13.8 to 14v will power the pump

 

Since I had the fuel pump out, I got an extra hand and plugged in the test connector to see what kind of flow came through the hose leading into the pump. With the switch to the front tank on, nothing came out. With the switch to the rear tank on, fuel was dribbling out.

Probably a sign the selector valve is the problem?

 

You can jumper the switch to test that theory however I believe you have a problem with the selector/reservoir valve. You had it apart and lost a screw I read in previous post you had.

 

Lost the screw, found a replacement of the right thread, but not sure about the length. Seemed like it drove deeper than it probably should have. I'll tear that apart again and maybe take a file to the bolt and shorten it, tighten it again, and try again.

 

Do you have a good flow of fuel from the rear tank to the input side of your selector/reservoir valve ? Do you have good flow of fuel from selector/reservoir valve to the HP pump? Do you have good flow from HP pump to output of the fuel filter? And the last thing I can suggest is see if you have a good flow of fuel back on the return line to the selector/reservoir valve and out of the selector/reservoir valve to the rear tank.

You need to stick with 1 tank and get the truck running then work on second tank. If the truck runs some off the rear tank focus on that side of the system. You can also bypass the tank reservoir/selector with the male fuel line ends and short piece of fuel line and couple clamps to see if taking the reservoir/selector valve out of the system helps.

 

Put in new fuel pump. Primed and ran well initially, but only ran for a minute before dying. Then it would not build up pressure again, and was dead. Tried it again after letting it sit for a few hours, and it was dead. Assumed new pump may have failed.

That was a few days ago. Today went out and cranked on it just to see what it would do. Started up well, sounded very good, high velocity pump was quiet, and on a quick test drive around the yard it ran better than at any other time this year. While it was hesitating on the "3rd gear up the driveway hill" test before, it now ran confident and strong. However, once at the top of the hill, the high velocity pump was screaming, like the old one did before it stalled. And, again, a stall. Since I was on the down part of the grade, I had to wait until the motor could start again to at least limp it back over the hill to coast down back to a workable spot in the yard. Five minutes of waiting, it started well, and reversed back down the hill well.

After getting it back into the working area on the drive way, I let it run. Didn't sound as good as when it started today, but seemed to idle well enough. Since the box is still off, tested the return lines, after noticing the rear tank is getting low and the front tank is getting full.

When the tank is switched to rear, no fuel comes from the rear return line back to the tank. There is a trickle from the return line to the front tank, but not very strong. When the front tank is selected, there is no return fuel coming out of either line.

I suppose I should assume I either made the valve dysfunctional by putting in the replacement screw and have to open it and adjust it again, or the valve has been screwed up from day one. Maybe when I saw rust on top of the valve when I first opened it, it was an indicator there is rust and junk in the rest of the valve plugging something or making it not work correctly.

Tomorrow I might take off the valve again and poke at it again, maybe shorten the screw in case it is too long and doing something. But I have a feeling I'll probably be replacing it at this rate.

NO leaks of any kind under the truck. So the return line isn't leaking. Could the return line be blocked, kinked somewhere I haven't checked?

 

For the money you spent to replace the pump, (which I don’t think is bad) you could have replaced the DFR, that you know is bad.

 

The DFR or selector/reservoir valve has some little check valves and Orings and that is where your trouble is I think. The 87 I worked on ( still working on) sat for 14 years after rear tank got hole in it.

I replaced the rear tank,fuel pump in it. I tested the inline HP fuel pump it would not run so got that and while I was under truck testing HP pump I pulled the DFR to find black tar substance in fuel bowl and an Oring in the bowl. Threw it in trash can ordered along with HP fuel pump put new 1's end no more problems. Still waiting to do front tank and fuel pump as front tank pump is bad.

I think it was 300$ for the DFR but I can tell you it was money well spent as to having to tear it apart 2-3 times and install and remove.

 

I agree with the DFR being the problem. The fact that he has been in there and installed some generic screw also isn’t helping. I think it is hung up in-between allowing not full fuel pressure from either tank as well as the fuel from returning to the selected tank.

Last night I saw new reservoirs for $65 on EBay and other websites were still less then $200. Years ago mine was stuck on the front tank because the truck had sat for almost 10 years. I don’t recall how exactly how much it was but the one I got from the junkyard for less than $50.

 

Replacing the DFR is no doubt in my mind gonna be your best solution. Based on the same experiences you’ve described here, I’ve found that the DFR’s will become more and more dysfunctional once they get mucked up with contaminates of any kind (rust, old fuel that has thickened, etc) and both the internal supply and return valves don’t switch direction of flow properly. Or at best they may partially work right - as in let enough fuel flow into the reservoir bowl to flow out towards the fuel rail for a sometimes good idle but not enough for the higher flows needed for driving, hill climbing and such. Can’t help but think your HP pump noise is coming from the pump pulling, at at least trying to pull, from a stuck DFR valve - causing a cavitation of sorts. Also there is another spring loaded valve in the DFR that you can’t even get to if I recall correctly.

I’ve had to replace a couple of them on the 8th gen trucks. And even the new DFR’s tend to always fail again eventually. Got tired of fooling with them so much and now tend to replace that set-up with a SFR and a 6-port fuel valve that eliminates that continuous point of failure of vac operated valves and uses electrically controlled solenoid valves that holistically control supply and return lines to either one tank or the other (see a reference or two in my signature line). So no more return line mis-routing to wrong tank.

To swap them over to that type set-up, some rerouting of fuel line connections (all in the area of the DFR) and some electrical connections would need to take place, but that was relatively painless.

 

Did you ever get it fixed?

 

Ye. Replaced the tank valve and now it runs. Last thing if anything is to finally chase after the Thermactor reading, but it seems to be running great now.