I am new to this forum...I am on others but I have yet to find a fix for my problem

I've got an 89 with a 5.8, about 2 years ago I swapped it in from the 5.0. I did plenty of motor work and it runs pretty good. I just recently did a maf conversion on it, I know I shouldve did that when I did the motor but I had no idea I needed to. After the conv I started having pinging problems, I tried everything, I had to put my egr back on, and finally ended up having to put 24# injectors on it due to leaning out on the top end. Well with the 24's I had to put higher flow fuel pumps in, I was told 160 lph pumps would be needed to feed the inj. So thats what I did, I eliminated the high pressure pump on the frame rail and put high press pumps in the tanks. It didnt require to much modification to the old tank unit, beings as my truck had the low press pumps. Well everything worked great for the first day, then I started getting massive amounts of fuel pressure at my fuel rail. Well turned out that my return fuel wasnt making it passed the fuel tank selector valve. And thats where my problem lies. I could go to Ford and buy a new valve for 200 bucks but I'm afraid I will run into the same prob. I have a feeling that old plastic valve isnt meant to have 100 psi running through it. I have looked at alternative electric tank selectors but nothing is going to work. Does anybody have any ideas short of having to get the entire fuel system off of a junk yard 90? Or has anybody else done this?

The reason I ditched the low press pumps in the tank was I didnt think that those would feed a 160 lph fuel pump on the frame. I think they are rated at about 20 to 30 gph. And a 160 lph pump is rated at 42 gph. Low numbers on the suction side of a fuel pump dont go very good. I do know that the tank selector valve has a resevoir on the bottom but I wasnt sure if that would be enough reserve to keep the pressure pump fed. ANY ideas are helpful, I'm bout ready to start pulling my hair out. Thanks in advance!

 

Is that a stock 5.8? You should be able to eliminate the selector valve but you will need check valves in each tank then to prevent gas from returning to the wrong tank.

 

No its not stock at all...its got quite a bit of motor work done to it. I'm not real sure how the 90 and newer systems work...where and how does the check valve work? Would I be able to just buy front and rear fuel pumps for a 90 or newer truck and do it that way? I've been looking for pictures and schematics of how those fuel systems worked but I'm not finding anything thats been helpful.

 

I'm not 100% sure but i think the fuel tank openings are the same on the pre and post 1989 trucks so a '90 and newer fuel sender could be dropped in. These newer sending units contain the check valves on both the send and return lines so there is nothing but straight fuel lines needed between the tank/s and engine. I have seen some fuel system diagrams posted here before by somebody else and maybe they will see this and post them again. Here's a pic of a newer sending unit, the check valves are integrated into the plastic piece that forms the top of the resovoir.

Flickr: Please wait...

 

I had looked at our 94 F250 and saw some T's under there, I tried following everything but when I looked at it...it was about 10 degrees and I was in the shed rolling around on the floor on a creeper. The shops all tied up so I cant get it in to look at it closer. The only thing that makes me wonder about the 90 pumps is will the sending unit work with my guage?

 

The gauge is driven by a float and they should be the same regardles what year.

 

One other prob that I would have if I got the newer pumps...is I still need a 40 gph pump. I'd hate to have to buy new units then tare them apart and put my 160's in. And I thought about getting old ones from a junk yard and taring those apart but then ya dont know if the damn sender is even good.

 

There are some guys on here with the newer trucks that have mounted frame booster pumps for high HP engines so it is possible and does work.

 

Does anybody have pics of how the 90 and newer fuel systems work?

 

Sure, is this what you wanted?





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I kinda thought thats how it worked but I just needed to make sure. Ive seen pics of how the fdm works but I wasnt sure if the two fuel lines just had a T that connected the two or how that worked. Thanks!

 

Thank god. I thought the previous owner did a hack job on my fuel system. Haven't had time to get a Haynes/Chilton yet.