Spark plugs and a miss

How old are your ignition parts ?

You may want to look at your leads and coil as well.

AF 42 is the Autolite spark plug most commonly used and you should been able to manage a gap of .040"

Ps: MSD's nickname - Might suddenly die.

I am not too sure how old the ignition parts are, but I do believe that the ignition box at least has been on the car for awhile. Yes I will be looking into leads and coil if plugs, rotor and cap don't solve things first. Thanks.

First, were you experiencing these symptoms before dyno tuning? Did you discover them on the dyno while trying to tune that carb for WOT? Or, did the symptoms surface after dyno tuning the car?

The simplest thing to try would be a new rotor, cap and plugs first. Set plug gap to .045"-.050" (or .040" as Aus Ford suggested should be fine).

If that doesn't solve your problem, check the distributor shear pin.

The problems were discovered during the dyno run. We were on a Mustang dyno which I am sure you know is a load type dyno, so we weren't concerned with WOT runs but were doing driving simulations on it (monitoring AFR) and then discovered it when we hit 5300 going into 4th. We pulled a plug just to check, it looks old and the cap doesn't look great either, the rotor doesn't look too bad and may have been replaced once already but I will change it anyways. I picked up some Autolite 24s yesterday and will try them soon, but will have to order the other parts. In regular driving situations the car seems to be running great and since the tune have been using way less fuel, which is also great since the car feels much more responsive as well.

Start with the correct plug for the car. Motorcraft AF32.

You can cross them over to other brands with this chart but be advised that there are inaccuracies now in the chart.



What caused that was that some numb nuts pencil neck at Motorcraft relisted the AF42 as being the same as the AF32. The 32 is the colder plug used with the 4v higher compression heads and the 42 is the plug for the 2v with lower compression.

Almost all of the other companies pencil necks picked this up and changed their cross over charts to say that their version of the Motorcraft AF32, now an AF42 is now equivalent. SOME COMPANIES DID NOT CHANGE THEIR LIST.



No one likes this when I say it BUT Champion has the most accurate heat range listings. I DID NOT say they are the best plug to use, but when you are trying to find the right range, the variety they offer helps a lot.



Confusing? You bet.

Motorcraft unfortunately dropped the 32 series completely in favor of the 42.

Now the engine will certainly run on the 42 but it WILL act as an rpm limiter of sorts generally causing a misfire in the 5,000 to 5,500 rpm range since it is too hot to run much over that.

Sound familiar?



I went with a NGK, but I have aluminum heads and they require a hybrid heat range. The aluminum cools off so fast that they are happier with the hotter 42 series and the Weber carbs just compound the issue.

So for me the hotter plug is ordained. Mine are NGK BP6ES.

Don't be fooled by the crossover chart though. They really are in between the 32 and 42's. Hotter than the 32's but colder than the 42's. That does not agree with the chart.

Remember I said the chart is a little screwy?


They HAVE NOT been tested on the track and it is entirely possible that they are too hot for 6,500 to 7,000 rpm. I honestly don't know that yet.

They are great on the street though.

They do burn very clean with the Webers. That is always a very good sign.



Use .035 gaps. The bigger gaps could be working like a rpm limiter for you also.

That could be the limit of your coil with your set up, i.e., 5,200 rpm.

I also agree with Aus Ford about the MSD distributor. They are nothing to rely on. For one thing the retaining pin for the drive gear is too small and has a very lethal habit of breaking.

I am using a Ford Motorsport/Racing A341 pointless distributor, a Crane box coil and a Pantera-Electronics Ignition controller.

Go d forbid you take a short intended for one of the plugs. You may not be with us any longer if you do.

http://www.sparkplug-crossrefe...vert/MTRCRFT_PN/AF32

Ok. Thanks for the advice. The Autolite 24's I picked up are on the list you provided, but are you saying that list is accurate or inaccurate? Sorry, just trying to confirm.

I'm saying that there is no way of knowing if they are the equivalent of the 32's which they are supposed to be or are subject to the mistake of saying the 32 and 42 are the same and therefore are equivalent to the hotter 42.

You would need someone to step up and say that they have been using the 24 as a substitute for the AF32 and are sure they are the equivalent.

I don't know of anyone using the Autolites.