With respect to my friend Nicmike, that's a little counter-intuitive. I have seen O-ring leaks between the oil and the fuel go completely the other way: The ICP pushes the fuel pressure up... but it's the ICP that sags. I have even seen people here and there call the ICP "fuel pressure" - which is almost correct, but not quite the same thing.

I'm not saying O-ring leaks alone aren't going to cause low fuel pressure - but I'm struggling to wrap my head around a root cause. A bad bottom O-ring would allow the fuel pressure to escape into the cup, but the cup should eventually equalize in pressure - unless there is a bad copper washer to go along with it. A bad copper washer would introduce combustion pressures into the cup - and slide right past the bottom O-ring. We're back to spikes of fuel pressure because the fuel is surrounded by pressures much higher than 60 PSI.

Now... take out the integrity of the cup, and the low pressure of the coolant is very inviting for the incarcerated fuel pressure to escape.

You mentioned swapping the sticks. Did you try the O-rings only before swapping the sticks?

 

No, I did not try only o-rings first. I had my injectors flow tested and 5 of the 8 failed for one reason or another. Plus a few had bad o-rings to start.

Part of my struggle is I am relaying all of this information to my mechanic, and he is trying to figure out the problem at the same time.

 

Sorry for the confusion there. I was curious if Nicmike's fuel pressure problem was possibly from the bad injectors themselves.

In your case - I strongly suspect fuel pickup issues.

 

Thanks @Tugly. My plan is to drop off my Excursion back with my Mechanic and have him check every part of the fuel system, including vacuum test it, and read everything you suggested above. Here are some pictures of the fuel filter connections. I'm going to have him get rid of the quick connect fitting. What's the best way to do this?

 

I ran 3/8" hose from the tank sending unit directly to the PS120 and then to pump. At all connections to the pump, PS120 and tank I used fuel injector hose clamps (double on the pump) and gasoila thread sealant on the PS120.

This thread has a bunch of pictures from my install, but the ones you are really interested in are below.

https://www.ford-trucks.com/forums/1...ne-almost.html

Fuel pump inlet



PS120



Sending unit after modification




Since doing this tank/fuel mod the truck idles and drives at speed much quieter. In addition, I increased the OEM tank capacity by 7 gallons from 26 to 32 with no puking each time. As an added bonus, I widened the fuel port hole to accept "big rig" pump nozzles.

 

Sous, when you switched hose and clamps did you cut anything off of the inlet or did you just slide the new hose on and clamp it?

 

If you mean the inlet to the pump, I removed the quick connect and then slide the hose on the inlet, then clamped down. As you can see, I used some sort of sealant (yellow in color in the pictures) on the ends of the hose after clamped, but cannot find the name or product now. I don't think this was a necessary step, but figured it could not hurt at the time. The blue colored stuff is loctite as I did not want to bolts backing out from the vibration of the pump or frame.

 

I see it. It's right there. Smack in the middle of the picture, there is a vacuum leak. The pump has it going on with dual clamping, using fuel injector clamps - then there's that pitiful single worm drive clamp on the filter.

I wouldn't take it to the mechanic until after you've beefed up the clamping situation with your prefilter. Once that's done - evaluate if you need to take it further.

 

Yep, I did, thanks. That glue looks like liquid nails that they use on drywall, but I'm sure it's not.

 

Isn't that filter on the outlet side?

 

I hear what you are saying, Rich. I can only surmise that, since the pressure sensor is not in line with the fluids exerting pressure on it, that it is not "sensing" the full effect of the higher pressure pushing back into the line. It is kinda in a nook off the side of the fuel bowl. In my mind, I picture it like an eddy current in a river. I could be totally wrong on that mental image. Wife would say I am wrong for sure.

There is no question the oil was getting into the fuel filter...and fast. The drop in pressure usually did not last more than a few seconds in my case, because this isn't a hot rod truck I drive around for amusement. I rarely need to dive into the skinny pedal hauling kids around the countryside. I only noticed the problem because I installed a fuel pressure sensor at the same time as the hutch mod, FRx and fuel bowl mod. I did not replace the o-rings on the injectors, because I knew I was getting new-to-me injectors in the not too distant future at the time.

The problem is completely gone with new injectors/o-rings. Nothing else was done when the problem went away. Prior to that, I checked every single thing that was mentioned in this thread...and then some.

 

Yes, that is the filter on the outlet side. Does the filter need double clamping? I paid my Mechanic to install the RiffRaff Hutch kit, and looks like he only used some of the fuel injection hose clamps, and a few worm gear clamps. I don't think I have a way to see what the clamping situation looks like on top of the fuel tank unless I were to drop the tank. I am assuming that the top of the fuel tank needs double clamps as well?

I am going to add double clamps where I can get to, and check to make sure the FRx spring is seated correctly.

 

If the filter is on the OUTLET side of the pump, it shouldn't be sucking air. If there is a leak, it would be FUEL coming out

 

Forgive me, I just skimmed the posts today. Are you sure that filter is capable of diesel flow @ 50 + pressure?
As a trouble shooting test, remove that filter and install a wix 33972 or another disposable filter that is diesel rated. See how it responds.

 

The filter is sold by RiffRaff, so I would have confidence in using it. Although, I decided to go with the PS120 as mentioned before because it is the closest to matching the OEM in tank strainer.