Alright so when I traded my EK coupe for my 97 Prelude I knew the Prelude was going to get worse gas mileage than the Civic. What I didnt expect was 16mpg! This is utterly retarded. I do all city driving but it should still be getting like 20? at the worst. The other day it started throwing a code 12. I did some research and tested it using this method:

"Create vacuum on the line going to the egr solenoid, if the car dies the passages are free enough for air to flow, if the car doesnt die the egr passages are clogged"

The car died so apparently the passages are free flowing enough to get by. I also tried replacing the control solenoid and cel still appeared. Any thoughts on how to fix this and if it is at all related to my terrible gas mileage?

 

Buy a can of sea foam, take the egr out, now dump the sea foam into a container, place a house into the opening left from taking out the egr, turn the car on and yes the car will have a huge vacuum leak, and leave it on untilthe house finishes sucking all the seafoam, turn off the car, and let the seafoam sit, then turn it back and leve it on until the car stops smoking, and voila you just cleaned ur egr ports

 

Just to make sure I understand what youre saying, you meant hose, right? Also could this be whats causing the bad gas mileage?

 

Yes I meant a hose, the procedure I stated was to clean up your egr ports, and since your trying to improve the mileage, check your air cleaner if you still have one, spark plugs and wires while your at it.

 

For fuel mileage that poor, I would check the front o2 sensor, and what kind of condition the catalytic convertor is in.

 

Air box was just replaced with short ram and Spectre filter. Spark plugs, wires, and cap are for my next paycheck.

Will def replace the o2 with an almost brand new one I have leftover from my B18 swapped Civic. Also probably going to gut the cat, remove resonator, and put a Thrush muffler in place of the oem restrictive setup

 

The sea foam trick worked. Thanks for the info

 

BTW, i get better mileage in my prelude by using
a higher octane fuel. You could try that also.

 

I use 92

 

Your octane rating in America is different from ours, hopefully a
fellow American can let you know what they use for the best
mileage. Here in Australia, the main unleaded fuels come in
91,95 and 98. Honda recommends using 95 or higher only
as 91 will result in engine knock. I only use 98, and find that
i get much further on a tank than using 95. Its most noticable
when travelling long distance at highway speeds.

 

93 is pretty much the highest octane you can get in the U.S normally. you can find some 100 but thats not in alot of areas. I have always put 93 in my prelude and got fairly decent mileage with upgrades

 

Still getting 16. Anyone?

 

Did you replace the oxygen sensor? Still getting a CEL after cleaning the EGR?

 

Just got the o2 today will be replacing tomorrow. What are the odds that it's bad without a cel? Also the light came back on for a day but found it to be a torn vac line so it's good once again

 

Anyone?

 

If you have replaced the o2 sensor, checked the air filter, plugs and wires, and cleaned your egr, and are still getting horrible milage....you might want to check the airlfuel ratio and check the timing. Also try cleaning injectors....seafoam will work for this also. Good luck, hope you find it

 

That's weird. I got 24mpg city/30mpg highway with a shitty catalytic converter on my car. I was doing 70-90mph.

I agree go with a new air filter (helped get better gas on my mum's Mustang). Was getting 14mpg before switching that out.

Get new filter, spark plugs, spark plug wires, seafoam it, check the converter, etc.

 

To answer your question, yes an O2 can go bad and not throw a code. it will only throw the code when readings are consistently off the scale, or the heater wire is broken.