Hi all,

First, let me reference this excellent thread. I have a hard start/stalling problem with my 1990 F250 7.3l IDI, and I am tearing down and replacing the o-rings in the filter/separator header. So far so good, the heater came apart, and I replaced the o-rings (fuel heater o-ring -014 and -016, in viton, for reference).

Now comes the fun part - figuring out what previous owners have "hacked". First obvious thing (and possibly also contributing to my problem), the first 8 inches of the IP output line had been replaced with a rubber hose (which was in pretty poor condition). I will replace this section with a viton hose, hopefully that will be good enough (or do I need to locate a metal line and replace the whole line?)

The next thing I noticed was that the return line output is capped off. This is a return line to the tank, right? I think I found where the return line should connect - there is an unconnected (short, i.e. cut) rubber hose connecting to a metal line, which runs down in the same direction as the input line from the lift pump. So my question is, should I go ahead and re-connect the return line? The truck has run flawlessly for many years/many miles without it...

I also have a new filter with the WIF sensor port, unfortunately my new sensor didn't arrive yet... I don't think I have a contamination problem, but it would be nice to see the WIF sensor working. Oh, last question - I have seen people talking about filling the diesel filter with ATF before starting. Is that *really* a good idea? I have both ATF and a diesel addative on hand (and no diesel), which I could use, or I could just crank it over until it fills (its on a battery charger anyway). Any recommendations?

Thanks,
Chris.

 

ctann,
Welcome to the IDI diesel forum.

Finding the filter to IP line metal line is getting harder these days, it is a low pressure line so you should be OK with Viton or fuel line.

On a stock engine, the filter return, IP return and the return lines from the injectors all tie together at the rear drivers side of the intake manifold and run back down to the fuel selector valve so the fuel gets returned to the tank you are running on at the time.

The exact routing did vary a couple times over the years, but that is not really important.
What is important is all of the above have a way for fuel to return to the tanks.

Now for the part about the return line on the filter.
If any of the return lines, the return line O rings on the injectors let air leak in, the vacuum that hold fuel up in the engine when it is not running will be broken, which lets the filter drain back to the fuel tank.
When that happens, the engine starts and then dies when the air in the filter reaches the injection pump and the engine will not restart until all air is worked through the system.

So back when the engine was rather new, Ford came out with a TSB which said "Remove and block off the return line from the fuel filter".

Doing that stopped the fuel filter from draining back to the tank, but is also meant the only way any air in the fuel supply line has to go is through the IP.

My position, keep the return lines, O rings and related parts in good shape, leave the return from the filter in place like it was originally intended.

As for changing the filter, fill it with fuel, fuel addative or auto tranny fluid before you install it.
I personally fill mine with Diesel Kleen, which the engine will run on.
ATF is fine, but if you have fuel checks in your area, the red may cause you problems at the fuel checks.

It takes a lot of cranking to fill the filter and work that much air through the injection pump, which is very hard on the starter.

When cranking the starter, 20 seconds max time cranking then at least 2 minutes cool down time before cranking again.
Starters are easy to overheat, and rather expensive.

 

Thanks Dave, I've been around for a while, but mostly lurking. And thanks for one of the most comprehensive answers I have ever received on the internet!

So I used 5/8" fuel-injection line to replace the missing metal section, we'll see how that holds up. I got her mostly back together, so as soon as my WIF sensor turns up, I'll give it a go. I think I'll leave the return line capped then, given the unknown state of the rest of the return line. It was tough not to just throw the old (non-WIF) filter back on and try it, but I restrained myself...

It actually sounds fun to use ATF. I have some redline "85 plus" addative, would mixing that with the ATF when filling the filter be a good thing? Or just using the adative by itself?

One last question - is the schrader valve just a regular automotive tire valve? I figured while I was getting everything else squared away, I would replace that too...

Thanks,
Chris.

 

The inside is exactly like a tire valve.

Very seldom is there a problem with the schrader valve.

Return lines and O rings under the return caps are a rather common problem.
The O rings cause lots of problems, the hot fuel makes them just hard enough that if the are disturbed, they will not reseal and start leaking air into the system.