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730Industries · 07-11-2023, **(Subject: spn 157 fmi 18 )**

(01-19-2023 )Rawze Wrote: Here is the correct way to test the rail. Seems no one does this any more properly and then does nothing but guesses at their issues, wasting moneys. Putting this here as a reference.

ref: http://rawze.com/forums/showthread.php?t...2#pid69262

So I've got the truck and started diagnosing it.

We cleared the code and drove it up here and the 559 code doesn't appear until i get into the throttle.

Cleared it once again and followed the above video for testing the pressure, and the pressure peaks slight above 29000, after shutting it off and watching it, it doesn't dip below 29000. Stays within 100psi of the final mark. For over 1 minute. For almost 3 minutes until i stopped observing it.

So if the truck is asking for fuel and its not losing any once its supplied.... is my issue the pump itself? If there was a leak and thats how the truck wasn't getting what it was asking for, then i should see it with this leak down test, correct? The pump was replaced a hair over 300k ago by the previous own, and there has been a plethora of work done to the fuel system.

As a final point, the fuel pressure hasn't dropped 300psi in the 6 minutes i've typed up this response....

Give me guidance and direction please. :)

tree98 · 07-11-2023, **(Subject: spn 157 fmi 18 )**

If you know for sure that your relief valve is in good operating condition, you could try unplugging the pump actuator and take it for a test drive. Unplugging it defaults to max pressure ALL the time.

730Industries · 07-11-2023, **(Subject: spn 157 fmi 18 )**

(07-11-2023 )tree98 Wrote: If you know for sure that your relief valve is in good operating condition, you could try unplugging the pump actuator and take it for a test drive. Unplugging it defaults to max pressure ALL the time.

I'm very new to all this with diagnostics. I just followed the video for the fuel rail test and it didn't lose any significant psi after 6 minutes. I know nothing about the relief valve. Is that part of the rail that was tested by that pressure test?

And so i understand you, you're talking about the bit on the top of the fuel pump? Thats the actuator? The truck is up on some jackstands right now for other work, so could i just unplug that actuator and run the rpms up? or would it need to actually go down the road for a real test?

Thanks for your guys' patience and help :)

tree98 · 07-12-2023, **(Subject: spn 157 fmi 18 )**

The relief valve is on the end of the fuel rail pointing at the radiator.

The fuel pump actuator is the only part of the fuel pump that wires are coming out of

You would likely need to drive it to get it into a condition where it's getting starved for fuel (if that's really what your problem is)

Rawze · 07-12-2023, **(Subject: spn 157 fmi 18 )**

(07-11-2023 )730Industries Wrote: ...
We cleared the code and drove it up here and the 559 code doesn't appear until i get into the throttle.

...

That is the exact symptoms for the fuel pump of total engine destruction scenario. The scenario that common rail ISX's get into where the fuel pump is sending metal shavings into the entire engine, destroying it completely, and in a hurry!!.

You have not pulled that pump apart yet and inspected its guts???..

Personally, I would have been in total panic mode and ripping that pump apart right away if it passes a rail test and only got fuel pressure codes when getting onto it hard like that. Seen too many engines become boat anchors (noting could be saved) over those fuel pump failures.

here is a fine example...
http://rawze.com/forums/showthread.php?t...9#pid15389

730Industries · 07-12-2023, **(Subject: spn 157 fmi 18 )**

(07-12-2023 )Rawze Wrote:
(07-11-2023 )730Industries Wrote: ...
We cleared the code and drove it up here and the 559 code doesn't appear until i get into the throttle.

...

That is the exact symptoms for the fuel pump of total engine destruction scenario. The scenario that common rail ISX's get into where the fuel pump is sending metal shavings into the entire engine, destroying it completely, and in a hurry!!.

You have not pulled that pump apart yet and inspected its guts???..

Personally, I would have been in total panic mode and ripping that pump apart right away if it passes a rail test and only got fuel pressure codes when getting onto it hard like that. Seen too many engines become boat anchors (noting could be saved) over those fuel pump failures.

here is a fine example...
http://rawze.com/forums/showthread.php?t...9#pid15389

This was my original thought, but the truck has been parked for 3 months about. No driving whatsoever. Just did the leak down test yesterday. So we’ll get the pump pulled off and inspected. :) I’ll keep you guys updated and be back for more once we’ve got it off and have more info.

Thanks!