fuel filter light lit- intermittent

[WVOpower]

Been having intermittent issues with fuel filter light going on and off.
94 F250 Ext. 7.3 idi
1) fueled up/fuel additive/cold outside 20 degrees / truck ran good for 18 miles
on rear tank (front tank not avail. at the time. taken off) / started tp sputter
restarted 5-6 times / truck towed / engine was air locked / no problem found
by Ford dealer.
2) Same as above except front tank available. switched to front tank ran fine.
3) Took off rear tank fuel cap. ran fine on rear tank. replaced rear fuel cap.
4) On rear tank - fuel filter light stays lit. removed fuel cap still lit.
5) front tank - (installed "hot fox" heated fuel pick up made by artic fox) fuel light
lites when taking fast turns or accelerating quickly. this was happening before
the hot fox install.

Conclusion: Tanks not properly vented/sending unit-rear/flapper valve broke inside tank? Any other ideas? Thanks to the previous posts by masam, remote, bluemule, and lmjd.
I'm new to diesel engines...is anyone near NW suburbs chicago that would be willing to show me the ropes? Case of fav beer! LOL!

[Bill1013]

From your profile, looks like you have been using WVO. Checkout the forums on BIO_Diesel.

Bill

[cdnsarguy]

Most likely your filter is plugged up........that light is what indicates a vacuum in the filter header........... other choice is the fuel lift pump is fubar.

Take the filter header Schrader valve core out and hook a hose and pressure guage to the outlet.........crank engine see what you get for pressure, should have 4-6 psi from a good lift pump.
Volume test same place hook a hose to it crank over the engine 10 seconds you should get 1/3 pint of fuel minimum or 1 pint at 675 rpm in 30 seconds... engine running

***Important the fuel shutoff solenoid (FSS) wire on the IP should be disconnected if you do not want a start just cranking. Re connect FSS after test complete.

[WVOpower]

Two replies:
Thanks Bill. Some good info. in the BIO section.
Hey canadian Guy, fairly new filter, less than 1000 miles with NO WVO ran through it yet. Too cold for me (-4 w/-20 windchill couple days ago) to try running WVO. Anyhow, what does not make sense is that when I am running on the rear tank the fuel filter light comes on all most immediately (full tank). Then I switch to front tank and light goes out within 5 sec. It was OK on the front till yesterday..when it started coming on when taking a high speed turn or accerlerating quickly. Sorry left that part out earlier.. Basically, getting mixed results last couple times I used the truck. The fuel lift pump does sound logical, however when it was tested couple months back it tested OK. Then again that was TWO months ago or so...well, the Carter machanical pump is less than $40 at NAPA. I have been reading about a electric replacement by Holly and Carter..maybe try one of those. What do you think? Anyone got any HELM shop service manuals for sale? Thanks again for your time in advance.

[cdnsarguy]

Go with the electric it will push more then the manual lift will pull........ Could also be the screen pickup in the tank is plugged if WVO has been used???????

FYI ..... I normally do not answer BIO or WVO related posts re fuel system....... too many variables to contend with.....sorry!!!

[WVOpower]

Thanks for answering/ info canadian guy. Will go with the electric.

[jski55]

Originally Posted by cdnsarguy

Most likely your filter is plugged up........that light is what indicates a vacuum in the filter header........... other choice is the fuel lift pump is fubar.

Take the filter header Schrader valve core out and hook a hose and pressure guage to the outlet.........crank engine see what you get for pressure, should have 4-6 psi from a good lift pump.
Volume test same place hook a hose to it crank over the engine 10 seconds you should get 1/3 pint of fuel minimum or 1 pint at 675 rpm in 30 seconds... engine running

***Important the fuel shutoff solenoid (FSS) wire on the IP should be disconnected if you do not want a start just cranking. Re connect FSS after test complete.

Its also possible that you have water in your filter.... could bleed the valve under your filter while its running to check. I had similar issue once with wmo.

[rkpatt]

It also could be a simple as a problem with the connector to water sensor. There might not be any water in the filter but the wire could have become disconnected and grounded against the engine causing the ligh to come of and flicker . Check the wiring and connected . BTW , the connector so the post on the filter on my truck is pretty loose and needed to be replaced . I am currently using an insulated alligator clip until I can find the proper push on connector replacement - what is called and where do I find it ? . - Thanks

[DeepRoots]

i'd disconnect the darn fuel filter light sensor and put a real vacuum/pressure gauge in there too.
especially if you have any interest in running homemade fuel.

make sure there aren't any air leaks while your at it. a handheld vacuum gauge is really useful.