1992 Jeep Comanche 4.0 No Start/no Spark

[HOrnbrod]

I've held the coil wire against something metal and also cranked it with an extra spark plug in one of the wires. I'm not getting anything.

 

I don't know why I can't get the engine light to come on. The only lights I am able to get have been the one's for parking brake and no seatbelt.

 

I thought in your first post you said you had a new coil installed?  :hmm:

 

Since you cleaned the ECU connector, try to flash the fault codes again. The text in RED above if correct is probably causing the no-start condition. Check all the fuses with an ohmmeter in the PDC and the fuse panel on the drivers side interior firewall. If you're not getting power to the ECU it will never start.

[monkbonk]

All the maxi fuses in the PDC read 0.00 ohms on the 20k scale. The minifuses are new.

 

Tested/compared pins on some of my spare relays and they all compare similarly with a multimeter. I also cleaned the corrosion off of/checked all the regular fuses in the interior firewall.

 

I have a new coil installed, but was wondering if I could've bought a dud (at least, that's what my dad wants to think).

 

It might be that the ECU isn't getting any power though. I've had it apart, and aside from looking at a big gel coating.. I could see one capacitor. It looked like it might've been leaking? It had a little brownish looking stain on it (can take pics if needed).

[1989 Eliminator]

Another big factor that happened with my no-start was bad grounds. Upgrade your grounds on the engine block and on the firewall....

 

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal.  All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals.  Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com.  He makes an incredible cable upgrade for a very reasonable price.

 

[Bornindesert]

I know you replaced the CPS, an open or bad connection will produce a no spark condition. I'd unplug and really look over the harness and connector. My '88 actually had two plugs at the fire wall that the CPS would plug into. Plugged into the wrong one, and no spark.

[monkbonk]

Thanks for all the help. My dad sourced another computer (finally). Plugged it in this morning, got the check engine light I've been missing, gave it a couple turn overs, and it cranked!

 

Had a lifter tick at first, but that's cleared up. Good to go. :bowdown:

[HOrnbrod]

:cheers: :banana: :clapping:  Good to hear.

[87manche1]

Awesome

[Eagle]

Thanks for all the help. My dad sourced another computer (finally). Plugged it in this morning, got the check engine light I've been missing, gave it a couple turn overs, and it cranked!

 

Had a lifter tick at first, but that's cleared up. Good to go. :bowdown:

 

"Turning over" and "cranking" are the same thing -- they refer to the starter motor making the engine rotate. If you mean it started, then you would say it "started." If you mean it coughed and tried to start, but wouldn't, you would say something like it "fired but wouldn't catch and run."

 

It's really difficult to diagnose by remote control when standard terminology isn't used. If you now have a running MJ, good.

[monkbonk]

I understand. My apologies.

[HOrnbrod]

Since you mentioned in the same post "Had a lifter tick at first, but that's cleared up" I figured out that you had it running. It's tough to detect a lifter tick while cranking. No apology necessary IMO.  :thumbsup:

[monkbonk]

Thanks. My dad was really excited after he made it home from work. I told him that he couldn't drive it until we replaced the oil and filter. The previous owner didn't take good care of the Comanche, so we have a couple of maintenance items that still need replacing.

[HOrnbrod]

Don't stop with the motor oil and filter. With a newly aquired vehicle with a questionable maintenance history; it's best to change all fluids and filters;  oil, tranny, tcase and differentials, power steering, brakes, and radiator coolant. Plus the hoses and belts unless obviously new.