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V8 Question.

88 Nick

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Hi,in my never ending quest to sort the missfire on my 3.9 efi,the next item Im going to try replacing is the AFM, the one fitted is the 3AM type. My question is,is the 5AM type interchangable as there is one coming up on eblag shortly? Thanks in advance,Nick.

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Contrary to popular belief they are interchangeable but you will need to setup the 5am correctly, but I would doubt that it is the cause of your misfire unless the mixture is very, very lean. ………………IIRC early'ish RRC's had a 3am and the early 90's discos had the 5am.

The trim pot needs to adjusted to 174ohms using a digital multimeter …………. Do not use an analogue meter.

Another way to set this is to connect a multi meter ………… negative to the Red/Black and positive to the Blue/Red and set the voltage to 1.25 volts with the ignition on and the engine not running. These figures assume that you have already set the throttle pot up to 300mV …………….. IIRC this procedure is shown clearly on the RPI site.

These settings will ensure that the CO is more of less correct.

BTW: Adjusting the trim pot anticlock (less resistance) richen's the mixture and clockwise (more resistance) weaken's the mixture.



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