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Old 07-24-2021, 02:39 PM   #1
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High fuel pressure reading

This AM I was fueling up, I had let the coach run since I hadn't been on the road that long and thought getting it to temp was a good idea.
I pumped ~34 gallons of fuel an hit the $100 limit. Swiped another card and as I was starting to pump diesel the engine started to sputter and stumble and puffed black smoke out the exhaust. Quickly finished pumping fuel.

No lights came on the dash and I checked the VMSpc diagnostic display. It showed.


ENG PID 94 10 Fuel Delivery Pressure Abnormal Change 7/24/21 7:58
ENG PID 94 0 Fuel Delivery Pressure High Reading 7/24/21 7:58


Both codes were inactive. I started driving with my fingers crossed. Drove about 350 miles and the engine didn't act up a signal time.



I do have a FASS transfer pump installed, not sure if it putting ~16psi to the injector pump might have caused the problem. It never did this before, have ~4500 miles on the rigs since the FASS installed.



Any suggestions???
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Old 07-24-2021, 03:25 PM   #2
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Which pump did you install?
Is the pressure adjustable?

I used a airdog, pump only, no filters. Has an adjustable pressure setting.
Mine runs at 12 psi at idle.

The old system had basically zero pressure, so my mind says anything is more than what it had.

EDIT, seen you used the pump with filters...odd that it would start this while you were fueling at idle.... maybe 16 is to much? What are others pressure at?
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Old 07-24-2021, 03:53 PM   #3
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I installed the FASS pump with two filters. I also left my primary and secondary filters in place.
When running it usually is ~13ps, doesn't fluctuate too much.



I ran fine the rest of the day, boost was +23psi on harder pulls. No stumbling or lack of power.
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Old 07-24-2021, 05:49 PM   #4
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This is curious.

I would think it has to do with the main CAPS accumulator and injection pump, but cannot understand why. Clearly, from the stumbling and black smoke, excessive fuel was apparently being injected so a bad sensor is likely not the cause.

The lift pump, in your case the FASS pump, only supplies fuel to the main pump accumulator. That is where the fuel return line carries excess fuel back to the tank. The injector pump is where the fuel from the accumulator is taken, pressurized, and eventually sent to the injectors. My understanding of the system does not make a connection between your lift pump pressure and excessive fuel flow from the injectors, as the two are separated by the accumulator and a return line.

Now, here's the kicker. My Quickserve parts diagram shows the fuel pressure sensor located in the fuel accumulator. This points to excessive pressure within the accumulator may be the factor, but I don't know enough of the mechanics as to how that would lead to more fuel being injected by the injector pump. (But what do I know?)

Disclaimer, I am not a CAPS expert nor diesel mechanic, but if you truly have an issue, and this was not just a one-off glitch, you may be facing a problem with your main CAPS system. Just be aware, and watch closely for any similar events. It is possible that they have already occurred but you did not notice them while driving. Hard to know.

For now, chalk it up to the FASS system overpowering the return line due to engine idling and not enough fuel being drawn into the injector pump. Maybe avoid fueling when idling for a while, then try and repeat the incident on another occasion. If this proves to be the case, it is the first time it has been reported, to my knowledge, but maybe your fueling event was somehow unique.
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Old 07-24-2021, 06:45 PM   #5
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Thanks Larry



I had not seen this before so hopefully it is a one off occurrence. From now on I'm not going to let the coach idle for an extended period of time and I'll see if that solves the problem.
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Old 07-24-2021, 07:10 PM   #6
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Quote:
Originally Posted by Ljwt330 View Post
This is curious.

I would think it has to do with the main CAPS accumulator and injection pump, but cannot understand why. Clearly, from the stumbling and black smoke, excessive fuel was apparently being injected so a bad sensor is likely not the cause.

The lift pump, in your case the FASS pump, only supplies fuel to the main pump accumulator. That is where the fuel return line carries excess fuel back to the tank. The injector pump is where the fuel from the accumulator is taken, pressurized, and eventually sent to the injectors. My understanding of the system does not make a connection between your lift pump pressure and excessive fuel flow from the injectors, as the two are separated by the accumulator and a return line.

Now, here's the kicker. My Quickserve parts diagram shows the fuel pressure sensor located in the fuel accumulator. This points to excessive pressure within the accumulator may be the factor, but I don't know enough of the mechanics as to how that would lead to more fuel being injected by the injector pump. (But what do I know?)

Disclaimer, I am not a CAPS expert nor diesel mechanic, but if you truly have an issue, and this was not just a one-off glitch, you may be facing a problem with your main CAPS system. Just be aware, and watch closely for any similar events. It is possible that they have already occurred but you did not notice them while driving. Hard to know.

For now, chalk it up to the FASS system overpowering the return line due to engine idling and not enough fuel being drawn into the injector pump. Maybe avoid fueling when idling for a while, then try and repeat the incident on another occasion. If this proves to be the case, it is the first time it has been reported, to my knowledge, but maybe your fueling event was somehow unique.
Sounds logical... I've never seen a high fuel pump pressure DTC on a caps engine....and I've seen many transit buses with that setup.

I wonder if the OEM lift pump bypass relay or power to relay setup "hiccuped" at a time the lift pump should have not been on?


fwiw, I don't let mine idle at all when I step out, I use the cruise button and raise it to about 1100 rpm.
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Old 07-25-2021, 06:18 AM   #7
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Fuel going into the tank can swirl around and cavitation can occur. With the engine running it sucks up this very foamy fuel and starts to stumble. It depends on where the pickup tube is In relation to the filler. Seen it before on several semis. If you put fuel in slower you may be able to leave it running.
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Old 07-25-2021, 06:46 AM   #8
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I cannot help with your problem but why is the engine running while fueling ? In many jurisdictions that is considered a fire hazard.
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Old 07-25-2021, 10:28 AM   #9
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Jacwjames,
There have been so many threads about FASS installations that it's impossible to keep straight. Given that, I've had a couple of thoughts.


First, did you by-pass the lift pump completely when you installed your FASS system? If so, nothing about the old lift pump could have caused the incident. If not, there is a possibility.


Second, did you add a dummy solenoid to fool the ECM into believing the lift pump was still there? If so, additional pressure from a glitch could not activate the old lift pump. If not, that is a possibility.


Third, did you add the FASS filters to your system? If so, they are supposed to remove all the air in any fuel that is discharged. If not, it may be possible that excessive air was passed into the accumulator.


Fourth, the symptom you witnessed from the engine, stumbling and black smoke, may have been due to excessive air, then quick recovery with a surge of fuel. This may be what always happens when we hear these reports, but very few get to witness the events at the exhaust pipe because they are driving.


I know this doesn't answer to the cause, but it could eliminate some possibilities.
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Old 07-25-2021, 06:16 PM   #10
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Ljwt330


Yes I bypassed the old lift pump other then the return line.

Yes, i did put in the relay to fool the ECM
Yes, the Fass System I installed does have 2 filters and is suppose to remove air.


When the engine stumbling started the tank was almost full. I only put in another `15 gallons. But with the recirculation of the fuel it could have put foam/air into the tank. The pickup tube is on the other side and it goes to the bottom of the tank.



Drove about 250 miles today without a problem.
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Old 07-25-2021, 06:34 PM   #11
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Quote:
Originally Posted by jacwjames View Post
Ljwt330


Yes I bypassed the old lift pump other then the return line.

Yes, i did put in the relay to fool the ECM
Yes, the Fass System I installed does have 2 filters and is suppose to remove air.


When the engine stumbling started the tank was almost full. I only put in another `15 gallons. But with the recirculation of the fuel it could have put foam/air into the tank. The pickup tube is on the other side and it goes to the bottom of the tank.



Drove about 250 miles today without a problem.
Well, everything has been eliminated except the FASS system. Having never heard of this before points to an unusual event due to an atypical fueling situation.

However, there’s more to consider, especially regarding the pressure sensor. Complex, but understandable. Read the pdf in the following link for insight.
https://www.dmcpubs.com/pdffiles/873.../Sect10C12.pdf
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Old 07-25-2021, 06:42 PM   #12
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Yup, right now the coach seems to be running fine. No more fault codes.



I'm headed home and will change the primary filter on the FASS system and see if there is any signs of contamination. When this happened I had +3600 miles on the FASS system. I would have thought if there was a problem there I would have seen something before now.
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Old 07-25-2021, 08:54 PM   #13
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Yup, right now the coach seems to be running fine. No more fault codes.



I'm headed home and will change the primary filter on the FASS system and see if there is any signs of contamination. When this happened I had +3600 miles on the FASS system. I would have thought if there was a problem there I would have seen something before now.
In your free time, I really suggest you read the pdf in the link. Lots of diagrams and part indetifications. The CAPS system can produce the symptoms you had that are precursors to main pump failures or simple bad connections to the pressure sensor or injector control valve. Getting familiar with how the parts interrelate will help.

My point is, monitor your engine performance closely from now on. Any repeat, especially after changing fuel filters, is a red flag, IMO. I really can’t see how the FASS could be responsible.
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Old 07-26-2021, 05:58 PM   #14
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I've had a Silverleaf VMSpc since 2013 and have laptop mounted to monitor the engine performance. I'm anal about being able to see the main engine and transmission perimeters. So I have that pretty much covered.



Drove almost 600 miles today without a problem. No issues with the engine at all and I was passing most semis going up grades. Couldn't complain about the performance at all.



I'll look at the information in the link. I've downloaded the entire service manual for my engine off of the Cummins Quickserve site but haven't had time to look at regarding my problem. Now that I'm home I do some reading.
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