TQ: Fuel Pump/Relay Woes

[PaulHere]

Peter has a problem with his 1982 2.0 car, can anyone help? PaulYou were good enought to help last year when I had an ignition problem which I eventually got sorted but I have now had a different problem for close on a year which I cannot solve - perhaps someone has had similar. My fuel pump relay does not activate the fuel pump unless I bypass ithe electro magnet inside the relay. I read in the Haynes manual that the relay also activates the warm up regulator and the aux air intake valve (hence possibly the massively poor running at start up which I had managed to solve previously by replacing both of those). Haynes states that the 'ignition in the start position pulses from the transisitorised ignition control unit energise the fuel pump relay...' The ignition control unit is on the right front wheel arch inside the engine compartment and smells a bit inside so I rather thought might be the culprit in not transferring voltage through to the fuel pump relay and I today contacted a breakers yard for a price (£89+vat +p&p). They indicated that this box controls the spark to the plugs(?) referring to it as the spark box and that it is unlikely to be that since the car will start when fuel pump bypassed? Wiring diagram seems to suggest a green negative lead from the relay direct back to the ignition coil negative no1pole and a tachometer, and a black positive lead to the relay for the electro magnet (which appears to feed on my car from the fuses for the pop up lights and additional headlights both of which work). The relay has a separate fifth lead earthing back to the bulkhead which is ok. I have purchased a new relay but still no joy. The fuel pump fuse is 16amp as the vehicle handbook shows and ok(although I notice the Haynes wiring diagram shows 25amps protecting the fuel pumps, warm up reg and the aux air intake valve)! Any suggestions why i cannot get the electro magnet in the relay to kick in? Is it inadequate voltage to or from the coil Regardspeter Haddock

 

[Mike_Pollock]

Hi Paul
I've got no idea but I'm sure some of the 944 guys would have ideas
Mike

 

[924nutter]

I would rule out the low voltage at the relay terminals as the pump runs when you bypass it. Check the conductor to term 1 on the coil for continuity from its pin within the relay socket. This, I have always believed, is a fail-safe device to kill the pump in the event of a stalled engine with ignition on. My understanding is that the back emf from the decaying spark voltage is detected by the circuit in the relay, enabling it when changing voltage is detected. FYI earlier models had an earth return on the metering unit, earthing through the plate-stop. When the plate lifted(i.e. engine sucking air) the earth was broken. Of course this didn't help in a crash with the vehicle upside down. This will at least give me the chance to review the circuit diagrams again.

 

[924nutter]

Okay. Check for 12v at terminal 50 and terminal 15 of the relay socket, when the starter is cranking. 12v at 50 should drop to zero on key release. Term 15 should hold 12v ign on.

 

[PaulHere]

PaulThanks to your '924 nutter' - will have to pursue when i get back from 1weeks hol from tomorrow . I can check the continuity term 1 on coil to relay socket pin ok -however the relay socket doesn't have a terminal 50 to test 12v - it has 30 and 87 which are the battery feed and the pump feed; 31 which is the earth to bulkhead above ; and 1 and 15 which appear to operate the electro magnetic contact in the relay - 15 the ignition live feed and 1 connecting back to the coil negative 1 terminal (I think). My bypass method is rudimentary - just wedging the points together within the old relay. My horn and the 2 handbrake dash lights have also stopped so maybe there is a lack of connection in the key ignition - any likely connection?

 

[924nutter]

Having double checked, only the early wiring diagram shows a connection to 50 which is actually feed to the starter solenonoid.
Try disconecting the feed to the tacho which also comes from Term 1. It is probably a green wire. The tacho may have a fault dragging the signal down.