MPG: 4.3L 99 silverado ACDelco 41-932 to 41-993
 

4.3L Silverado had been idling a tiny bit rough for a year or so, so a few months ago, at 150k, i changed plugs/cap/rotor/PCV/AirFilter/FuelFilter. Pulled the 41-932 plugs. Installed a set of 41-993, their replacements, since 932s are no longer being made. Didn't help the idle. Mileage dropped. When i finally decided three weeks ago to track the mileage, it got 320 miles on 23 gallons, just under 14 mpg. Twice, on to fill-ups. Using a locking gas cap.

Since no codes were being triggered, I figured the drop in MPG was due to a gas leak somewhere, though never smelled gas and the connections at the new fuel filter were dry during idle. (fwiw, also replaced a dead fuel pump about 6 months ago) Last month, a parts store clerk suggested the drop in MPG was due to the plugs. I said "always ACDelco". They shrugged. Well last week I reinstalled the 932s. BAMMM! 390 miles on 20 gallons. 19+ mpg. Back to normal.

When new, both the 993 and 932s had been gapped by me at 060. After 60k the 932s measure just a trace wider, indicating negligible electrode erosion. The diameter of the white insulators are identical, so the boots fit equally snug.

Only other tune was at 90k, where the factory 932s were pulled and a fresh set of 932s installed (plus new cap/rotor/...)

maybe the 41-993 need a different gap?

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Huh. Interesting. I just put in a set of Bauch platinum PN# 4007 into my 305 V8, and it really seemed to add some power and idle smoother. I can't speak for MPG because my odometer is busted, but I know it doesn't seem to drink gas like it used to. I can at least go check to check with it now.

I say you look at some Bauch Platinum plugs for your engine too.

Trying the 993's with a tighter gap.
 

Hi all,

This is interesting. So after reading all the above and studying a bit online, I'm trying the 41-933 at 180,000 miles. I'm going to re-gap them to a tighter 045. The mileage has always been kindof crappy, but now it's getting worse. It has gone down to 12 mpg during mixed driving. That's down from 15 mpg. I don't know what plugs are in it now because I didn't install them.Some worker did back in 2005...before it left the factory. :eek: (I know, I know)

If anyone has an interest, I'll post the results in a month or 2. And maybe a pic of the original plugs.

I would be interested. Look under the hood on a dark night with the engine running. Sometimes bad plug wires will allow voltage to leak out - looks like a night glow or mini lightening bolts.

I will do that, thanks. Had planned on changing the plugs today, but had some family stuff that was more important. Will post results when I have the time to change them and look for bad wires.