CP3 electrical issue, help needed please

[stacks04]

there should be some current to that wire, the amount depends on the pressure switch reading as said before. if you have nothing then you need to view the diagram above find the terminals at the ecm and ohm the wire from the ecm plug to the jumper plug near the intake tube. i am thinking though never tested that the ecm will default to a set parameter to limp the truck if it loses a determining factor in delivering reg current. meaning i dont think the ecm will just cut the signal from the it to the reg because it lost another input. the "purple/white" wire from the above diagram is actually brown/white. i had a squirrel eat my engine harness last week

 

[TrentNell]

Nope talking about the three pin connector off of the main engine harness that goes to the valley CP3! With the key on, my LBZ and two other trucks that were tested had 12v., 3v., 0v. Nates truck is not getting the 3v. (center pin on harness) to the CP3!

Unless i am remebering way wrong , the CP3 regulator plug is ony a 2 wire plug ? or are you talking about the rail pressure sensor ? I dont know were the sensors are at on the LLY's. To my knoledge the sensor is a 3 wire plug and the reg should only be 2 a wire ?

 

[rgullett83]

Unless i am remebering way wrong , the CP3 regulator plug is ony a 2 wire plug ? or are you talking about the rail pressure sensor ? I dont know were the sensors are at on the LLY's. To my knoledge the sensor is a 3 wire plug and the reg should only be 2 a wire ?

At the CP3 it is a two pin connector, but there is another connector farther down the line that has three wires( the extra is just ground). I was suggesting checking the reluctor wheel and crank sensor, since the ecm references crank signal to determine rail pressure. Especially since the comment on belching white smoke. And seeing how the motor has been out and apart, the reluctor wheel may have been damaged. Just a thought.

 

[RPM Motorsports]

Unless i am remebering way wrong , the CP3 regulator plug is ony a 2 wire plug ? or are you talking about the rail pressure sensor ? I dont know were the sensors are at on the LLY's. To my knoledge the sensor is a 3 wire plug and the reg should only be 2 a wire ?

Trent, you are correct on it being a two pin on the CP3 side, there is a 6" removable section between the two pin side (Cp3), and the three pin side (Harness).

 

[rgullett83]

Have you given any thought to inspecting the reluctor wheel yet?

 

[SHOTZY]

Have your crank and cam sensors ever been removed at the same time? I ask this because they look identical but the clocking of them are slightly different. It took 2 weeks after work for my buddy and I to find this. Truck would fire and shut down. I was actually able to drive it to the store and back with slight issues one time. Rail pressure did weird stuff as well. Good luck.

 

[RPM Motorsports]

Have you given any thought to inspecting the reluctor wheel yet?

Would that make the ECM drop the 3v. @ idle signal?

 

[stacks04]

Would that make the ECM drop the 3v. @ idle signal?

techincally it should not. i thought the crank/cam sensors where for injection timing, and i thought the fuel was based on throttle/mm3 command.

 

[rgullett83]

If it is receiving a skewed signal from a damaged reluctor wheel/crank sensor, or swapped cam/crank sensors, that can change what the ecm chooses for the actual rail pressure. After reading this, I have seen a very similar condition on an LBZ, that had just been repaired after a cracked piston replacement, the motor came back out and apart, and the reluctor wheel was replaced, and all was good after that. Just a thought. Also when you said it will occasionally belch white smoke that tells me that the injection timing is off.

 

[stacks04]

If it is receiving a skewed signal from a damaged reluctor wheel/crank sensor, or swapped cam/crank sensors, that can change what the ecm chooses for the actual rail pressure. After reading this, I have seen a very similar condition on an LBZ, that had just been repaired after a cracked piston replacement, the motor came back out and apart, and the reluctor wheel was replaced, and all was good after that. Just a thought. Also when you said it will occasionally belch white smoke that tells me that the injection timing is off.

true, but it should not default to zero voltage. it is very odd that there is no voltage in that circuit.

 

[RPM Motorsports]

We had time to Ohm out the wiring today, and all checked out ok @ (4 Ohm's). Just for the hell of it, we pulled the rail sensor out of my truck and installed it in Nates Rig. Nate has an ear to ear smile right now, can you guess why:happy2:. Time to order a sensor, because you can't keep mine.

 

[PhilsLB7]

Glad to see you guys finally got this one figured out! :thumb:

 

[NastyNate]

:thumb:

 

[stacks04]

Thats odd and good to know. I would never guess the ecm would kill the signal voltage. I will file that. Glad you guys found it. Were you guys getting a reading from the rail sensor?

 

[rgullett83]

We had time to Ohm out the wiring today, and all checked out ok @ (4 Ohm's). Just for the hell of it, we pulled the rail sensor out of my truck and installed it in Nates Rig. Nate has an ear to ear smile right now, can you guess why:happy2:. Time to order a sensor, because you can't keep mine.

Excellent I am glad you have this figured out and that this was a simple fix:coolspot:

 

[rebel7777]

I bet the fuel rail pressure sensor showed no pressure and the FPR demanded no pressure therefore no signal.

Did you ever compare your actual vs demanded fuel pressure?

 

[stacks04]

the fpr would not command anything. it is there only to make changes in pressure. the ecm would be the one to command pressure changes.

 

[rebel7777]

the fpr would not command anything. it is there only to make changes in pressure. the ecm would be the one to command pressure changes.

Sorry, I meant the fpr was the one that makes the changes based on the ecm turning it on or off.

I only asked about the actual vs demanded as this would have shown a bad fpr or bad pressure sensor.

 

[stacks04]

i got you man.

 

[SHOTZY]

Glad you guys found it! I'm familiar(sp?) with the ear to ear smile. It took my buddy and I a lot longer to find my issue though.