87 XJ no spark

pleontks · Oct 15, 2012

Searched but could not find

I was given a 87 xj 4.0 2wd. It does not start. Has fuel, but no spark. Has power to the coil, but nothing out of it.
Am getting 12v and .5v at the plugs under the coil.
The ground cable at the rear d side of the engine is disconnected (still bolted to firewall, but not to engine). I checked spark to a good ground, and still nothing.

Have several FSJs, but know nothing about these XJs.

Ecomike · Oct 15, 2012

The ground needs to be cleaned and reconnected to the spot near the oil dip stick. There should be 2 pair of small wires (ECU computer sensors) and a large battery cable negative post ground all on the same post on the engine block near the oil dip stick.

So far your problem sounds like a bad CPS. Crank Position sensor. Google the posts here for "Renix CPS NAXJA

.org" and or "Renix CPS Test NAXJA

.org" for threads on it. Also check the FAQ tab above for no start problem solving guidelines.

http://www.naxja.org/forum/faq.php

cruiser54 · Oct 15, 2012

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 07-30-2012

cruiser54 · Oct 15, 2012

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011

cruiser54 · Oct 15, 2012

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.
　
　
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.
　
Revised 11-28-2011

pleontks · Oct 16, 2012

already did the coil/icu connection. found the wire to the cps appears to have been cut about 2 or 3 inches from the cps. Is there an easy way to get to it? On the FSjs, there's a panel in the floor above the tranny. Is this the same with the XJs? Is that the easier way? The jeep is in the dirt and stickers in the back corner of the yard.

Thanks for the responses

cruiser54 · Oct 16, 2012

No access panel. 11 mm socket and about 2 ft of extensions to get to the CPS bolts.

pleontks · Oct 17, 2012

was surprisingly extremely easy to take off and remount the cps.
Spliced those wires together, and still no spark.
The plan now is to check compression, and decide from there. If compression's good, I will do the aforementioned tests.

Thanks for the help, and will let ya know when anything happens

Ecomike · Oct 17, 2012

Not sure what you mean by "Spliced those wires together, and still no spark."

Did you install a new CPS, or try and repair the damaged one?

You should have replaced it!!!! The damage may have extended into the guts of the sensor, pulled the wire loose inside?

cruiser54 · Oct 17, 2012

Test the frickin' CPS output before going one step further.

Ecomike · Oct 17, 2012

cruiser54 said:
Test the frickin' CPS output before going one step further.

X2, X2!!!!!

pleontks · Oct 17, 2012

by 'spliced the wires back to gether', I mean just that. Rats had chewed through wire, I spliced it back together.
Left old cps on, because don't wanna spend 30 on a new one if engine is bad.

and as for testing that cps, I'll go ahead and do that this afternoon after work. And then I'll compression test it. Don't wanna spend too much time diagnosing the ignition if the rings are blown or something.

If the cps IS bad, is there a way to rig it or fool it so I can test the rest of the components?

Again, thanks.

Ecomike · Oct 17, 2012

If the cps IS bad, is there a way to rig it or fool it so I can test the rest of the components?

No.

POSJ · Oct 17, 2012

Compression has nothing to do with spark...

pleontks · Oct 18, 2012

so, I tested the cps per instructions above, and got no reading at all. Had digital multimeter set to AC, and stuck prongs into plug going to cps, cranked engine over.

compression test after work

Ecomike · Oct 18, 2012

pleontks said:
so, I tested the cps per instructions above, and got no reading at all. Had digital multimeter set to AC, and stuck prongs into plug going to cps, cranked engine over.

compression test after work

Did you have it on the lowest scale like 5 volt scale? Does "no reading" mean 0.00 V? If yes, it is bad, and will cause a no spark. It needs to read at least 0.50 volts on the AC scale to convince the ECU to fire the spark!

pleontks · Oct 18, 2012

yes, no reading means 0.00v

Not happy that it is bad, but happy to know.

If she passes the compression test, I'll go get a new cps and see what else is bad.

Ecomike · Oct 18, 2012

Be sure to get a good brand, or OEM CPS. A lot of aftermarket CPS sensors are JUNK! My last junk one was A zone. Got my good ones from Rock auto, Standard brand, made in Italy, not China.

Also check on the CPS mounting MOD to boost the signal strength!!!! Cruiser54 has it.

pleontks · Feb 9, 2013

did dry comp test. All cylinders were within 55-71 psi. Other than lowness, nothing else significant revealed.

Put on brand new cps. Still no spark. Gonna go test cps and look at the grounds.

cruiser54 · Feb 9, 2013

pleontks said:
did dry comp test. All cylinders were within 55-71 psi. Other than lowness, nothing else significant revealed.

Put on brand new cps. Still no spark. Gonna go test cps and look at the grounds.

Good plan.

87 XJ no spark

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