CAT 3126B no start

[Aussie Steve]

What's the engine serial number? I'll have a look into it when I get 5
It's not fitted with an 'E' stop or similar is it. I've seen a few occasions where some ones tearing their hair out and missed that before. Pretty frustrating

[Smokin64]

E.S.N.# 7AS11266
And no E-stop on this one, it's a sileage truck on a dairy farm.

[DVT873]

Try starting with the IAP sensor unplugged.

[Smokin64]

Sorry for the delay, it will not start with the IAP sensor unplugged. I'm hearing rumors that CAT has received a bad batch of engine harnesses for the 3126s. the bad harnesses are all showing 38 RPMs, because the harness connectors at the timing sensors have the wires installed backwards. For example, instead of terminal A being a blue wire, and B being a yellow wire, these harness have terminal A with a yellow wire and B with a blue wire. I'm waiting to hear back from this guy for verification.

[Aussie Steve]

Have a look at this procedure, it has the wiring diagram for each sensor in there back to the ECM

  Speed timing testing.pdf (Size: 277.03 KB / Downloads: 156)

[Aussie Steve]

HUEI pumps are well known for failing without warning as well. They have had more updates than I've drunk cold beer. Solenoid failures, high pressure pump failures - the list goes on.
Test the injector actuation oil pressure, check the reading with ET and compare to actual, cranking pressure should be above 870 psi with ET. gauge in the test port in head with everything left as is so the engine can run and fire. Confirm with a manual gauge. If the injector actuation pressure is below 870 psi your HUEI oil pump is possibly shot, it's exchange only no serviceable parts available. You can also remove the high pressure oil line to the head and install a gauge in the pump outlet, pressure should be a minimum of 4000 psi. That will confirm if it the pump or the IAPCV valve.
And if all else fails check the drive gear isn't loose on the HUEI pump, that's a possibility with a freshly rebuilt engine. Oh and the engine oil level is correct.

[Aussie Steve]

(04-19-2022 )Smokin64 Wrote:  Sorry for the delay, it will not start with the IAP sensor unplugged. I'm hearing rumors that CAT has received a bad batch of engine harnesses for the 3126s. the bad harnesses are all showing 38 RPMs, because the harness connectors at the timing sensors have the wires installed backwards. For example, instead of terminal A being a blue wire, and B being a yellow wire, these harness have terminal A with a yellow wire and B with a blue wire. I'm waiting to hear back from this guy for verification.

Do you still have the original harness? It ran with that harness didn't it? Get the mutimeter out and compare old to new. It may be a quick fix to change the wires around to the correct position. If your "rumor" is correct Cat usually remove those parts from circulation pretty quick.

[Smokin64]

PROBLEM SOLVED! CAT has a bad batch of engine harnesses for the 3126s! We switched the wires at the timing sensors and it started immediately.