General Maintenance & Repairs - Gas Mileage went down after Tune-Up

I know, it sounds strange to me too...I just got my '00 T/A (LS1, RamAir, rest is stock) a tune up last month, Bosch Platinum plugs and MSD ignition wires, and while I was at it had the front brakes done (they shimmied a bit when braking and on my way home from work every evening there's a great place to pull gears. If you're going to go fast, you should make sure you can stop fast too...lol)..

Anyway, before the tune I was getting about 16 mpg and now I'm getting 12, what's up with that? Shouldn't I be getting better gas mileage?

I have never seen anything good from Bosch platnium. About 7 years ago, I had multiple ones fall apart on me , thought it was a fluke or bad batch, til when I was a service writer and seen several people have either the platnium center fall out or the actual porcelain break.

Sorry for the rant , not sure if the tune up is related or not, is it possibly you drove it harder after the tune up? Does the car seem to run ok?

Wow -- you really don't like those plugs, do ya!? LOL.

So far she's running great, only change is in the MPG.

I would first double check the work--make sure all the wires are on tight. Also check the engine while its running to see if you car hear any obvious blowby becuase a spark put is loose/not seated properly or a ticking sound indicating a short in a wire or ignition coil. Also check your O2 sensor wires in case one got clipped while the shop was working on your car.

Does the exhaust have a noticable gasoline smell?

usually platinum plugs lower the voltage required to jump the gap, this reduces spark energy for ignition. If you are running a higher octane fuel, platinums will make it harder to ignite. Also keep in mind if you feel your car is running great, your right foot is heavilly involved in the gas mileage.

Depending on my mood I can drain a 1/4 tank within an hour's worth of driving without traveling too far heh

I've also noticed that unless your car's ignition system is truly on it's way out, you won't see an increase in gas mileage.

I made the mistake of the Boschs a while ago, get them out of there. My car didn't like them at all. I put NGKs in and it was like night and day. Just my .02

usually platinum plugs lower the voltage required to jump the gap, this reduces spark energy for ignition. If you are running a higher octane fuel, platinums will make it harder to ignite. Also keep in mind if you feel your car is running great, your right foot is heavilly involved in the gas mileage.

Depending on my mood I can drain a 1/4 tank within an hour's worth of driving without traveling too far heh

I've also noticed that unless your car's ignition system is truly on it's way out, you won't see an increase in gas mileage.

Platinum is a worse conductor than copper, so plantinum itself would actually require more voltage to make a spark. However, platinum plugs have a smaller electrode tip, making spark easier. In any event, what voltage is sent to your plugs is controlled by the ignition coils, so using platinum will not "lower the voltage."

Also, let's not forget that our cars came from the factory with platinum plugs, so there's nothing wrong with using platinum plugs. Whether Bosch platinums are a crappy brand of platinum plugs is a different question.