaced just about everything well I was in there as well, the entire cooling system, distributor and wires, plugs, intake, o2 sensor, and ALL “drive” sensors. This is where it starts to get fun! No spark! No power at the coil. Cranks and Cranks...Grounds have been checked and checked again. Timing has been checked and checked again and tried different ways as well. All fuses checked out. I’ve tried 4 different CPS, all ohm out a little differently and I’ve bought them from all different places except Jeep OEM. I then fell into the rabbit hole of the ASD relay. I’ve tried jumping ASD relay inputs 30 to 87. Replaced relay of course. Relay does click now (didn’t at first) and fuel pump primes for 1-2 seconds. (I have fuel and pressure) I’ve done everything that is online for the ASD relay “fix”, so much so that I don’t even remember what I’ve done, I’ve been at this no spark for almost a month. I’ve done my best to test the PCM and he are some results. (I can get numbers from ASD too if that would help you)

Pin #6:
Ignition off – 2.4v
Ignition on - 5.05V
cranking – 5.35V

Pin #7:
ignition off- 2.39v
ignition on – 7.85v
cranking – 8.75v

Pin #3 and #9:
Between 11.5-12V

Ground at Pin #11 and #12:
Good

At this point I’m thinking it’s either something VERY silly or PCM? I’m in too deep $$ to stop here. I’m also out of ideas. We don’t believe the jeep has the factory security system as I read online that could be a problem. Battery always fully charged. Coil looks new. At this point I’m just coming up with random ideas that are getting me nowhere! So here I am. First post here, Any help or ideas would be great. Thank you.

Put all the old sensors back in.

i will try that tonight. are you thinking one of the new sensors is faulty? thank you!

just to add, when we first got the jeep it would die while driving but it would start right back up. About once a day this would happen. so that's when I replaced most of the engine sensors. the jeep started right up even with new sensors. but before I got that problem figured out, the motor popped. Since we've done the new motor all I've replaced for sensors was the CPS. and I've tried all of them from the one it had to 4 new different ones.

The symptoms described are typical for a faulty Crankshaft Position Sensor on the bellhousing, but don't rule out wire harness or wire plug issues. Inspect for chafed or melted wire insulation, failed wire splices, and corroded, bent, or pushed back wire plug pins. Confirm the distributor was installed correctly at TDC.

The O2 sensor should be NTK and NOT Bosch, and all the engine sensors should be genuine Jeep.

Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

Does your check engine light come on when you turn the key to the run position? Usually, it will light as a check bulb function. If it doesn't it can be an indicator of sensor issues. The input voltage has to be near spec. It is possible for a faulty sensor to partially short and draw the voltage down on the input circuit. The CEL light may not illuminate.
It may be something as simple as a faulty ignition part, rotor, faulty high voltage coil to distributor wire etc.
It isn't always sensors.

The engine light does not come on. That was something I noticed but didn’t put in post. No dummy lights come on at all with ignition on.

Thank you guys for the help thus far. I’m going to try and track down some OEM sensors

ZachRitchie said:

The engine light does not come on. That was something I noticed but didn’t put in post. No dummy lights come on at all with ignition on.

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Some differences year to year, not sure if a low or no input voltage to the CPS kills all the idiot lights, but do know it will kill the CEL on some models.
Should be 8 volts into the CPS on the orange wire. Easy enough to check. The cam position sensor in the distributor also shares the same input voltage with the CPS as does the speed sensor. I'd unplug the CPS, then cam position sensor and see if the CEL comes back on, if so you likely have a shorted sensor. The cam position sensor is somewhat prone to failure, not as often as the CPS, but it happens.

#2 Orange pin reads 8.7v, #1 pin reads 5v, and #3 pin ground is good. I will look at cam shaft position sensor now. Also while CPS was unplugged no CEL.

I was assuming it was good as I thought the new distributer came with a new one. But now I know to double check the none OEM sensors. ����

Not getting 8v from camshaft position sensor orange wire

ZachRitchie said:

Not getting 8v from camshaft position sensor orange wire

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Check both plugged in and unplugged. Should be the same *8-volt source* as the CPS and speed sensor. I'm not sure of the test procedure for the 92 cam position sensor. I do know there is an indexing possibility on some models.
If you get no 8 volt at the cam position sensor unplugged, I'd be looking at an open circuit or less likely possibly a short to ground on the orange wire. If you get no 8 volt with it plugged in but 8 volt unplugged it is likely a shorted sensor. Check the CEL with the cam sensor unplugged.

Ok will do. Thank you.

Something to try, is to use a NOID Light on one of the injectors. THey are a little dish that plugs into the injector. When you crank it lights up, if the injector is OK, or getting a pulse. Also, watch if the Noid light does not light up when cranking. See if it lights up just as you release the key. If so, then it might be the ignition relay switch on the steering column. Also, I'd check the Induction ring in the distributor, and the coil. You did say it over heated.

Also, some or many of the 'Cheap' sensors are not much cheaper than MOPARs if you look around.

Ok thanks so much. Still no resolve. I think I’m going to try a new PCM. At this point I’m lost. Also will try OEM Jeep CPS.

Also going to try and read up on how to test ignition switch like you said. Thanks again

Swapping out sensors gets expensive. Did you ever test for 8 volts at the cam position sensor, with the plug plugged in and unplugged? Could be something as simple as a broken rotor, it has happened to me.
How did you test for spark? IMO you have to have a plan or a system for troubleshooting or it gets really confusing fast. Swapping out sensors or components hoping to get lucky isn't the answer.
If you are getting near battery voltage on the coil, alternator and injectors with the motor cranking your ignition switch is likely OK. Believe it is the dark green orange wire. The auto-shutdown relay won't supply power to the ignition etc. if you have a sensor fault on some sensors or the motor isn't cranking.
The PCM would be my last choice, they seldom go wrong. Fuse, relay, sensor, wiring, check from easy to more difficult. Relays seldom go bad.

Might be time to go back looking for id10t errors. Many years ago after a tune up I completely forgot to put the distributor rotor on, that took a while to chase down.

ok thank you. will purchase one today. still no luck on everything else. waiting for new PCM to come in