C4 plug gap ?????
Thread Starter
Heel & Toe
Joined: Sep 2014
Posts: 22
Likes: 5
C4 plug gap ?????
I have an 85 and recently done a plug check and decided to go ahead and do a tuneup. New cap, rotor, wires and AC plugs. The forums said that GM changed the gap form 45 to 35 on this engine. My old Delco's were at 45. So I done them at 35.
It runs terrible now. Stall out on take off, I dropped 3 MPG highway and has a rough idle. I am thinking about re-gapping them at 45 to see if there is any difference.
Any suggestions
It runs terrible now. Stall out on take off, I dropped 3 MPG highway and has a rough idle. I am thinking about re-gapping them at 45 to see if there is any difference.
Any suggestions
Drifting
Joined: Sep 2014
Posts: 1,579
Likes: 59
From: Trieste Italy
Have you fit your car with tune up kit?
Rock auto parts catalog says .045 as gap in this case no .035, i would came back to .045, thought that .035 gap is for high modified engine, not just for a luttle tune up
Rock auto parts catalog says .045 as gap in this case no .035, i would came back to .045, thought that .035 gap is for high modified engine, not just for a luttle tune up
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
I would be more suspicious if the parts you installed are all good....if the re-gapping does not correct the issue. Not knowing if all of the other parts were Delco parts....You could possibly have some bad plug wires even though they are new.
If I have suspicions on a car that is running bad...I use my Kv tester and check the plug wires at the plugs and see what the KiloVolts are for each plug while running.
I also am very picky when installing the plug wires to make sure they are installed back on the factory spark plug stands and using the correct retainers for them....but that is just me. I DO NOT 'zip-tie' them together in a bundle. AND the 3 spark plug wires that go under the distributor...I MAKE SURE that they are AWAY from the 4-wire connector for the distributor...just like the manual states.
DUB
If I have suspicions on a car that is running bad...I use my Kv tester and check the plug wires at the plugs and see what the KiloVolts are for each plug while running.
I also am very picky when installing the plug wires to make sure they are installed back on the factory spark plug stands and using the correct retainers for them....but that is just me. I DO NOT 'zip-tie' them together in a bundle. AND the 3 spark plug wires that go under the distributor...I MAKE SURE that they are AWAY from the 4-wire connector for the distributor...just like the manual states.
DUB
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 112
From: Michigan
Did you change plug brands? Get the correct heat range? Get the correct plug for iron heads?
I've seen too big a gap hurt performance and swore a diff brand drove diff. Still won't take long tah regap and test it out, lets us know.
I've seen too big a gap hurt performance and swore a diff brand drove diff. Still won't take long tah regap and test it out, lets us know.
Thread Starter
Heel & Toe
Joined: Sep 2014
Posts: 22
Likes: 5
After working 14 hour days I was to pooped to even think about doing a re-gap on my plugs til yesterday.
I use ONLY AC Delco parts on my toys. The plugs are delco R45TS . I also double checked to insure the wires were properly strung, loomed, and not running over the four wire connector.
SO I gapped them at 45 and I had a meeting to go to today which was a 100 mile run.
It ran SOOO sweat and purred nicely. Gas mileage came up, but then when you get on it who really cares about mileage.
Thanks for all the input guys, I appreciate your comments and suggestions.
My peanut motor is now a wild horse and runs like a scalded dog. lol
I use ONLY AC Delco parts on my toys. The plugs are delco R45TS . I also double checked to insure the wires were properly strung, loomed, and not running over the four wire connector.
SO I gapped them at 45 and I had a meeting to go to today which was a 100 mile run.
It ran SOOO sweat and purred nicely. Gas mileage came up, but then when you get on it who really cares about mileage.
Thanks for all the input guys, I appreciate your comments and suggestions.
My peanut motor is now a wild horse and runs like a scalded dog. lol
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I read recently that there were problems with the high output coil so GM specified a normal output coil as a replacement. The high output coil used a 0.045" gap and they specified 0.035" for the normal output coil.
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 112
From: Michigan
I thought the gap was based on the .5 lower compression for the iron heads(c4 9.0 iron, 9.5 alum). A c3 with HEI compression is the same 9.0 L82 or lower 8.5 L48 and they use a .045 gap. Still I've also herd of early HEI coil problems in general.
Drifting
Joined: Sep 2014
Posts: 1,579
Likes: 59
From: Trieste Italy
You didn't say us, which is now you re gap 0,45? And this is workin properly
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Drifting
Joined: Sep 2014
Posts: 1,579
Likes: 59
From: Trieste Italy
After working 14 hour days I was to pooped to even think about doing a re-gap on my plugs til yesterday.
I use ONLY AC Delco parts on my toys. The plugs are delco R45TS . I also double checked to insure the wires were properly strung, loomed, and not running over the four wire connector.
SO I gapped them at 45 and I had a meeting to go to today which was a 100 mile run.
It ran SOOO sweat and purred nicely. Gas mileage came up, but then when you get on it who really cares about mileage.
Thanks for all the input guys, I appreciate your comments and suggestions.
My peanut motor is now a wild horse and runs like a scalded dog. lol
I use ONLY AC Delco parts on my toys. The plugs are delco R45TS . I also double checked to insure the wires were properly strung, loomed, and not running over the four wire connector.
SO I gapped them at 45 and I had a meeting to go to today which was a 100 mile run.
It ran SOOO sweat and purred nicely. Gas mileage came up, but then when you get on it who really cares about mileage.
Thanks for all the input guys, I appreciate your comments and suggestions.
My peanut motor is now a wild horse and runs like a scalded dog. lol
Heel & Toe
Joined: Apr 2020
Posts: 21
Likes: 6
From: Massachusetts
Based on some research and looking at different ACDelco plugs there are different gaps for iron and aluminum head engines, 45 for iron and 35 for aluminum heads. Mine is an 87 so will be ordering the 35 plugs