Diesel electrical expert opinion please

[widman]

Ford F550 with 6.0 Navistar turbo diesel

I am in Bolivia. My truck is dead. Died with lack of power, first thinking it was a fuel problem. I had it towed 120 miles to town. 3 "experts" have examined it. The first said the computer was shot after scanning it with a Snap-on scanner and getting different codes. He had it running once, then could not get it running again. He tried cycling the injectors and it stopped after 3.

Towed to the Ford shop (they have never seen an F550 or a 6.0) They connected the ford scanner and got nothing. no signal. no power. They say I need a new PCM.

A friend who has worked for Toyota and Nissan in Japan went over it and says he does not believe it is the PCM. There is no positive or negative at the main computer (International). The check engine light stays on even when you take out the computer and PCM. He says there has to be a short to send power to the check engine light.

I do not want to buy a PCM or computer if it is not bad. Nor do I want to buy one and put it in if there is a short or something that might have caused one to go bad.

When you turn the key the injectors start making noises.

First question: does the power go from the PCM to the computer or from the computer to the PCM?

Second: is he right that the check engine light should go off when you disconnect the computers?

Any other suggestions?

I've been asking on thedieselstop, but no answer yet.

 

[brianl703]

The check engine light on every Ford vehicle I've ever looked at the wiring for is connected to the PCM. The PCM grounds the check engine light to turn it on. Therefore removing the PCM should make the light stay off.

However, newer Ford vehicles may have the check engine light driven by logic in the instrument cluster, which communicates with the PCM through the data bus. In this case the PCM sends bus messages to turn the check engine light on and off. Perhaps the instrument cluster lights the check engine light when it cannot reach the PCM through the bus.

Oh yes--there is the possibility of a bus problem, where something is messing up the bus by either shorting it or transmitting continously. This would certainly prevent the scantool from seeing the PCM, and would also possibly prevent the engine from starting IF there is any sort of anti-theft system.

 

[mechtech2]

It may be a bad PCM.
But first, clean ALL power and ground leads - BOTH ends of each.
A faulty ground to the PCM is common.