XJOZ

I have made couple posts about this. I wonder if theres anything I may have missed.

Threw code on way home. Turned it off and it restated with code. Next morning no code. No check engine light for a moment when starting. No power to fuel pump. Main ECM and Fuse box fuses in engine bay toasted.

Ordered new ECM. Wait and it arrives damaged. Put it in and fuel pump ran continuously, parking lights on and the fuel gage got a reverse polarity as it pinned with the light on as far counter clock wise a sit could go.

Checked crank sensor and its open. Replaced fuel pump and ballast relays. With noc change.

Ordered new ecm.Wait it arrives from cardzone even more damaged. case split and cracked. Post broken off.

Put in new O2 sensor and new ecm.

Same deal. fuel pump on cont, gas gage pinned counter clockwise and parking lights on. no flash of check engine and won,t start.

Both ecms operating the same way from a heavy shock seems some what coincidental.

Anyone have any ideas on where to look for what is causing this? Another ecm on the way but if anyone can suggest something else to check id be obliged.

Thanks.

tjwalker

What was the code? The fact that you have a code and symptoms is not a coincidence, and that code is by far the most important clue of where to look....whenever you have a code, job #1 is to retrieve it; use the technology provided to you by your Jeep. Even if the check engine light isn't currently on, you will still have a "stored" code. Below is how to pull codes on your vintage XJ. Easy. Do it and report back.

Try unplugging the crank sensor and THEN checking your gauges. If the gauges work properly with the crank sensor out of circuit, you have smoking gun proof that your crank sensor is toast.
---------------------------------------------------------------------------------------
Retrieving OBD codes on the Jeep Cherokee (XJ) OBD1 Models: 1991-1995

1) Start engine (if possible). Move transmission shift lever
through all positions, ending in Park. Turn A/C switch on and then off
(if equipped).

2) Turn engine off. Without starting engine again, turn
ignition on, off, on, off and on within 5 seconds. Record 2-digit
fault codes as displayed by flashing MIL.

3) For example, fault code 23 is displayed as flash, flash,
4-second pause, flash, flash, flash. After a slightly longer pause,
other codes stored are displayed in numerical order. When MIL begins
to flash fault codes, it cannot be stopped. Start over if count is
lost.

NOTE: A "5-5" will always occur to signal the end of the sequence. Some will flash the "1-2" code indicating a recent battery disconnect even if you haven't done it. Ignore these two codes, and mark down all others.

BlueRidgeMark

If you are blowing multiple fuses, AND killing ECMs, you have a major problem you need to find before you fry a few more ECMs.


Start checking ALL your engine compartment wiring. Pay particular attention to your grounds.

Bustedback

You have to find out why those fuses blew. Once you find the short and repair it, I bet you fix the real problem. An ECM won't blow a fuse, it's usually an ECM input or output that will cause a fuse to blow. Inputs are the sensors, outputs are the actuators and motors. Start checking the wiring for shorts to ground.

Black89

If your on a long haul trip I would guess a wire harness either rubbed through someplace or melted and shorted a crap ton of wires causing the fuses to blow. I'd go for the melt through someplace. Start checking all major harnesses and look for melted spots. My money says you've got a bunch melted together and shorted out some place.

XJOZ

I did try and get the code the following day. However the code was gone and it wouldnt start. It ran for about 5miles with the code before I got here. Must have blown the fuses after I got here. Wish id pulled the code at the time.

Ill look for shorts. At one point it did run with the fuel pump constantly running, park-lights on gas gauge in the red. Now with ecm #2 wont start but has other symptoms.

Wish it was still blowing the fuses but its not. Then again its stationary. So no short at the moment, did start but was as i stated.

Ill go out and look at the wiring throughly. I see so many at the wreckers at the same mileage as mine. Differing years. Self destruct feature??? ;0

Ill grab a auto shut down relay tomorrow.

I assume the wiring for the 93 and 91 are very similar if not identical as i cant get a good one for a 91. The high draw must have originated in an arae thtas common to both those circuits. The fuse panel and the engine.

Maybe ill have an ecm that doenst look so beaten up tomorrow.

Thanks for the help. Ill go look for a short. and try with with the crank sensor off

DFlintstone

The 91 uses a Powertrain Control Module. (PCM) 87-90 uses a Electronic control Unit. ECU. Best to match your year I think, but 91 to 95 might be OK.

You might have a bunch of stuff that grounds there on the right side of the block near the dipstick. (TCU, PCM, injectors ect)(not sure there. It's always good to know that "gang" is clean and good.

You might peek at Cruisers ground checking/refreshing in my, or his signature. Plenty there applies to your 91 as well.

XJOZ

Great looking link. Ill give that a run through and check the ground point. From what i understand if an ecm goes they can cause all sorts of problems. Its the common component with the ignition switch that would effect the fuse panel under the dash and the fuse box in the engine bay. For it to blow those fuses from a short id suspect it always would and two at the same time would mean common component drawing to much or a short. Threw a code. Restarted. Wouldn't start and fuses blown. Wouldn't turn on the check engine light as an indication it posted. What the code was stating wanst enough to blow the fuses or i would have been stuck in the middle of the road. Not able to drive it for 5 miles. Wasnt significant to stop it from restarting. It didn't move between then and the next morning to jiggle the short active. Over night something changed that allowed the fuses to blow the next morning or something was stuck on that i didn't notice and drew the current. Over 60 amps. But not reoccuring.
Sucks that the ecms I've gotten seem like junk. Different symptoms than the original one. That wasnt putting power to the fuel pump.
How do the parking lights come into this. Thats beyond the circuit for the engine. Gets power from hazard or headlight switch. Grounded so if yeah its shorted to positive. But then a fuse would go again. Regardless of the ignition being on it stays on.
Ill look at that circuit first tomorrow.

XJOZ

Hoked iy all up again this morning and was almostthe same with the exception that the parking lights were off.
Disconneceted battery and PCM. Pulled at the relays in the box on passenger wheel well, hooked up battery and the fuel pump still ran. Disconnect batt, disconnect PCM, hook up batt and no fuel pump running with or without relays.
Fuel gauge now reads as it should. Come sup slowly with ignition on and PCM disconnected. Having the CPS plugged in or not is no difference.
The Orange wire to the CPS has only residual voltage going to it. There is continuity between it and the PCM, as well the other two checkout fine for shorts as well. PCM is getting power.

Hopefully the new PCM will be in soon. I looked for shorts and couldnt find any. Lots of places I couldn't see though. Not sure how this is these days for other but here we are getting the crapiest parts Ive ever seen. Same place sold me a master for the clutch on anther car. Two didnt work i got one elsewhere and it did. Small town in Canada so parts suppliers limited to one for some parts.

Any other ideas would be welcome to debug this thing.

XJOZ

Pulled the circuit breaker that has a red batt wire that goes to the seat and trailer lights. That stopped the fuel pump running when not on. Figure theres short in the trailer wire so i just cut the red wire.

Have new PCM to try tomorrow. This one is undamaged(no mounts broken with or without 1" holes broken on the case. Obviously a short is not good. Im concerned that it may have fried a sensor that may in turn fry the PCM when i try it. Any suggestion on what to do to test that the others are good first? Or am i worrying to much here?

DFlintstone

I'm at a loss, really just learning my Renix anyway. Putting "the code", instead of telling us the code, might help others....

It's my take the puters' are pretty hardy. Short of an electric-arc welder, I myself am not aware of anything that would be expected to damage it.

DFlintstone

If an un-fused wire shorts it can melt right through it's insulation and the insulation of wires next to it. Hidden in a harness that can be hard to find.

Also, if it acts just goofy and seems to make no sense, check grounds.

XJOZ

The 91s dont show a code number just an indicator on the dash. Yup would help if the PCM would have shown one but as it as toast the procedure to retrieve the code wouldn't work. Check engine light wouldn't flash on ignition so it was done. Hence the not knowing the code. Yup electrical are PITA.
Thanks. Wizzer as Id just restored it this summer.

DFlintstone

The "Key Tricks"
Older (OBDI) models - Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. ("On" is NOT "Start" and "Off" is NOT "Lock"). The "check engine" light will flash. Count the flashes. Each code is a two digit code, so a (for example) 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). It will never flash more than 9 times, so watch for those pauses!

If you got a number they are listed in "info threads", sticky on-top of this forum.

XJOZ

That was why I thought the PCMs were dead as that didnt work. Put the new one in and vroom. The old ones didnt even put out any juice to the CPS. Put a new one in just in case. They ended up giving me the PCM for free due to the other two failed ones. Cardone is crap.

Thanks all guess I can head home over the northern Canadian rockies tomorrow.