lvcherokee

Searched for the answer to this, maybe someone can point me in the right direction.
Our '87 XJ 4.0 suddenly stopped on the road two weeks back. I found it had no spark, so used roadside service to tow home until I could investigate.
Saw some good threads about the CPS going bad, so tested that. The Renix unit ohms tests at 200 (within the 125-275 range), but it was only putting out 0.1vac when cranking (should be 0.5vac).
Bought and installed a NTK CPS. The engine cranked right up, fast idled for about 20 seconds, then shut down. Tested and found no spark, and the CPS putting out 0.1vac. Figured I got a bad one, so ordered another, this one an Omix-ADA unit. Installed that, and the exact same thing happened. 20 seconds of fast idle, then no spark, CPS putting out 0.2vac.
Am I missing something here? How should I start troubleshooting this issue?

thanks for the advice!
(And thanks for the advice from other threads so far! Installing the CPS from the bottom, feet first under the XJ, with a long extension with swivel on the end, and 11mm socket - worked out great! With practice and a cold motor it's only a 10 minute job now)

cruiser54

Have you visited my website and completed tips 1 through 5?

Batman33165

This is probably a dumb question, but how are the connectors? i had to remove mine because they were not connecting at the terminals so i just butt connect them for now... even though now has been for a couple years now lol

lvcherokee

Not a dumb question at all! The plastic bit that keeps the connectors from slipping off did break on the vehicle side, I attribute that to 31 years in the desert. I did make sure the connection was good though.
Ran out of time tonight, but am going to check the coil and signal to the coil tomorrow, just to make sure it's not one of those things that are the issue.

lvcherokee

Good point, I have, but it's been a few years. Pretty dry out here in LV, so corrosion doesn't happen too quickly. Will check the connections on #1 and #4 at least while I check the coil. Even did #18 a while back, helped, but the gauge voltmeter still reads lower than my multimeter on the battery, and the turn signal blinking is v-e-r-y slow, son just says the Jeep isn't in a hurry to turn.
Was wondering if something in the ECU happens after 20 seconds of running that could cause our situation... but will take it one step at a time - good learning opportunity!

Batman33165

Im not saying it is the ECU but i remember running out of certain ideas. So I decided to take off my ECU and read somewhere on this forum that someone cleaned there's from the inside out. When i pulled mine off i had corrosion in the corners (inside) and as i was posting my findings someone had posted that it looked by the pictures that diodes were removing from the panel. I took a leap of faith and ordered a new ECU but from a younger jeep.... Cruiser 54 tip # last one i believe

lvcherokee

So, the battery tested low at 11.39v. It's only a year old, and the XJ does sit a lot, so not too surprised. Pulled it and put on the charger overnight.
But before that, tested the voltage supplying the coil. There are two harnesses, one 3 wire and one 2 wire (but only has one in it).
The single wire in the 2 wire harness read 4.89v.
In the 3 wire harness: yellow was 10.57v, the black and green wires did not show any voltage. Is it the green wire that is the signal wire, and should show flashing light with a probe while cranking the engine? Other threads say to test for that, but are unclear which color wire is the signal.
(and I did see that the 3 wire clip is broken, but the wire harness was installed tightly when I pulled it, good connections.

lvcherokee

OK, back to basics. We've never got a 0.5v from the CPS, so targeting that again. Followed the advice from another thread and drilled out the bolt holes from 5/16" to 3/8" to push the sensor closer. That did help, increased the voltage from 0.2v to 0.4v. Dare I drill it out further, or am I risking making contact at that point? Going to call the dealer and order a factory unit too - hard to find that CPS online...

cruiser54

You still have the c101 connector?

lvcherokee

yes, sir.
Factory CPS on order too. They are hard to find, local dealer said they weren't available anymore, had to find online.

cruiser54

The CPS signal runs through the C101........

You cleaned it right?

lvcherokee

I did clean the C101 a couple of years ago. I've been testing the voltage directly on the wiring harness of the CPS, so didn't figure the C101 would come in to play yet.
But now... may be a different story.
I drilled out the mounting holes of the CPS another 1/16" now getting 0.5+ vac from the CPS at the harness. Plugged back in - still no spark.
Put a test light on the yellow wire in picture above (with key on) got solid light. Tried light on green wire, nothing while cranking. From other posts, expected to get a flashing light as the CPU sends a signal to the coil to fire. Sound right?
I'll go back and clean the C101 again, just to make sure. Found the C101 removal video (thanks cruiser54) will do that when time allows.
Any other areas I can test to determine what else may be causing the computer to not call for spark?

fyi, factory CPS came in, and was only putting out 0.2 volts... not the great success we were expecting! Stuck with the Rugged Ridge that had already been drilled out some, ended up with a 7/16" mounting hole diameter. Good voltage and no contact! Had to leave off the plastic cover the CPS usually pokes through. Once everything else is sorted out, will try to put it back - assuming it's needed...

cruiser54

Unless your Jeep has had the CPS wiring bypass mod, the signal travels through the C101 to the ECU.

lvcherokee

thanks for the info! I feel silly asking, but which one of those is for the CPS? (not that anything there couldn't do with a better connection!)

cruiser54

C1, violet with tracer and D1, white with tracer.

You could check CPS output across both those terminals by backprobing the ECU connector.

Or, you could find those wires going into and out of the C101 and bypass just those 2. They go through B2 and B3 in the C101.