The V8 Owners Forum -

Hi all we have just installed a Hotwire EFI 3.9 into a Range Rover that had flapper we have replaced the harnes.
We've checked there is a live supply and a switched live supply and the 2 earths go to the battery neg. the gearbox inhibit switch is working and putting an earth to the ecu. The problem we have is the fuel pump is not running the relay is getting the switched supply but it isn't getting the earth signal from the ECU.
I know there is a wire from the earth of the coil to say the car is cranking and this is connected. We have tried the ECU on another car and it works.

Will the fuel pump run when just switching on the ignition or do you need a signal from the coil before it will run? Is there something else that can stop the pump ?

Mick

On a CUX14 ecu
Turn ignition on and fuel pump will run for about 3 seconds then turn off

Start cranking and the fuel pump starts up again

There is a wire from distributed to air flow meter that is easy to play verso ok and causes Jon starting

Ian

Sorry Ian don't understand your last statement, the problem I have is the fuel pump relay is not pulling in there is power to the relay but the signal from the ECU to Earth the other side of the relay is not present.

Mick

texpis wrote:Hi all we have just installed a Hotwire EFI 3.9 into a Range Rover that had flapper we have replaced the harnes.
We've checked there is a live supply and a switched live supply and the 2 earths go to the battery neg. the gearbox inhibit switch is working and putting an earth to the ecu. The problem we have is the fuel pump is not running the relay is getting the switched supply but it isn't getting the earth signal from the ECU.
I know there is a wire from the earth of the coil to say the car is cranking and this is connected. We have tried the ECU on another car and it works.

Will the fuel pump run when just switching on the ignition or do you need a signal from the coil before it will run? Is there something else that can stop the pump ?

Mick

The pump should run for a couple of seconds when you switch on (without starting) to prime the fuel rail. It stops to prevent flooding if there was a weeping injector, and the ignition left on. Can you hear the relay click, if the pump doesn't run?

Also, are you using the correct relay for the hotwire? It is an odd twin output type, with a series diode to the coil. If the wiring to the relay coil got swapped round, the relay wouldn't operate. As you probably know there are several relay variations that fit the same 5 pin base.

According to my diagram, +12v goes to pin 86 and the coil ground to pin 85.

Thanks for the reply Dave I thought that is how the pump worked unfortunately mine isn't doing that. The live comes from the ignition switch to pin 86 and pin 19 on the ECU. The earth which comes from the ECU pin 16.
The relay is the one that came with the engine and loom purchased as a working set. The relay doesn't really matter because I am testing at the relay base for power, I get 12v at the base from the ignition but do not get the earth from the ECU. We know the fuel pump system works because when I earth the relay the pump works.

Mick

Just to check - you have tried it with the relay in place? Some types of solid state switching won't work without getting the 12v via the relay coil.

Is the ECU getting 12v? Pin 2 and 15.

Thanks agai for the reply yes the relay is in place when testing I have power at pin 15 haven't checked pin 2 where does pin 2 get its supply from?

Mick

Pin 2 is, I think, the feed to the ECU from the main relay.

Thanks for the help guys sorted now the main relay was pulling in but the contacts weren't making so no supply to ecu pin 2.

Mick

Thanks for the help guys sorted now the main relay was pulling in but the contacts weren't making so no supply to ecu pin 2.

Mickq

Thanks for the help guys sorted now the main relay was pulling in but the contacts weren't making so no supply to ecu pin 2.

Mick

Word of warning here those Bosch Hotwire relays are notoriously unreliable so if you have got yours working by cleaning contacts etc I suggest you get a couple of spares they are bespoke for the Lucas system so not any old generic 5 pin relays will do both are identical

They are basically a single pole on/off relay with twin output terminals, and a series diode to the coil. You can just about see this in my schematic above.

Vehicle wiring products do one which is suitable - but you'd have to add the diode externally. If the genuine item is a silly price.

The flapper uses a similar relay, but without the diode. Think the diode ones are identified by a red strip.

They don't seem unreliable on the flapper, though.

DaveEFI wrote:They are basically a single pole on/off relay with twin output terminals, and a series diode to the coil. You can just about see this in my schematic above.

Vehicle wiring products do one which is suitable - but you'd have to add the diode externally. If the genuine item is a silly price.

The flapper uses a similar relay, but without the diode. Think the diode ones are identified by a red strip.

They don't seem unreliable on the flapper, though.

The same relay with the diodes was used on BMW'S back in the day too Dave, euro car parts sell a quality alternative

Hmm we used the relays off the old Flapper system they worked fine what is the diode for?

Mick