My 98 gx gets mid to high 30's gas milage but my friends 98gx get like low 20's.
he replaced the distributer, new cap, rotor, wires and plugs and crank position sensor
Currently has CE code P0420 but i have that code too, had it for sum time
Where else should we look?

 

I don't know much about cars at all but maybe it is burning the gas to lean. It seems you can kinda tell if it is too lean, since the smell of gas is more.


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Has the ignition timing been checked?

 

He put on a new distributor but i dont know if he check the timing. I'm farily sure he would do that. i swapped MAP sensors and i think that was it. seems to run better but i haven't driven it enough to calculate the gas milage yet.
thx for replying!

 

check the timing, check the fuel filter, than let him borrow the map sensor for a day or so and see how it goes. sound to me timings off. simple fix

 

I'd start with fixing the know CEL which i believe is for the cat, just because you guys have the same check engine doesn't mean his problem isn't worst. Driving habit is a large effect on mpg I can drive my coupe hard and get 22mpg and drive it easy and get 34 mpg

 

Don't assume. Ask the mechanic or check yourself using a timing gun.

 

I'll ask him if he checked the timing.

 

he and i should change the CAT but we're in CA and it's expensive, but you are right
i know what you mean about driving habits but i drive the same, nice and mello, basicly all the time and i got 25 mpg when i put his trottlebody in my car and when i switched the MAP there was a noticeable improvement.
i've ordered him a MAP and TSP. his has a dead spot and close it reads .6v and the adj screw has never been tampered with

 

How exactly are you calculating the mileage? Compressed natural gas goes by weight doesn't it? not gallons.

 

they have units called “gallon equivalent”
it doesn't matter what the unit is along as your consistent... right?

 

I think 94EG8 was just curious. We don't see many GXs in this forum.

How many "gallons" does your tank hold?

 

Sort of. It was really a sneaky way of making sure it actually was a GX and not another Civic with a GX badge or trunk lid more than anything else.

It's supposed to be equivalent to 8 gallons.

 

suppose to hold 8 gge
it was the MAP that caused the bad mpg

 

Was a MAP sensor code thrown? Did you test the MAP sensor?

 

my 98 lx automatic gets about 21 mpg. mine is all city driving though. no interstate or anything.

 

Yeah, automatic Civics get bad city mileage.