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.

[PolishHammer]

There is a relief on the back of the fuel rail that would open far before 42000 psi. I would what were the pressure when normal acceleration and driving ? Or even cranking and stay up ? No code just means the sensor voltage is not out of spec but could still be reading incorrectly. The high pressure pumps with ceramic are a known failure point I believe they are upgraded now.

[windowrattler]

While watching fuel pressure desired versus actual it always looked normal until the the truck is in fuel cut. The pressure relief was changed by the dealer when the pump head was done. That relief valve certainly could be opening and that is why it holds 42k psi and stops climbing. I recently had a truck with a valve opening at @38-39k psi that was causing the truck to pop a code and derate so I know that relief opening is higher.

[Rawze]

Fault code 4727 = Fuel rail pressure is higher than expected (above normal).


Just some random thoughts...

== Could be cold fuel (and engine still warming up) that builds pressure/expands rapidly (cold climates) and expands.. then throws the engine into fuel-pedal pause for a few moments until the pressure bleeds off. It is a normal protection in the system. This scenario is actually quite common ... however .... once fuel temps stabilize and engine warms up good, this should go away.

== Could be the regulator at the back of the pump is acting up, not kicking out properly.

== could also be a leaky injector that is only leaking pressures back into the fuel system under higher cylinder pressures (but this would be quite rare if it is passing injector leak-down tests.).


=== You need to also get that garbage-can tuning box off that engine ASAP too.. and flash it back to its factory programming.... throw that engine killing box right into the garbage can where it belongs!.

=== Make sure the program matches the engine ser# exactly too. Incorrect program can command the fuel system incorrectly vs. actual hardware.

[windowrattler]

Figured I'd update the ending of the story. We ended up putting in the fuel pump actuator. After this the driver reported fuel mileage back to normal and the code would pop less often but was still there. I racked my brain for a solution. I poured through some cummins training documents and found my culprit. The fuel actuator doesn't mount into the fuel pump head, there is a fuel actuator adaptor/block. In this block on older ISX's (2250 block we had around) there is an venturi air bleed. On the later years it is a small 300 micron drilled hole. In the XPI training slide show it specifically points out this small passage and that when blocked it could cause high rail pressure codes during engine decel. We replaced this block and the issue is resolved.

[Rawze]

Thanks for sharing this. I am sure it will help others out there in the future.

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(something related but for older engines) ...
The older CM570's, CM870's and CM871's have a similar orifice in the IFSM to bleed off air and excessive pressure due to expanding fuel, etc. too. If it gets dirty/clogged, it causes hard starts, over-pressure within the head itself past the fueling/metering solenoids, etc. in the head itself.