Here's a bit of a head scratcher; my '94 6.0 runs fine when the tank is full but at about 1/2 capacity it will stall under certain conditions, i.e. brisk acceleration, sharp turns or a sweeping turn. The engine stalls due to lack of fuel but then will come back on while moving once things have calmed down. Seems like the fuel fails to get to the pickup when the tank reaches that point and sudden movement causes the fuel to slosh from side to side or aft in the tank.This occurs once it has consumed around 12 gallons. However, if I drive more judiciously from that point on it will continue to run fine.

What are your thoughts on this? The pumps were replaced before my purchase and I know that both of them are running. I was thinking that the pots (if that is the right term) that the pumps sit in were not reinstalled maybe or damaged where they might not be holding a reserve of fuel under the above circumstances.

 

As you already know, you have two fuel pumps.

I wonder if you are certain (a) that they are both plugged in and (b) whether it would make a difference if the pumps were connected to the wrong harness? The primary is plugged into the secondary harness and vice versa. I know that the harness will be interchangeable between the two pumps. It could be that the secondary pump might be acting as the primary?

 

Oh yeah, went through a whole lot of testing and checking when I got stranded last year. Hot wired both of them and they both ran. Relays and colored plugs are all correct. I could be wrong but with a full tank under heavy or even full throttle there is no sputtering or power loss as there should be if the second pump were not working under brisk acceleration. Even with sport mode engaged and rapid acceleration there is no fault with a mostly full tank.

 

Seems crazy, but the return hose should empty out to the "pot" (as you call them), not just to the tank. I wonder if that hose somehow fell down? The 4.0 tank has that hard piped back inside the tank, but maybe the 6.0 doesn't? That would be odd.

Also, any hoses inside the tank have to meet SAE J30R10, which is a submersible hose. Gates Barricade hoses, which are the gold standard for fuel hoses, are NOT submersible hoses. They will slide off the pumps.

Another idea is to ask whether you have any whoosh sound when opening up your fuel tank cap?

You do have a anti-slosh module, but I believe that only affects the needle on your fuel gauge.

 

Jagman99R,

I've not heard of this problem before. It seem the only thing that could vary with a very low fuel load might be if the inlet filter on No. 1 pump was loose or not fitted and the pump couldn't adequately pick up fuel under very low conditions. As I'm sure you know, No. 2 pump doesn't run that often as it operates under revs, not load or throttle position. It only cuts in at 2840rpm so therefore only under heavy acceleration in the V12.

As the pump modules are identical and dispense the fuel from the tank through a common pipe, you could try swapping the wiring at the tank top connector to make No.2 pump act as No. 1 pump and vice-versa. This could help eliminate whether the inlet filter on No. 1 pump is at fault.

Good luck

Paul

 

On my 94 6.0, I was having fuel problems.
I removed the tank and found the hose clamps were loose and could easily be pulled off.
This I found was not the issue I was hunting down, but could have been an issue in the future.
You might have one or more hoses that have been loose.
If you have tried hot wiring the pump harness to 12V and the problem goes away, all bets are off.

 

I'm not sure that I would consider 1/2 tank a very low amount. I only fill 10-12 gallons when I start to experience the problem. I can allow it to go lower driving at a moderate pace. Got a little nervous on a trip when pushing 250+ miles on one fill up but it should easily run that far under normal circumstances.

Thanks everyone for their input. Haven't had time to fool with it yet as I have other priorities to address on the car.

 

I don't know how similar the set up is between your car but I had a 92 with a V-12 that had a similar problem and it was caused by failed o-rings/ seals in the fuel pickup contraption that the fuel pump is mounted to. So when the fuel level was high, the fuel pump was sucking fuel through the leaking fittings in the system. But when it was low, it would suck air under those exact situations you described.
Pull out your fuel pump assembly (s) and I bet you'll find the culprit.

 

Thanks for the input, that seems like a very plausible explanation. Mine has two pumps verses the one you had but more than likely a similar problem.
Thank again,
Chris