Fueling issue

[Philip Parker]

Hi everyone, I have a new problem that I am sorting out. The car runs great with a full tank of gas, however I am getting a hard engine cut off at like 4500 RPM under heavy throttle. The fuel gauge only shows half full as well, but I am purely assuming that the tank is full and that the sending unit is off, however I have not verified this.

Today the car started running poorly under moderate throttle and detonating like it did not have enough fuel with the fuel tank getting near empty.

I filled it up but only put 8 gallons in. It will only verify half a tank still.

My hypothesis is that there are two fuel pumps and one is not working, as well as two sending units. Whatever is going on the car is running out of fuel at various stages depending on how full the tank is. Has anyone ever dealt with this?

I replace the driver side fuel pump in the tank about a year ago. Is there another one on the other side? Or a transfer pump?

Philip

[Bob Martin]

SOunds like the transfer pump on the passenger side has gone kaput. There is a controller under the driver's seat for it. There is also a switch in the tank that cuts the pump off when the fuel gets too low on the passenger side. The pump itself is external to the tank under the passenger side floor board back just in front of the tank. You can replace it with any low pressure electric fuel pump.

Bob

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[Joel Sass]

I second this. Bob fixed an issue like this on my GTX when I first got it, but it was a little different. My vehicle was showing half full even though it was completely full from the gas station. It turns out that it was because the float on the passenger side was not functioning properly, and telling my car that it was only half full. This also caused the pump to not operate properly because the vehicle perceived the passenger's side as empty.

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[Philip Parker]

Joel your issue sounds very similar to mine. Did you have to replace the sending unit and transfer pump on the passenger side to get it sorted? 

On Dec 22, 2022, at 1:25 PM, Joel Sass <sass...@gmail.com> wrote:



[Scott Forrest]

Is there a database of part numbers of substitute fuel pumps, transfer pumps, level senders ?

Walbro this or that's?

What are good trouble shooting practices when inspecting these components?

[Daniel Roy]

Actually, on the passenger side there are both a sending unit for the fuel gauge that is wired with the one on the driver side, this has no relation to the transfer pump. There is also a switch for the transfer pump. It is a float with an on-off switch. The transfer pump runs as long as the fuel level is high enough and stops when the switch reaches a low level. The pump control unit under the driver seat is a delay to prevent the pump to cycle on and of repeatedly when the level is near the trigger point.

See service manual at page 4B-44 to 46.

Dan

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[Joel Sass]

I believe Bob had a full unit for me to swap in, so it was a simple plug-and-play.

[Fantastic Yahoo]

My black car will use half the fuel about 6-7 gallons, show half full on the cluster gauge, the low light will glow and the car “runs out of fuel”.  There is still fuel in the tank. 

Thank you, Steve.

via device - excuse errors. 

On Dec 24, 2022, at 10:53 AM, Joel Sass <sass...@gmail.com> wrote:



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[Joel Sass]

Alright, in that case, it's the transfer pump or transfer pump switch at fault. Here's troubleshooting steps from the book:

The fuel tank is shaped like a saddle sitting astride the driveshaft. It has one fuel pump which pushes fuel to the engine, which is on the driver's side of the vehicle, and one transfer pump which pushes fuel from the passenger's side to the driver's side in an attempt to keep fuel around the main pump. There are two fuel sensors in the fuel tank: one per side. Each sensor has a float arm which gives a variable resistance to the ECU based on the float position. This signal is added together by the ECU, and the result is displayed on the fuel gauge. The fuel level warning light only monitors fuel around the engine fuel pump side, so if the light illuminates, that means you are about to starve your engine of fuel, regardless of the fuel level shown in the tank.

In order to resolve the problem, you will want to look at the transfer pump. First, you can follow the instructions above: turn the ignition key "ON" (don't start engine). According to the instructions, you should hear the pump running. When you short the two terminals in the third image (short BG >B) with a piece of wire. Since the transfer pump should be considered "on" all the time, if you don't hear the transfer pump kick on (You will have to listen intently. The transfer pump is outside the fuel tank, under the vehicle. It will be more easily heard through the hole you opened under the passenger's side rear seat, and the hoses are visible there as well), then you have a transfer pump problem. Working with the transfer pump is kind of a pain because of its location on the fuel tank (under a protective plate, attached to the upper side of the fuel tank I believe), but it's not the worst thing. If you need to replace it, any transfer pump that will fit in place is acceptable. It's not an in-tank pump, so there's a few options out there that will fit the location. You will need to splice in the GTX connector, but that won't be too bad. Careful for soldering near the vehicle with open fuel lines though.

Any questions, let me know.

-- Joel

[s n]

Joel, good information.  I will check all my stuff when I can get back to the car.  Makes good sense.. Thanks