ModernMuseum

Hopefully you guys can help, because I am at a loss and my car is at a buddy's house.

Engine: cammed LS3
Fuel Pump: Walbro 255
Regulator/filter: Corvette regular that everyone uses (not sure of model number)
Tank: DSE (Mechanical fuel pump style) tank



The car was dyno'd on a previous pump: a Walbro 255 from ebay and I got about 3 hours out of it before it failed. Once I got the car home from the dyno shop, within a day or so it started sputting on take-off. Eventually it got to where I could't even drive around the neighborhood and wouldn't speed up past idle. Due to the ridiculously loud whine of the Walbro, I thought it might be a bad pump.

I replaced the pump and it still whined a little, though the problem seemed to be fixed except for a very slight hesitation on take-off. Yesterday was the first day that the car was legal, so I took it out for a spin. Today, about 3 total combined hours or so after running the new pump (hell, maybe even only 2 hours), the car started sputtering again and now I can barely putter down the street. It falls on its face upon take-off and I'm stranded in town.

The pump/regulator setup that I'm using (below) may be a little obscure, but quite a few people have told me that it should work without issues. Basically, instead of sending the return line back to the tank, I am sending it back to the pump suction. I guess I could order a new pump just to get the car home, but I'd like to stop throwing money at the problem, though I'm sure I'll need a new pump anyway.

I put a mechanical fuel pressure gauge on the rail and it is reading about 55 pounds constantly. I am not sure what the pressure was right after I put the pump on; could have been more or could have been the same - not sure. What pressure are these things supposed to run? Is it a problem with the Walbro, perhaps the regulator is bad, or is there a problem with my plumbing? I would have run a return back to the tank, but there is no port for a return on the DSE tank (mechanical fuel pump version).

Help, I'm stranded!

Lonnies Performance

iTrader: (16)

You cannot plumb the return back directly into the pump. The fuel continually recirculates & eventually overheats. This will eventally destroy the pump.

Plumb the return back into the tank & it should be OK.

mantycarguy

I dont think your return line is the problem. These pumps are designed to push fuel only. They are subject to overheating when pulling fuel from the tank.I have had the same problems with past builds and solved my frequent replacement issues by going with an in tank unit.I have used a Ford Escort pump adapted to my stock sender as it was the only unit that would fit thru the stock sending unit hole on my Nova You can plumb in a return fitting anywhere in the tank thats convienent.

Lonnies Performance

iTrader: (16)

I wasn't speculating.... just stating fact. After building a few thousand fuel systems, I know what works.

That pump is located low with respect to the tank, it will be OK just fix the return plumbing.

one fast zo6

iTrader: (490)

Lonnie is all ways their to help A+ guy!

ModernMuseum

Thanks for the prompt responsed, guys. I had a feeling that was the issue, but unfortunately the solution isn't that straight forward using an external pump with this tank. The mechanical fuel pump version of this tank doesn't have provisions for a return line, so I will probably have to trailer the car back to my house, remove and dry the tank, and then take it to get an 8AN fitting welded onto it. I am fairly sure, just as you guys mentioned, that the plumbing is the problem.

PRAY HRD

iTrader: (119)

or you can install a bulkhead fitting with a nylon washer on the top of the tank and avoid welding as long as you can get your hand inside to thread it on and tighten it down. hope that helps.

http://www.jegs.com/i/JEGS+Performan...00561/10002/-1

Lonnies Performance

iTrader: (16)

Not sure what the application is, but if there is a removable filler neck, you cold possibly weld a bung in the neck without modifying the tank.

mantycarguy

I still dont think your return line is causing your problem as the fuel is not getting that hot. In older applications where all of the fuel was sent to the rail and then returned back to the tank via the regulator, heat becomes a real issue. Fuel is a great heat conductor. That is why the OEs run in tank pumps. I fought this same problem until I moved to in tank pumps.I have had no problems since. Middle 80s Ford Trucks had many fuel pump issues due to external mounted pumps.

ModernMuseum

Thanks for the link. I was actually looking for one of those until my search skills failed. I was thinking about trying to use one of those, but unfortunately I don't think I can get inside to hold that back nut. The tank has a lot of baffles in it. Here is the tank type:



Good suggestion; I didn't think of that. Yes, I do have a removable filler neck, but I'm not sure if I have enough room to get in there and weld an AN fitting on it. I will have to double check and see what kind of room I have.

If I re-plumb the lines and fail yet another pump, I'm probably going to have to switch to a different tank and pump, which will be a $1200+ endeavor.




edit: wait, you know what? I may just be able to get in there with that nylon nut. I can probably take my fuel level sending unit out and snake my hand in there since I have woman hands.

Old Geezer

iTrader: (3)

Take the neck out of the car, and do what Lonnie suggested.
You don't need a AN8 fitting for the return. The return on a Vette filter is 5/16....
This tank have a vent in it? Is that it on the top/left corner? Is it open?
If the tank is not vented/or you have it plugged off, you WILL get the problem[s] you are describing.

ModernMuseum

Assuming that this part is the same concept that Lonnie is talking about...



I could do that, but how do I safely go from that braided type "hard" hose to that slip-on type flange in the neck posted above? Just push like hell to get it on and put a hose clamp around the connection at the neck?

Yes, the tank has a vent in it. That is the connection that you see on the top left. The gas cap is not vented though.

PRAY HRD

iTrader: (119)

i have seen Lonnie post in the past and agree completely that you should not push the hose on and trust a worm clamp will keep it on there at LS pressure. 1 way or another i say keep the braided hose and -AN fitting for safety. We're talking about nearly 60#'s of pressure and GAS!! lol just my opinion and you're welcome for the link. good luck to you sir!