2 Spark Plug Questions

[RRoller123]

(1980 2L FI): This is probably a silly question, but I wonder what you folks do about the loose terminals on spark plugs (I use Champion RN9YC) that have the removable type terminal. I tighten them up significantly with pliers when installing, but inevitably find that they come loose over time, and I suspect that this is the cause of a recent minor misfire.

I have wondered if using a Loc-Tite product might cause problems, either due to high heat or its lack of conductivity, so I have been just retightening them when cleaning and resetting the gap on the plugs.

Second question: What plugs are you folks using with the Computronics DIS-4 waste spark system? I am still using the standard copper (RN9YC Champion), but I only drive 1000-2000 miles a year at most, so the wear/erosion issue from the reverse spark hasn't been too noticeable yet. Do you spring for the extra cost of Double Platinum or Iridium plugs, or just replace them with standard plugs when needed? (at far lower unit cost!) Alternate plugs for waste spark systems need to be DOUBLE plated since the spark jumps from ground back to the center post on the waste charge. Having just the center post plated doesn't solve the erosion problem.

Thanks.

Pete

[Kevin1]

I have a stock ignition system so can't help with computronix advise.
For spark plugs though, I can say I have wasted time and money trying different types and have always ended up with champion or NGK. It seems the our runs better with stock plugs.

[131]

Slightly crimp the screw on terminal in a vice, so it's a fractionally out of round. It'll be tight to screw on, but it won't move.

[So Cal Mark]

per the instructions that accompany the Computronix system, use copper core plugs, NOT platinum or iridium

[RRoller123]

Thanks, Mark. Is there something different about the Computronics DIS-4 system such that it doesn't have the reverse spark (Ground to Center Post) event? i.e. Are all the sparks in the DIS-4 emitted from the Center Post to Ground? I had read dozens of articles researching this question of proper plugs and erosion wear for Waste Spark Systems before posting here, and every one of them recommends plugs that are resistant to the reverse erosion of a waste spark system. (i.e. plated on both center post and ground post). Maybe the Computronics has a different approach, I don't know. There is no mention of it in the manual.

What do you use for spark plugs? The only reference to spark plugs in my Computronics manual is: "High quality spark plugs, in new or good condition must be used. Recommended spark plug gap is 0.045". This is somewhat vague to me.

And wondering what to do about the terminals that invariably loosen over time? Use a Loctite product or vise crimp them, as suggested, etc?

Pete

[TimpanogosSlim]

What 131 said. Use a vise to put them slightly out of round, for interference fit.

Bosch 7900 are a popular copper plug for our cars.

I was pretty sure that wasted spark just means exactly that - that there are twice as many spark events as normal. I can't even figure out how the potential between the coil and the plug would invert.

[131]

I was pretty sure that wasted spark just means exactly that - that there are twice as many spark events as normal.

Exactly that, firing at the top of each stroke, rather than worrying about cam timing to fire on the compression stroke.

[RRoller123]

There are many dozens of references to the side-to-post "reverse" spark for the waste side of the DIS process, here is one of them, short and to the point.

https://crxsi.com/info/ignition-spark-p ... YSTEMS.htm

Here is what NGK has to say, confirming the reverse spark design.

https://www.ngksparkplugs.com/about-ngk ... -ignitions#!

This is an excellent video on the subject:

https://www.youtube.com/watch?v=9TqB76mZzhM

For general consumption, here is a really good overall review of ignition systems, plugs, etc, that is informative and useful.

http://www.autolite.com/media/14882/tec ... manual.pdf

I suspect that, for marketing reasons, DIS manufacturers would rather not suggest that expensive double platinum or iridium plugs be required, as the effect on their system sales would likely be quite negative. You go from a couple of bucks a plug times 4, to over 10 bucks a plug times 4.

Now that being said, if it is true that ONLY the erosion of the plug center tip is the problem due to the reverse spark, then it does make sense, if the car is only driven a couple of thousand miles per year, to just live with the greater wear and replace the cheaper plugs more often.

Pete

[RRoller123]

I need to revise my earlier statement regarding the costs for double platinum and Iridium plugs. At my local Advance Auto parts, they are listed at $4.99 each for Auto-Lite #APP63. NGK Iridium are listed at $6.99 #BPR6EIX, and Champion Iridium at $7.99 #9804. Standard Champion RN9YC are $2.49. Not a huge expense difference.

Pete

[TimpanogosSlim]

There are many dozens of references to the side-to-post "reverse" spark for the waste side of the DIS process, here is one of them, short and to the point.

https://crxsi.com/info/ignition-spark-p ... YSTEMS.htm

Here is what NGK has to say, confirming the reverse spark design.

https://www.ngksparkplugs.com/about-ngk ... -ignitions#!

This is an excellent video on the subject:

https://www.youtube.com/watch?v=9TqB76mZzhM

I have a few problems with generalizations made in that video.

Not all distributorless systems are wasted spark.

The systems he's referring to have a coil per pair of cylinders, and due to the way the coil is wound and wired one of the cylinders is always at the opposite potential, not back and forth as i had thought you meant.

Not all distributorless systems are wired that way.

The compu-tronics system does seem to use coils exactly that way, so the question is valid.

Since DIS means "distributorless ignition system" which would appear to be a category that includes coil-on-plug and coil-near-plug systems, I think it's problematically vague. Not having a distributor does not automatically mean you are using a wasted spark system. Having a wasted spark system does not automatically mean that half of your plugs are run in reverse. The terminology is correct for a majority of applications, but not all of them.

You could, in theory, use the compu-tronics system with a different coil configuration. Not that I'm suggesting that there's a reason to.

But you could, in theory, put a rack of GM "LS" series coils over the exhaust heat shield (stock location in original application) and wire them to the computronics unit. Or get a set of motorcraft "mustang" coil packs and convert to a coil-on-plug configuration. They are even angled so that the #4 will fit. I don't know for sure whether the computronics coil pack has built in ignitors, but my guess is that it does, and this would mean that it is sort of compatible with other "logic" coils. i mean if warranties and customer support aren't concerns that you have.

[RRoller123]

That is why I asked the question in the first place. The Computronics uses two coils for the 4 cylinders, so it appears to be wired as a Reverse Spark configuration.

This is another one on this subject, the Computronics is closest to the middle example that he covers.

https://www.youtube.com/watch?v=PHla1hR2EG0

And another shorter, simple one:

https://www.youtube.com/watch?v=6-hAZnEJQxk

[TimpanogosSlim]

That is why I asked the question in the first place. The Computronics uses two coils for the 4 cylinders, so it appears to be wired as a Reverse Spark configuration.

Yeah, it's weird that computronics doesn't say anything about spark plug types on their website.

[RRoller123]

I have a misfire issue that just recently developed, so bought new NGK plugs and will swap them out and see if that does the trick, and measure the wire and coil resistances, etc. The Champions have only been in there for maybe 2000 or 3000 miles. (Not sure exactly when I installed them.)

[seabeelt]

Pete, What do you mean by misfire? Is the engine skipping, like a plug did not fire, or is it firing at the wrong time?

[RRoller123]

Appears to be a Plug(s) not firing. This afternoon I measured the Computronics wires and coil pack and sent them the measurements requesting that they confirm the numbers are proper. I have the older DIS4 unit from March of 2014. Awaiting confirmation. For reference:

Plug Wire #1: 1833 ohms
Plug Wire #2: 1699 ohms
Plug Wire #3: 1582 ohms
Plug Wire #4: 1459 ohms

Coil #1 (1-4): 8.55K ohms
Coil #2 (2-3): 8.72K ohms

I changed to new plugs (NGK with fixed terminal, that takes care of one of my initial questions) and the misfire has improved but is still there. Other possibilities are that I may have an ignition timing issue, as I so far have only used the dashboard tach for reference and I don't trust it at the lower rpms, so I purchased a hand held tach that clips over the spark wire. I will reset the idle and then the ignition timing tomorrow. It is possible that I may have it too far advanced, and the engine does seem to be running a little hot, so this may be the culprit. If that doesn't work, I will look at the cam timing and see if a wheel/belt has slipped. There are no apparent air leaks, and I recently checked fuel pressure and replaced the filter and pump, plus a new CSI, so I am not thinking the problem lies there.

It could be the A/F ratio, so I will check the O2 sensor too. I found an old analog voltmeter in the tool box, and maybe it works and will do the necessary averaging on the readings. It seems almost impossible to do more than guess that the average O2 reading is 4.5DVC, when using a DVM, because the readings jump around so much.

Eventually the cause will make itself known! Until then the car drives well and with great power and I have been zipping around in it all over town.