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HX 308 with HEI

Hi guys,

I've got a 77 hx monaro with a red 308

i'm experiencing a bit of random backfiring when the car is under acceleration and sometimes if i rev the car in neutral.
i'm going to replace the plugs and leads and give the dizzy cap a clean on the weekend but i'm trying to run down the list of things to check and wanted some help on the hei dizzy, coil and ignition as it was already setup on the car before i brought it and i think i have a coil / electrical issue.

The car has a Bosch HEI with a points cap that looks exactly like this
https://www.kingswoo...

The coil is a Bosch GT40 coil

and the ignition looks like something out a vn i think - like this FileSC00025 1.JPG - Holdenpaedia

my question is - should i be using the GT40 coil with this setup or should i be using the Bosch HEC-716 coil?

while the car was running put my multi meter on the + and - of the terminals of the gt40 and the volts were fluctuating between 4.5-6.5v -is this correct? shouldn't it be getting 12v here? is it because i might have a resistor in my wiring somewhere? or is it from the electric ignition module?

i'm a bit confused what i should be looking at as I've gone over both pages
Bosch Hall Effect Ignition - Holdenpaedia
Bosch HEI - Holdenpaedia

and the setups are different

cheers

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I would check as to whether the resistor has been bypassed. From memory on that model of car, the 'resistor' is a very long length of wire coiled up. Others here will be more accurate with advice.

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yes the original resistance was built into the wire...so you need to make sure you have full 12V when engine running and a 12V coil...the original setup applied 12V only during start and then dropped to about 8V when running via the resistive wire.. if you follow the wiring back from the coil there will be a junction and there will be a yellow and pink wire running to ignition switch...you can cut the pink running to the ignition coil (not the ignition switch) and bridge the yellow to the ignition coil to the pink wire ..that way you will always have 12V for run and start...from the pink that runs from ignition switch to fuse panel... ....check the spec of the coil as well and make sure you have a type that is compatible with the HEI..

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Andrew

thanks for your replies guys, i didnt get a chance too look at the car this time i was home but next time i should and will report back

appreciate the replies

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In addition to the above, you should check the module it has a thin silicon paste under it, this paste is conductive (it also acts as a heat insulator), if the paste gets old it can affect the modules performance
Jaycar sell the paste, I have also had issues with the newer modules (not as good as the Bosh originals)

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Q37JR

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