Sparkplug

[miser143]

I have a 1991 mustang gt 302 engine what's the best type of sparkplug to use .

 

[nickyb]

I like copper core plugs.

 

[91AOD5.0LX]

I have a 1991 LX (No Mods) and use Motorcraft Copper ASF-42C plugs as the car calls for with a 0.054 gap.

 

[AeroCoupe]

If the heads are stock then a Motorcraft ASF42C. I run Autolite 3924's on both the Edelbrock and AFR heads in my cars.

 

[miser143]

Thanks for the information. I ask because I have trouble with my car it starts but rpm dips down and back to about 850 rpm .I tested idel control everything check out good tps is on 98v .checked for vacuum leaks good. Maybe spark plugs I have are no good I have motorcraft sp502x and think they are bad.

 

[nickyb]

If new plugs don't fix it the surging idle checklist is the next step.

 

[AeroCoupe]

“I ask because I have trouble with my car it starts but rpm dips down and back to about 850 rpm .”

Does it surge or just drop once and then level out at 850 rpm?

 

[miser143]

It drops and comes back up but it does this all the time .it's does not surge up it dips down.

 

[AeroCoupe]

So you start the car and at some point while idling the rpm’s drop but then come back up to 850 and from that point on it has a stable idle?

 

[miser143]

No it dips down come back up and dips down and up and repeat those not stay stable. Stays on but dips almost like if it wants to turn off .

 

[AeroCoupe]

Then like nickyb indicated the surging idle check list is your friend. Follow it step by step and do not skip around. The success rate of fixing the problem is really high if you do it that way.

Thread 'Help me create the "Surging Idle Checklist"'

Apr 10, 2005

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help.

Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of a systematic process that checks and eliminates possible causes. This idle problem checklist will use the same troubleshooting strategy and methodology.

By the term surging idle, I mean an idle that...

• jrichker
• 1986 1993 86-93 check engine light code 67 cranks ok dump codes eec-iv mustang no start
• Replies: 575
• Forum: Fox 5.0 Mustang Tech

•