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Old 05-20-2017, 01:07 PM   #1
cottondoc

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Bad PCM?

I was driving my 1995 the other day and while going down the road the tach and speedo stopped working. All other gauges continue to work normally. The truck then dropped out of overdrive. I assume because the transmission lost pcm input, but I'm not sure. I cut the truck off and then back on. The tach and speedo started working again, but cut off again in just a few miles. I haven't been able to get them to work since. I checked the PCM connections, and they seem to be intact. It continues to not shift into overdrive since the tach and speedo quit. I can lock the converter with my lockup switch, but it no longer locks on its own. Any thoughts? Maybe a replacement pcm would fix it? How much are used PCMs for a 1995 with 47rh going for?

The truck is a 1995 regular cab, 4x4 with the 47rh. I probably need to update my sig but it has a Darren Morrison built all billet shaft trans, 5x18 injectors, 366 over 480 compounds and a mildly built 215 pump on the original short block. Thanks in advance for any information.


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
Old 05-20-2017, 01:13 PM   #2
BRE
 
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Change the tach pickup. That's all that's wrong most likely.
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07 Dodge 3500 - Tow mirrors, silencer ring MIA, Spectra air filter.
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Old 05-20-2017, 06:11 PM   #3
12valvetater
 
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Check the fuse.
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Old 05-20-2017, 08:37 PM   #4
cottondoc

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Ok, I'll check the tach pickup. Which fuse? Thanks


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
Old 05-22-2017, 04:56 AM   #5
12valvetater
 
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I think it's labeled ENG.
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Old 05-22-2017, 05:41 AM   #6
cottondoc

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Originally Posted by 12valvetater View Post
I think it's labeled ENG.


Got it. Thank you


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
Old 05-22-2017, 07:29 PM   #7
GAmes

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Since the speedo stopped working the engine speed sensor theory isn't likely. If you lost cruise control, tach and alternator (gen light) that would point to the ESS. There are several grounds under the hood that I would remove, inspect, clean and reinstall. They are all shown in the factory service manual.
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Old 05-22-2017, 07:31 PM   #8
BRE
 
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The 5v source that feeds the speed sensor also feeds the tach pickup.
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07 Dodge 3500 - Tow mirrors, silencer ring MIA, Spectra air filter.
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There really is nothing better than OEM. That goes for anything from turbos to boobs.
RIP Dex KCCO
 
Old 05-22-2017, 07:37 PM   #9
GAmes

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Quote:
Originally Posted by BRE View Post
The 5v source that feeds the speed sensor also feeds the tach pickup.
If that has failed then it would, in fact, be a failed PCM.
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Old 05-22-2017, 08:00 PM   #10
BRE
 
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Quote:
Originally Posted by GAmes View Post
If that has failed then it would, in fact, be a failed PCM.


Not correct at all...
it could be but it does not just automatically mean the pcm has failed. A wire could be shorted to ground.
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Rick
07 Dodge 3500 - Tow mirrors, silencer ring MIA, Spectra air filter.
Quote:
Originally Posted by jfaulkner View Post
There really is nothing better than OEM. That goes for anything from turbos to boobs.
RIP Dex KCCO
 
Old 05-22-2017, 08:31 PM   #11
cottondoc

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Bad PCM?

Sounds like I have several things to check. I'll have to time to give it a good look this weekend. Thanks again to everyone for all good info


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
Old 08-02-2017, 02:13 PM   #12
cottondoc

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Just got the truck fixed. It was the crank position sensor. New crank position sensor installed and all is working good again. Thanks for everybody's input.


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
Old 08-02-2017, 05:35 PM   #13
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It's nice when it really is something simple.

Mark.
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Old 08-02-2017, 07:57 PM   #14
cottondoc

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Quote:
Originally Posted by Mark Nixon View Post
It's nice when it really is something simple.

Mark.


Yes it is! Couldn't have worked out better


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2006 QCSB 4x4, 48re, Laramie, EFI Live tuned by HPP

1995 RCLB, 12V, 4x4, ProStreet Diesel built full billet auto, compounds 366/480, 5x.18 injectors, pump mods, fire rings, ARP 625 head studs - For Sale
 
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