Engine Spark plug condition

sav22rem22 · Sep 2, 2023

I just recently had tuning through a quarterhorse finished on my car and I decided to pull the plugs to see how they fared throughout the tuning process. I’ve developed a pretty bad shake at idle but nothing past 1600 rpm’s or so and I’m wondering if the plugs should be replaced.

Here is one of the plugs

What do you all think? Im not sure why the part where the ground strap attaches is so dark and why only one side of the porcelain has a brown streak

JD1964 · Sep 2, 2023

That plug looks fine to me.

What kind of mods does the engine have? I’m assuming some mods since you had it tuned.

sav22rem22 · Sep 2, 2023

JD1964 said:
That plug looks fine to me.

What kind of mods does the engine have? I’m assuming some mods since you had it tuned.

Gt40p heads, explorer upper and lower, TFS 1 cam, 24# injectors from a 3v mustang, 30# pro m maf (tuner recommended bigger maf as to not hit airflow limit), 1.6 RRs, 65 mm throttle body. Mainly just wanted it tuned for absolute best drivability because of the cam and injectors. Good to hear that the plug looks fine because the gt40p heads make it very difficult to change all the plugs

JD1964 · Sep 2, 2023

The TFS 1 is going to have a slight lopey idle.

AeroCoupe · Sep 3, 2023

24 lb/hr injectors and an MAF calibrated for 30 lb/hr injectors? Not that it matters with a tune but by larger MAF I’m assuming the tuner meant larger in diameter than the stock MAF like a 75mm or 80mm.

I usually change the plugs and oil after getting a tune but that is just me. Also, I run Motorcraft copper core plugs (nothing fancy) as they seem to work better and I have less issues with them.

Possible you have an arcing issue so if you can watch the plug wires when it dark out with the motor running you can see it but it has to be dark. Another thing to check is the resistance on the plug wires.

Make sure the cap and rotor are in good shape as well.

Have seen a couple issue with the porcelain on a plug being cracked and causing the symptom you are describing. Only way to see the crack is to pull the plug and wipe it down with a dark grease or used motor oil. Will make the hair line crack stand out.

sav22rem22 · Sep 3, 2023

JD1964 said:
The TFS 1 is going to have a slight lopey idle.

I should have specified that the car did have a choppy cam shake at idle after tuning but nothing crazy. After a few shakedown drives and letting it sit for a few weeks it’s a really bad shake like shake your teeth loose shake. It feels like when I got sent a distributor that had the trigger wheel making contact with the hall sensor causing a horrible shake. It kinda came out of no where

sav22rem22 · Sep 3, 2023

AeroCoupe said:
24 lb/hr injectors and an MAF calibrated for 30 lb/hr injectors? Not that it matters with a tune but by larger MAF I’m assuming the tuner meant larger in diameter than the stock MAF like a 75mm or 80mm.

I usually change the plugs and oil after getting a tune but that is just me. Also, I run Motorcraft copper core plugs (nothing fancy) as they seem to work better and I have less issues with them.

Possible you have an arcing issue so if you can watch the plug wires when it dark out with the motor running you can see it but it has to be dark. Another thing to check is the resistance on the plug wires.

Make sure the cap and rotor are in good shape as well.

Have seen a couple issue with the porcelain on a plug being cracked and causing the symptom you are describing. Only way to see the crack is to pull the plug and wipe it down with a dark grease or used motor oil. Will make the hair line crack stand out.

He told me with the TFS 1 cam that I’d want to go up a # size or two vs my injector # because he didn’t want the MAF voltage to peg out at 5v before the car is even done pulling. I was confused about it too but it all worked out. Definitely doesn’t make that much sense to me but he rebuilt my entire MAF transfer curve. I definitely plan to change the plugs and the oil as well that way everything is fresh and good to go to start driving a lot.

I definitely plan to make sure I’m not getting arching but like you said I’ll have to do it when it’s real dark out. I’m worried about plug wire #7 because of the awfully tight space between the headers due to the GT40p heads. I do have a heat blanket around that wire but I’m not sure how much good it’s done.

I’ll swap out my cap and rotor with a known good cap and rotor just to be sure because it is a used distributor that I bought off eBay thanks to LMRs junk distributor they sent me.

limp · Sep 3, 2023

sav22rem22 said:
because the gt40p heads make it very difficult to change all the plugs

Get one of these spark plug sockets from Trick Flow.... It slides over the spark plug allowing the end of the plug to stick through, then you take a 3/4" end wrench to loosen or tighten the plug..... Works great on my P heads.

https://www.trickflow.com/parts/tfs-90500

sav22rem22 · Sep 3, 2023

limp said:
Get one of these spark plug sockets from Trick Flow.... It slides over the spark plug allowing the end of the plug to stick through, then you take a 3/4" end wrench to loosen or tighten the plug..... Works great on my P heads.

https://www.trickflow.com/parts/tfs-90500

That actually looks like it’d work perfect. Of course it’s out of stock as with everything else trickflow. Thanks for the link though I’m going to try and find it anywhere else in stock

85GTStangGuy · Sep 3, 2023

Found one, but it's pretty pricey (a ripoff actually, imo)....

Amazon product ASIN B00CE2L7ZE

JD1964 · Sep 4, 2023

Try an offset box end wrench on those hard to get plugs. If the threads are in good condition you really only need 1/2 turn to loosen it. Then you can do the rest with your fingers.

Engine Spark plug condition

sav22rem22

JD1964

there is enough sticking out to grab on to

sav22rem22

JD1964

there is enough sticking out to grab on to

AeroCoupe

lube between the nut and the face. I know my lubes

sav22rem22

sav22rem22

limp

wrap a little cheese around it and its a done

sav22rem22

85GTStangGuy

JD1964

there is enough sticking out to grab on to

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Engine Spark plug condition

there is enough sticking out to grab on to

there is enough sticking out to grab on to

lube between the nut and the face. I know my lubes

wrap a little cheese around it and its a done

there is enough sticking out to grab on to

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