ptt Posted November 12, 2019 Share Posted November 12, 2019 In a recent thread of mine it was suggested that a .060in sparkplug gap should be used with the Delco coil conversion and a .045in sparkplug gap with the stock Magnavox coils. My sparkplugs were all still gapped at what the FSM noted (.060in, my thinking it to be the FSM gospel) when I started that thread. During that thread I replaced the older(7yrs) Magnavox coil with new Magnavox coil and just for comparison I regapped the plugs at .045ln. It still starts with just a tap of the ignition key but I have detected a slightly noticable rough idle. But I havent driven the car enough until recently to see any other difference in anything like seat of the pants Power or MPG. If I recall it was said that the FSM reference to the .060in sparkplug gap was for a "fresh" ignition system. Would the fact I have installed a new Magnavox coil somewhat refreshing the ignition system and gapped the sparkplugs at the suggested .045in possibly be the reason for my rough idle? For unforseen reasons I will be using the '90 Coupe as a daily driver this Winter (after rust-proofing the underside) so possibly I will be able to see if the smaller .045in gap will be best as the new Magnavox coil gets some use and age on it. Thanks all! Link to comment Share on other sites More sharing options...
Ronnie Posted November 12, 2019 Share Posted November 12, 2019 3 hours ago, ptt said: Would the fact I have installed a new Magnavox coil somewhat refreshing the ignition system and gapped the sparkplugs at the suggested .045in possibly be the reason for my rough idle? My opinion is it wouldn't cause a rough idle. I would stick with the .045 gap because it should make the spark plugs easier to fire with the weaker Magnavox ignition system no matter if it's new or old. A narrower gap helps the most when the engine is under load at low RPM... like when trying to accelerate up a hill with the transmission in 4th and the torque converter locked up. That is when the cylinder pressures are the highest which makes it harder for the spark to jump the gap. There is very little load on the engine when it's idling so I doubt the difference in the gap would make a difference. I wouldn't expect to see a difference in power or fuel mileage with the narrower gap either. Link to comment Share on other sites More sharing options...
padgett Posted November 13, 2019 Share Posted November 13, 2019 What kind of plugs ? I use only AC Rapidfire or Iridium because I have experienced a miss with others. Link to comment Share on other sites More sharing options...
ptt Posted November 14, 2019 Author Share Posted November 14, 2019 The plugs are ACs. Link to comment Share on other sites More sharing options...
padgett Posted November 15, 2019 Share Posted November 15, 2019 errr, which ACs ? Link to comment Share on other sites More sharing options...
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