Hi everybody,

I sold my 86 F250 6.9 litre and just bought a 1990 Ford F-250 4x4 ext. cab diesel with the 7.3 non-turbo. I am planning on doing a vegetable oil conversion on this truck, and I had a question about the fuel system.

It seems that on my 7.3 litre, non-turbo, there are TWO return lines coming from the injectors. One is back at the firewall and returns to the tank, while the other return line is at the front of the motor and returns to the fuel filter.

I have a separate spin-on heated filter for my vegetable oil, and I really don't want the vegetable oil to return through the diesel filter via that injector return line.

Can I eliminate (i.e. plug) the fuel line that returns back to the diesel filter and just have the single return line going to the tank?

...Or would that create too much back pressure in the system?

Thanks guys. Any help would be greatly appreciated.

Happy 4th!
-Joe

 

That line from the fuel filter, goes to the tank, not filter. It's there to get trapped air out and make starting, driving easier. There should be a check valve there to prevent back flow.

 

Thank you for your reply, but after looking at my Ford shop manual, the schematic also shows that there are two places where fuel is returned. When you are facing the engine, the far right injector cap has a return line that goes back to the tank, and the front left injector cap has a hose that runs up into the top of the fuel filter, next to the check valve. When I get home tonight, I'll scan it and try to post the picture.

In the fuel filter, I have the entrance-line coming from the lift pump, and the fuel exit which goes to the injector pump. The third line is that return line that comes off the front left injector right next to that check-valve. That's the line that I want to plug so that the vegetable oil won't return to the diesel filter.

 

Now thats different than mine. On mine all the lines from both rows of injectors, the pump, and filter all go to a long tee on the driverside intake bolts.

But in any case, because your constantly pumping fuel at a positive displacement, vs' the pump/injectors, all those lines are positive flow back to the tank. You'll be glad for that one if you need to replace a filter along side the road.

 

Yes, this one is definitely strange. If your truck doesn't return to the filter as well as the tank, I think I'm just going to plug this line up and hope for the best.

I'm just trying to figure out what the reasoning behind this fuel setup would be anyhow....I'm not too sure why I've got those two return lines. My only guess was for it to offset the fuel pressure maybe....

 

On the advise of a local diesel mechanic, I eliminated the return line going back to the filter because the check valve in it had failed. I was told it was meant to send warm fuel back to the filter to help prevent gelling in cold weather. However, if you have any small air leaks in your return lines you are also running air back into your injection lines (not good). I currently have other return line issues, however, that I hope are not related to eliminating this line.

 

As a few folks said, one of the return lines goes to a one way valve on the filter (schrader valve). I had the infamous "start, run 20 seconds, and die, then act like you ran out of fuel" problem. After changing the return lines, it still did it. After taking off the line going to the schrader valve and plugging it, it was fine. I did replace the valve, and if it is bad, it will cause issues for sure. But, mine ran and started perfectly well without it for over a month.

Wayne

 

my 88 has had the line to the fuel filter head removed and plugged since 89, and all of the other 6 trucks i bought had the same line removed and plugged by the dealer before i took delivery.

all are still running with the line plugged except for the 92 that was totaled by a drunk driver 3 years ago.

 

I think this thread may have solved my intermitten air intrusion problem!

 

I just went out and put a 5-16" bolt in the line and a pipe plug in the filter head. That's the first time I've ever plugged a rubber line with a bolt but I've seen it done a thousand times.
It's 1 AM so I didn't want to start it and run it, we'll see what it does in the morning.

 

it should start rite up.

that "plug the line" trick was a T.S.B. issued by ford back is 89 to solve the cold start filter drain caused by air intrusion.

 

The filter TO #1 injector is/was to allow any air in the filter header to go to the return lines instead of the IP. If the check valve is working there will be NO problems. If you plug the filter header hole and disconnect the line and plug it the only thing is any air in the filter/header after a filter change or empty tank will pass through to the IP first before returning to the tank selected.

TJC I will try to find that TSB today and file it.

 

i think it is one of these
88209 SEP 88, Engine - No Start or Hard Start Condition
89189 SEP 89. Diesel Engine - Idle Surge/Hard/No Start

i let my alldata expire years ago, so i can not read the T.S.B's, only find the numbers.

i also found this one from 92.
92268 DEC 92=Engine - No Start Condition