12.7 questions

It makes sense the timing sensors control rpm, You said they’ve been changed twice. Wow!! Experts can’t figure it out!! Must be a wire In one of the harnesses.Way out of my knowledge. Can only share my experience in 19 yrs . Only 3 typical problems. Ecm fuse, bad frame ground and lost prime.Id have lost money on that bet. Wonder if plug, or a chaffed wire for one of the timing sensors??? The thought of a tech and a test light guessing and probing wires while on the clock is nauseating.

 

Speed sensor(s) on trans, Mine has 2, from what I remember RPM always worked. Bottom sensor for speedo, top one for cruise control. I never knew about top one. I guess my last Truck 99 had one also. Replaced bottom one twice in 9 yrs. This Truck both in 11 yrs.

 

I don’t know, I’m a parts changer. Lol Electrical is where I get lost.But I’ve heard of bad sensors without a code. Why not bad wire without a code. amodelcat said It does controls rpm.I think he said srs

 

That’s where to focus, I would think, last thing Detroit did to it. They at least owe you some free advice. Funny now that things picked up, nobody gives you the time of day unless you own 100 Trucks. 10 yrs ago, they’re were begging for O/O business. Too bad

 

What year is engine , or truck?
Is it EGR?
If so you have a ddec 5 engine.
There is no check valve in ddec 5 head.

Have you tried to prime engine?
Is fuel filter sucking air?

What rpm does engine turn over with starter?

 

When we are talking speed sensor it's not the speedometer.........

We are talking engine rpm speed. Nothing to do with your transmission or speedometer.
Everything to do with your rpm guage .

A lot a times just because it says srs sensor or trs sensor it's not always the sensor that is the issue but the wiring going to it. And on a 25 year old engine this is usually the case.