I've got a 94 SE with 119,000 miles on it. Ever since I bought it new up until about 1 year ago the car always got about 19-21 mpg in average in town driving. Now it'* down to about 18. Highway was always about 26-29. Now about 24-25. I can't feel the car miss, no check engine light, plugs look OK, no stumbling. Just lower mileage. The O2 sensor has never been changed. Would that cause lower mileage and if so where is the best place to buy one and what brand seems to work best?

Any other ideas would be most appreciated.

Mike

If its got 119k on original 02 its time to change it.
Its a matter of personal preference on the brand although most say
the delco works best. About $51 AT AUTO ZONE.
I assume you did all the obvious, filters, oil, tire pressure, alignment etc.
How many miles on the current plugs?
A scan tool will best tell you what is ailing such as the 02.

SSEBONNE4EVA,

New Bosch platinums installed 10,000 miles ago (Oct. 2002), new air filter 13,000 miles ago (June 02), new EGR valve 10,000 miles ago, tires run at 31-32 psi.

I thought about taking it local Pontiac dealer and having him scan codes but hate to pay his rate of 445.00 just for that. I guess I may have to before I spend $50.00 on a sensor that may not be the problem.

Thanks,

Mike

Pontiac dealer rate to check codes was $45.00 not 445!

Sounds like your o2 sensor. I had one go bad, it left the car running on full-rich the entire time causing it to get horrible milage.

I installed Bosch Platinum plugs. It was their part number 6241 gapped to .060. I will pull a couple of plugs and look at them. I'll probably go ahead and get new AC Delco plugs and O2 sensor. Is there a particular AC Delco plug I should buy. Do mostly in town driving. Not much on the highway anymore as Bonne is second car.

Thanks for the advice.

Get the o2 sensor from GMparts direct. it'* only about $30-35 depending on your model. Check techinfo for that information.

Don't forget sometimes a simple bottle of fuel injector cleaner could bring
mileage back to life if the injectors are clogged.
I like to add one at each oil change.
I didn't experience any problems with my Bosch Platinums so I cannot
comment. Just had good results. I have a stock ignition with triple silicone wires
on both my Bonnevilles.
If you pull the plugs and they are chalky white at the tip its not the plugs.

Is there any way on a 94 SE to read engine codes by using a sequence of ignition switch on-off actions like can be done on other cars? I'd like to see if my O2 sensor is showing a code or not before I buy one but I don't want to pay the dealer $45 just to scan the codes. I'm not getting any check engine light indications.

I looked at my Bosch plugs and the tips look OK - light beige. No sign of oil or excessive richness that I can tell. Any other ideas before I change plugs and O2 sensor.

Thanks,

Mike

A weak O2 won't set a code. Ditch the plugs and O2 sensor. They're due, anyway.

Bosch plugs may look ok when you inspect them, but the electrodes erode inside the plug. I know this from experience. Don mentioned AC Delco plugs or Autolite. NGK is also a good choice, as they make the GM plugs. My personal preference is the NGK V-Power.