plug gap confusion

goochs · 07-08-2005, 04:24 PM

I have a 97 sl2 with 140k miles std tranny
I bought it with that many miles and it ran great. On the hiway I got 37mph and in town 32.. zippy little car.

Figured I would even make it better. Changed plg wires and plugs!!
Milage went down???

originally I had autolite plugs in the car and switched to ngk gapped to 040 I thought.
got less pep and less mpgs like 33 hiway and 30 city.

switched to splitfire triple platinum and got a real peppy car but no increase in mpgs???? also gap'd at .040.

decided to check the old autolites and they were gapped at .048 measured with a digital caliper.
took the caliper to the ngk's and they were only .035
didn't measure the splitfires for I think I'll be returning those.

Finally my question is will I get my mpg back if I gap the npk's at .045 as verses .040 for that is the only difference I can find from the initial great mpg's..

Thanks
Phil

ian12 · 07-09-2005, 03:05 AM

for some reason i ran into the same problem with ngk, my gas mileage went down and throttle response was down. i put in splitfire triple platinums and increased gas mileage by alot and throttle response is great. i believe the gap specified is .040 but i gapped my plugs at .035

but i got to ask, have you driven the same distance and way as you did when you were getting 37 and 32? you could be driving just so differently that its affected it or maybe your plug wires, even though new, are junk. what kind of wires did you get? also if you havent replace the fuel filter.

goochs · 07-09-2005, 04:32 AM

Quote:

Originally Posted by ian12

for some reason i ran into the same problem with ngk, my gas mileage went down and throttle response was down. i put in splitfire triple platinums and increased gas mileage by alot and throttle response is great. i believe the gap specified is .040 but i gapped my plugs at .035

but i got to ask, have you driven the same distance and way as you did when you were getting 37 and 32? you could be driving just so differently that its affected it or maybe your plug wires, even though new, are junk. what kind of wires did you get? also if you havent replace the fuel filter.

The plug wires were those carquest 33 dollar jobs and no I haven't replaced my filter. My driving might be a tad more windy.. I usually for 2nd and up take the rpms up to the arrow indicator before I shift. I think befor I was just taking the rpms up to about 2500 then shifted.

ian12 · 07-09-2005, 05:18 AM

oddly enough, changing such a simple normal thing can disrupt what was once running in a way you wanted it to run. yet you knew it was time for a change and the change was good but brought a new problem that was bad before the change yet since the new items havent been run with the other parts it proves there is another problem.

hopefully you understand that

goochs · 07-11-2005, 03:21 PM

ok I seemd to have worked it out. I bought autolite plugs like the ones that were in the car from the beginning and gapped them at 044. seems to run smoother and faster and the milage seems to be improving. I did note that the plugs that came out of the car were a hotter plug than what the local carquest or autozone said they should be. The auto store and walmart store say they should be 3924's for autolite but what was strange the autolite site says to use 3926's??
well 3926's are whats in there now.
Next I gues I'll tackle the throttle body cleaning and then move onto the cylinder clean stuff.. what ever that is.

Thanks
Phil