in my e350, i had bypassed the stock water separator some months ago to solve a leak, and just this last friday i got around to installing a racor filter/water separator in its place. saturday i started it up on the front tank, switched to the rear tank after it warmed up, and switched back to the front when i got back home 50 miles later after some errands, and all was fine.
then on my way to church this morning, same thing, i warmed it up on the front tank (clean diesel), then switched to the front tank (WMO mix, same as i ran yesterday), and the truck stalled out several seconds later like i was out of fuel, though it had plenty and i can usually run that tank nearly empty without any problems. i switched back to the front tank while holding the throttle to the floor, and around the time it hit 30 MPH the engine came back to life. a few miles later i decided to try again. thats when things got interesting.

at that point, the fuel gage went dead for a number of miles, probably around 15 or so. for some miles after that, the gage was fine, but i couldn't switch to the rear tank. the front tank was reading 3/4 and the rear should have been reading 1/4, but no matter which position the switch was in, i had the front tank reading and that was it. so i drove the remaining 25 or so miles to where i was going on the front tank, trying the switch a couple times in the process, but not getting results. later in the afternoon, the problem went away by itself and appears to be working normally again, the gage is switching as it should, and i know its switched by the TSV, so therefore i assume the valve is working.

when i removed the stock water separator, there was a 3-pin harness resembling a headlight plug, and a ground wire attached to it, all of which were left unplugged. would either of these have anything to do with the operation of the TSV, or is it likely to be unrelated?

FWIW, the TSV was replaced with a generic aftermarket unit several months ago to solve the problem of fuel flowing between tanks by itself, causing on overflow at various times.

any insight into my issue here?

 

sounds unrelated.i would double check your connections at the replacement selector valve to insure solid,clean connections and heat shrink around connections.sounds like they may be questionable.slushy wet snow effecting them etc.

 

Outside temp?...crud in valve?..good luck

 

outside temp was slightly below freezing, which is nothing new here. it was about the same the morning of the problem as it was the day before and after, when i drove it and had no problem.
because the valve was labeled as requiring filters before it in order to have a warranty on it, it has those little clear fuel filters often used right before a carburetor. i don't know their micron rating, but they're small enough that nothing will get past them and be big enough to prevent the valve from working.
not to shoot down all your possibilities, i'm the one wanting a fix and not seeing much

and f250, you speak of slushy wet snow, this is the greater seattle area, so thats likely.
the wiring was done using standard butt connectors, so it is possible that some corrosion could get in there, possibly even enough to prevent the valve from switching for that hour... and that could go away by itself until a bad time.... i'll go inspect those, and if i have any doubt i'll go with solder and heat shrink.

 

i inspected the wiring connections, and they all look nice and clean. they were sitting quite inboard of the frame rail, so i tucked them into it, just on principle. if it happens again, i'll redo all the connections, but if not, then i might just count it as a 1-time freak thing.

i'll definitely post back if the problem repeats itself or does anything else weird

 

Check your connections. Your getting air bubbles.

 

air bubbles are something to think about, but they don't explain the valve's refusal to switch tanks for that hour, or the resulting refusal to switch the gage to the specified tank. the stalling would appear to either be the valve stuck halfway or an air bubble.
i was under it last night, and saw no signs of any leaks, other than a little bit of engine oil that had jumped over to the bottom of the water seperator. it was on the side of the bottom bowl, not up to its rubber gasket above, and starting well above its drain, which implies it didn't come from the seperator, but rather from elsewhere.
so i have no sign of any fuel dripping out, but of course i know how return line leaks can suck are but not drip... i'll check again and re-torque all the hose clamps down there

 

A good test too would be to bypass your selector valve completely.

 

ok, air bubbles are now obviously the problem. today has had a lot of the power surges and related screwing around of air in the fuel. i'll study it when i get home tonight

 

well guys, i'm kinda stumped here.
all the symptoms point to air getting in, but i can't for the life of me find out where. all the hoses have been checked and rechecked. for a test, i ran the electric pump for several minutes while i was crawling around under the truck looking for any sign of a leak, and found nothing. so i pinched off the hose entering the mechanical lift pump, while the electric was still running, thus pressurizing that section, with no sign of any leaks.
the electric sits just forward of the selector valve. everything from the water seperator forward is wet with engine oil, and the test i just described proves that its only engine oil not fuel. but nothing behind that point shows any sign of being wet, not the tanks, lines, selector valve, e-pump, nothing back there is wet.
also, the air intrusion happens on both tanks, and happens just as much when they're dead full as when they're almost empty.
i guess i could try bypassing the selector valve or the new water seperator, but i can't find anything else to look for

 

you said electric pump ...if you are running both electric and machanical pumps..check to see if machanical pump has not failed, check oil for fuel??........fuel at shrader valve?? you said Seattle ,,,Sedro-woolley here..

 

Put in a clear fuel filter used on a gas truck. That will help you find your air.

 

let me clarify a couple things here
1) yes i have both electric and mechanical pumps, but the electric is wired to run only when the glow plugs are lit or i'm holding a pushbutton down, so its not in use most of the time.
as we know, its not acceptable to have the e-pump pushing through the mechanical all the time, as a mechanical pump problem could leave the crankcase full of fuel.
2) the mechanical pump is definately not pumping fuel into the crankcase. i check the engine oil every time i have the hood open, which this week has been daily studying my fuel issue, and its been going down quite slowly, which lines up with the leak around the oil cooler.
3) i have those clear filters on both lines right before the selector valve, and the one for the rear tank is totally full, and the one for the front tank has just a tiny bit of air in it. but good idea, i'll go back out, turn the pump back on manually, and watch those filters. thanks for the idea!

speedwrench, i say seattle, because nobody else has a clue where index is - highway 2 milepost 35. you're up north by a couple hours drive, but not that far away i guess.

 

well, i took that clear filter idea a step further. to start with, i had a filter on the line from both tanks before the selector valve, and tonight added one between the valve and the e-pump - pic here - https://www.dropbox.com/s/399qw901ln...2022.08.41.jpg and found that with the e-pump running and the valve selected to the rear tank, both filters were full, leaving only a tiny air bubble in the top. but on the front tank, the first filter would stay at half full, even though i tipped it up trying to get the air out. however, the downstream filter stayed full regardless of what tank i was on.
but while considering all this, i very distinctly remember having the air issue while on the rear tank just as much as while on the front tank. i feel like i'm getting somewhere, but not very fast

 

Just keep at it until you find the air. You may find out you need injector o rings or something.

Some also suggest clear line but you can't run it too long as it is not fuel rated.

Your filters look fine to me. When i bypassed my valve i found air coming in from the sender with those babies. I thought it was tight but a few more times and no air bubbles.

They also help keep junk out of the selector valve.