Help with a friend's 97
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CF Veteran
Joined: Sep 2010
Posts: 21,168
Likes: 5
From: Milwaukee, WI
Year: 1987
Engine: Check
Help with a friend's 97
97 XJ, 4.0, manual.
The truck cranks, but there is no power to the coil, the injectors get no power, the gauge cluster does nothing, but the ECU gets warm when the key is on.
The thing will crank all day long, all the fuses get power except the ASD relay. (apparently) But nothing changes if you give power with a probe.
Any ideas?
I'm kinda just walking into this, have done nothing myself really, so please forgive me if I left something out or messed something up.
Thanks...
The truck cranks, but there is no power to the coil, the injectors get no power, the gauge cluster does nothing, but the ECU gets warm when the key is on.
The thing will crank all day long, all the fuses get power except the ASD relay. (apparently) But nothing changes if you give power with a probe.
Any ideas?
I'm kinda just walking into this, have done nothing myself really, so please forgive me if I left something out or messed something up.
Thanks...
CF Veteran
Joined: Nov 2010
Posts: 5,841
Likes: 117
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
I don't really understand the computer getting warm; that is a symptom that I've never heard of before.
Did all these symptoms occur at the same time? Some history of how this came to be is pretty important to understanding this.
If there is no power to the gauge cluster whatsoever, I'd definitely freshen all engine grounds for starters. Simple things first.
In general though for the no-start, crank sensor and possibly ignition switch are suspects.
Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.
Did all these symptoms occur at the same time? Some history of how this came to be is pretty important to understanding this.
If there is no power to the gauge cluster whatsoever, I'd definitely freshen all engine grounds for starters. Simple things first.
In general though for the no-start, crank sensor and possibly ignition switch are suspects.
Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.
Last edited by tjwalker; Apr 13, 2012 at 06:13 PM.
Thread Starter
CF Veteran
Joined: Sep 2010
Posts: 21,168
Likes: 5
From: Milwaukee, WI
Year: 1987
Engine: Check
I'm relaying this from my buddy who runs this shop, so I'm the middle man here. Sorry.
The computer being warm was just something the mechanic mentioned, I'm guessing because that means it has power.
Anyway, he says it seems there is a short to ground on the power side of the ASD relay causing problems. Fuse 10 (20a) is shorting to ground.
The truck has a fresh crank sensor, coil sensor, new coil, new plugs, wires, cap, rotor, and alternator.
While the owner was driving the volt meter dropped to zero, he turned it off for awhile, and tried again. It then worked for a bit, shortly after the battery ran out and that was the end of anything they did.
Again, sorry for not knowing much, I'm kinda walking in mid problem here. :/
Just tryin to help a guy.
The computer being warm was just something the mechanic mentioned, I'm guessing because that means it has power.
Anyway, he says it seems there is a short to ground on the power side of the ASD relay causing problems. Fuse 10 (20a) is shorting to ground.
The truck has a fresh crank sensor, coil sensor, new coil, new plugs, wires, cap, rotor, and alternator.
While the owner was driving the volt meter dropped to zero, he turned it off for awhile, and tried again. It then worked for a bit, shortly after the battery ran out and that was the end of anything they did.
Again, sorry for not knowing much, I'm kinda walking in mid problem here. :/
Just tryin to help a guy.
Thread Starter
CF Veteran
Joined: Sep 2010
Posts: 21,168
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From: Milwaukee, WI
Year: 1987
Engine: Check
There is a short to ground on the ASD fuse, engine controller.
There is also a short on the ASD fuse, o2 sensor.
When the ECU is unpluged, fuse 10 is no longer shorted to ground...
There is also a short on the ASD fuse, o2 sensor.
When the ECU is unpluged, fuse 10 is no longer shorted to ground...
CF Veteran
Joined: Mar 2010
Posts: 47,923
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From: Broward County Fl.
Year: 1989 xj sport 2dr
Model: Cherokee
Engine: 12 hole bosch Injectors
check rear o2 wiring for issue around transfercase/drive shaft areahttps://www.cherokeeforum.com/f2/96-...er-hood-19793/
Last edited by freegdr; Apr 13, 2012 at 06:50 PM.
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CF Veteran
Joined: Mar 2010
Posts: 47,923
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From: Broward County Fl.
Year: 1989 xj sport 2dr
Model: Cherokee
Engine: 12 hole bosch Injectors
Thread Starter
CF Veteran
Joined: Sep 2010
Posts: 21,168
Likes: 5
From: Milwaukee, WI
Year: 1987
Engine: Check
Sorry for not following up.
Ended up being a short somewhere that caused the ECU to fry.
I wasnt there when it was finally fixed, so reporting back slipped my mind.
Ended up being a short somewhere that caused the ECU to fry.
I wasnt there when it was finally fixed, so reporting back slipped my mind.
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