Stumped on this one!

[Anak]

I would still question the coil.

A weak coil might still give you a spark, but not be able to sustain that under load.

 

[freqrider]

Well I found another issue when removing the throttle body. OILY, BLACK SLUDGE/SOOT! I have been suspecting an intake/exhaust manifold gasket leak for a while. Going to replace gasket and clean manifold, injectors off. Maybe just do valves/head gasket while I'm at it. Compression/leakdown was good.

 

[RCP Phx]

I didn't see any test numbers posted, but if you think they are good than I would be thinking valve stem seals!

 

[lawsoncl]

We're talking CPS here. It's a magnet alternator basically so produces VAC.

[/QUOTE]

(putting on my nerd hat for a moment)

Well, you're both right depending on the year. The older 2-wire Renix sensor is literally a coil and a magnet, producing a/c spikes as the windows pass the sensor. The later 3-wire sensors have some electronics and produce 5-volt pulses as the windows go by. So the a/c voltage test to assess the health of the sensor only makes sense on the old sensors. Plus that measurement depends greatly on the quality of the meter, since it's not a nice clean sine wave.

The older sensor was much more sensitive to the condition of the wiring and connectors between the sensor and the ECU. The real old renix had a service bulletin and mode to bypass the C101 connector and rewire it straight to the ECU.

 

[freqrider]

I would still question the coil.

A weak coil might still give you a spark, but not be able to sustain that under load.

Solved! It was a bad ignition coil. Popped a new one in and it fired right up. It's running great again! :spin1:

 

[Anak]

:cheers:

 

[90xj06]

I had a similar issue and it was a bad connection between the coil and the icm. I tapped it lightly with a jack handle and it came back. and worked fine for 5 more years until I disassembled the jeep.

 

[Bent]

I had similar issues. Turning a corner. After filling the tank. Same thing on the freeway. Then it sounded like it was running on one cylinder. Then it wouldn't start at all.

After turning the ignition on and listening to the fuel pump cycle, to make sure I was getting gas through the pump I noticed a slightly different sound from the fuel pump. Replace the fuel pump and it's all the problem. In my case I got lucky by noticing this slight difference in sound on the fuel pump before I started digging into Diagnostics. This was on my 87 MJ.

 

[lawsoncl]

If the MJ had the fuel pump ballast resistor, you might have noticed the difference with it in-circuit versus not. It might not have been able to keep up with the lower voltage with the power going through the resistor.

 

[Bent]

RENIX, no ballast resistor.

 

[Ecomike]

1990 renix. Went to pass on highway. Kicked it into power mode. Punched it a little to pass. Truck died. Wouldn't restart. Trailered it home. Cleaned all grounds, unplugged and replugged sensor connectors a few times, checked cps, map, tps, temp sensor ohm, voltage. All to spec! Fuel pressure >31 psi and holding very well. Fuel filter not clogged. Cranked and it started! Ran a bit rough at idle but smoothes out at higher rpm's. Stalls at idle or if I whack throttle hard. Esp off idle. (Stalls) IAS does not seem to work as engine does not idle fast when starting. Checked dist. timing, seems ok. I cut ears off dist and brought cap a bit closer to rotor JIC. Thinking about opening up the holes on cps and pushing it closer to flywheel? Anyone use a wire brush, etc... in the hole while cranking engine to clean rust off flywheel? I'm in coastal Florida, btw and the humidity is destroying everything here! Can't figure this one out and I need my truck! HELP!

Sounds like a small but critical vacuum line leak at the MAP sensor or Throttle body side or one of the brittle lines going to the Fuel Pressure Regulator or AC controls in the dash or brake Booster, etc... CPS issue is usually a no start issue.

 

[Bent]

MAP will definitely cause it to not start.