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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

odd spark plug color

Old 09-03-2008, 08:57 PM
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mattwright101
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Default odd spark plug color

so i pulled my plugs this afternoon to check and see how they were doing
they were all a maroonish color..
anyone have any idea wtf that means?
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Old 09-03-2008, 09:07 PM
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mjr46
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have you been using a fuel additive such as octane booster?? or leaded race gas??
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Old 09-03-2008, 09:11 PM
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mattwright101
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no
just 91 octane fuel
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Old 09-03-2008, 09:13 PM
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sometimes it can be a result of additives that are in the fuel
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Old 09-03-2008, 09:18 PM
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mattwright101
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well i ran some octane booster a while back but it was before i put the new plugs in
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Old 09-03-2008, 09:21 PM
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I wouldn't be to concerned with it as I stated , most likely additives in the fuel
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Old 09-03-2008, 09:24 PM
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mattwright101
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well
the only reason i asked is cause its been cutting out lately
i just put in some redone 24# injectors and a MAF
it ran fine for a week or so and now its cutting out
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Old 09-03-2008, 09:34 PM
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67mustang302
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A light reddish or dusky reddish tinge is common with modern unleaded pump fuel, due to the additives. Posting pics helps, but I can tell you in all likelihood they're fine. Mine are the same way, and I read my plugs with a scope to tune my car.

The things you do NOT want to see in a plug are black soot/ash deposits covering everything, chipped/cracked insulators, glazed over looking insulators, or a burnt look from excessive heating, black peppering(comes from mild detonation that you won't hear or feel) or silver peppering(bits of melted aluminum from the pistons due to detonation that you may hear and feel), signs of physical damage, or heavy melting/erosion.

You can also tell heat range and ignition timing by the threads and ground strap respectively. WOT fuel marking should be a light brown or grey "fuel ring" at the very base of the insulator where it meets the plug body, down where you really need a scope to see. 3/4 to 7/8 of the way around is typically the "lean best power" marking for the tune, but some engines may make more power with a full turn of fuel ring, or it may be needed to avoid detonation.
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