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Random stalling issue. runs great, then just dies.

T

tayman

NAXJA Forum User
Location
Niceville, FL
Didn't really want to start a new thread, but my phone won't let me search for some reason.

Anyway, 90xj, 89 mj motor, ax15 trans.

Like the title says, I have a random stalling issue that I can't wrap my head around. I've checked/tested/replaced everything I can think of that would cause it. I haven't been able to drive it much of anywhere for fear of being stranded. It'll be running just fine and dandy, then the rpms will dip really low, sometimes it will come back up, sometimes it just dies. Some:smoker: of the time I can catch it by giving it throttle, but sometimes even that doesn't work.

Cps is brand new, fuel pressure is good, tps is good, map is good, asd relay is functioning, grounds are good, vacuum lines are brand new, fuel pump is brand new, throttle body is clean, I don't know what else to check. I'm lost.
 
Best place to start is the Crank Position Sensor. I had the dealer replace mine and it fixed the problem. I had the same symptoms. It can be replaced in the garage with the right tools.....
I know yours is new, but that doesn't mean it is good......
 
Cps is good. Not to mention, it's the third one in a week. Replaced the old one thinking it was the issue, didn't solve anything. Noticed the wires touched the exhaust and melted slightly, so I replaced that one hoping that was the issue, and now I'm on this one. What are the chances of having 3 bad sensors in a week?
 
High resistance in the CPS will do that. Either the CPS itself or the wiring between the CPS and the ECU or both. The resistance in the CPS can change some as it heats up, it may work OK cold and then may act up warm.

I eventually replaced the wires between the CPS and my ECU just to eliminate them as an issue. Not a bad idea to clean the connector also, a little bit of oil or whatever in the connector can also cause issues. You only get around half a volt pulse through that circuit, it doesn't take much to mess it up.

People most always assume it is the sensor, I learned a long time ago (especially on the Renix) better than half the time it is in the wiring. So now I ohm test the wiring before I spend the cash on a new sensor and have save myself a bunch money. A marginal sensor may work through good wiring, it is doubtful a good sensor will work well (enough) in questionable/marginal wiring.
 
Cruiser, your link isn't working for me. It might just be because I'm on my phone (no Internet in the new house yet)

ARE They THE Same As Your mostly Renix Tips On cherokee forum?
 
Okay, I've actually done all of those already except for the coil/icm. I'm really leaning toward failing ecu at this point. I have good spark, and no missing. It just up and stalls out for no apparent reason.
 
I don't have the little bracket, but it's not touching the exhaust either.
 
New cps is good, but I'll test it to be completely sure. It's starting fine almost every time, leading me to think it's not cps.

Also, I'm leaning toward ecu because my IAC hasn't worked properly in years. I tricked it into closing, then used to be able to just hold the rpms up with my hand throttle until it warmed up and it would run fine. My thought is if the IAC is failing at the ECU, something else important could be also. All the wiring looks good leading to the ecu.
 
I'll do the icu/coil refresh. Probably tomorrow, but we'll see how I feel. I just had surgery monday
 
Did the icu/coil refresh and now it won't start at all.....
 
How can I test the coil vs icm to know which one I need?
 
ICU, not ecu. Lol

the coil seems to be fine, but I'm not sure how to test the icu. Each of the pins seems to have some sort of path to the two contacts for the coil, and I feel like that's not supposed to happen. I put my ohm meter on each of the connectors, and touched each of the pins, and all have some sort of path. Some are low resistance, and some high, but I feel like it must be shorting somewhere if all pins lead to eachother
 
Well color me disappointed. I had autozone test the coil, and ICM. Both test good. Now it's looking like the issue goes back to the computer.

I'm going to do a more thorough cleaning of the contacts and see if that does anything, but if not, that means computer right? I have no spark...

I guess I'll test the cps again to make sure it's working right.
 
Cleaned the contacts better, and it starts and runs again, but still dies after a couple minutes of idling.

CPS tests good. My multimeter sucks, but looks to be putting out almost 1v when cranking With it unplugged.

We're looking at ecu now, right?
 
Have you checked your fuel pump ballast resistor? Can definitely cause the issue you are having.
If you have not already bypassed it, remove the connectors, jumper them and see if the issue goes away.
 
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