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Spark leaking from plug to head
https://slantsix.org/forum/viewtopic.php?t=47977		 Page 1 of 2
Author:  65CrewCabPW [ Tue Feb 21, 2012 10:09 pm ]
Post subject:  Spark leaking from plug to head
I'm using a later head ( small diameter hex, no tubes), and I'm having issues with the spark leaking to the head around the plug. I put dielectric grease in the plug boots and it stopped it... for a while.

The spark plug wires are brand new Bosch, and I've also used some others. Same problem.

Right now, I'm not even running resistor plugs, and not a wide gap, either. This gets really annoying, and I have yet to come up with a good solution.
Author:  ceej [ Tue Feb 21, 2012 10:22 pm ]
Post subject: 
Wow. Even with HEI, MSD capacitive, and various magneto fired systems, I've never had those kinds of problems.

What wires?

I rate Bosch a couple fathoms beneath whale poop, but that still doesn't make a lot of sense.

CJ
Author:  SlantSixDan [ Tue Feb 21, 2012 10:29 pm ]
Post subject: 
If you have arcing down the side of the plug, you'll get a carbon track (which may not be clearly visible). If you do not replace the plugs and the wires at the same time, you'll transfer that carbon track from plug to wire and/or from wire to plug until you do replace the plugs and the wires at the same time.

Run good quality plug wires and good quality (NGK) plugs, and the problem won't reoccur.
Author:  65CrewCabPW [ Tue Feb 21, 2012 10:43 pm ]
Post subject: 
Let's see... I did precisely that... change the plugs and wires at the same time. And they are NGK plugs.

The Bosch wires can't be all that bad. They are steel core, spiral wound, with the boots bonded to the wire, and the metal snap on connectors are very, very well stuck to the wire, so they don't slip off.

It happens only under load, mostly at low speed, of course. If you let it idle and pay real close attention, every once in a blue moon you can hear it snap. Remember, this is an EDIS ignited engine, three coils, so it has twice as many sparks as a normal ignition. Not every spark leak results in a misfire.

BTW, I've owned 3 slant sixes, and all of them have had the same problem, and I've tried different brands of both plugs and wires, to no avail. The worst was Autolite plugs, the best has always been champion plugs, but I can't get Champions in the heat range I want.
Author:  ceej [ Wed Feb 22, 2012 12:05 am ]
Post subject: 
Wait a minute. Weren't you running propane?

CJ
Author:  SlantSixDan [ Wed Feb 22, 2012 8:51 am ]
Post subject: 
Quote:
The Bosch wires can't be all that bad (…) I've owned 3 slant sixes, and all of them have had the same problem
Most of us don't have this problem, even with high-zap ignition systems. It is clearly something you're doing or buying or using.
Author:  WagonsRcool [ Wed Feb 22, 2012 2:08 pm ]
Post subject: 
Take a 12V test light, conn the alligator clip to something metal on the engine. While the engine is idling, (carefully) wave the tip of the test light VERY close to the spark plugs & boots. If you get a sudden misfire & steady spark jumping to the light, then you found a weak spot in your igniton.

If you don't have high secondary resistance (open circuit in a coil or plug wire) then what I usually see drive up ignition kilovoltage is a lean run condition. (I assume that you didn't use pliers to install your plug wires).

(I am part of the multitudes of /6'ers who only have had spark problems with old/ worn out/ oil soaked ignition parts- & I had GM waste spark coil packs with 0.045" gap plugs on a previous EFI Dart)
Author:  ceej [ Wed Feb 22, 2012 4:48 pm ]
Post subject: 
Ionization of the compressed Air fuel mixture is more difficult with propane.

Interesting problem. Even with the best of parts, this could happen.

CJ
Author:  KBB_of_TMC [ Thu Feb 23, 2012 9:31 am ]
Post subject: 
What spark gap and compression ratio are you running?
Author:  slantzilla [ Thu Feb 23, 2012 2:34 pm ]
Post subject: 
Just asking, but do you have a good ground strap from the engine to the frame?
Author:  65CrewCabPW [ Fri Feb 24, 2012 3:26 pm ]
Post subject: 
The engine is 10.5:1 CR, the boots are undamaged. I have copper shielding covering all the wires from boot to boot and it is tied to ground, by large copper stranded, to reduce the noise for the CB radio (made a big difference), and it's not leaking to the shielding, it's leaking from plug to head.

The plugs are NGK racing plugs ( non resistor). If memory serves, the gap is set at .030 rather than spec.

Engine to frame ground is actually a stranded 4 gauge battery cable. Very well connected.

The ignition is a Chrysler 3.3 coil, using a Ford EDIS crank - triggered ignition, with timing controlled by a MegaJolt.
Author:  Sam Powell [ Sat Feb 25, 2012 4:58 am ]
Post subject: 
Well, at least you found your miss, and it seems like a simpler fix than tearing down the engine for valve or head work. HOw have you determined that the spark jumps only from the wire? From your previous thread it seems this happens only going up hill at 3200 RPM and after some time. That seems like a situation that would make close observation difficult. I only ask because maybe it is a wire problem. Is it always the same plug,and how do you know that? I'm not being a wise guy, it is just that you want to be sure you have really excellent reason to eliminate a variable. These kinds of questions have to be asked. Otherwise you spend your time chasing ghosts. It sounds like you have a very well thought out, excellently executed engine management system that has one weakness that needs to be tracked down. I would change the plugs around and see if it does anything. If this happens always on the same plug, then install a new one there. They cost about 3 bucks. That's a pretty cheap experiment.

Sam
Author:  65CrewCabPW [ Sat Feb 25, 2012 10:14 pm ]
Post subject: 
Quote:
Well, at least you found your miss, and it seems like a simpler fix than tearing down the engine for valve or head work. HOw have you determined that the spark jumps only from the wire? From your previous thread it seems this happens only going up hill at 3200 RPM and after some time. That seems like a situation that would make close observation difficult. I only ask because maybe it is a wire problem. Is it always the same plug,and how do you know that? I'm not being a wise guy, it is just that you want to be sure you have really excellent reason to eliminate a variable. These kinds of questions have to be asked. Otherwise you spend your time chasing ghosts. It sounds like you have a very well thought out, excellently executed engine management system that has one weakness that needs to be tracked down. I would change the plugs around and see if it does anything. If this happens always on the same plug, then install a new one there. They cost about 3 bucks. That's a pretty cheap experiment.


Sam
The uphill miss is NOT plug wires. I believe it's a sticking valve.

I determined it was plug end leaking, by using dielectric grease on the plug end of the wires. Could it be the same one? Possible. I did all of them at once. I did the coil end first, and it didn't fix it.

But dielectric grease doesn't tolerate the heat of the plugs long term. It eventually dries out and the spark leak returns.

I'm about to change plugs again ( this was an experiment, I didn't expect to use these long term) I guess I can change wires again, but it's a 2 - 3 hour job to transfer the shielding to another set of wires.
Author:  Charrlie_S [ Sun Feb 26, 2012 5:00 am ]
Post subject: 
Quote:
I'm about to change plugs again ( this was an experiment, I didn't expect to use these long term) I guess I can change wires again, but it's a 2 - 3 hour job to transfer the shielding to another set of wires.
I'm thinking with good quality magnetic suppression wires, you should not need extra shielding. By magnetice suppression, I mean spiral wound wire, not "carbon' wire.
Author:  Sam Powell [ Sun Feb 26, 2012 6:38 am ]
Post subject: 
So when does the plug wire/sparkplug leak happen? At all time times under all conditions? If it happens at idle, then maybe you can see this in the dark. I have never seen this on new parts. But then, you are applying late technology high energy ignition power to old fashioned, low tech delivery equipment.

You might try the wires Charlie suggested instead of shielding them yourself, at least as a start. Magnocor wires made my AM radio unusable. Switching to stock radio suppression wires with internal shielding wound around wire cores, the AM radio became much better.

Sam
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