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Username Post: Di-electric grease = misfire???        (Topic#279711)
Senior Member
Posts: 1590
Reg: 01-10-03
04-15-12 03:09 PM - Post#2215439    

Lately I noticed a random misfire in the Corvette. Air/fuel looked fine except there were spikes when it misfired. I suspected ignition so inspected the ignition parts. When I got to the plug wires I got a surprise.

I had smeared di-electric grease inside the plug boots when I installed the wires. Now I saw soot tracks on the inside of boot, from the terminal to the edge of the boot. Then the soot mark went around the edge to the outside of the boot. It continued about 1/4 on the outside to a small black dot where it had jumped to the head.

I've never seen anything like it. That's over an inch the spark traveled including the air gap to the head. All that rather than jump the 0.030" spark plug gap??? Wow!

As the boots looked undamaged I cleaned them thoroughly inside and out with a rag soaked in carb cleaner.

Just back from a test drive. Misfire gone, engine runs great.

Anyone else had a problem like this? I thought di-electric grease was what was supposed to be used on plug boots? If not, what should be used to prevent the boots from sticking to the plugs?
Markus 1971 Vette

Senior Member
Posts: 1448

Loc: kingman,az
Reg: 04-29-00
04-15-12 08:56 PM - Post#2215577    
    In response to zwede

i am with you, if this stuff does not work, what are you supposed to use to get the boots off, especially on an engine with headers.
and also i have suspected it, slowing my race car et. down.
MSD sells it, GM recommends it, doesn't mean it works, so i am lost.
rod in AZ

"4th Year" Silver Supporting Member
Posts: 2289
Loc: Salt Lake City
Reg: 06-20-09
04-15-12 09:28 PM - Post#2215585    
    In response to rod

What about using clear silicone grease?

'94 Silverado K2500 4X4 5.7 5spd Xcab LB. SOLD. :-(
'00 Contour SE 2.5 24V

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke

Posts: 22

Loc: Midwest
Reg: 11-09-04
04-16-12 01:50 AM - Post#2215615    
    In response to CowboyTrukr

I had put brand new "xxx racing" spiral core plug wires on my new 454. After breakin, I started noticing a miss which turned out to be a large hole in one of the boots. Used that stuff in there. Replaced wires with new Taylor's with same dielectric grease - no more problems. I wonder if you either used too much or if the grease is contaminated with something, or maybe something with the wires. I've never had problems using the stuff over the last 30 years.

Posts: 26421
Age: 44
Loc: Texas
Reg: 08-01-03
04-16-12 04:30 AM - Post#2215621    
    In response to papastoy72

Greg - dielectric grease is pretty much just silicone.

I'm with papastoy - probably used too much. Dielectric grease is nonconductive, so if a huge glob of it was in there, it could certainly be a barrier to a good connection between the spark plug and the wire's terminal.

I think there's a misconception that dielectric grease is "good no matter what" inside an electrical connection, but in fact, too much is a bad thing. It's great for preventing corrosion inside the connection but if you're having trouble with it on the spark plugs, maybe try just wiping some around the insulator before installing the wires, avoiding the actual tip of the plug.

94 C2500LD / 97 Suburban LS1 / 06 300C SRT8 / 06 Magnum SRT8
Check out my truck shop projects

Senior Member
Posts: 1590
Reg: 01-10-03
04-20-12 06:17 PM - Post#2217408    
    In response to someotherguy

Well, short lived happiness. miss came back. Fresh soot marks inside the boots. I've since learned it is called "flash-over".

Plug wires are Taylors. Even though they are 5 years old they look brand new. The boots are still soft with no burn marks or discoloration.

One thing I did notice is that the design of the boots is fairly loose on the end. It then tightens where the ribs are on the plug. When I applied the grease I always put a blob in at the end of the boot. Maybe that was wrong.

This time I put grease on a q-tip and smeared it further in where the ribs go.

We'll see if that makes a difference.
Markus 1971 Vette

Senior Member
Posts: 1590
Reg: 01-10-03
04-23-12 08:00 AM - Post#2218206    
    In response to zwede

Another update. Drove the car to work today and it ran really well. No miss, very smooth. But will it last? Stay tuned.
Markus 1971 Vette

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