ECU/Alternator Problem
 

I have a 97' xj that has me baffled. I seem to be having intermittent
computer problems that is primarily affecting my alternator. I first
notice the problem when the alternator begins overcharging. The gauge
will indicate that the alternator is charging at 19 volts which seems
to indeed be the case judging by the way my headlights respond.

At the same time the ABS light will come on and the transmission will
not shift out of a high gear. However, I can still manually shift the
automatic transmission. These three things happen pretty much occur
simultaneously every time the problem occurs. About the half the time
the other gauges (speedo, temp, rpms, etc..) will swing across their
full span wildly and repeatedly. Shutting down and restarting resets
everything to normal until the next occurrence.

I initially hoped it might be a grounding issue as I had replaced the
battery a few weeks ago, so I checked and cleaned the battery
connections. That seemed to decrease the frequency to once/every other
week for several weeks until the last few days, where it is now
occurring nearly every trip.

I know the voltage regulator is in the computer, so I suppose I will
need to replace it, but I wanted to make sure there was nothing else
obvious I need to check? Could the alternator or maybe a bad ground
freak out the computer like this or is the ECU puckered?

Re: ECU/Alternator Problem
 

Try cleaning the battery terminals. If there is some resistance the current
won't flow and the voltage will rise. You may also want to clean the other
ends of the cable as well. And check the ground straps.

ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

Try cleaning the battery terminals. If there is some resistance the current
won't flow and the voltage will rise. You may also want to clean the other
ends of the cable as well. And check the ground straps.

ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

Try cleaning the battery terminals. If there is some resistance the current
won't flow and the voltage will rise. You may also want to clean the other
ends of the cable as well. And check the ground straps.

ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

Try cleaning the battery terminals. If there is some resistance the current
won't flow and the voltage will rise. You may also want to clean the other
ends of the cable as well. And check the ground straps.

ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

I use a multimeter and take is for a walk while looking for a bad
connection.

With the engine on and the lights, heater fan on high, wipers, stereo,
etc., all turned on I take a volt reading at the battery terminals. I
then leave the positive on the terminal and walk the negative probe to
the clamp, then the engine block, then the alternator case, then the
vehicle body looking for a drop in voltage. If you see hundredths of a
volt drop, no problem, if you see tenths, you have found a bad connection.

I also check the positive clamp and cable by leaving the negative probe
on the post and walking the positive probe.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

I use a multimeter and take is for a walk while looking for a bad
connection.

With the engine on and the lights, heater fan on high, wipers, stereo,
etc., all turned on I take a volt reading at the battery terminals. I
then leave the positive on the terminal and walk the negative probe to
the clamp, then the engine block, then the alternator case, then the
vehicle body looking for a drop in voltage. If you see hundredths of a
volt drop, no problem, if you see tenths, you have found a bad connection.

I also check the positive clamp and cable by leaving the negative probe
on the post and walking the positive probe.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

I use a multimeter and take is for a walk while looking for a bad
connection.

With the engine on and the lights, heater fan on high, wipers, stereo,
etc., all turned on I take a volt reading at the battery terminals. I
then leave the positive on the terminal and walk the negative probe to
the clamp, then the engine block, then the alternator case, then the
vehicle body looking for a drop in voltage. If you see hundredths of a
volt drop, no problem, if you see tenths, you have found a bad connection.

I also check the positive clamp and cable by leaving the negative probe
on the post and walking the positive probe.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

I use a multimeter and take is for a walk while looking for a bad
connection.

With the engine on and the lights, heater fan on high, wipers, stereo,
etc., all turned on I take a volt reading at the battery terminals. I
then leave the positive on the terminal and walk the negative probe to
the clamp, then the engine block, then the alternator case, then the
vehicle body looking for a drop in voltage. If you see hundredths of a
volt drop, no problem, if you see tenths, you have found a bad connection.

I also check the positive clamp and cable by leaving the negative probe
on the post and walking the positive probe.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)


ds1234567890@hotmail.com wrote:
> I have a 97' xj that has me baffled. I seem to be having intermittent
> computer problems that is primarily affecting my alternator. I first
> notice the problem when the alternator begins overcharging. The gauge
> will indicate that the alternator is charging at 19 volts which seems
> to indeed be the case judging by the way my headlights respond.
>
> At the same time the ABS light will come on and the transmission will
> not shift out of a high gear. However, I can still manually shift the
> automatic transmission. These three things happen pretty much occur
> simultaneously every time the problem occurs. About the half the time
> the other gauges (speedo, temp, rpms, etc..) will swing across their
> full span wildly and repeatedly. Shutting down and restarting resets
> everything to normal until the next occurrence.
>
> I initially hoped it might be a grounding issue as I had replaced the
> battery a few weeks ago, so I checked and cleaned the battery
> connections. That seemed to decrease the frequency to once/every other
> week for several weeks until the last few days, where it is now
> occurring nearly every trip.
>
> I know the voltage regulator is in the computer, so I suppose I will
> need to replace it, but I wanted to make sure there was nothing else
> obvious I need to check? Could the alternator or maybe a bad ground
> freak out the computer like this or is the ECU puckered?
>

Re: ECU/Alternator Problem
 

Thank you for all the suggestions.

Still trying to figure this one out.

Last weekend, I probed the battery cables from the battery to the
alternator, to ground, etc... checking for voltage drops. They
appeared to check out ok, but I checked and cleaned ground connections
all over the engine compartment anyway.

Next, I bought a used engine control unit at the junk yard for $25.
After swapping them out, the problem still occurred.

My next thought was the alternator, so I swapped it out earlier this
week. Here comes the head scratcher. The problem seemed to greatly
decrease in frequency. However, instead of overcharging at 19 volts
the needle will only breifly sweep up to 15 or 16 volts. Even more
strange is that it only does it while accelerating through fairly
sharp corners or turns. In the past few days, it has done this
probably 3 or 4 times, but only swept high enough once to click on the
ABS light and cause the shifting problems with the computer I
described earlier.

I had replaced a dead battery a few weeks before this problem cropped
up, so I thought perhaps the new battery had some intermittent
shorting issue. Replaced it this morning with no apparent impact to
the problem.

So to recap, I have ruled out the voltage regulator in the computer,
the battery, and maybe the alternator (improved the problem, but
didn't eliminate it).

Anyone have any advice or ideas?!