I had noticed my fuel economy on my Si going down over time, so I thought I'd do some routine maintenance and replace the plugs and plug wires. I used NGK for both and I checked the plug gap and they were all correct (.042). I can't imagine I screwed up the install (the car still runs exactly the same as before), but now my MPG is 27mpg (was 28ish before) and this is much worse than the 32-33 mpg I got 20k miles ago when I bought it. I know my heavier wheels (15" Rotas and Azenis) and generous toe-out (1/8th inch) aren't helping, but damn, what's going on? Why would economy go down after new plugs and wires?


[Modified by tylerdurden, 5:21 PM 4/1/2003]

 

change fuel filter (honda oem), clean throttle body/intake manifold.
edit- and possibly advance your timing a little. what octane gas do you use?


[Modified by 22lbGS-R, 11:28 AM 4/1/2003]

 

Distributor cap and rotor. Air pressure in the tires. Heavyer wheels and tires. Valve clearance. ALIGNMENT. Higher viscosity oil. Air Filter. Windows opened or closed. "Body Kits" Fog Lights.

All these items can impact MPG. Most are very subtle but when added together are pretty significant.

 

Fuel filter is a 10-12k miles old. I guess I could try changing the cap and rotor, but I'm just puzzled why I would get worse gas mileage after this change. Oh, well.

 

Def check your tire pressure, a few lb in each tire can make a good change in mileage, course id be pissed if i got 28mpg period, my 90 dx auto beater = 34mpg

 

ever think u drove differant .. i mean going from 32mpg to 27 .. could just be how u drove on each tank man.

 

It seems like previously my driving style would only affect my economy by 1-2 MPG per tank unless I beat on it really hard. I didn't use a torque wrench to do the plugs, could that have something to do with it? I would figure it either works or it doesn't, but I'm willing to try anything.

BTW, the mileage decrease has been gradual over the last 20K, it didn't go from 32mpg to 27mpg with the plug change.


[Modified by tylerdurden, 8:31 PM 4/1/2003]

 

you prolly need new 02 sensors. How many miles are on the car?

Blaze

 

165K. Wouldn't I get a code if the O2 sensor was bad?

 

yes you would but that doesnt mean that you dont need a new one, should incrase mpg if you do get one tho.

Blaze