[loco]

i installed an hei and supercoil(thanks warchief) on my 66 326 today.
started it up, set timing and gapped plugs up to .045". starts perfect, idles smooth as silk but pops and backfires thru exhaust like a mofo ONLY when decellerating. responds crisp and full when i touch the pedal.

i set the plugs back to .035"-no help there.

plug color right on. i was gonna gap at .050" on up to .060"and see what happens. new 8.0 wires, everything tight and plenty of dc power to coil.

any other suggestions?

car did not backfire at all previously.

thanks pontiac people

[Malky]

Doesn't sound like you touched the exhaust at all but any chance you have an exhaust leak? That can cause popping on decel.

[Formulabruce]

whta the heat range of plug?, you have greatly changed it with the super coil and should keep gap around 40 max, as more gap is higher load on ele system and hotter spark.
may have to"richen"up carb, or back off timing, or cooler plug, a 44 maybe?

[Brian D'Amico]

Sounds like you might want to check your timing again... Maybe back it off a little.

[TransAm525]

Is that supercoil for reverse rotation distributors, or is it some universal Chevy item? The coil must be matched to the specific direction the distributor rotates. The pickup coil is matched to the coil and the rotation of the distributor. If you are running a clockwise rotation coil in a counterclockwise rotation distributor, the timing will be off and the polarity will be reversed, causing all sorts of timing issues. The fix is either to install the correct coil (with the correct white or yellow lead wire from the coil) or to swap the pickup coil to match the coil being used. Red/yellow coils go with yellow connector plug pickup coils. Red/white coils go with clear connector pickup coils.

I too ran into the same situation. I am running a 71,000 volt Petronix race only coil, but they only make them for clockwise rotation distributors. My fix was to swap the pickup coil to a clockwise rotation pickup. As long as the two match, the polarity will be correct.

[loco]

unfortunately i had to paint the kitchen and dining room today so i didn't get to play but i'll check timing and exh manif bolts and a/f mix tomorrow.

i hope the coil is the correct polarity/direction. it would probably sound like chitty-chitty bang bang if it wasn't. i won't rule out anything though.

i am also gonna disconnect the vac advance and retard a couple degrees.

if none of those work i'll do what i always do-mf the car for a few minutes and start again

happy motoring

[Schurkey]

Originally Posted by TransAm525

Is that supercoil for reverse rotation distributors, or is it some universal Chevy item? The coil must be matched to the specific direction the distributor rotates. The pickup coil is matched to the coil and the rotation of the distributor. If you are running a clockwise rotation coil in a counterclockwise rotation distributor, the timing will be off and the polarity will be reversed, causing all sorts of timing issues. The fix is either to install the correct coil (with the correct white or yellow lead wire from the coil) or to swap the pickup coil to match the coil being used. Red/yellow coils go with yellow connector plug pickup coils. Red/white coils go with clear connector pickup coils.

I too ran into the same situation. I am running a 71,000 volt Petronix race only coil, but they only make them for clockwise rotation distributors. My fix was to swap the pickup coil to a clockwise rotation pickup. As long as the two match, the polarity will be correct.

Distributor rotation has NOTHING to do with the color codes.

The main problem seems to be when the car is cranking. electro-magnetic interference from the starter can cause misfiring if you have the "wrong" coils. The black and clear/no-code pickup coils are identical except for the longer leads on the clear/no-code pickup coil. They are wound "backwards" from the yellow coded pickup coil. Since there are two ways to wind the wires on the pickup coils--clockwise and counter clockwise--there are two igniton coils to match them. Again, this is not the direction the distributor spins, it's the direction the wires in the pickup and ignition coils are wound.

Chevy, Cadillac, and Olds Toronado use the yellow coded pickup coil and the red/yellow ignition coil.

Buick and Olds except Toronado use the black coded pickup coil, and the red/white ignition coil.

Pontiac uses the clear/no-code pickup coil, and the red/white ignition coil.

Note that the Olds engines uses either coil set, depending on whether it's in a rwd or fwd car. The distributor rotation does not change. The FWD Toronado has the starter motor on the opposite side of the engine for transmission clearance.

You can verify this from Delco service information at:

http://fiedlerh.home.att.net/HEI.pdf

[TransAm525]

Here we go again...

Yes, it does matter. I do agree with the location of the starter cable, but the polarity is also different. The engine will start, and in most cases run fine, but the timing will change and the user may experience backfiring and eratic timing. Below is a picture of what the signal looks like when the coil fires. When the coil is mismatched, the signal is reversed. Do a search in the forum and you will see a 5 page discussion on this topic. One of the electrical engineers on this forum performed his very own test and found the same results I speak of.

[SlowSpitzer]

Okay, I will throw this in there.
MSD dist and MSD box. If the pick up coil is not wired properly, wierd stuff happens and engine does not run correct. Change wires, everything is smooth again!

[Schurkey]

Yes, there is different (magnetic--NOT electrical) polarity--that's why one coil set is wound backwards from the others.

The ROTATION of the distributor means nothing. That is why Oldsmobile can use either coil set and it is correct--depending on the location of the starter.

It is also why Buick (distributor rotates clockwise) and "most" Oldsmobiles (distributor rotates counter clockwise) use the same coil set--and that coil set has the same polarity as Pontiac (distributor rotates counter clockwise) although Pontiac uses longer leads on the pickup coil, and so it gets it's own color code.

As best as I can figure, the module triggers off of a pickup coil waveform when that waveform starts to go negative. The magnetic polarity of the pickup coil is chosen so that interference radiating from the starter/starter cable/alternator will cause a positive spike that the module is able to ignore. So, yes, polarity of the coils is important--but NOT because of the direction of distributor rotation. I do not know why the ignition coil is also magnetically matched to the pickup coil--but it is. That is to say, the car will run with mis-matched components, but it will work BETTER if the pickup coil is matched to the engine family/starter position, and the ignition coil is then matched to the pickup coil.

The "five page" thread you were talking about is an excellent but very long read:
http://216.178.81.108/forums/showthr...&highlight=HEI

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