So, before it dies, the fpl PID (fuel pump low) changes from not low to low?

 

No,, Kaya, it goes from not low to low as it dies. I fixed the frame pump to run all the time with a jumper wire and the truck still stalls and because of the jumper wire, the pump is running when it stalls.

FTR, When this little experiment failed, I returned the wiring back to normal to resume testing.

 

Do you use any additives?
That is not a pump command from the PCM. That is supply pressure being lost.
What I would do is install a vacuum gauge teed into the supply line between the tank and low pressure pump.
This will tell you if there's a restriction in the tank

 

Hi Kaya, I teed in at the sending unit and found one inch of vaccum while pump was running. I had both lines off at first and noticed that as soon as I turned the key on, fuel was returning very quickly from the return line to the tank.
No, I dont use additives.
BTW thanks for getting involved

 

you need to observe vacuum as it dies. you are teed into the lpfp supply?
and sorry, just want to be sure, it goes from not low to low before the engine dies?

 

Modified fuel volume control solenoid

Would one of these benefit a 6.7 with low fuel pressure problem when there's no obvious cause for the p0093 code?

 

Low fuel pressure = somewhere in the fuel system something is plugged or the high pressure pump is going or a sensor is bad

 

Thanks for the comment and I am sure you are right. I am trying to find out which component is causing the problem.

 

The vacuum disappeared as soon as the engine died and it went from not low to low at the same time.
On the scanner, the drop in high pressure can be observed to drop as the engine winds down to 0 rpm. It's like it only lost high pressure "because" it lost low pressure first but like I said, when I tripped the low pressure pump to run all the time, the drop in high pressure was the same.

 

I have a question.. On my scanner with key on engine off, frame pump running, I see 0 lbs of fuel pressure. I also know about the fuel pressure switch on the low pressure feed pipe to the high pressure pump.

Do you know at what pressure this switch activates and deactivates the system while the engone is running?
(Learned) This switch is designed to deactivate the fuel supply when the low pressure does not prescribed level.

 

Lets not spread out your topics, thread merge.

 

Not sure what the threshold is for the switch. But 39psi is quite low. I usually see in the area of 80psi. For pressure, you are testing on the supply side, after the lpfp?
How many inches did vacuum reach immediately prior to dying?

 

39 lbs is what the scanner reads. I am going to tap into the pressure switch port after the fuel filter towards the high pressure pump so I can use a mechanical gauge. I wont have the adaptor I need till in the morning.

I had 1 inch of vacuum during the entire time the truck was running. As soon as the engine stalled, vacuum went to 0.

I'll try to stay on topic from now on.

 

Let's not mask the issue. Let's resolve it

 

I agree. But, all I can do is eliminate possibilities until I find the culprit..

I was actually hoping would read this thread and see all the thiings that have not fixed the problem and say "Hey! I had that happen to me once and it was XXXXXXX causing it"

 

answers to post 12, please

 

Ok, so 39psi is the frp reading. I thought you already had a gauge on the supply.
I await your supply pressure readings

 

Ok, I made an adaptor for my fule gauge...
1.KOEO fuel pressure reads 60 lbs.
2.KOER fuel pressure drops to 55 lbs. ( Note) I use the PTO to increase engine speed to 1400 rpm. fuel pressure stays steady at 55 lb.s until it shutsdown by itself.

3. Cycle key from on to off to on again, fuel gauge jumps to 75 then 50, then 75 to 50 several times within ten seconds then levels out at 60 before timeout.
4. Cycle key again and crank engine. fuel pressure jumps to 75 then levels at 55 at idle again.

5. I also measured fuel pressure leak down.
(a) KOEO until timeout, 60 to 30 instantly and 25 seconds from 30 to 0
(b) Engine running until stall, 55 until about 3 seconds before stall (rose to 60), then instantly to 0 when stall occurred. (note) I did the (b) test 3 times and every time, the rise of pressure came before the fall.

I hope I gave you enough info to go by

 

are you absolutely positive you were measuring vacuum correctly? this is very important. your gauge must be teed into the supply line between tank and pump, and monitored for a spike just prior to dying.

 

All I noticed was the drop in vacuum as soon as the motor shut off. Am I looking for a large spike, that is to say, like one caused by something clogging the pickup tube in the tank?

My gauge is teed into the supply line at the fuel tank sender.

 

Exactly. A spike

 

No spike. I was looking for one too. I understand how the diesel engine works and the fundamentals. This little querp in this 6.7 has me stumped since I haven't seen any evidence of low pressure. The only tool I have to test the high pressure side is my snap on scanner.
It seems that every part has been replaced except the fuel volume solenoid.
The truck died and one mechanic replaced the high pressure pump and it still wouldn't start.
When I got the job, I found that when I exercised the fuel pressure control valve with the scanner, the test would abort at 20% down and 80% up.
I replaced the pressure control valve and it cranked like it had never had a problem. On the first road test, this problem I'm dealing with, showed its ugly head, so here I am.

 

The vcv would have been included with the hpfp.
If the fpl PID is changing from not low to low, as you've described, prior to the stall, the issue should be in the supply side.
Satisfied it's not a restriction, next what I'd do is install a section of clear half inch line immediately after the lpfp, on supply side. Checking for aeration.

The line i made actually has a tee to test pressure, aeration, and if installed between tank and pump, vacuum. All in one.
You will need a male and female quick connect fitting to make this. I robbed them from a core contamination kit. Then crimped them to a foot long section of clear line.

 

The hard plastic u shaped supply line at the secondary fuel filter. I believe it has a male and female end and is fairly cheap from Ford. You can buy that, slit the ends, and remove the barbed fittings to make the line.

Edit: come to think of it, I think that line has 2 female ends. Could zip cut the end off an old secondary filter tho if you have one

 

Edit: come to think of it, I think that line has 2 female ends. Could zip cut the end off an old secondary filter tho if you have one


That's where I got the nipple for my vacuum tester....

There are more tiny bubbles than I can count in the clear line as the pump runs... I have the tubes made into a circle to keep from kinking the tubing. When the pump shuts off, all the bubbles collect at the top of the circle where the tee in installed.

I pulled the sender and found the accordian line for the suction side loose at both fittings. I replaced it with new hose with clamps. There is an occasionnal stream of bubbles after letting it run for 15 minutes.

Now I notice the pump whining and my pressure gauge is rapidly fuctuating between 55 and 65, never steady, whether engine is running or not.
When I engage PTO for RPM increase the gauge will fluctuate from 55 to almost 70, one time it hit 80 for a split second but, after the engine stalls, I have fresh stream of bubbles for a minute after cranking again.

Can air enter the return line without the suction side being at fault? There are no leaks on the suction side of the sender and no leaks visible to suspect the line going to the pump. The reason I ask is because the bubbles dont start until a few minutes after the truck has sat for a bit, if it didn't stall before I let it sit.. driving me batty

Results from repairing leak at sender= gauge going crazy and very few bubbles until rpm increase

 

Recap of the days quest for "Kaya". I got the supply line(the clear tubing) to the point where no bubbles existed even when the pump shut down the fuel stayed in the line. After this, the fuel gauge went practically stationary, give or take 5 lbs but averaged between 60 and 65 lbs. No more big swings of the needle. I attribute this to the fact that all the air is missing from the supply fuel.

Now, though I hoped it was fixed, I can run the PTO for almost 10 minutes before the stall where before, it would only take 2 minutes before stall. Now, when it stalls, it still sets the same p0093 code but, I got the read a difference between the actual and desired on the scanner. It was at 1900 rpm, the desired and actual were both at 11,542 lbs and suddenly the actual dropped to 1,227 and the low pressure dropped from 63 to 0 instantly.

What are the chances that the aerated fuel has damaged the HPFP?

 

Hello Kaya

Hey Kaya, Did I run you off? I was hoping I could get some help to finally come to a conclusion on this problem.

I'm getting the feeling I said something wrong. I apologize if I did....

 

Hey Kaya, Did I run you off? I was hoping I could get some help to finally come to a conclusion on this problem.

I'm getting the feeling I said something wrong. I apologize if I did....

Haha. Sorry buddy. I lost track of this thread.
So you've confirmed that there is NO aeration just PRIOR to the stall?

I think you're focusing on the wrong side of the system by going after the hpfp. The hpfp will not cause the supply side to drop to zero. If the key is on, the supply should remain stable.
Does the supply pump remain running while the zero reading is apparent, immediately after the stall?

 

Using data display to find a pressure related problem

Is there anyone here who can help me with a fuel related problem on a 2011 f550 with the 6.7?
I am getting a p0093 code after it stalls. I have noticed a slight drop in the duty cycle % of one solenoid and am wondering what this solenoid was intending to do when the stall occurred.
Dellis

 

Interested to know so I'll comment to refresh the topic. My truck will randomly shut down and have the P0093 code. Only does it once a month or so. Strange issue to say the least. I had that code and the P228F but after throwing a fuel pressure regulator at the truck, I'll only get the P0093 soft code...

 

HI dsmracing1,

Yesterday, while watching the scanners data display, I finally saw something happen right before the stall occurred. There was a point where the desired pressure increased and vollume control solenoid was given more duty cycle (.eg from 37 to 60) while at the same time I saw no increase in pressure. On the graph, the time elapse was only about 3 seconds, but the stall, so I am presuming) happened because the pressure did not increase.

I was hoping to find someone who is familiar with the 6.7 so I could see what normal pressure should be at given rpms. 600 and 1800. Do you know?

 

"It's very strange to say the least. It feels like a complete PCM shut down as there is no notice that it is about to happen."

Well, I had to take a break so I could catch up on some other pending jobs. Now I'm back and will be removing the HPFP today.

Whether it fixes or not, I'll post some results.

 

You have to reset the high pressure fuel tables after replacing an hpfp on these. As well as min/mass adaptation.
So reviewing this thread again, sorry, beating a dead horse, but we must be clear, does the supply drop off PRIOR to the stall?
It can be seconds or milliseconds. But is it prior?

Unfortunately, I don't use injector balance readings on a 6.7 powerstroke, so I have no experience with that. But if your hp fuel tables and min/mass tables haven't been reset, then I wouldn't be looking at them anyways.