Diagnosing a Non-Firing Cylinder - SS454

[jays55]

Hi Gang,

Looking for some diagnostic help with a non-firing cylinder; 1970 SS454 stock motor, updated with Pertronix electronic points replacement kit and coil in 2016 (no points/condenser).

Recently began to "miss".  Pulled the plugs and #4 was "wet".  Pulled the plug wires at the distributor and there is no spark jumping at #4.  I went ahead and replaced plugs, wires, distributor cap and rotor.  #4 still not sparking at the cap/wire connection.....

That's about as far as I know to go with diagnostics.  Maybe a problem with the Pertronix unit?  I contacted Pertronix, but haven't heard anything back.  I would like to know what I'm looking for, before I start pulling the distributor, etc.  Anyone have experience with one cylinder not firing and not a rotor/cap/ware/plug issue?

Thanks for you input......  

[1970mcss]

I was going to say cap but I see you replaced it. I have the same setup so I'm interested to know if Pertronix has any issues with there unit. Keep us posted to what they tell you....good luck

[imr]

do you have spark in the other 7 cylinders? how much play do you have in the distributor shaft?

[jays55]

16 hours ago, imr said:

do you have spark in the other 7 cylinders? how much play do you have in the distributor shaft?

Didn't check them all.  At the distributor cap, I pulled #4 first, since the plug was wet (other plugs looked normal).  I pulled 3-4 more wires at the cap to check them and all had spark flying.  Didn't check the shaft for play, but don't know what would be normal.

The only thing I did differently before it began missing, was I had the car idling for a while as I charged the A/C and the temp went up to 225-230 degrees (185 is normal).  Was running smooth when I shut it down.  At next startup, the miss was there.

Thanks

[cny first gen 71]

What has Pertronix said? have you talked to there tech line? I have that system in my 71 350 and it works great. When I installed it I did call tech line with a couple questions and they were helpful.

[imr]

odd to have no spark in 1 cylinder. recheck cap, rotor wires. make sure the tang in the cap drops in the notch of the distributor. the ones that have spark what color is the spark?

[Ian]

I would try swapping wires, you are saying if you pull the wire at the cap it does not jump the gap between the wire and the cap? Sounds like a broken wire...

[jays55]

59 minutes ago, imr said:

odd to have no spark in 1 cylinder. recheck cap, rotor wires. make sure the tang in the cap drops in the notch of the distributor. the ones that have spark what color is the spark?

odd .... for sure!  Cap is aligned, spark on firing cylinders was white (if I remember correctly, will check again).  One day is was running smoothly, the next day missing.  Replaced cap, rotor, wires, spark plugs .... no improvement/change from prior.    I am baffled!

[jft69z]

When you're pulling the wire at the cap to check for spark, is it with a wet/fouled plug still in the head? Even though it was replaced, if it's not firing it can get wet and not fire pretty quickly. If so, maybe try getting a new plug (Leave the wet one still in the head if you want), hook it up & lay it on the block or something to ground the shell. See if it sparks then. Reason I ask, if the plug is fouled out/wet it probably won't spark if checking at the distributor cap. A new plug laying outside without the chance to get soaked, should spark if all is good in the ignition system.

If it works, then maybe something else is happening in that cylinder that's causing that plug to get soaked. You mentioned it got hot, and then started missing after that...that may be a clue to start thinking about if the spark test above works fine.

[MC1of80]

One cylinder not firing at the distributor does not sound right. Especially if the rotor cap and wires are new.

I agree with jft69z. Try that first. I feel it's a bent valve, broken valvespring or something with the valvetrain. 

Good luck! 

[jft69z]

I'm just hoping the 'wet' spark plug is fuel, and not antifreeze related.

[jays55]

Thanks for the great input.  I am a long-time "shade tree" mechanic, so I keep hoping I'm overlooking something obvious! 

Pulled the #4 plug wire and attached a new plug outside the cylinder.  Engine running, there is no spark at that plug when held to a grounding surface.  There is no spark at the distributor cap, when the #4 wire is pulled from the cap.  The other cylinders have a spark when the wires are pulled from the distributor cap.  Seems to me that rules out the rotor, cap, wires and plugs (all of which have been replaced since it started missing).

How would a broken valve spring, or bent valve effect the spark at the distributor, if the cam is turning the distributor (7 cylinders have spark and engine runs, but with a miss)?  I will probably pull the valve cover and check for a broken spring, though I would be confused how that could cause a miss-fire.

I don't understand how this can be a problem with the Pertronix unit, but I did contact them and haven't heard anything back, yet. 

[MC1of80]

It won't. Like you said, it makes no sense that one plug, moreover one terminal of the distributor doesn't fire. The valve springs and bent valve were if you did have spark to check further.

Silly question, did you ohm out the new wire or switch it with another to rule out the wire? Chances are it's good,but nowadays ya never know. 

Do you have another distributor you can switch out with? 

[jays55]

OK, I just called Pertronix and did get through to tech help this time.

He said the kit's ring that goes under the rotor has 8 magnets.  He seemed sure one of the magnets flew off.  Without hesitation, he is sending me a replacement ring, so I can fix it when I pull the distributor.

On hold until that part arrives, but very hopeful.  I will update, as this would be great info for anyone having a Pertronix unit to know.........

[jft69z]

Wow, that's great to hear. Hope that fixes everything up nice & easy.

Only other thing I might do would be to swap that wire with another one that is about the same length that is known good. Just because the wires are new, doesn't mean they are all good. Or, like Tom said, use an ohmmeter to measure the resistance of the #4 wire compared to another one. Doubtful that's the problem though, what's the chance the same wire would be bad on your originals and the new set.

[MC1of80]

Wow! That would be great if thats it! Will be waiting to find out with my fingers crossed for you! 

[Paul Bell]

1 hour ago, jays55 said:

He said the kit's ring that goes under the rotor has 8 magnets.  He seemed sure one of the magnets flew off.

That would certainly prevent just one spark tower on the cap from producing an arc.

Glad you figured it out!

[cny first gen 71]

Is that what they are magnets I wondered about that. It makes sense, I'm glad they stood behind it. Hopefully that's it.

[imr]

oh you have one of those. that definitely makes sense. let us know.

[jays55]

Replacement ring arrived from Pertronix.  Pulled the distributor and the ring had a rub/tear in the material below the #4 magnet!  Replaced the ring and now car is running great again!

This is "must-know" info for anyone running a Pertronix electronic conversion.  I will create another post about this fix, so it will show up better in searches.

Thanks everyone for your help.........

[MC1of80]

Glad that was the problem and that pertronix stood by their product. Thanks for the update. 

[cny first gen 71]

Glad its fixed, there tech guys do seem to know there stuff, and assume they didn't charge you? good they stand behind there product.

[imr]

can you show a pic when it is assembled. trying to get an idea

[Rob Peters]

Glad the fix was not too terribly difficult.

rob