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3.9 v8 fuel pump priming but not when cranking ?


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I recentley done a 3.9 serp hotwire convertion and was running lovly wen fuel pump was running constantly on original wiring but not good for safty reason SOOOO i wired the pump up to the fuel pump relay (white /purple i think) now the pump primes when ignition is switched on but nothing when cranking. Ohh and the little wire by the airflow meter to neg side of coil .

Can any 1 shed any light pls

Many thanks del

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I checked the wire between coil - and ecu pin 39 2day and I had 6.8 oms PLEASEEEEEE HELP I SOOO confused

As I can't get hold of any specialist by phone cheers del

As I say it runs lovely if fuel pump is powered up manually

Cheers again del

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The metal original relay . I have wired the ecu pickup to the neg side of coil.

As i say when ignition is switched on the relay clicks and the fuel pump primes the fuel system .but nothing when craking car runs for about 2-3 secs and cuts out

Cheers del

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I would double check that the coil is correctly wired up. The Coil is fed it's 12v from the amplifier loom (there's a T connection in there) and the -ve of the coil is then attached to the other side of the amplifier which handles the switching. It's worth disconnecting the amplifier and coil making sure you have 12v at the wire that was going to the coil +ve

It's possible to get the wires swapped and if you have the coil inverted the ignition will run fine but connecting the ECU signal wire to the -ve won't give a pulse to the ecu.

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I would double check that the coil is correctly wired up. The Coil is fed it's 12v from the amplifier loom (there's a T connection in there) and the -ve of the coil is then attached to the other side of the amplifier which handles the switching. It's worth disconnecting the amplifier and coil making sure you have 12v at the wire that was going to the coil +ve

It's possible to get the wires swapped and if you have the coil inverted the ignition will run fine but connecting the ECU signal wire to the -ve won't give a pulse to the ecu.

I tell u what u may be on to something here I've wired a switched ignition feed to + side of coil from them muiltyplug plug on the bulkhead I remember a wire having t wire I think from the same feed though

I check 2 mo thanks

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