The V8 Owners Forum -

Hi eveyone,
I have just upgraded my engine from a 3.5 with a flapper to a 3.9 Hot wire.
Question is, is the 14CUX compatible with my MSD ignition? I have the 6AL with the MSD dizzy too.
I had to use a tach adaptor in the old flapper system from the tach output on the msd to the ecu, is it the same on the new ecu?
I think it should go to the white&black wire on pin 39, but will this affect the tune resistor? I guess i need to keep it in place?

Thanks Bieny

i have a mallory 685 ignition unit on my car,
and that was not compatible with hotwire system, we tried a tach adaptor and this did not help either,
in the end we had to use an ezi-trigger set-up from mallory, this cured the problem but we had to have two coils,

the new vems ecu works perfect wiothout any of the above adaptors

I have read that MSD works fine with the 14CUX, but we were also told so did the HYFIRE and then found out we could not start our cars when it was hot.

However I do feel that this may have been down to voltage drop across the main cable as I also suffer from the same problem now when my fans are running.

I think you will need the tach adapter to be honest.

ok ill try it with the tach adaptor, i remember from when i installed in the flapper it that i could not get it to work from the negative side of the coil but only from the tach output on the side of the unit.
i also ran the rev counter from there but not through the tach adapter if that makes sense.
Do you think it will affect the tune resistor in anyway? a technical explanation of just what the tune resistor does and how it works would be great
cheers for the quick response

it wont effect the tune resistor at all. The tune resistor basically just tells the ECU what map it should be running on.
Dont run anything of the neg side of the coil when running capacitive discharge ignition like the msd or highfire. These units put around 400 volts to the coil and not 12 like a normal system. If you connected your old ecu to the neg of the coil your very lucky you didnt blow it to bits. The ECU must have been better protected than I thought it would have been.
Always remember that all electronics have blue smoke built into them and once you let that smoke out it wont work anymore and you can never get it back in

katanaman wrote: Always remember that all electronics have blue smoke built into them and once you let that smoke out it wont work anymore and you can never get it back in

you have such a way with words mate

Your a funny man Marki

so am i correct in thinking its the black and white wire on pin 39 that is the pulse input to the ecu? some has told me its should be a blue and white wire?!? confused now

bieny wrote:so am i correct in thinking its the black and white wire on pin 39 that is the pulse input to the ecu? some has told me its should be a blue and white wire?!? confused now

It's pin 39, on mine (hotwire around '93 vintage) the wire is white with a black tracer iirc.