Can plug gap cause detonation? What gap to use?

Fett

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Nov 2, 2004

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Aug 14, 2006

#1

• Aug 14, 2006

• #1

With stock E7 heads, gasket-matched ported, an e-cam, 24lb injectors, and an MSD 6AL....what should the plug gap be? I am using OEM Motorcraft plugs.

Before the MSD you could smell it running rich, 24lb injectors at 40psi, 93 octane. But since the MSD it doesn't smell rich....I will be getting it tuned soon.

At 5000+rpms it was detonating with a 99 degree outside temp. I was just wondering if plug gap could have something to do with it...and what should they be gapped at anyway?

 

T

TheUser

Active Member

Jul 25, 2003

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Springfield, MO

Aug 14, 2006

#2

• Aug 14, 2006

• #2

I would use the stock gap .054. I believe you generally only decrease the gap when using a power adder so as not to blow out the spark

The heat range of the plug can cause detonation; if the heat range is too warm, it can cause detonation. Too cold of a heat range can cause fouled plugs. Fouled plugs are always better than detonation, so if you don't know what to get (stock should be fine, I assume, in your case), colder is better than warmer.

If you're detonating, what is your timing set at? That's where I would look first. Stock timing is 10* BTDC, some go 12-14, but the higher you go, the more likely you are to detonate especially if you don't use higher octane fuel.

 

JChalfan

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Nov 27, 2002

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Bellevue, WA

Aug 14, 2006

#3

• Aug 14, 2006

• #3

I asume your setup is naturally aspirated?

The stock motorcraft plugs should be the correct heat range. The .054 plug gap TheUser mentioned sounds about right.

I agree that timing is a likely cause. What is your base timing set at? Did you take the spout out when you set it? You said you are running 93 octane, so you can probably run up to 14 degrees base timing.

Detonation can be caused by running lean, but it doesn't sound like you are too lean.

Jeff

 

1fastsn95

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Apr 22, 2005

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Carthage, tn

Aug 14, 2006

#4

• Aug 14, 2006

• #4

If you are running a K&N or someother type of "performance" filter, check you M/A for oil on it. Get a spray cleaner for electrical parts. Also you may want to check your fuel pressure. It may be too lean for your app. Good luck. Chris

 

HISSIN50

"How long does it take to get help in here?

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Nov 29, 1999

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Aug 14, 2006

#5

• Aug 14, 2006

• #5

The fuel aspect was what came to my mind too. If this only occurs at WOT or near WOT at super high RPM's, I wonder if you're outrunning your FP. When they are kinda on the outs, the diaphram tends to get weak when it's hot, and it wont take much heat if it's 99*F outside.

Can you see Fuel pressure in real time (when it pings)?

I'm with James about the plugs too - I run 24's in the '94 because it's prone to the ping-thing.

Good luck.

 

4

460beast

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Mar 4, 2006

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Morris,IL

Aug 14, 2006

#6

• Aug 14, 2006

• #6

what kind of cap and rotor do you have? you definetly want to have one with brass conductors with an msd. the cheap aluminum ones cant handle all that voltage at high rpms. you might be having some misfiring at high rpm going on. i had this happen to me one time.

 

Jozey

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Nov 11, 2003

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Tucson,AZ

Aug 14, 2006

#7

• Aug 14, 2006

• #7

you can check the burn line on the plugs also.that will tell you alot on how your car is running.

 

Fett

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Nov 2, 2004

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Aug 14, 2006

#8

• Aug 14, 2006

• #8

Cap and rotor are Excel, came with the distributor. I honestly never looked closely at the contacts.

I always run 93 octane, and my timing is set at 15*. I don't have any pinging issues during normal driving....but I rarely take it over 25k.

After I fix my fan issues, ground issues, and hide my wiring....hopefully tomorrow...I am going to schedule a dyno session to get my A/F, and timing right.

 

JChalfan

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Nov 27, 2002

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Bellevue, WA

Aug 15, 2006

#9

• Aug 15, 2006

• #9

I would try bumping the timing back 2 degrees and see if the pinging goes away.

Jeff