I have a 94Z M6. About 8 months ago I put a new opti (twice, most recently 3 months ago), new plugs, wires, O2 sensors and fuel filter on it. It was running great and averaging 20mpg mixed city and highway. For the last 3 fill-ups, my average fell to about 16 then 14 and now is at 13. This is mixed city and highway driving and the car would normally get around 19 or so in the exact situations. So now I am getting 13 mpg which is horrable because I drive the car alot. My question is what would cause this horrable gas milage? The car does not leak gas, does not throw a light, runs great, no noticable loss of power, no noticable black smoke out the rear. I am thinking maybe it could need O2 sensors again, but they are only about 8 months old? Anyone had a simmilar situation? Thanks for the help

 

non AC/Delco O2 sensors have a bad rep. if you're not using them get them.

you covered most of the basics except fopr air filter. your sig says K&N. when was last time it was cleaned and charged?

I have no proof or data but the |CAGS does override the shifting that figures into good mileage; and it has to have an affect on a car that does more local than highway driving MPG.

I use AC/Delco stock plugs with Accel 9000 wires with setup in sig and get 30 MPG on highway and 20+ local driving. I can get it down to teens depending on driving style.

I run real clean on emissons testing for inspection too.


good luck

 

also give ur MAF a cleaning if you havent done it...

 

how would you reccomend cleaning that? could you use throttle body cleaner like sea foam deep creap?

 

I used Denatured Alcohol and Carburator cleaner with cotton swabs.

Very Gently Rub the swabs on the tiny resistors all around them and also on the metal bars that conect the resistors. Someone may say not need to clean the conecting bars but then their temp changes may be part of the whole equation too. Put it this way It will not hurt. Clean all around the resistors not just one side.

I did not use seafoam nor deepcreek here only because they appear slightly oily and may leave a greasey residue behind that will quickly collect more particulate matter on the resistors again.

Thats my input.

Marvin