wozzoom

The patient: 1989 GTUs
The Symptoms: No fuel pressure

What I've checked so far...
1) If I jumper the fuel pump relay bypass connector that is located by the front passenger strut tower, the fuel pump turns on and I have fuel pressure. The car will start and run normally. If I pull the jumper, the car dies when the fuel pressure runs out.

2) I checked the "Fuel Pump Resister Relay" and "Fuel Pump Circuit Opening Relay" according to the S5 factory manual. Both relays pass the resistance checks.

What's next on the list of things to check? I'm thinking possibly the neutral switch on the transmission? I'm not looking to rewire the car, so I would like to fix the problem.

Thanks for any help/insight,
Jeff

wozzoom

3) I also checked for any ECU codes. There are none.

satch

iTrader: (1)

Does the car start and immediately die w/o the fuel check connector jumpered or does it not start at all? If it doesn't start at all then check the Black/Red wire at the circuit opening relay (top row far left wire) and it should have voltage w/key to start and the clutch pedal depressed. If it does not have voltage then that's your problem. If the B/R wire checks out okay and the car starts and then dies then the likely cause is the ECU as it is supposed to supply a ground on the Brown wire w/the car running.

wozzoom

The car does not start at all without the fuel check connector jumped. It just cranks. I checked the Black/Red Stripe wire: With the clutch pressed and the key to start, I'm seeing 9 volts. I have 11.9 volts at the battery. The service manual says I should see 12 volt on the STA lead while cranking. Does this point to ECU?

Something else I just noticed: on page F1-57 of the FSM, the section for testing the Circuit Opening Relay Voltage, it states I should have 12V with the ignition SW: ON, at terminals Fc and B. I'm seeing 11.9V at terminal B, but nothing at terminal Fc.

Fc is the lead to the Fuel Pump Switch.

Thoughts?

satch

iTrader: (1)

I'm familiar w/the wire colors and not the code you provide. You know the B/R wire is supposed to have voltage w/key to start. The Blue wire runs to the resistor relay which then runs to the pump so the Blue wire must have voltage w/key to start or the pump will not be powered. And the solid Black wire (bottom row far left wire) must have a ground on it for the car to start. W/the meter set to continuity you would place one meter lead to the Black wire and the other lead to ground and if the meter rings out then you know the Black wire is grounded.

wozzoom

The solid black wire on the bottom row far left does ring out for continuity/ground. (This is the E1 wire in the FSM.) The Black/Red wire directly above it shows 9V while cranking.

The Brown wire with silver bands on the bottom right of the plug never shows voltage. According to the FSM, this brown wire that leads to the fuel pump switch should have 12V with the ignition on but I'm not seeing anything.

satch

iTrader: (1)

The Brown wire has voltage w/key to on because of voltage bleeding through the relay. And you forgot to mention if you find any voltage on the Blue wire w/key to start. Again, this wire feeds voltage to the pump via the resistor relay and it's a must that this wire has voltage w/key to start or it is not possible for the pump to run.

pfsantos

iTrader: (1)

I'd say try swapping the circuit opening relay with another of the same type. Just cuz it shows the right resistance doesn't mean it's actually completing the circuit when it activates.

Find the same relay, unplug the one in the car (leave it mounted for now) and plug in the replacement (without mounting it on). Just as a quick test.

pfsantos

iTrader: (1)

^ too late to edit: maybe someone knows an identical relay that can be temporarily swapped just for testing. One that isn't *needed* for the car to start and run?

wozzoom

I tested the blue wire. (Known as Fp in the FSM) I have 0V with the key to start. So there's my reason the pump isn't getting any power. So what's the culprit if there is no power on the blue wire?

satch

iTrader: (1)

If you have voltage at the B/R wire w/key to start and a ground on the Black wire but no voltage on the Blue wire w/key to start then the culprit is the relay. In your specific case the B/R wire and black wire are connected to one of two coils within the relay but that particular coil must not be working effectively or it would pass voltage from the B/W wire to the Blue wire.

wozzoom

Gotcha. Let me source a new relay and I'll let you know how it goes. Thanks for the help.

wozzoom

Ok, so I got a new Fuel Pump Circuit relay in the mail today. Plugged it in and...no good. Still no fuel pressure. I tested the B/R wire and the Blue wire and both had 12V, so that was an improvement. I went back to the fuel pump connector and found that I had 12V at the tank. Also an improvement! Next I swapped the fuel pump and bingo, we have combustion.

In conclusion, it was a combination of a 25 year old pump and a 25 year old relay going bad at the same time. If I had to guess I'd say a failing pump caused the relay to go bad. Thanks for the help solving this one.