No tach, Alternater or grid heater..... Suddenly

Kronic_187

Kronic_187

Mekanical injection junky
Joined
Sep 27, 2009
Messages
1,343
1996 2500 EC LB
4x4 5spd, used to be Auto

Fired truck up, drove about 3miles tach and alternater died.

Figured it was just crank sensor, truck was driven the rest of the way home then parked. This was end of oct.

Flashed truck up this week, swapped crank sensor off my 95 2wd cummins. No luck.

Upon further inspection noticed "wait to start" light isnt lighting up anymore.


Any clue what this could be? Like i said its not the crank sensor.

Any info on how to diagnose ECM problems?
 
Check engine light isnt lighting up when key is turned either
 
It may be the PCM. It's on the passenger side fire wall. The 12V's don't have an ECM. Check all wiring and connectors for the ESS and the PCM. There are also a couple of fuses that could be blown under the hood and in the end of the dash.
 
Its not a fuse, check'm all. Next up when i get back from UCC is scrub all grounds and let pcm sit without power for a day or two n see what happens. I got another pcm off a 96 gasser, would that work for tach, speedo and alternater? Putting grids on a switch is easy enough
 
I know you said it isn't a fuse, but did you check the 120 amp fuse under the hood?
 
Checked them all

No tach, no speedo, no alternater, no check engine light

Truck starts and drives fine. All lights work
 
Communication.

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Last one I had do this, the speed sensor wires were shorted out.

If you follow the diagrams, the same 5v reference that feeds the speed sensor also feeds the tach pickup out of the pcm.
 
Just throwing this out, but, when I did my 12V conversion I had the same symptoms that ended up being a loose connector. On the fire wall, right above the master cylinder, there are three connectors. Make sure they're connected good and not corroded.
 
Thanks for the info, i'll pick my way through it tommorow and see what i can come up with
 
Everything works now but speedo...

I clocked the speed sensor 90* from where it was after i cleaned and greased all my grounds.

Anyone got instructions on how to trouble shoot speed sensor issues?

Or which way they should be clocked?

I ordered a new one just incase but i may be able to adjust it?
 
Is there a good reason you clocked it?
Turning the sensor is for a tire diameter change. The sensor is eccentric, and turning it moves the sensors axis so a larger (or smaller) driven gear can fit.

It should have tabs and numbers indicating tooth count on the round part that plugs into the Tcase


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Last edited:
... i turned the speed sensor n it started working again

All i did was clean grounds. I had speed sensor unplugged when i flashed it up, tach started workin. Pulled speed sensor, cleaned out connector, noticed blue paint. Lined up paint. Fired it up again... everything but speedo works now
 
I said in plain English how it works. Take it out and look at it.

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