intermittents fuel pump issue

[l6rth]

Hi all, I have an intermittent issue with the fuel pump not priming and I have changed the relay and this has not cured it. apart from checking the wiring obviously is there something I else I should be looking for or is the pump on its way out?

Thanks

Rob

[paulathome]

Have you changed both relays as the power for the fuel pump goes through both.
Also check the connections at the pump located near the nearside rear wheel on the side of the chassis.
These conections get pretty cruddy especially if the rubber boots covering the spade connections are missing.

Paul.

[l6rth]

just the fuel pump relay paul, I was not aware the other relay had anything to do with the fuel pump, is it the same relay?

[paulathome]

Hi Rob, both relays are the same type. The first relay powers up the ecu which then switches the fuel pump on and off
via the second relay. That's why swapping relays around will make no difference if one of them is faulty.
Both of them are on the loose bit of the loom dangling in the foot well.
Paul.

[Richard 858]

+1 regarding the relays and as you've already alluded to Rob I'd check the fuel pump connections, if the rubber boots are damaged alot of crap can get in, another example of excellent TVR locating !

[davep]

As far as I can make out the 14CUX Fuel Pump Relay and Main Relay operation on my '92 TVR Griffith works as follows:

1. Prior to ignition a battery voltage of ~+12 Vdc (N) is applied to the Fuel Pump Relay (COM pin 30), the Main Relay (COM pin 30 and Coil pin 86), and ECU +ve supply (pin 15) where it maintains battery backed memory values.

2. When ignition is switched On, a battery voltage (WS) is applied to the Fuel Pump Relay (Coil pin 86) and to ECU ignition sense (pin 19). The ECU, via pin 16, now earths the Fuel Pump Relay (Coil pin 85), the relay is energised feeding +12Vdc (WO) to the Lambda sensors, the fuel pump (WP) via a fuse and the Inertia Switch, and the Purge Control Valve (if fitted).

3. Next the ECU, via pin 12, earths the Main Relay (Coil pin 85), and the relay is energised feeding +12Vdc (NO) to the injector circuits, the AFM, and ECU pin 2, where Main Voltage is monitored for injection pulse width purposes.

4. During step 2 the ECU starts a fuel pump delay count, if this reaches zero before cranking occurs the ECU removes the earth from pin 16, and the Fuel Pump relay is de-energised.

Other cars may work differently but I HTH.

Edited by davep on Thursday 19th March 16:25

[spend]

The positive power arrangement varies quite a lot across model development life cycle (both LR & TVR + perms/combs of both) so take each case as it comes for all combinations of main & fuel for both coil & load supplies. The only thing that seems constant is that the ecu grounds the fuel relay coil to activate the fuel pump (and only for a moment as the ecu is powered up until the engine is running).

The ECU relay wiring is a very tricky area to write definitive posts on, as many of the cars have cunningly different schemas (up to the extent of early cars only having one relay ~ and thats even in the fusebox!)

Caveat Emptor reading or writing on the subject is the best approach IMHO.