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3.9 EFI (hot wire) over fuelling

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My 3.9 hot wire efi is suffering from excessive over fuelling. The plugs are jet black after only 50 miles or so.

I have changed the ECU temperature sensor and fitted a new air filter.

Any other ideas? What should I be looking at checking / replacing next

Thanks in advance.



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Is the fuel pressure relief valve / pressure regulator working? There is an air temp sensor in the airflow meter, also if the airflow meter is knackered that would do it. If there is an air bypass on the AFM (like flapper) try opening it up to lean it out.

Do you have lambda sensors, if so are they working?

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I read somewhere that your require a 470ohm resistor in there somewhere if you are not running Lambdas....

Mine was running rich and sooted the plugs after a while... Resistor was duff... Fitted new resistor which effectively told the system there were not Lambda's and all working fine now...

Might also be worth checking advance / retard mechanism.. Mine was dead (Diaphram holed) which meant I wasn't getting the best burn in the cylinder....


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