No spark from dizzy, #6 cyl. only

[jebbach911]

There is surely a simple explanation for this or something I am overlooking but it is hurting my brain to decipher this problem, so here it is. No fire out of the distributor on #6 cylinder only. All other cylinders fire hot. Engine is 76 911S, 2.7 w/ 40 IDA Webers, MSD 6AL ignition, Crane Cams Fireball PS91 coil, Magnecor KV85 plug wires. I've changed plug wire on #6 but there is nothing coming from the brand new distributor cap on #6 only. I just today replaced the distributor cap and rotor with new parts from Pelican. When this issue started was when I let a friend AutoX this car and he spun out and killed the engine. When he tried to restart the car he pumped the hell out of the throttle and it was missing on one cylinder when he brought it in. I thought maybe he just fouled a plug so I changed out #6 but it didn't make any difference. It will hit every once in a while but won't pick up that cylinder. I checked compression on #6 and it is normal. It is definitely ignition related but why would it affect only one cylinder and all the others have normal hot spark?

Thanks in advance for any help on this issue!!!

[Jonny H]

Is that #6 distributor wire right next to the engine tin for the left side heat? Make sure there is least 3mm clearance or the spark will prefer to take the short path to ground.

[jebbach911]

Thanks for the response, but no. Not near any tin and not able to get any spark from the #6 hole. I've even put a screw driver in the #6 hole and ran another one to ground to check for any spark and that hole is dead.

[Mr Beau]

Swap high tension wires around...

[jebbach911]

Mr Beau, thanks but already tried that.

[Mr Beau]

If you stick a known good wire into the distributor and don't see a spark on only #6 then wouldn't it be a problem with the cap or trigger?

[911obgyn]

Check play on the distributor shaft?

[jebbach911]

Originally Posted by Mr Beau

If you stick a known good wire into the distributor and don't see a spark on only #6 then wouldn't it be a problem with the cap or trigger?

I completely agree, but this is the third distributor cap I've tried and same results. Two used ones and now a new one that just arrived today.

On the trigger, it has a Pertronix conversion so maybe the distributor shaft bushings are worn as was suggested by 911obgyn and the pick-up rotor is touching the sensor at the #6 spot.

I will wiggle the shaft, reset the air gap and get back to you on that one.

Thanks for all the comments!!

[porschyard]

Originally Posted by jebbach911

I completely agree, but this is the third distributor cap I've tried and same results. Two used ones and now a new one that just arrived today.

On the trigger, it has a Pertronix conversion so maybe the distributor shaft bushings are worn as was suggested by 911obgyn and the pick-up rotor is touching the sensor at the #6 spot.

I will wiggle the shaft, reset the air gap and get back to you on that one.

Thanks for all the comments!!

I was just getting ready to ask if it had a Pertronix or points. check the windows to make sure there is no obstruction.

Richard

[jebbach911]

Originally Posted by porschyard

I was just getting ready to ask if it had a Pertronix or points. check the windows to make sure there is no obstruction.

Richard

Ding,ding, ding. We have a winner!!!
This Pertronix set up didn’t have windows but has 6 tiny strong magnets and #6 magnet had fallen out of its groove. Simple fix and very much appreciate the brain trust of this forum!!!

[porschyard]

Originally Posted by jebbach911

Ding,ding, ding. We have a winner!!!
This Pertronix set up didn’t have windows but has 6 tiny strong magnets and #6 magnet had fallen out of its groove. Simple fix and very much appreciate the brain trust of this forum!!!

I have not seen a Pertronix unit in 20 +years but back in the day i had a couple that got a small amount of debris in one of the window slots and had the same symptoms.
I did not know they had gone to magnets so we both learned something

Richard