I'm so confused.

So I finally braved the 100 degree weather to install a nice electronic fuel pressure gauge on the return fuel side (left side) on my 1990 XJ-S. Replaced the old fuel line which was hard and difficult to work with with a new one and fitted a T-fitting and pressure sending unit. Long story short, after I installed everything and started the car up. The gauge read zero, didn't move when I hit the accelerator either. Bollocks, the guage must be bad.

So bought a mechancial guage and plumbed that in today. Also on the return side, just ahead of the electonic sender unit. Started the car, and what the &$#@ the guage didn't move, read zero. The car appears to run fine, I hit the accelerator and the guage still doesn't move.


If I squeeze the return fuel line (left side) the guage does move, so at least the guage appears to be working.


I did all this because of my problem of the car cutting out after 20/30 minutes of driving, and not restarting until the next day. Thinking it was a fuel starvation problem hence the gauge.

What am I missing?

Toby

1990 XJ-S
1986 XJ6
2007 S-Type R

 

If you've actually plumbed into the *return* hose I wouldn't expect much if any pressure.

On the left side of the fuel rail there's a pipe/hose combination coming off the pressure regulator and attaching to the fuel rail. It has threaded meatl fittings at each end. You wanna splice into the rubber section of that hose.

I think you may have spliced into the return line....the one that attached to the left feul regulatir with a hose clamp and goes down to the fuel cooler

Cheers
DD

 

So in addition to fitting a fuel pressure gauge I have now fitted a voltage meter across the fuel pump. I have both gauges mounted on the dash. This is what I'm seeing.

1. In run mode, I get 38 PSI, and 13 volts. after 2 seconds drops to 0 PSI and 0 volts
2. In crank mode, I get 38 PSI, and 9 volts. Engine coughs and stumbles
3. Trying cranking again, I get 0 PSI, and 0 volts.

wait 10 minutes, and it repeats again.

So this is what I'm planning:

1. Replace the fuel pump relay
2. Clean out the entire fuel system and tank
3. Replace the ECU

I'm reluctance to do 2 or 3 without knowing for sure what the problem is. Does anyone have any thoughts on this?
Many Thanks

Toby

1990 XJ-S
1986 XJ6
2007 S-Type R

 

So I replaced the fuel pump relay, and the symptoms persist. So what can cause the fuel pump to receive zero volts?

 

To narrow things run a jumper ground to the orange wire at the f/p relay. This bypasses the ECU. See if anything changes. The fuel pump should run whenever the key is "on"....providing it has supply voltage.

If no change unplug the f/p connector and run a direct 12v voltage feed to the pump. This bypasses the relays. See if anything changes. The pump should run at all times.

Cheers
DD