CM2350 Code 4727

[windowrattler]

Have a truck that came in today. The story of what has happened over the past few weeks at the dealership has me kind of worried. He stated that he was getting a code for an injector. They replaced one injector and released the truck. As he was coming back from over the road he started to have issues and was getting a 559 code. He was able to limp it back to the dealership. They ended up replacing the hpfp head and the fuel rail pressure relief valve. The customer told me that it had broke a ceramic plunger. Something I certainly didn't want to hear.

Since that repair, in about a week or so of driving he has had code 4727 pop up on three occasions. Unfortunately the customer had flashed a different tune into the truck (PukeDits carb compliant hand held tuner, yes I know) and the freeze data and code were wiped but customer had the code written down.

First thing I did quick was a leak down test. Passed with flying colors. A few hundred psi of drop in a minute. Then we went for a drive and that is when I noticed what I believe to be the symptom. On decel fuel cut like coasting down a hill the fuel pressure continues to climb. It will climb up to 42k and stay there until back in the throttle. It did not pop a code during this though.

So my couple questions.

1. Fuel pump actuator operation. I believe the ecm sends power to bypass fuel back into the return. No power to the actuator would allow all fuel to flow into the pump.

2. Is there any type of check valves internal on the body of the pump that could block return flow back to the filter head?

3. The dealership had him convinced it was just the fuel pressure sensor. I 100% don't think it is. He wanted to just toss the sensor at it. If I'm loading up a parts cannon would I be crazy to replace the actuator as the most likely culprit?

I only had 30-40 minutes with the truck today and it will be gone before I'm back in state on Monday. I'm worried about this whole ceramic plunger thing but I'm not sure since it's been driven so much if there is really anything we can do besides address the issue we see.