(this is a full blown race car with MOTEC, sequential and all that jazz, street driving and emissions aren’t a concern.)

I’ve been battling a fuel issue for a few years and trying to address it now. Basically I never transfer fuel from the passenger side at a rate fast enough. Basically it takes about 7 minutes to pull 1 gallon of fuel over from the passenger side.

in testing I can pull about 10 gallons from the driver side tank before the pump runs dry. If I then cap the system and cycle the pump for 7 minutes I get about a gallon transferred over.

I have replaced several items…

’ve now replaced pretty much everything and still not getting a fuel transfer.

New Pump and assembly (driver side)
New Syphon Jet/level sender assembly (passenger side)
New Filter
New Y hose with the check valve from pump to filter

A previous mechanic had removed some of the other fuel lines to include one that went to the rear canister to someplace in front of the car. I didn’t work on my car back then so I’m not sure exactly what was removed, I just know that I’m missing a line that I can see in diagrams.

my question would be, was I required to have the red abs blue lines in this diagram?

 

I have had this problem. It was the internal nozzle in the jet pump being plugged, which does not seem to be your case since you replaced your jet pump.

I checked the Chilton manual online through my library. It provides procedures for disconnecting jet pump inlet and outlet lines and measuring flows, but it has been revised to where it is pretty unintelligible. Maybe the FSM is better.

If you can identify which line is the output from the jet pump to the left tank, you may want to try disconnecting it, plugging the left tank portion, and measuring the output from the right tank portion.

I think, but am not 100% certain, that the removed lines are only related to vapor recovery and should not have anything to do with transfer.

Beside motive flow blockage, another cause of jet pump low performance could be a leak or blockage in the portion of the lines within the tank, but your replacement should have fixed or identified that. Additionally, there is an unidentified device (filter or pressure regulator?) in the right tank motive flow line, but your jet pump replacement should have replaced that.
In your testing, you apparently capped the left tank output to the engine, which would allow the right tank pump to maintain pressure, but if the left tank pump is running dry as stated, you would not expect the jet pump to work, since the left tank pump cannot provide any motive flow to the right tank jet pump.

I am not by any means an expert c5 mechanic or troubleshooter, but I am familiar with jet pump systems since I used to design aircraft fuel systems.

 

Yeah it sucks. We determined those removed lines aren’t needed in my case.

today we tested the flow from the syphon jet and I’m getting about 75ml/8 seconds which apparently is still less than 20% of the actual flow.

we are stumped since we’ve replaced anything that has a regulator, jet, or check valve. We will probably just run a pump and just manually pump fuel across.