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Smokin64 · 04-04-2022, **(Subject: CAT 3126B no start )**

Here's one for ya: FL80 with a CAT 3126B, E.S.N.#7AS-----, complete reman engine, dyno tested, came with all new sensors, covers, etc. Replaced the engine harness due to too many rubbed spots. Shows 850-900 psi IAP. Fuel flows from return line while cranking. Injector solenoid tests show all are good. Engine is turning at least 150 RPM, but ECM only shows 38 RPM(occasionally 40). Test ECM made no difference. Re-installing old timing sensors made no difference. No smoke, no fire. I'm lost.

Rawze · 04-04-2022, **(Subject: CAT 3126B no start )**

I don't know much about cat engines.. but if the rpm in the ecm does not match the actual .. I would assume that something is wrong with the sensor, the wiring, or perhaps the tone ring.

Also, is the fuel pressure up to spec (or higher) while cranking?

RollinCoal · 04-04-2022, **(Subject: CAT 3126B no start )**

Exactly what Rawze said
Rpm not matching could very well be a problem

Aussie Steve · 04-06-2022, **(Subject: CAT 3126B no start )**

You have an electrical fault for sure. Cats have two speed timing sensors, one picking up crank speed l/h side of block (it's usually a pain in the backside to get to) and one measuring cam speed at the rear L/H of the timing cover. If they loose the signal from one sensor they will swap over to the other sensor but will also log the fault. They will run on one sensor. So it might be that something was disturbed/dislodged etc when the new harness was installed. The engine has to crank above 150 rpm to fire and turn a minimum of three full revolutions before it will fire.
The ecm has to be able to see that the engine is turning fast enough, maybe reinstall the sensors as per the procedure and try it again

Aussie Steve · 04-06-2022, **(Subject: CAT 3126B no start )**

Edit - is the new harness correct? Try the old harness to check, It doesn't take long to swap a Cat harness

Smokin64 · 04-06-2022, **(Subject: CAT 3126B no start )**

Thanks for the replies, I agree that the 38 RPMs while cranking is the problem, he's suppose to be getting back to me about fuel pressure while cranking. And I also told him to install the old engine harness to see what happens. There are no codes at all in the ECM currently, and all of the engine vitals are where they should be while cranking. It's just the RPMs that are causing the no start. Any other thoughts are welcome and thanks again.

Smokin64 · 04-06-2022, **(Subject: CAT 3126B no start )**

Also, according to the schematics I have, the circuits for both timing/speed sensors have the correct pin locations at the ECM connector. And those circuits in the new engine harness have been load tested with a halogen headlight. These tests were done at the same time the ECM powers, grounds, and ignition were load tested.

Aussie Steve · 04-06-2022, **(Subject: CAT 3126B no start )**

Are the batteries up to the task? Is there enough voltage at the ECM?

Smokin64 · 04-07-2022, **(Subject: CAT 3126B no start )**

(04-06-2022 )Aussie Steve Wrote: Are the batteries up to the task? Is there enough voltage at the ECM?

Yep, batteries were fully charged and load tested, and have been on a battery tender the whole time. There's 12.7 volts at the ECM and all powers, grounds, and ignition wires have been tested and then load tested with a halogen headlight.