6.9 Keeps dying at WOT - need some ideas

[Locopyro]

I am new to the diesel world, but not new to turning wrenches. I recently was given an 1986 F-250. She has 290k on the odometer and runs good at lower RPM's and on surface streets and I immediatly took her for an oil change since I didnt know how long ago it had been done. Mechanic said oil was clean and he emptied about 9.5quarts. Was pretty happy about that. But, When I took her up on the interstate, heading up a couple miles worth of 4-6% grade, she would bog down and eventurally die. Engine Temp was well within normal range. After a couple minutes of cranking, she would kick back over and we'd go again. Best description for feeling would be a vapor lock or an iced carb if this were in the gas world. I began troubleshooting a couple months ago with injector cleaners, fuel additives, then checked return lines and such for leaks as I was seeing air bubbles in the clear tube that ran from filter to fuel return rail, and replaced the fuel filter. Eventually the injector pump failed - verified by zero fuel output at several injectors. I replaced the Injector Pump - truck is now running with trace amounts of black smoke under heavy load - but it is STILL dying at wide open throttle for long durations. Vertical lift pump appears to be operating well as I get fuel sprayed across the engin compartment when I open the schrader valve down stream of the filter - but I dont have an actual fuel pressure tester. Transmission does eventually downshift - probably a little too late - but that seems to compound the problem as now the engine is at higher RPM.

Paul

[ellis93]

If the strainer in the tank has trash around it the supply pump can suck the rubber hoses in the fuel line together causing this to happen.

[Douglas]

hey-Hey!!!,
It may also have a leaky foot valve in the fuel separator( if yours has them separate ). If that is leaky it will suck up air through it, as well as drip a bit. If you were fueling fully, WOT would be more like pouring ink into water.
cheers,
Douglas

[ahale2772]

just replaced a pesky lift pump on my buddies 7.3 idi, one of the check valves fell out....then installed itself....then fell out again, but i agree with the trash around the suction line in the tank, seeing that it likes to do it under load

[Locopyro]

After my posting and seeing a couple of responces about trash around the sump... I got to thinking about the Vertical Lift Pump. It was putting out, but since I didnt have a way to see what the actual pressure was - I got to thinking it may be a little soft. I also figured it would be a little easier of a replacement than dropping the tanks. So a couple of bolts, 1 jamb nut on the fuel line and a couple of hose clamps later - new vertical lift pump is installed. Still runs great at 65mph w/o a load - but while climbing a grade, about 2 minutes into the climb - I found myself sitting on the side of the road trying to get her started again.

Looks like its time to drop a couple of tanks....

Thanks for the help

[Locopyro]

hey-Hey!!!,
It may also have a leaky foot valve in the fuel separator( if yours has them separate ). If that is leaky it will suck up air through it, as well as drip a bit. If you were fueling fully, WOT would be more like pouring ink into water.
cheers,
Douglas

Where would I find said foot valve? I dont find any reference to it in the chiltons manual either. And where would I look to find this drip as well - that might point me to where the thing is located.

Thanks again
Paul

[PToombs]

I find it interesting that a guy joins a Dodge /Cummins forum and asks questions about a ford. Did the powerstroke guys snub you because your truck is too old?

[Douglas]

Where would I find said foot valve? I dont find any reference to it in the chiltons manual either. And where would I look to find this drip as well - that might point me to where the thing is located.

Thanks again
Paul

hey Paul,
Where is your water separator? Is it part of the main fuel filter on the pass side front of the engine( fuel filter will have a bit screwed into the bottom of the main canister ), or is the filter canister smooth on the bottom and there's a die-cast separator by the base of the windshield on the driver's side( with a pull ring to open the valve and drain water from the bottom)? It is the one with the pull ring that made me some trouble from time to time as it got older.
cheers,
Douglas

[ellis93]

Not all had them. I've seen some with just a solid cover and some just had a screw type filter( though I think they were off of newer 7.3s). Some had fuel heaters in them too. When you talk ford your getting into a lot of diff model changes. Better ideas

[Locopyro]

I find it interesting that a guy joins a Dodge /Cummins forum and asks questions about a ford. Did the powerstroke guys snub you because your truck is too old?

nope - didnt know where to begin after a month of trying to self diagnose. So I started hitting forums to see what others had to say. And as for the truck being old... ita about the only way to dodge the California emissions test

[Locopyro]

hey Paul,
Where is your water separator? Is it part of the main fuel filter on the pass side front of the engine( fuel filter will have a bit screwed into the bottom of the main canister ), or is the filter canister smooth on the bottom and there's a die-cast separator by the base of the windshield on the driver's side( with a pull ring to open the valve and drain water from the bottom)? It is the one with the pull ring that made me some trouble from time to time as it got older.
cheers,
Douglas[/quote]

Water seperator is up high on the passenger side almost directly above #1 cyl. Its is a single piece unit - think oversize oil filter. only thing I see on it is the schrader valve on the side. Fuel line comes from tank selector switch back by tanks, comes up solid line the length of the truck with a 6" piece of rubber hose (new) going into the vertical lift pump. Then back to solid line up to the water seperator, and solit to the injector pump. I dont see any other inline fuel filter, heater, or gizmo in the chain.

[Locopyro]

Not all had them. I've seen some with just a solid cover and some just had a screw type filter( though I think they were off of newer 7.3s). Some had fuel heaters in them too. When you talk ford your getting into a lot of diff model changes. Better ideas

Yep - no heater in the chain. And I havent noticed any other inline filters (see previous post). After hitting the local salvage yards - its actually been eye opening - lots of changes in electricals, door parts, and other peripherals - but I havent seen many variations in the 6.9's. Course it could be I dont know all the subtleties to notice a difference in them yet.

[ellis93]

Some that I've fooled with are old farm trucks and county maintenance and none are in good shape. Most have been molested to the point that you'd really not know if it came with some items or not.

[Douglas]

hey-Hey!!!,
The filter separator should have a heater element in it. My '85 had the filter only with a heater on the line feeding it( betwen the LP and the filter mount ). Low temperature conditions would cause a fatal gelling that took a pot of hot water to submerge the filter in to warm it ; the early heater just didn't have any guts.
cheers,
Douglas