Speedometer/Odometer Failure
Thread Starter
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Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 364
From: Candy Mountain
So, this problem persists.
I have had the PSOM rebuilt, just to cut that out of the equation, but same symptom. Random PSOM power failure.
Today, I have it all apart again and am checking for shorts and so forth. So far no dice.
The only thing that is on that same fuse 18, circuit 296 that I have touched recently is the shift interlock solenoid. When I removed an aftermarket alarm system last year I found the solenoid was unplugged. I plugged it in, and it seemed to function normally. If it was shorting to ground shouldn't it blow the fuse? Ditto for a short to ground from a chafed wire? I have looked over my work from removing the alarm system and so far I haven't seen any other connection with the PSOM.
The last time it happened I still didn't have the presence of mind to take note of any other dead systems... So far no luck in replicating the problem in the driveway.
So far I have been focused on the power side. I guess I need to check the ground circuit as well.
Thoughts appreciated.
I have had the PSOM rebuilt, just to cut that out of the equation, but same symptom. Random PSOM power failure.
Today, I have it all apart again and am checking for shorts and so forth. So far no dice.
The only thing that is on that same fuse 18, circuit 296 that I have touched recently is the shift interlock solenoid. When I removed an aftermarket alarm system last year I found the solenoid was unplugged. I plugged it in, and it seemed to function normally. If it was shorting to ground shouldn't it blow the fuse? Ditto for a short to ground from a chafed wire? I have looked over my work from removing the alarm system and so far I haven't seen any other connection with the PSOM.
The last time it happened I still didn't have the presence of mind to take note of any other dead systems... So far no luck in replicating the problem in the driveway.
So far I have been focused on the power side. I guess I need to check the ground circuit as well.
Thoughts appreciated.
Cargo Master
Joined: Mar 2003
Posts: 2,333
Likes: 296
I had a PSOM rebuilt not that long ago and the problem wasn't fixed with it. The rebuilder took another look and claimed that the PSOMs glitch was likely in one of the chips, which are not replaced during a rebuild.
A rebuild is basically replacing two capacitors.
A known good PSOM is the only way I discovered that the rebuilt PSOM, which tested okay on a bench test for 1/2 hour, was still bad.
A rebuild is basically replacing two capacitors.
A known good PSOM is the only way I discovered that the rebuilt PSOM, which tested okay on a bench test for 1/2 hour, was still bad.
Thread Starter
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Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 364
From: Candy Mountain
Discovery.
The Fuse 18 output connector was no longer seated in the fuse block.
Pushed it back in, got an appropriate click, and it seems to be secure.
I am going to put it all back together and what happens.
I hope that closes out this thread.
The Fuse 18 output connector was no longer seated in the fuse block.
Pushed it back in, got an appropriate click, and it seems to be secure.
I am going to put it all back together and what happens.
I hope that closes out this thread.
Fleet Mechanic
Joined: Oct 2006
Posts: 1,351
Likes: 242
From: North Florida
I had a PSOM rebuilt not that long ago and the problem wasn't fixed with it. The rebuilder took another look and claimed that the PSOMs glitch was likely in one of the chips, which are not replaced during a rebuild.
A rebuild is basically replacing two capacitors.
A known good PSOM is the only way I discovered that the rebuilt PSOM, which tested okay on a bench test for 1/2 hour, was still bad.
A rebuild is basically replacing two capacitors.
A known good PSOM is the only way I discovered that the rebuilt PSOM, which tested okay on a bench test for 1/2 hour, was still bad.
So, this problem persists.
I have had the PSOM rebuilt, just to cut that out of the equation, but same symptom. Random PSOM power failure.
Today, I have it all apart again and am checking for shorts and so forth. So far no dice.
The only thing that is on that same fuse 18, circuit 296 that I have touched recently is the shift interlock solenoid. When I removed an aftermarket alarm system last year I found the solenoid was unplugged. I plugged it in, and it seemed to function normally. If it was shorting to ground shouldn't it blow the fuse? Ditto for a short to ground from a chafed wire? I have looked over my work from removing the alarm system and so far I haven't seen any other connection with the PSOM.
The last time it happened I still didn't have the presence of mind to take note of any other dead systems... So far no luck in replicating the problem in the driveway.
So far I have been focused on the power side. I guess I need to check the ground circuit as well.
Thoughts appreciated.
I have had the PSOM rebuilt, just to cut that out of the equation, but same symptom. Random PSOM power failure.
Today, I have it all apart again and am checking for shorts and so forth. So far no dice.
The only thing that is on that same fuse 18, circuit 296 that I have touched recently is the shift interlock solenoid. When I removed an aftermarket alarm system last year I found the solenoid was unplugged. I plugged it in, and it seemed to function normally. If it was shorting to ground shouldn't it blow the fuse? Ditto for a short to ground from a chafed wire? I have looked over my work from removing the alarm system and so far I haven't seen any other connection with the PSOM.
The last time it happened I still didn't have the presence of mind to take note of any other dead systems... So far no luck in replicating the problem in the driveway.
So far I have been focused on the power side. I guess I need to check the ground circuit as well.
Thoughts appreciated.
Thread Starter
|
Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 364
From: Candy Mountain
Logistics Pro
Joined: Nov 2013
Posts: 3,928
Likes: 1,199
From: Mojave, Ca
Did this fix the problem?
Thread Starter
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Fleet Mechanic
Joined: Aug 2015
Posts: 1,835
Likes: 364
From: Candy Mountain
Yes. The wire not being secure in the fuse block was the main problem.
The wire was stiff enough that fuse was not pushing it out of housing completely, but was only making an intermittent contact. With the fuse removed it pushed back into the housing and visually looked like all the other connectors. Only caught it when it moved when checking with the meter.
The wire was stiff enough that fuse was not pushing it out of housing completely, but was only making an intermittent contact. With the fuse removed it pushed back into the housing and visually looked like all the other connectors. Only caught it when it moved when checking with the meter.
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Joined: May 2006
Posts: 12,341
Likes: 1,314
From: Central Mississippi
^^^ Went through this with power port fuse.
Apparently the connector at back of fuse block heated the plastic enough over time for it not to be strong enough to hold it
Put another good fuse in, nothing. Had to free the block & push wire in, hold it while pushing fuse in.
Another "nobody expected it to do this" faults.
Apparently the connector at back of fuse block heated the plastic enough over time for it not to be strong enough to hold it
Put another good fuse in, nothing. Had to free the block & push wire in, hold it while pushing fuse in.
Another "nobody expected it to do this" faults.
Trailering
Joined: Jul 2022
Posts: 17
Likes: 2
From: North Alabama
I just went through this EXACT problem on my 1993 and it turned out to be the Fuel Heater Wires that went to the Fuel filter. it had been deleted and the wires never correctly taken care of and they were grounding out. that circuit shares the fuse with Fuse U? IIRC. The very same fuse that also provides power to the Electronic transmission control and the PCM power relay coil. it killed power to the TCM/PCM and killed the speedo/Tach and sent the transmission into limp mode.
Glad you figured the issue out! if it comes back i'd highly recommend checking those wires as well.
Glad you figured the issue out! if it comes back i'd highly recommend checking those wires as well.
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