Proper Gap for Plugs (long, but please read)

007_SuperCoupe

Registered User
I've seen a few posts relating to this recently, but the information is not quite "hitting the nail on the head" for me.

First off, I'm experiencing a "missing" problem and have been for quite some time now. I've tried a number of different fixes (Just ask my wife! LOL) but all provide very little if any improvement. I'm now suspecting that my plugs are gapped incorrectly and or inconsitantly. I made the mistake of not gapping the plugs when I installed them. That's my bad, but now I need to fix it. It is also worth noting that I replaced my plugs (I purchased them from the dealership...not sure if they are the douple P or not since they have replaced our plugs with a different one) less than 13,000 miles ago. So, in my opinion, they should still be good.

That said, I've got a '95 supercharger with an '89 pulley on my '89 SC. The usual, air silence removal, etc. I'm still running the stock exhaust set up for now, so I haven't done more on the intake yet. This always happens at or near WOT. However, it does not always happen when I'm accelerating hard. Sometimes it is a seemingly regular miss under acceleration. I'm suspecting my #3 cylinder as I have an exhaust leak at the header there and the sound (ticking) becomes less regular when I feel the miss. Other times the engine completely cuts out and comes back on. To me it is obvious that it is an ignition issue. Whether it is the plugs or not has not yet been determined. (That's what I'm trying to do) I do not hear any pinging as would be associated with detonation and I don't think that I have enough mods to be too concerned with detonation at this point. I simply think that for what ever reason, I'm not always getting spark. After reading an article on the iridium plugs (under another post) I thought that maybe my smaller pulley could be contributing to that problem. Especially since my dumb @$$ didn't gap the plugs to begin with.

Now to my question: Would it be worth it to simply remove my plugs (assuming they are good) regap them to the proper gap and reistall them or simply get new plugs? Either way, what would be the recommended gap that I should run. I'm pushing 14 to 14.5 lbs of boost at WOT, if that helps. Please let me know so I can get this done and make my baby run good! Thanks.
 
Sam,

Your problem is more likely a bad wire than the plug gap. Stock gap should be fine on your car, if you were heavily modded a little tighter gap .045 would be better.

The stock wires are fine for about a year then because of the heat the inner core can easily be broken when changing the plugs. I would suggest a set of Taylor wires, they are cheap (about $49) and more importantly because the core is wrapped they are much more durable. I've had mine off and on a dozen times without damaging them. The clips at the coil pack are easy to break but the wire still stays firmly attached.

Let me know if you need part numbers. I would also suggest installing a new set of plugs while your working on it.

David
 
Aaron,
I replaced the wires at the same time that I replaced the plugs...About 14 months ago. And when I replaced them I went with the Factory Ford replacement parts. I figured that the originals lasted quite a few years so the replacements should as well. I guess I was mistaken.

David
Yes I would like the part # for those wires. Also, would it be worth it to go with iridium plugs? I'm not too sure about the durablility of them. How are they. I'm not planning on too many more mods in the near future as I'm getting ready to start a *big* project T-bird in the next few months. That will take the vast majority of my resources to complete. So in the meantime, I want to get the SC running well as it is my daily driver for now.
 
David may beat me on this but if you replaced the wires with factory wires I doubt they are the problem. I also agree with David that the gap is probably not off. Are you having any other problems except the high end miss, even if it sounds completely unrelated? You may just need to pull plugs and read them to figure it out.
 
Sam,

Like Aaron said, the factory wires shouldn't have failed this quickly unless you have removed them for some reason. Mine got damaged installing headers.

Taylor 8mm Spiro Pro series w/135 degree boot direct fit part numbers are as follows.

#074269 Red
#074669 Blue

I perfer the standard length tips Iriduims gapped to .040 (NGK-TR51IX 7316) but would start with stock gap on your car.

David
 
Aaron,
To specify, it is not a "high end miss." That is when the miss is most pronounced, at or near WOT. However, it also occurs just before the car will downshift. For example, at aprox 42-43 mph in OD, I will gently press on the accelerator. The RPMs will rise a bit and the engine will begin to work "harder." More air and fuel are getting in and the engine goes under load. Sometimes I will have a miss then. Not always, and it usually feels like only 1 cylinder, but occasionally the engine will again cut out completely and come back. I've double and tripple checked the wires and made sure that they were seated properly on the plugs and coil. I've also replaced the DIS module (at about the same time as the plugs and wires) the cam sensor and crank sensor. I've regreased the DIS module on a couple different occasions thinking that it was getting too hot. I used regular heat sink to do this. The miss is also more pronounced and occurs more often when my car is on the high side of warm, i.e. right about when the fan kicks on. This problem has had me in cirlces all summer!
 
This may be a long shot but check and see if the bypass hose on your blower is cracked. It may be that it has a small crack that only presents itself under boost. Just a thought.

Hmm, just rethought. Wouldn't be a prob under boost. Would be more of a bottom end half throttle/idle prob. Any prob with idle?
 
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Thanks for the info David. About the only thing I haven't replaced is my coil, but if it were going bad I'd think that I'd have a much more violent response and it would occur regardless of throttle position.
I haven't had a need to completely remove the wires. I have removed them from the plugs and put them back on to ensure that they were seated properly. But I haven't moved them around a significant amount. I'm not sure if that would qualify or not. I have noticed that of late, the miss has become much more apparent. As an example, in July I ran a 15.2 and then in Aug ran a 15.8 best on a colder night. The only difference that was made between the two runs was new tires to replace my BALD tires and a 4 wheel alignment and a slight adjustment in the TV cable to provide slightly stronger shifts. I was hoping with the new tires ('W' rated) and the tv cable I'd shave a couple tenths off my time, but after my first pass at over a 16.1 I suspected something drastically wrong. And to this day I haven't been able to narrow it down. I don't have any codes and the cylinder balance test passes. I can check it again to make sure. But every time I hook up my code reader, the car runs better. (I do notice a slighly rough idle on occasion, but I was attributing that to my engine mounts.)
*Edit:
Aaron, The problem is definately more pronounced at WOT than any other time.
 
I have removed them from the plugs and put them back on to ensure that they were seated properly. But I haven't moved them around a significant amount. I'm not sure if that would qualify or not.

Sam,

Yes, that can be enough to damage one. I still think it's a bad wire that's causing your miss. If it were the coil you would be missing on two cylinders.

David
 
So the recommendation is to put on new plugs and wires and go from there? That is what I had figured, but wnated to make sure that I wan't wasting $$ in the process. But I guess sometimes you just have to "throw" parts at it! Thanks for the help guys. I'll see how much this helps. Hopefully it will cure my problems.

Just an afterthough...I replaced the plugs and wires among other things when I bought the car last July (02). After that (2000~ miles) my DIS went bad. I happened to be about 700 miles from home when this happened. I was able to get the car home, but would driving it that far when my DIS was acting up damage the wires? It ran good after I replaced the DIS, but could it have significantly reduced the life of the wires? Just curious.

Thanks again for the help.
 
Sam try teh denso iridiums at factory Denso set gap..Plug is an IT20 and slightly colder then stock..I cant reccomend these plugs enough as they completly cured my high boost miss with 21psi
 
Update

Dave,
I got the iridiums and taylor wires. Installed them last night and wish that I could still go to a track to get a 1/4 mile time. I put $$ that I'd run my fastest. I gapped the plugs to .054 and fixed a vaccum leak from the intercooler tubes (3 joints were leaking). I'm amazed at how fast my car will start now. I barely have to turn the ignition key and it's on. I'm very happy with the plugs and wire. Thanks for the info on them. I did find that I had been running pretty rich for some time now. Thanks, of course, to the vacuum leaks I had. I'm sure that played a larger roll in the plugs and wires going bad than anything else. Now I have the IC tubes sealed with Wynn's gaskets. Awesome!

Anyway, just wanted to give an update to let you know that it is resolved.
 
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