98 3500 5 speed with 186k miles. I was driving down the highway today with everything working as normal and all of the sudden it died and all may gauges went to zero. Tried to restart it several times and it would fire up and die right away. Tied up the fuel shutoff solenoid and drove it home with no gauges. Also for the past year my radio has been cutting in and out and my overhead display went out. I also had to wire in an external voltage regulator. I hate electrical issues so I figured the old mechanical 12v was the truck for me, I guess I figured wrong. Do you guys think my pcm is going bad causing all my issues or where do you think I should start?

well,  you did in fact  find out the  12v  is  indeed  THE  truck to have!      (piece of  baling wire...  and  away you go) 

 

Do  you remember  any  harsh  bumps  just  as  stuff would   conk out?      you said your  gauges  went dead..  just the gauges ,  or the whole dash go dark?

 

Sounds like a  'run'  circuit..   bad key switch, or  wiring  up the steering column?

 

Next time it  happens,   jiggle the key and see if  the  dash comes to life again...  or  you have to   'cycle' it   completely  to  get  juice.

 

Then  if no difference there,   would it  restart or at least crank going immediately to  'crank' after  it dies?  (not  returning to  'off' first)

 

if  it  does,  then  I'd  think it's  your  pcm..   especially since  reading you said  you had  to  mess with the  voltage reg..

Edited December 23, 201410 yr by rancherman

If you're loosing power to everything, then it's likely the green w/black tracer wire has lost power.  It is fed by the ignition switch, then goes through #9 fuse.

 

The wires going up the steering column are also known for rubbing and causing issues.

 

Here's a wiring diagram, it's for diagnosing the FSS, but it's all fed from the same wire.

 

Ha ha you're right it was nice to be able to get it home with a chunk of speaker wire a had laying around. Thanks for the replies guys I will look into your suggestions and let you know what I find out.

I had my 12 valve for a month and miss it a lot

offhand,   I'd say   he is  facing  2 different problems.       From your  schematic,    I agree  the   12v  'pull'  is  good  when  he is  cranking..  but  engine  dies   right after releasing the key.    'Hold'  is  the problem.   This is  where  he should find   a problem  with  the green tracer'd  wire 

 

I can't however  see how  the  green tracer'd  wire  would effect  the gauge cluster, overhead or the radio.

 

For some reason,  I thought the PCM   did  a  'little' for engine control...   such as    shutting down the engine  in a roll over..  crash,  etc.     but  I see the  pcm  really only does     gauge control, tach, anti lock?   alternator?  airbag?  AC?      hence the  reason for my first post..     I stand  corrected  on  the  PCM's  job  in the 12v.   About the only  'trouble code'  would be   "Engine not running"  ha ha..

 

(which is good,   I'm  on the brink of  diving into my  12v) LOL.

 

The one  machine I have  with  a  electric  fuel shut off,  is   our   combine with a  ford  genesis  diesel.   It's  'hold'  however is   energized  through  a  OP  sender... Ya gotta have  OP  otherwise  the engine  won't   run.    Makes  it  a little    'prickly'  on  cold mornings.

Edited December 24, 201410 yr by rancherman

offhand,   I'd say   he is  facing  2 different problems.       From your  schematic,    I agree  the   12v  'pull'  is  good  when  he is  cranking..  but  engine  dies   right after releasing the key.    'Hold'  is  the problem.   This is  where  he should find   a problem  with  the green tracer'd  wire 

 

I can't however  see how  the  green tracer'd  wire  would effect  the gauge cluster, overhead or the radio.

 

For some reason,  I thought the PCM   did  a  'little' for engine control...   such as    shutting down the engine  in a roll over..  crash,  etc.     but  I see the  pcm  really only does     gauge control, tach, anti lock?   alternator?  airbag?  AC?      hence the  reason for my first post..     I stand  corrected  on  the  PCM's  job  in the 12v.   About the only  'trouble code'  would be   "Engine not running"  ha ha..

 

(which is good,   I'm  on the brink of  diving into my  12v) LOL.

 

The one  machine I have  with  a  electric  fuel shut off,  is   our   combine with a  ford  genesis  diesel.   It's  'hold'  however is   energized  through  a  OP  sender... Ya gotta have  OP  otherwise  the engine  won't   run.    Makes  it  a little    'prickly'  on  cold mornings.

 

You are correct, looking at it I miss-worded some things there.

 

The green tracer wire is losing power, but because of the radio, overhead console, and gauge cluster.  It is obviously not the issue.

 

There are three different switches inside the ignition switch, one that powers the green/blk wire, and one that powers the radio.  Both those get fed by the same wire, a red one that goes through #3 fuse in the PDC.  If it were me, I would check that fuse, check for power before and after the fuse, and then check for power at the inlet of the ignition switch.

 

As far as trouble codes, I don't think it would even throw that lol.  I had mine apart to the frame, and then back together.  And for grins I checked for codes... nothing.  They have a ASD relay (Auto Shut Down) but it doesn't do anything, I've tried shorting it, nothing.  It's probably there from the gassers, cause mine also has all the wiring/relays/fuses for a in tank fuel pump.

Do you have a tilt steering wheel? Do you use it much? You may have a broken wire or two in the steering column. Pull the cover off and see if any wire stretches.

 They have a ASD relay (Auto Shut Down) but it doesn't do anything, I've tried shorting it, nothing.  It's probably there from the gassers, cause mine also has all the wiring/relays/fuses for a in tank fuel pump.

 

The ASD controls the charging system, as I've pulled the relay and that's the only thing that seemed to change, it also seems to have some connection with auto trans control as well.

The ASD controls the charging system, as I've pulled the relay and that's the only thing that seemed to change, it also seems to have some connection with auto trans control as well.

My transmission won't shift without the ASD relay too. Well, eventually it does shift, but it may take a couple miles to get into O/D.

Hmmm very interesting, mine hasn't had an ASD since I through it together, better make sure it's charging correctly! 

 

Sorry OP,   over.  

hmmmm...    it'd  been  too easy  to  run the  fss   through the  asd..       *just speculating here*        especially  when   we  learn  how  many systems  overlap  each other.     I'm  surprised   they didn't!  Even in the 90's  they  were  pretty   safety  minded.

 

 

Lots  of  posts  of  this  on CF.         guys  with dead  dashes,   but  still  shows   charging   on   that  gauge.    Most immediate  fear is  the  pcm  is  dead/dying.     Then   the  responses  come in to  check and double check   bulk head  connectors  and  grounds.     Then the  many  responses  to  'check the  CSS'     Really??    you'd only lose  the  tach  with  a  bad CSS  wouldn't you?

 

I see  it's  pretty common to  lose  the  pcm's  capacity  to  externally  regulate the  alt....  and  like   this  OP  ^^^^    a   20 dollar   'stand alone'  regulator   works  just fine.

Then the  many  responses  to  'check the  CSS'     Really??    you'd only lose  the  tach  with  a  bad CSS  wouldn't you?

 

I see  it's  pretty common to  lose  the  pcm's  capacity  to  externally  regulate the  alt....  and  like   this  OP  ^^^^    a   20 dollar   'stand alone'  regulator   works  just fine.

When the CSS no longer functions the PCM thinks the engine is not running and shuts the guages down, shuts the A/C (if running) down, and shuts the alternator down. The most common problem with the CSS is the connector that is just about at the head staight above the CSS itself. Even if the CSS quits the engine will stay running since the hold side of the Shut Down Solenoid still hes power.

Thanks  mntom!      that  was  the  perfect  answer to  my  subliminally   loaded  question!!        You probably have noticed,   in my  couple years of being 'here'..  a lot of my questions  are  outside-the-box,   hopefully  to  not only answer my questions, but   anyone else  reading.  ( I don't mind being the sacrificial goat)    See how I drew in the perfect answer from  Yankneck? (# of  reflashes on ecm)     

   This  kinda how we've  homeschooled  our  kids...    we  ASK  a lot  of  questions..  to open  the  dialog and get their  brains  churning...     

 

Is  there  a simple... almost  a " pcm for dummies"..  type  flow chart   that   gives   the  basics   on   how   the various   systems   tie-in/tied together   or are managed  by  the  pcm?   Not a  schematic..    maybe  Mike's  already  forged one in here.

I can confirm pulling the ASD relay screws with charging!  Turns out I did have mine in, when the in-tank pump went out, I put the relay in the ASD slot as my "spare" holder haha.  

However, Tom, are you sure that it a bad CPS will turn off the whole gauge cluster?  Well testing the charging issue, I also tried disconnecting the CPS.   Still had oil pressure, volts, fuel level, and MPH for sure not sure about the water temp cause the engine wasn't up to temp yet.

I had a problem with my CSS a while back and all I lost was my tach and charging.

I had a problem with my CSS a while back and all I lost was my tach and charging.

Huh! I was told that if the PCM doesn't 'see' the engine running it won't register anything on the guages..... Maybe I was mis-informed?