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3v8 efi injector problem PLEASE HELP


oldgit1

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Hi guys I have a 3.5 v8 efi engine in my range rover based race truck, it was running great till saturday at king of the valleys when it cut out and refused to start, after trying to fault find it became obvious the injectors were not firing, we tried a few things then changed the engine bay wiring harness still to no avail, it was at this point i installed a 3.9 efi hotwire system to it and again still have no injectors firing. can any1 help?

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The ECU doesn't fire the injectors until it gets pulses from the coil -ve terminal (white/black wire, sometimes via a relay on a white/blue wire). 1st check you've got sparks, if the ignition amp is dead then no sparks = no pulses = no injections.

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we have lovely spark just no injections. we have tried 4 different wiring harnesses all with the same outcome, im at wits end with it and am starting t feel I should just dump in a tdi lump but id much rather stick with a v8 if I can

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what was the original system? If it was a 4CU I assume you changed the injectors over as well, I dont think they would play nice with the hotwire system. Are you testing the injectors with one of those noid light things? either way I would check that there is 12v on one of the injector pins with the ignition on to start with and fault find that if necessary as it is easy to do. Maybe check the fuel pump relay as well (I have had one of those fill up with carp and click but not work). And my last thought would be to check the wiring from the coil to the ECU, I think there should be a black resistor in there with spade terminals on each end, if memory serves there may also be a funny relay mounted near the airflow meter, mine had this removed before I got it and the wires connected.

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The flapper system requires the flap to be slightly open (you can hear the fuel pump run when you poke the flap) & pulses coming in on the TACH wire from the coil -ve. I don't know about hotwire, it may only require the pulses as there's no switch contact in the airflow meter that I'm aware of.

If you have flapper-type (low-Z) injectors on a hotwire loom you will be missing the resistor pack for limiting injector current and may burn something out, either the injectors or the ECU. The other way round (hotwire injectors on flapper loom), you will have high-Z injectors plus the resistor pack and probably the injectors won't get enough current to fire.

You need to check for continuity from the coil -ve to Pin 1 of the ECU if it's flapper, Pin 39 if it's hotwire. There may be a small black resistor in-line with that wire.

Also check that, with the ignition ON you have power to the ECU and injectors, including when cranking as it's possible to have it wired so it's live but goes dead when cranking.

Flapper loom:

lucas_efi_1982_1984.jpg

Hotwire loom:

lucas_efi_1988_1989.jpg

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