12 valve fuel pressure problem that a few diesel shops couldnt explain

[32valveturbo]

Good evening and thanks for taking some time to read this. I'm new on here, please forgive me for any mistakes....... I've searched Google and a bunch of other forums including this one, joined the searched about 10 pages of posts, called a few experts and have still come up short......so here goes,


'95 12 valve with around 155,000 miles......bought the truck used about 4 years ago to put in my Excursion.......did the conversion.......new fuel lines, draw straw in the tank, fuel cap vented, new fuel filter and oil filter.......primed it, fired right up after sitting in the garage taped up for 4 yrs.......ran great, gave it more fuel via the usual stuff, 30 psi of boost, light haze at WOT 18 mpg .......awesome...........9,900 miles later, I'm towing steady cruise about 75 mph and I feel the truck lose a little power and then come back........so I make sure my foot is steady on the pedal and I watch the gauges.......boost goes from 15 to 10, EGT takes a second then goes down also......boost comes back and then EGT goes back to normal..........I was real busy with work so over the next 2 days it progressively worse.........
so, I put a mechanical fuel pressure gauge on the P Pump inlet with a snubber and 36" of fuel line so I can see it from the cab.......truck starts and does everything (except the random power loss) it did for the last ~9,900 miles.......Fuel pressure ZERO!! ........ So, I install the tork tech OFV, new lift pump, delete heater, clean screen, check elbow hose for cracks, fuel lines for cracks/leaks..........crack the OFV and hand prime it till fuel comes out than tighten it.......she fires right up........fuel pressure now 20 psi, awesome she fixed (not really).........watch the gauge for a few seconds and it goes from 22 - 15psi.....then 22 - 10 psi......then 17 - 5psi......back to 22 psi then down to 2 psi.......back to 20 and steady.........for a minute then more of the same......so I guessed
maybe its got a little trapped in there and just needs to work its way out......let it idle for 30 mins......go drive it.....no change......everything happy then fuel pressure drops to almost ZERO......truck falls on its face about to die, I ease up on the throttle pressure comes back and all is good for a minute or two...........go home double check everything, pinch off return line and pressure goes to 40 psi......change back to OEM OFV.......does the same thing......switch back to tork tech OFV and fully pre load the ball.....now about 25 psi at idle but still wild swings to the low side.........pinch off return line 40+ psi.......quick drive with the return line pinched.....truck is back to awesome.......fuel pressure however is slowly rising the more I drive and at one point hit 80 psi so I quickly took off the vise grips .........problem back again.........I know this was long and I appreciate your time and effort!!! Thanks for any help, Jake

 

[twolabsdad]

I’m no expert, but this might be electrical. Have you tried replacing the fuel pump relay in the fuse box under the hood?

 

[Bob4x4]

I’m no expert, but this might be electrical. Have you tried replacing the fuel pump relay in the fuse box under the hood?

Mechanical pump

 

[Bob4x4]

Try it on an external tank and plumbing to eliminate stock lines an in tank issues

 

[GAmes]

The first issue is the snubber. They regularly cause fuel pressure fluctuation. A better choice is a needle valve just barely cracked open. I believe the rest is caused by an obstruction. Maybe a collapsed rubber fuel line or even something in the tank like algae.

 

[The patriot]

No mention of the rubber return line behind the filter. replace it.
I too was thinking something in the fuel tank, maybe a rag?

 

[MLee]

check the simple things first, and then expand further. Full travel on the fuel Solenoid, fuel pump pressure? etc.

 

[surfbeetle]

When you take off the fuel cap, do you hear a woosh sound? Maybe your breather in the tank is clogged?

 

[32valveturbo]

Hi all and thanks for taking the time to help me out!! I apologize for my delay as the flu bug got me......Anyway, I put a 12 valve in my Ford Excursion.....when I did that, I had to drop the tank, clean it, weld a fuel intake and return line (which were pressure tested underwater before installing) the pickup tube is about a 1/4" off the floor of the basket (which the old elec. fuel pump assy came with) I cleaned both fuel entry ports to the basket and put new filter socks on.....all new rubber hoses including the tank vent and the fuel filler hose (all diesel compatible)........ I used the factory SS steel quick disconnect fuel lines until just past the frame mounted fuel filter......I hooked the suction side directly to the new frame mtd fuel filter (also diesel compatible) and I cut and swaged the return line and hooked the pressure side of the system to that.......







I took the FSS out of the picture to see if moving that fuel arm would make a difference and nothing..........I hear what people are saying about the snubber but Im not talking about a rapidly fluctuating needle between say 20 and 25 psi.......it goes to zero like you shut the truck off and stays there for a while...........

 

[32valveturbo]

Oh, sorry...... I don't have a lot of tank vacuum and just to be sure I took the fuel cap off and it didn't change anything........I called around a few pump shops to se if there is a pressure regulator inside the pump and all but one said no..........I'm guessing that I may have gotten 2 bad brand new out of the box OFV's..........Cause when I clamp off (almost all the way) the fuel return line right before it hooks to the factory steel return line it maintains 40 psi at idle and while driving although it continues to creep higher and higher like 60psi...... I have 3 different OFV's coming today........I'll let you guys know what comes of it
Thanks again for all the help!!

 

[GAmes]

If I understand correctly you are using the stock mechanical lift pump and put a fuel filter between it and the tank? Stock lift pumps won't pull fuel through a filter, that is why Dodge put only a screen in the pre-filter. Assuming you still have the stock original type fuel filter between the lift pump and the injection pump, I suggest you bypass the frame mounted filter and see what happens.

 

[ntsqd]

I went thru something similar with a VW diesel years ago. Turned out to be water in the fuel. Not a lot of water, but enough to plug the RACOR fuel filter. It seems that "paper" fuel filters can clog with water and it does not SHOW. Replace the filter and drain the supply lines before re-priming.

Mechanical fuel pumps do appear to pull fuel better than do electric fuel fuel pumps (for whatever reason), but any restriction between the pump and the pick-up in the tank can cause the pump to cavitate.

I would be tempted to replace the fabricated pick-up with the Excursion's OEM fuel pump assembly. Wire it off a relay using the OEM Inertia Switch to run key-on. Plumb it with a by-passing type regulator if you're worried about too much pressure to the lift pump & beyond.

 

[LarryB]

Before throwing much more time and money at the problem determine if the issue is before the lift pump or after. As suggested in a prev reply, run a hose from the lift pump inlet into a fuel can and start it. If your pressure is stabilized then your issue is probably with the added filter or the tank. If the problem persists it may be with the lift pump etc.
LarryB

 

[JeffPo]

Note sure if this is pertinent, but I will put it out there for you (and anyone else experiencing fuel delivery problems) to consider.

When repairing my fuel sending unit on my 96 2500, I did some testing with the fuel tank sitting on the floor. I discovered that the stock sump assembly would run dry if I did not have the return line flowing back to the stock sump return. I initially just had the return line running to a bucket. It did not matter than the tank had plenty of fuel in it and said fuel was plenty high on the pickup assembly. I still do not fully understand why it works in this manner. I performed multiple "tests" to repeat the scenario, and each time the sump would go dry (and the engine would shut off) and not pull fuel from outside of the sump to inside the sump unless the return line was hooked up and returning to the sump. I did clean the filter screen that is on the bottom of the pickup assembly as well. With it hooked up and returning as the factory laid it out, it has been running for 2 years (and the sending unit still works).

 

[usmc1349]

I have '97 2500 with 5.9 12v with over 260K miles. Encountered similar problem. No modifications to fuel system on truck. Used pressure gage to test fuel pressure which led me to replaceing the pressure regulator valve on the injection pump. Obtained FUEL OVERFLOW VALVE KIT - BOSCH ('94-'98, 12V - 5.9L)
Item #: 2-417-413-101-KIT valve from GENOs. Running strong like a Cummins should.

 

[JMcCoy]

Sounds to me like your sucking air from one of your fuel lines. Like stated above, I would isolate and test your fuel lines. Years ago, I had a pin hole in my fuel return line that absolutely killed my power. Good luck and keep us posted.

 

[32valveturbo]

Hey fella's and thanks for all the replys!! I've been too busy to get much done, but this is what I did do........Oh, first, I did not realize about the pre-lift pump filter, thank you!! It does make me wonder why it ran fine for almost 10,000 miles with the filter. Anyway, for me to delete that filter I'll need to resize my fuel feed line and cut and swage the factory metal line which I wont have time till this week. I DID do the 5 gal bucket test......pump immediately built and held pressure, just like when I pinched off the return line..........Mr. McCoy, I do have a spot where the hose has slight bit of wear it has come into contact with a swaybar end link.......so If a pin hole is big enough to do damage I'm just gonna run new lines this week when I delete that frame mounted fuel filter and see what happens. Thanks again Guys I'll keep you posted!!

 

[32valveturbo]

Hey Jeff, thanks for the reply, the fuel basket on the excursion has a couple entrance spots for fuel AND the return line dumps into the basket

 

[GAmes]

It does make me wonder why it ran fine for almost 10,000 miles with the filter.

I replace my fuel filter based on fuel pressure. When the pressure drops enough the filter is starting to clog. This takes place with as little as 15,000 miles and rarely more than 20,000 miles. Based on that knowledge my swag is at 10,000 your filter won't pass enough fuel to keep the lift pump happy.

 

[32valveturbo]

GAmes...... I owe you lunch!! I circumvented the frame rail fuel filter and she's good!! The torktech adjustable OFV set at ~30 psi at idle.....she goes down the street at 28-30psi at cruise, under normal accel it's at 22 psi and at WOT it drops to 10 psi but stays there.......... I guess I just got lucky that the frame rail filter was "good enough" for about 10,000 miles....... I guess I have to be thankful it didn't give me problems on start up cause I'd have been chasing all kinds of "what did I screw up" problems after the swap...........Anyway, Thanks to all who took the time to help me out and I hope I can return the favor one day!! GAmes if you're ever in Central Florida I owe you lunch!!

Jake