Poor gas mileage on 97 SL1

The last few tanks of gas have indicated that my gas mileage has
dropped considerably since I changed plugs.
I could not get to the Saturn dealer to get the oem plugs, so I bought
some at an auto store that are supposed to be the right plugs. But, I
have only used the Saturn plugs since buying the car new and wondered
if the after market plugs could cause such a dramatic drop in mileage.
This is the only thing I know of that has changed since the drop in
mileage.
TIA,
MR

 

I doubt it, but it's possible since you might have the completely wrong
plugs in there and not just a different brand . Another possibility is were
they gapped properly? As I recall there was some incorrect information on
plug gap for around that year. If I recall correctly, the gap should be
..040 inches and not .060 as published in some documentation. This is from
memory and it isn't what it used to be so I'm sure others will correct me if
I am not right here, or you can ask the Saturn dealer if you are not sure.

Bob

 

The gap on the old plugs was probably at .060 from wear and most of
the new instructions call for the .040 gap. That is one of the
reasons I installed new plugs was the rough idle which happens with
the large gap. But, it was not suffering the poor gas mileage that I
am experiencing now. I did clean the throttle valve also now that I
think of it due to high idle when first starting. I could have
screwed something up there I suppose, but that cleaning is pretty easy
to do.
Thanks,
MR

 

What brand and type of plug did you get and what is the condition of
your wires? It isnt likely a plug problem I dont think. I guess we
should first ask what you consider to be "considerably". 1mpg? 5mpg?

 

Not sure about the plugs, but think they are Champions. Wires are
fine. Changed those out ~75k miles ago.

I usually get ~35-40 mpg depending on city/hwy, but has dropped to
about 25 mpg.
Thanks,
MR

 

I usually get ~35-40 mpg depending on

Two non-plug factors:

1. Air conditioner use. You might take it to a local A/C shop and
have them check things out (or you can screw on some gauges and check
out the high and low side pressures yourself.)

2. Summer gas. Depending on where you live, in June/July they switch
to a different gas formulation that has lower vapor pressure and also
lower mileage.

Tim.

 

Tire inflation is also something to check and the single largest contributor
to poor mileage.

Bob

 

Can you give numbers? MPG before and after?

As for plugs, I've not had much luck with anything other than NGK's
for my Saturn.

hth,

tom @ www.CarFleaMarket.com