2005 LLY Kodiak

[dirtballdiesel]

We've had a truck (2005 Kodiak) brought to us as a crank-no start issue, on first inspection it was apparent that someone had already been messing with it as harnesses were already open, intake and doghouse removed, and CCV hoses disconnected. The truck communicates with a scanner fine, and shows no codes. Acutal FRP shows stuck at 26106psi, and desired at 5,801psi. Commanding the regulator higher or lower makes no change, unplugging the FRP sensor makes no change, and the regulator on the CP3 pulsates/buzzes on & off rather rapidly. We've ohmed out the wiring from the ECM to the FPR, verified communication with the FICM, ran completely new wires from the ECM to the FPR to bypass any bad spots in the harness, all to no avail. Had a new ECM programmed to rule out the possibility of a bad ECM, still no change.

If anyone else has had symptoms like this, any additional diag help would be appreciated!

 

[2004LB7]

What pressure do you get with key on engine off? If it's still high then it's the sensor or related harness. If it drops down to a few hundred psi after a few minutes then it's the regulator or it's harness

 

[dirtballdiesel]

Rail pressure is stuck at 26,xxxPSI with KOEO. And even though the circuits from ECM to FRP sensor and FPR all ohm out OK, we tried running completely new wires to both to eliminate any issues with the harness. Still the same symptoms. Looking like our next step is to remove and disect the entire engine harness

 

[2004LB7]

Might be a bad ECM too

 

[Cougar281]

Might be a bad ECM too

Two of them? He said they programmed and tried another ECM to rule that out.

 

[2004LB7]

Two of them? He said they programmed and tried another ECM to rule that out.

Sorry, missed that.

Would look closely at the pins of the harness on both the ECM and sensor side

 

[2004LB7]

Rail pressure is stuck at 26,xxxPSI with KOEO. And even though the circuits from ECM to FRP sensor and FPR all ohm out OK, we tried running completely new wires to both to eliminate any issues with the harness. Still the same symptoms. Looking like our next step is to remove and disect the entire engine harness

If the ECM thinks the rail pressure is that high it's going to try and clamp down the pressure by increasing the regulator current. This can make the actual pressure too low to be able to start the engine. To see if the engine can start, you can unplug the regulator connector which will make it produce maximum pressure

 

[Cougar281]

If the ECM is showing 26106psi no matter what - pressure sensor plugged in, unplugged, KOEO after sitting a while, etc, and you've tried another ECM with the same results, it seems like a wiring problem. Unless 26106 is the open circuit value, similar to how -40 is the usual open circuit value for temp sensors... in which case it could be a failed pressure sensor... have you plugged another sensor into the harness to see what you get? You've said you ohmed the wires and ran new wires to the FPR, but have you checked for a short to ground or voltage with some other wire for the FPS, or ran fesh wire to the FPS?

 

[dirtballdiesel]

Yes, we've tried a new FPR (plugged in, and unplugged both), ECM, and repaired some bad wiring right at the ECM connectors. Our next step is looking like removing the entire engine harness and disecting it.

Voltage pulsates at the FPR pigtail and right at both purple wires coming out of the ECM pins when back probed. Continues to do so until the blue connector is unplugged from the ECM. Voltage quits pulsating at the ECM pins when the blue connector is unplugged.

 

[Cougar281]

Yes, we've tried a new FPR (plugged in, and unplugged both), ECM, and repaired some bad wiring right at the ECM connectors. Our next step is looking like removing the entire engine harness and disecting it.

Voltage pulsates at the FPR pigtail and right at both purple wires coming out of the ECM pins when back probed. Continues to do so until the blue connector is unplugged from the ECM. Voltage quits pulsating at the ECM pins when the blue connector is unplugged.

Not the REGULATOR, the SENSOR. The regulator is not in the equation if you turn the key on after it's been sitting and hasn't even been cranked but is showing 26k rail pressure. That's simply impossible. If the ECM is seeing the same value no matter what, something is not right. Like I said, I don't know what the open circuit value is for the fuel pressure sensor, but if what you're seeing is the open circuit value, it could be a bad sensor that's internally open. That's why I suggested plugging another sensor, not regulator, into the harness to see if you get something different (like 0 psi since it would have no pressure).

 

[2004LB7]

Please elaborate on this pulsing? Are you using a scope? Or just a DVM? The ECM uses PWM with varying duty cycle to control the FPR. Most meters are going to register this correctly and may show a voltage that doesn't reflect reality. Plus the "pulses" would be too fast for a regular meter. Some with the duty cycle function can at least display the %.

The best tool for the FPR diagnostics is a scope. A DVM is really only good for ohm testing the lines

 

[dirtballdiesel]

Not the REGULATOR, the SENSOR. The regulator is not in the equation if you turn the key on after it's been sitting and hasn't even been cranked but is showing 26k rail pressure. That's simply impossible. If the ECM is seeing the same value no matter what, something is not right. Like I said, I don't know what the open circuit value is for the fuel pressure sensor, but if what you're seeing is the open circuit value, it could be a bad sensor that's internally open. That's why I suggested plugging another sensor, not regulator, into the harness to see if you get something different (like 0 psi since it would have no pressure).

We'll try plugging in another FRP sensor before removing the engine harness, I was under the assumption that if the PSI value didn't change when unplugged, the sensor itself wasn't relevant. We also just found out that the truck quit showing oil pressure on the gauge shortly before this problem started.

 

[dirtballdiesel]

Please elaborate on this pulsing? Are you using a scope? Or just a DVM? The ECM uses PWM with varying duty cycle to control the FPR. Most meters are going to register this correctly and may show a voltage that doesn't reflect reality. Plus the "pulses" would be too fast for a regular meter. Some with the duty cycle function can at least display the %.

The best tool for the FPR diagnostics is a scope. A DVM is really only good for ohm testing the lines

I'll try attaching a video in another reply, but the regulator itself is buzzing on/off about 4 times per second. When you unplug it from the engine harness you can hear the FPR itself click loudly into its normal "KOEO" position.

We havn't "scoped" voltage at the FPR pigtail connector yet but will before removing the engine harness

 

[Cougar281]

We'll try plugging in another FRP sensor before removing the engine harness, I was under the assumption that if the PSI value didn't change when unplugged, the sensor itself wasn't relevant. We also just found out that the truck quit showing oil pressure on the gauge shortly before this problem started.

The sensor will only report the pressure that's in the rail. If the truck isn't running, and especially if it hasn't been running for say a day, there's no way it would still have 26k in the rail when you first turn the key on without cranking. I'm not even sure it would be able to make 26k while only cranking. So If I'm reading things right, it always is reading 26k no matter what - first key on before cranking, after cranking, sensor unplugged or plugged in - that suggests that erroneous data is being received by the ECM, one way or another. Or am I missing or mis-reading something? Now, if you turn the key on and it's at 0 or maybe a few hundred PSI, then you crank it and it increases, then it starts and then shoots up to 26k and stays there, yes, that would likely be a regulator or regulator circuit issue. But if it's reading 26k no matter what, it's most likely something related to the pressure sensor that's causing the reading - either the sensor itself or a wiring issue. But I'd also suggest that even if there's a problem with the sensor or its circuit, that likely wouldn't prevent it from starting (I mean, if it thinks it's at 26k, and wants 5.8k, maybe it's pulling back the regulator so much it's zero, but if you unplug the regulator, which it sounds like you've done, that voids anything the ECM might try to command and it should still start). If the regulator is unplugged, the truck will still start and run 'fine', just noisy.

Since someone was monkeying with it, are the cam and crank sensor connectors plugged into the right places? They can be swapped, and if they were, that would cause a crank no start condition. Since we're talking about a LLY, the FICM is another failure point that could cause a no start.

 

[Bdsankey]

The issue is NOT IN THE FPR, this is either wiring to/from the rail pressure sensor or an internally shorted sensor. There is an off chance of an ECM issue but I doubt it.

Have you changed the rail pressure sensor or unplugged it to see if the value changes?

There is zero way for the FPR to skew the key-on-engine-off rail pressure reading.