Zoekat

Hello, here is my problem. I have a 1990 jeep xj with a 4.0L. When it was purchased it hadn't run for about 6 months. I put fuel in the tank adn changed plugs and it fired right off and ran perfectly!

For 3 days it ran like a champ, when all of a sudden it lost all power and it started backfiring and then nothing. When I checked for spark their was nothing! So I started trouble shooting the system. I pulled the ICM and had it tested and it was bad. Problem solved right? NO. So form their I replaced the CPS because it was out of range on the ohm scale and still nothing. So far I have replaced the ICM, the CPS, the Sync Sensor, the coil, cleaned all the grounds and added a larger chasis ground. Replaced the cap rotor wires and plugs and Still nothing!

Since then I have cleaned the relays and replaced the power latch relay with a known good one (i read something about the power latch relay being the ASD relay?) Now I am tracing wires for breaks and have not found any. I have 12V to the ICM and the ground is good. I checked the CPS wiring and their is continuity all the way to the ECU. The Cam sensor wiring is fine as well. So I figured it was the ECU so I picked one up at NAPA. brought it home plugged it in hit the switch and you guessed it no spark! I have no idea what to do now, I have basicly replaced every thing that I can think of and am at my wits end. Any suggestions would be appreciated.

On another note, I realize that duct tape can fix anything, but what is up with all the splices being covered in duct tape? The wiring loom was factory and never been opened that I could tell and all the crimped connections were covered with duct tape!

Zoekat

I was wondering if any body new where to find the ECU pinn layout. you know which sensor plugs in to this pin. I have been looking but can't seem to find anything. Thanks

Lowrange2

Zoekat

thank you for the diagram, should help in this little endevore

XJ.89.Limited

You do know you have a renix right? The ECU for the 91 and newer XJs is completely different.

Zoekat

Yes it is a Renix unfortunatly!
I have a scanner that works on everything but the renix, and I cant see spending that much money for a scanner to pull the codes.

tgordon

Hearing "backfiring" makes me think timing issues. When issue first began you experienced power loss and backfiring, yes? I would look for where my timing signals went. No timing signals = no spark. I may be completely wrong however. I have run the wild goose chase diagnosis pattern before. Watching with interest to learn from this situation.

Zoekat

yes it started backfiring first and then lost all power before it died totally.

After chasing gremlins all day, I was relaxing with a cocktail and the same thing occured to me. If I have power to the ICM, which I do and the ground is good it has to be in the timing signal or maybe I bought a bad CPS.

I plan on retesting the CPS and check the continuity of the trigger wire. I will let you know what I find out.

XJ.89.Limited

One of cruiser's many writings:

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

Radi

Here's the engine and ignition wiring + ECM pinout if it'll help.

cruiser54

I wouldn't be bothering with the ECU just yet.
TEST the CPS.
Do this:

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

A backfire through the intake can be fuel pump failure. The hose in the tank can be rotten and split. The fuel pump ballast resistor can be bad or have loose connections.

Zoekat

thank you Cruiser54.
When I put the new coil on the new ICM I used dielectric grease.
I am getting good fuel pressure so dont think its the pump either.
But that is good info for future diagnosis.

gregxgriffin

Try the pickup coil also

cruiser54

Renix has no pckup coil.