6.5TD Don't start

[Juan Emilio Castro]

Hi, I'm located in Buenos Aires Argentina, it've been suscriber member of TDP until 97 or 98 can't recall.

I've been reading this forum for a while but never had something to ask or to contribute till now.

I got a customer with a '96 GMC 2500HD 6.5TD M/T that a couple of weeks ago developed a starting problem. Then, it started, run for a while and died.
I've traced the problem to a ground of the ignition switch. Got a clue because when this happened some other things in the instrument cluster and the A/C didn't work either.
So far, I've changed the filters to it and delivered it.
Everything went ok till yesterday when the customer let the truck idling and walk to open his barn door. He heard the truck revying and then dropping, revying again to higher rpms, and dropping to idle, he thought his wife was the culprit so he didn't mind, until his wife a little scared get out of the truck and the truck started to rev again, this time he run to shut if off, ready to put it in gear, push the brakes and drop the clutch thinking the engine was running away due to oil in the intake, but he move the key and the truck died immediately. He saw the tach needle beyond 4000 rpm before shutting it off.
It never started again.
What can cause this revying when idling? I've checked the intake for oil from the turbo but it's almost dry, just the regular oily walls from the CDR.

Is there a way of testing the PMD/FSD to see if it's faulty?
The only codes on the scanner is:
215 engine shutoff control circuit (though it maybe because I've been fooling with the solenoids and relays to see if they were the problem)
238 turbo boost sensor circuit high

I'm lost and the troubleshooting guide is no help in this case.

Thanks

Juan Castro
Buenos Aires
Argentina

[JohnC]

Juan:

Problems with the Fuel solenoid and the Fuel solenoid Driver (PMD) can cause uncommanded reving. Usually, the PCM shuts the engine down via the fuel shutoff solenoid. Maybe this did not happen and caused the code you saw.

Given the number of symptoms, I'd suspect a power or ground issue, but it could be a massive pump failure as well...

[Juan Emilio Castro]

Thanks John,

How I diagnose if it's the FSD or the solenoid inside the pump (wich means a new pump)?
Is there a way of measuring with a scope the FSD or the pump solenoid?

Just the fsd+cooler is gonna cost this guy around us$ 850 (I'm in Argentina so you have to add freight and duties) and the pump is almost twice that, I don't want to tell this guy he has to change A or B without being 100% positive about it.

[JohnC]

Look at solenoid closure time. If it varies wildly, either the PMD or the solenoid is failing (or the wiring). When the PCM can't control the solenoid the engine can run away. The PCM is supposed to drop the shutoff solenoid to prevent this.