Club 80-90 Forums

When I switch the ignition on the fuel pump normally primes for a couple of seconds then stops. Today I noticed it continued priming indefinitely.

It is gti swapped but on a digifant ecu (with an Elvis loom) so starting point has many similarities to stock efi setup.

My first query is looking for an explanation of, or signpost to the mechanism for the fuel pump priming to switch off - does it aim to reach a certain pressure? Is it on a timer chip or similar? Relay issue?

Engine ECU controls the fuel pump relay, initially when the key is turned to ignition it will prime for a few seconds - just a timer, there's no feedback from pressure etc.

Whenever the ECU detects the engine is rotating from the crank/dizzy sensor, it will enable the pump again.

I have a - presumably faulty - 191...numbered TCI that makes the fuel pump priming cycle every few seconds, rather than the single 1-2 second burst that is usual.
It also gets hot very quickly, which makes me think that it has an internal short that is sending a false signal to the ecu.

silverbullet wrote: ↑08 Sep 2026, 19:08 I have a - presumably faulty - 191...numbered TCI that makes the fuel pump priming cycle every few seconds, rather than the single 1-2 second burst that is usual.
It also gets hot very quickly, which makes me think that it has an internal short that is sending a false signal to the ecu.

Rather than waiting for an accurate "lock" on of the engine RPM which needs quite a few pulses to calculate, the ECU is very keen to trigger the fuel pump and will do so as soon as it sees any change of state on any timing signal.
If a TCI is iffy backfeeding a bit of noise down the signal wire, this could happen.