Plug Analysis
Thread Starter
Intermediate
Joined: Dec 2001
Posts: 40
Likes: 2
From: Bay City MI
Plug Analysis
Need some help with spark plug analysis? These plugs recently came out of my 70 LT1. They are AC R43's. When I pulled the plugs I obviously had a miss. The various conditions of the plus has me wondering what's going on. Two to three of them are fouled or nearly fouled. The rest of them are either OK to a little lean. My only thought right now is that the mechanical lifters need adjustment. Any idea's out there. I have put in a set of R44's for now hoping a hotter plug will help. The attached link is to pictures of the plugs.
Thanks, Paul
http://webpages.charter.net/brentway/
Thanks, Paul
http://webpages.charter.net/brentway/
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
All of those fuel fpouled plugs (1,4,6,7) feed from the right side of a dual-plane intake, like the one on an LT-1. I would look at the idle mixture adjustment/ circuit if you have original jets in the primary circuit. R-44's won't fix this problem. 
Safety Car
Joined: Dec 1999
Posts: 3,596
Likes: 835
From: PA
Paul,
If your LT-1 is for the most part a street driven car, I would definitely move up at least two heat ranges with your spark plugs... The factory recommendation was fine for a car that was driven relatively hard on the street/track, but for cruising around town, the factory spec heat range is too cold.
What's the general condition of the engine? As you noted, most of the plugs look OK except for #1 and #4... Worn valve guides on those two cylinders might explain this. How about the ignition system? A properly operating TI system does a fine job of firing the plugs, but if there are issues there, that may also be causing a problem. Same goes for your wires and cap.
I'm trying to recall if cylinders #1 and #4 are fed off of the same plane of the intake manifold... If so, could be a fuel distribution problem although I think it's highly unlikely. Still, I'll throw it out there for analysis.
Make sure that you have the engine tuned and timed correctly... Including setting the valve lash before you attempt to get your plug readings.
Good luck... Let us know what you find out.
Regards,
If your LT-1 is for the most part a street driven car, I would definitely move up at least two heat ranges with your spark plugs... The factory recommendation was fine for a car that was driven relatively hard on the street/track, but for cruising around town, the factory spec heat range is too cold.
What's the general condition of the engine? As you noted, most of the plugs look OK except for #1 and #4... Worn valve guides on those two cylinders might explain this. How about the ignition system? A properly operating TI system does a fine job of firing the plugs, but if there are issues there, that may also be causing a problem. Same goes for your wires and cap.
I'm trying to recall if cylinders #1 and #4 are fed off of the same plane of the intake manifold... If so, could be a fuel distribution problem although I think it's highly unlikely. Still, I'll throw it out there for analysis.
Make sure that you have the engine tuned and timed correctly... Including setting the valve lash before you attempt to get your plug readings.
Good luck... Let us know what you find out.
Regards,
Le Mans Master
Joined: Mar 2004
Posts: 7,463
Likes: 1,485
From: Little Rock AR
The GM specified plug for my 302 is an AC 43 but I can not run them on the street without fouling. I stepped up to 45's and the problem goes away. The 43's are just too cold for most street driving.
Hope this helps.
-Mark.
Hope this helps.
-Mark.
