Renix help?

Hello, I'm hoping some one had run into this issue.
1988 xj
4.6 stroker
cuts off when hot. After about 15 or 20 minutes, it stops dead. Still getting fuel. Got frustrated and changed cps, ignition module and coil. Still having issue. Anyone have any suggestions about what to look at next?

Any help is appreciated.

Update -

Sorry if the earlier post was not clear enough, I sent it from my phone.

The jeep shuts off when warm and will not re-start for about 10 - 15 minutes. The outside temperature seems to have very little effect on this. The jeep still gets fuel to the cylinders, but loses spark.

Since this started I have changed the CPS, the Ignition module, and the ignition coil. No change to the issue at all.

I'm a bit baffled, can anyone offer an option to look at?

Thanks

Sure sounds like a classic CPS issue. If not the CPS it sounds Kind of exotic.

The larger yellow wire to the ignition module is the power in, it should be hot any time the ignition is in run or start. I've had low voltage to the ignition module before, it makes for a weak spark. You typically loose a volt or two in the ignition module power in compared to battery voltage, this is normal. The reason I doubt this is your issue, is it often shows up as poor starts, bad idle and low max RPM's.

The smaller yellow wire to the ignition wire is the trigger wire and tells the ignition module when to fire the coil. No real way to test this unless you have access to a special tester.

The CPS often increases resistance as it gets hot, anything around 175 ohms or higher and function is questionable.

The next time it craps out and refuses to restart, dump a bottle of water on the CPS and see if it starts then and/or do an ohm test on the CPS.

The CPS pulse to the ECU may degrade for various reasons. The only pulse signal that counts is the one that makes it all the way to the ECU. Low pulse out of the CPS, plus resistance in the wiring and connectors adds up.

I'd also do a volt test on the CPS pulse.

Just something exotic I've seen if all else fails. Water in the distributor can settle to the bottom under the cam position sensor mounting plate, evaporate as the motor gets hot and coat the inside of the distributor cap and short the spark. After the distributor cools back, the moisture condenses and settles back to the bottom of the distributor the motor will run again. Usually shows up as a really bad miss before the motor craps out all together.

I've had the motor crap out for various reasons due to fuel issues.

Ok thanks. Pretty sure I'm getting fuel correctly.

One thing I should have mentioned, I have a used (pull a part) ECM. The last one got wet and stopped working altogether. I'll try cooling the CPS, but 3 different CPS produce the same issue.

One of the oddest things about this is the consistency. External temp seems to have very little to do with it. 25 degrees, 75 degrees, about the same amount of run up time to shut down, and about the same cool off time to restart.

Really appreciate the input.

I've had more than one act up when the engine transitioned from open loop to closed loop (140-160 F.). Usually the motor doesn't crap out completely, it just runs very poorly.

I'd check the voltage to the ignition module when it gets hot and craps out. The ignition module is fairly high ampere, maybe a connector is heating up and the contact is flexing. Metal will move when it gets hot. You might also want to take a close look at the steering column connector, they are pone to melt down and/or turn brown, black and generally screw up.

Don't get stuck in the swapping out component rut. Better than half the time the problem is in the connectors or wiring, especially in the Renix. You get a marginal or even a good sensor, if the grounds are bad or the connections in the harness are bad, it is doubtful you will get any good info from the sensors.

I remember one post about similar issues, it turned out to be the a short in the engine temperature sensor.

I'd take a close look at the O2. engine temp and knock sensor harness where it runs up behind the power steering bracket. I've seen many where the harnesses is melting on the exhaust manifold.

I know you said it was spark related, but bad ballast resistor can shut your fuel off at odd times.

Maybe Cruiser has some ideas?

All good ideas. If the rain holds off, I'll get the multi meter out and start looking tonight.

See Below

So a new symptom arose tonight, up until now, it would die suddenly with no warning. Tonight, it stumbled a few times, let me get off the road under control and then died.

Not a big difference, but maybe it will help someone.

You say it's getting fuel, is this just while cranking?

have you tried bypassing the ballast resistor?
I had one that would fail when it got warm. It was cracked.

im calling ballast resistor or ECM

I'll check the ballast resistor this evening. I had removed it at one point. I don't think its the issue. Its getting fuel when cranking and just with the key on. Checked and it holds pressure through cranking and the plugs are wet with gas.

Is there any way to run diagnostics on the Renix ECM? Would checking the power to the coil be in any definitive?

bigdaddyjlove said:

I'll check the ballast resistor this evening. I had removed it at one point. I don't think its the issue. Its getting fuel when cranking and just with the key on. Checked and it holds pressure through cranking and the plugs are wet with gas.

Is there any way to run diagnostics on the Renix ECM? Would checking the power to the coil be in any definitive?

Click to expand...

You just have to make sure you are getting sufficient input voltage to the ignition module, the larger yellow wire. There is a significant line loss in this circuit anyway, typically a couple of volts. Add to that the starter sucking down the available voltage and the power into the ignition module can get so low spark gets iffy. Not common but it happens, especially if you are a mudder, all that mud and water can cause extra line loss.

Where are you checking the spark? First check the coil wire, then the plugs.

The small yellow wire to the ignition module is the trigger wire. The module is triggered by a square wave signal and many meters have a hard time reading it. You may get a digital meter to twitch some, some old analog meters will twitch as the engine is cranked over. You can try switching your meter from DC to AC and see what happens. The best I've been able to get is some kind of reading, sporadic and unreliable.

I'd check my ignition module ground and then maybe do an ohm test on the trigger wire all the way from the ignition module to the ECU. I've had pins back out of the connectors to the ECU. Now when I have it out I gently tug on the back side wire into the ECU connectors with a pair of needle nose pliers. I've had more than a few come out the back way to easily.

bigdaddyjlove said:

Is there any way to run diagnostics on the Renix ECM? Would checking the power to the coil be in any definitive?

Click to expand...

not without a snap on MT2500 with the renix adapter or a DRBII

you're getting power to the coil cold, so it would only be worthwhile to test after it fails.

I would take 8muds advice, clean all of the grounds, ALL of them. You'd be amazed at how many problem renix jeeps are magically fixed by that.

grounds is where i started. I ended up running ground wires directly from the battery to the ignition module, a second ground to block, cleaned and checked the chasis ground, etc..

I hadn't thought about pins backing out. The motor was swapped a year ago and every connection got cleaned and greased, but they do get moved around and I didn't check "depth" on them. I should have time to warm it up to failure tomorrow and test the wires to the module.

I checked spark at coil and plug.

Thanks again. I'll report back.

checked at failure. Still getting power to the coil still no spark. I'm assuming no signal .

check signal at the Crank sensor at failure. if good check @ ECM if good check at ecm out to coil. if good check at coil. pretty simple on that side of the house. The renix still fires without the cam sensor so rule that out.

what am I looking for ECM signal?

If the plugs are wet with gas the ICM spark module or coil may be bad, or the Dissy cap-rotor or dissy? If the plugs are getting gas I would rule out ground and ECM and sensor issues (even though the ground issues are common). Focus on the dissy and the ICM spark module. I had an ICM fail recently. Rare, but they do fail if they are 30 years old.

Also crank with gas peddle at WOT to shut off the fuel and dry out the system (WOT cranking tells the ECU to stop injecting fuel), flooded engines will not fire up!!!

Happy Easter folks, 8Mud!!!!

bigdaddyjlove said:

I'll check the ballast resistor this evening. I had removed it at one point. I don't think its the issue. Its getting fuel when cranking and just with the key on. Checked and it holds pressure through cranking and the plugs are wet with gas.

Is there any way to run diagnostics on the Renix ECM? Would checking the power to the coil be in any definitive?

Click to expand...

OK, read the first 2 posts. A stroker? Fuel injector size?

I see you covered this, but were the parts new? Were they good parts?

"Since this started I have changed the CPS, the Ignition module, and the ignition coil. No change to the issue at all.":

Next up is did the engine flood, and need time to dry out? Running too lean and need to cool off?

Any other history of issues?

Fuel flooding might be an O2 sensor issue!!!!! or a leaking fuel injector issue, or shorted wiring harness near the O2 sensor (on the exhaust).

Ecomike said:

If the plugs are wet with gas the ICM spark module or coil may be bad, or the Dissy cap-rotor or dissy? If the plugs are getting gas I would rule out ground and ECM and sensor issues (even though the ground issues are common). Focus on the dissy and the ICM spark module. I had an ICM fail recently. Rare, but they do fail if they are 30 years old.

Also crank with gas peddle at WOT to shut off the fuel and dry out the system (WOT cranking tells the ECU to stop injecting fuel), flooded engines will not fire up!!!

Happy Easter folks, 8Mud!!!!

Click to expand...

Happy Easter back at you and to everybody.