Hello all my name is:Chris in the UK.
My 92 TT will not start. If I put 12v to the pump and leave it running car starts a runs fine at full pump speed.
My MFI relay seems different to what the manual describes, only 4 terminal’s see photo.
I have probed this relay and it has 11.5 volts, this is also at the fuel pump relay(12v) terminal 3.
I tried connecting the black fuel pump test
connector to the positive side of the battery, pump does not run.
I removed the ECU plug and checked for continuity from the fuel pump relay connector 1 on harness side and I have continuity to connector 21 on the ECU harness so wire is in tact.
Could it be that the ECU at pin 21 is not grounding?If so this will not activate the fuel pump relay??
If this is the case can I prove that theECU is not connecting to ground by making a connection from terminal 1 on the fuel pump relay to ground?,will this cause any harm???
If you have definitely managed to get +12v down the BLACK fuel pump test connector (there is a fake cap on it, take that off or be sure to really get the wire down in there) then it means you must have a wiring issue from there to the fuel pump as that is a direct connection with nothing but wire and connectors inbetween.
When you say you put 12v to the pump, where did you do that, because between there and the black test connector lies your issue.
The car has been hot wired so the existing black/blue wire may be disconnected and replaced with a thick red wire. It has been used like this for 2 years.So I guess the test wire is not connected to the new “hot wire”. Cap on test connector was removed when I made the test.
To run the pump I just bridged the connectors on the new relay,( Eric Gross circuit that still uses two pump speed),that is connect both red wires on the new relay (thick red wire straight to battery the other to terminal 5 on the existing fuel pump relay.
5 years ago I had new sigma alarm fitted, I am just trying to find out how to disable it to do some fault probing it’s a little awkward with only having seconds before it disable things.
Really appreciate your support, summers passing and I am keen to run the car after the engine rebuild after spinning a big end shell.
In the common hotwire mod (where the relay is in the boot and there is another thick red wire coming from the battery) the black/blue wire doesnt usually become redundant and is instead used as the signal on/off for the relay. Sending 12v down the test connector should energise the relay and it then activates the big fused additional wire. Check for continuity from the test connector to the place where the black/blue wire is spliced into near the pump.
My additional relay is that shown in my last photo with the red and yellow wires. I cut the blue and black wire at the pump terminal and replaced it with the new thick red wire.So the black test terminal is now not connected to the pump.See photo.
If I take a lead from the positive side of the battery and connect to 4 on fuel pump relay the pump runs slow as this path goes through the resistor. If I take a lead from the positive battery terminal and connect to 2 on fuel pump relay pump runs fast.
So I wonder if either the MFI or the FUEL PUMP relay are not being grounded through the ECU?
I have had all relays off and tested with power to thier coils and meter to prove contact through on each relay connect.
On the fuel pump relay (which goes through the ECU to ground) is something in the ECU switching this on and off to regulate fuel flow and if so could this be a problem?
To conclude:
All wiring tested for continuity, all OK.
Then last thing I tested was the yellow wire from the added relay that is earthed by a nut that used to mount the original air filter, see first photograph. The was no connection to earth. Corrosion had formed between the nut and the eye connector.
Cleaned it up and all working.
