Resting fuel pressure at rail

[Nikkum]

I think my fuel pump is responsible for poor starting, occasional hiccups and surging. I decided to check fuel pressure on SCI fuel line and when I took the line off the injector there was no fuel in it. I'm sure I've read somewhere that there should be a significant resting pressure and if not the pump is probably dodgy! Is this correct? Could it the FPR?
incidentally my 1985 FI doesn't have a charcoal canister vapour circuit so this can't get blocked.
Very grateful for any advice.

[RRoller123]

Sounds like the FPR is not working. It should hold pressure over some reasonable period of time, like at least a day or so I believe.

[rridge]

The real test for a fuel pump is whether it can meet the engine's flow requirement at full power, not something that can easily be tested. Second best is to test pressure with engine running at idle. Resting fuel pressure with engine off tells you whether the check valves are holding pressure after the engine is shut down. One check valve is in the fuel pressure regulator. The other check valve is in the fuel pump. Either could be at fault. The most common cause of a faulty check valve is debris from tank corrosion and/or failing fuel lines. Before replacing any fuel system parts, remove the fuel sender on the top of the tank, point a flashlight at the bottom and take a look.

Fuel rail pressure can be checked at the cold start injector with the engine idling and the vacuum line to the fuel pressure regulator disconnected and plugged. The pressure should be between 36-40psi. If it is substantially more then there is a a regulator or gauge problem. If it is less then it could be either pump or regulator. Rule out the regulator by pinching closed the return hose from the regulator. If pressure does not rise with the return flow temporarily cut off, the pump, its filter or its electrical supply are suspect. Full test details are in the service manual.

A low pump pressure due to blocked tank venting can be ruled out by doing the fuel rail pressure test with the gas cap removed. I believe 1985 Spiders delivered to North America came with carbon canisters. Possibly someone has modified your car's tank vent?

[Nikkum]

V helpful and many thanks. Great post. I will do that!
I am in uk and I think someone has had a fair fiddle with this car. It's right hand drive. Had no lambda sensor fitted and p.o. had taken plug off idle mixture screw on AFM.
Gradually getting to grips with it! Many tx. Nick