Did a Dumb Dumb de dumb Dumb!

[Guest Greg Ross]

Some weeks ago, maybe a month ago Padgett mentioned if running the magnavox ignition we shouldn't be running any more then .040 plug gap. My MSD DISC 4 melted down last Winter so I was back on the stock Magnavox I.M. and BB was working OK. (first Rule to be broken-If it ain't broke....

I pulled my platinum +4's and regapped them to .040 and all seemed Ok. Then on a my weekend trip home I started getting a miss/ stagger/ stumble at about 2000 rpm. Ran a batch of injector/ fuel sys cleaner and it seemed a bit better. Return roadtrip same thing, stagger and serious hesitation during acceleration basically from any speed. Gently up to speed and it cruised fine at whatever speed.

According to the FSM, first thing to change was the fuel filter and check fuel pressure. Bought the Fuel Pressure Guage Kit, seemed on the low end of the good range so I ordered a pressure regulator, no difference. Had decided I was going to go ahead and order the Delco Remy ignition/ triple coil setup anyway, got it, installed it. Same, more of the same!

$600. later and just for the fun of it, the other night I swapped out the Platinums' for the old set of .060 gap AC Delco plugs from my travel tookbox.

All fixed, works just like it always used to!

The moral, you've already figured it out, leave well enough alone, look first at the last thing that was changed, etc, etc

[padgett]

Well, if the Magnavox and wires are up to snuff they are designed to be able to fire a .060" gap, that is what the cars came with. In 1995, AC came out with the RapidFire and said to use the #3 with a .040" gap on the "C" 3800. I personally consider the Magnavox ignition marginal (have two failed coilpacks in my garage) and problems usually show up as a misfire under load.

Consequently I have now changed over both of my Magnavox ignitions for later Delcos and have spare coils and modules just in case. Believe what I have said in the past was ->if<- a Magnavox starts giving problems, rather than spend over $100 on either the module or the coilpack, I would visit a junkyard and swap for a complete Delco type II ignition.

That said, back in the bad old days it was common to gap a plug at .035" or even .025" (Jaguars). With a rich mixture, that was enough for the relatively weak sparks of the day to fire.

GM had been working on transistor ignigion (Delcotronic) since 1963, brought out a CD ignition in 1967, and a slim version of the HEI in 1971 as options. In 1973 the High Energy Ingition (HEI) became standard across the board with .060" plug gaps since the large gap would better fire a lean and EGR laden mixture. The soon backed this down to .040" when tracked and holed rotors and caps left a significant percentage (Detroit considers a 3% failure rate "significant") motorists stranded with dead cars.

DIS (distributerless) ignitions were designed with these faults in mind and the 1988-1990 "C" 3800 came out calling for .060" gaps again however by 1995 when the Rapidfire came out the standard gap was .040" for the #3. Since I had already had one Magnavox failure, I made the assumption that GM had discovered that over time the Magnavox was likely to degrade past the point of firing a .060" gap reliably. This was a guess on my past, GM was not talking.

When a plug fires, there are two conflicting criteria: as the gap gets smaller, the spark gets hotter (and advances slightly but we can ignore that). As the gap gets larger, the likelihood of a sufficient concentration of gasoline molecules being in the region of the spark goes up.

Ideally you want the largest gap that will reliably fire without overstressing the components of the secondary ignition.

Next, the worst case is not wide open throttle, but high manifold vaccuum cruise at low rpm since this is where you are most likely to get the lean out condition. This is why a failing ignition will often show up as a miss when going up a slight hill at 50 mph cruise in 4th lockup.

My cars will not win a fuel economy rally, are set one notch back from maximum the MPG possible if I leaned the cruise mixture a bit. I suspect this is why there was almost no difference in feel beween the .040" #3s and the .060" #14s however overall performance does seem better with the Delco/#14 combination.

Heat range is also a differentiator, a hotter heat range will fire better under adverse conditions (usually oil burning) than a colder one bbut too hot a plug and it acts like a diesel glow plug - you get detonation. This is whay a race engine usually uses plugs one or two ranges colder than stock (and changes them often). However AC Delco refuses to give out any informaation on heat ranges. This is nasty since I have wondered if now that RapidFires are regappable, if regapping a #3 to .060" would make it a #14. (Scots heritage)

Greg is the second person I have heard mention a miss and reduced performance when going from a .060" gap to a .040" which makes me think that possibly his engine is running leaner at cruse than mine, something the injectors and O2 sensor should have no trouble compensating for. Of course I know nothing about the characteristics of Bosch plugs other than they seem to be popular.

In the last few years Delco has changed the recommendation for 3800s (including supercharged) from the #3 at .040" to the #14 at .060" and the #3 is now for Fords. I would assume that they know what they are doing.

So what I would suggest is looking at the crosscounts, BLM, instantaneous, and "OLDPA3" (knock) at the operating points where the miss was occurring to make sure that leanout is not occuring, a common problem with boosted engines though more usual near the shift point at max acceleration.

ps many years ago I had an XK 150S Jaguar that used N-5 plugs. Came across one plug that for some reason would not fire properly under about 2500 rpm. Had a very impressive lope at idle and when it came on line the sound was like an ultra wild cam. Replaced the plug and everything was fine again.

[Bob]

I'm pretty sure Platinum +4's should not be gapped, think it says it on every box.

[Guest Greg Ross]

Yes, we know that now.

What went back in her was AC #14s @.060

I may get ambitious, beadblast the Platinums and re-regap them. I am getting quite adept at changing spark plugs now.

Intent here obviously was to open myself to ridicule....

And to share an experience for the benifit of others.

[padgett]

Found this on the NGK web site (am told NGK is one of the suppliers of RapidFires to ACDelco):

"Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.

A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark."

Now either the Magnavox or the Delco ignition is a whole lot more powerful than any points ignition hence the original gap was .060". My impression was that they dropped it to .045" for the RapidFire because the Magnavox had trouble with .060" but it may have just been because that is what a #3 was gapped at.

I am concerned that you had a misfire at .040" beacuse that may indicate a lean condition hence my suggestion that you check the parameters. OTOH it might just be a partly fouled plug (and I have seen cracked insulators before).

[2seater]

I have watched the discussion of plugs and coils with some interest. There is no doubt technology does get better over time, but there are false steps along the way. Just look at the change in the Rapid Fire plugs. I have used platinum and plain old standard style plugs with what seems to be equal success. I have observed the spark from both types of plugs and have always felt the platinums look thinner and "colder" than a conventional style plug. Either one seems to work fine in the engine. The amount of voltage potential of the coil is only relevant if the fuel/air mix cannot be fired with the standard system. If it only requires 15-20k volts to fire the plug, that's all the coil is required to produce, and a higher potential only gives more headroom if the system deteriorates. The much maligned Magnavox does a pretty good job in stock form. If you have ever observed the distance that spark can jump, you will know it has a lot more potential than the old single coil systems. Even though each coil fires every revolution, it still has triple the dwell/recharge time of a six cylinder with a conventional single coil ignition, and four times a V8. I do watch every year at the GS Nationals what the GN guys are running and I rarely see add on ignitions or other than the stock Magnovox until the cars get into the 10's or faster. I haven't observed any misfire issues with my system, which is the stock Magnovox and plain old $0.89 Autolite plugs gapped @ .048". I do index my plugs when installed to expose the open side of the electrode to the combustion chamber, but that's about it. I can't say more isn't better, but so far I have not found a need for it.

[padgett]

To each their own. I thought the GNs used an earlier version of the triple coil Delco.

As far as I am concerned, there are two reasons to switch to a Delco

1) If facing over $100 to fix the Magnavox (either module or coilpack)

2) If can pick up a Delco cheap at a yard de junque.

Have done that to both of our "C" cars now for an investment under $40 (have more in the #14 Rapidfires replacing the #3s) and because it became a mission - the Magnavoxes are now in the trunks as spares.

I also expect parts for the Magnavox ignition (last use was 1991) to become scarce/expensive before the Delcos (still in use), just being able to replace one coil at a time is a help.

So have never said that a Magnavox in tip-top shape won't fire a plug in a stock Reatta as well as a Delco (though do suspect the Delco has a hotter spark), just that over the years I have experienced two failed Magnavox coilpacks and would rather not experience another.

Frankly, what got me started in this whole thing was the surprise that GM actually made the two ignition systems interchangable.

[Guest EDBS0]

I fired without any problems, my series II 3800 SC Riviera with #14s even though I had the smaller pulley installed to give extra boost and more fun.

[padgett]

Didn't the s/c Riviera come stock with the Delco ignition ?

[Guest EDBS0]

Yes but I also upgraded to the Jacobs coil system using the 3 coils with 2 outputs each.

Ran equally well with each coil package, Jacobs was a waste of money on the Riv.

Still have the originals in the garage (I think). Are you interested in them for the cost of postage?

[2seater]

I agree, it would be better to change to the more modern system if repairs are in order. It's sorta like the R12 vs 134 debate. Changing for the sake of changing probably won't pay for itself, but if it needs to be repaired, the equation changes. Reading GM Ross's description of the "chuggle" at some speeds does sound similar to a phenomenon I encounter also. The engine acts like it is on again, off again at low rpm in high gear, like 50 mph in fourth and locked up. I cannot find any sensor readings that are out of whack while this happens, but more spark or a wider gap may help this. Don't know yet.

[padgett]

"The engine acts like it is on again, off again at low rpm in high gear, like 50 mph in fourth and locked up."

That is almost the classic description of a failing element in a Magnavox coilpack. 50 mph lockup particularly in cruise on a slight uphill is about the hardest condition for the ignition - high load, lo rpm, high manifold vaccuum, lean. Is even more stressful than 5,000 rpm WOT.

I'd check the plugs and plug wires first, but if good there is a troubleshooting chart C-4F-2 on page 6E3-C4-14 of the 89 Manual to follow. I'd probably check the coil resistances first. Both times it has happened on my cars, that was where the problem was.

Might also be a clogged injector...

[Guest imported_dantm4]

I just changed to a Delco ignition/coilpack after experiencing some vibration/ hesitation a while back at 50mph. Wasn't sure if that was the problem (although it was recommended it was), just trying to keep my car running well, and it seems to have done the trick. Just took a trip to Dayton (120 miles roundtrip) and the car is willing to do anything I ask of it now. Still not sure if my coilpack was going bad (magnavox) but the "new" one seems smoother (Delco). I'm also running Bosch +4's which have been in there for 6 months or so and was thinking that the Magnavox, if it has declined might not have had the ability to jump the gap on the plugs as reliably as the Delco.

-Dan

90' Black/Tan Coupe

[2seater]

Thanks Padgett, I will look at the coil pack resistance. I have heard many stories of coil packs that test okay but it requires some sort of dynamic testing equipment to actually simulate them under load. Did your VOM testing turn up the bad ones?

[padgett]

As I recall, a good coilpack will read around 3.5 ohms across the primaries and 11.5 kohms across the secondaries. No promises though.

[2seater]

I checked the coil and the secondary is between 11.66 and 11.76 k ohms. The primary is 6-7 ohms. The manual only lists the secondary and I am almost dead center of the 10-13 k ohms listed. The ICM looks perfect on the inside. I may take the coil along to the GS Nationals next week to see if the guy with the coil load tester will have it there (Caspers Electronics). I should be able to pickup a stock coil for $50 or so or maybe they will have the later model Delco ICM and coil packs for a reasonable price. Maybe my "chuggle" is just a symptom of the reduced .048" plug gap I am running in defference to the boosted condition? Sensor readings all look good, timing is stable, fuel integrator bounces around 128, O2 crosscounts are in the high teens to low 20's, injector pulse width is pretty stable too. Plugs, wires and 24# injectors are all relatively new, maybe 2-3k miles on them. I just had the intake off to fix an oil leak and the injectors are dead clean on the business end. It feels like ignition. Thanks for the help.