94 vx only getting 25 mpg!?!

[rsport]

ok, i am new to the site here. and i am hoping for a miracle with the guru's here.
i bought a 94 vx las october knowing that it was going to be a project. but the guy didnt disclose all the problems the car has so now i am in it further than i thought i would be.
i have fixed alot of the cosmetic and critical problems with the car. she starts right up, feels very strong, does not smoke, tranny is smooth, handles very well, and sounds great. except i am only getting 25 mpg. 90% of my driving is city stop and go, about 20 miles/ day.

things i have done so far.
new oem spark plugs, correct gap.
new fuel filter.
fresh oil and oil filter.
new air intake with new filter.
new tires, with lightweight rims.
alignment
DC sport headers, custom 2.5 inch exhaust
lowered 3 inches.
vx transmission with new clutch.
new battery

other issues:
the CEL comes on at 45 mph.
the speedo does not work right.

I just ordered the 5 wire O2 sensor for it.

I think i might need to do a timing adjustment and valve adjustment.

I would greatly appreciate any help. thanks for your time.

[add|ct]

Check PSI in the tires, should be into the high 30s at least. Most on this site recommend near or at max sidewall pressure.

Which 5-wire did you order?

Replace your Vehicle Speed Sensor. Easy but somewhat pricey, depending on where you get it. Check RockAuto or Amazon.

[bowtieguy]

the thermostat is often over looked. does the car get fully warmed up?

[rsport]

o2 sensor is the 5 wire ntk 24300.
thermostat is fine.
i will check tire pressure as soon as i can. i only have maybe 400 miles on the tires so they shouldnt be any lower than what the tire shop set em up as.
i am looking into the vss right now.

[Matt Timion]

Your CEL is the key. get a new o2 sensor ($135 on ebay, I think). Your VX will never enter lean burn mode without a properly working o2 sensor.

[GasSavers_TomO]

That 2.5" exhaust piping isn't going to help with City driving either...1.75" diameter would be best but 2" is usually cheaper if making your own exhaust. And 2" will be ok to use.

[add|ct]

I'm thinking the exhaust mods may be somewhat of a culprit here as well. Let's see how the performance changes with the new 02 once the OP installs it.

[rsport]

yeah, the funny thing is, i starting collecting parts for a civic course race car before i bought the car. i found the civic hatch for really cheap (cause it was in baaad shape) knowing i was going to be replacing alot of parts with performance parts anyways. i didnt realize the car was a vx until i did some more research on the car. so i still put on my performance parts but instead of doing an all out race car, i wanted a well balanced fuel efficient car for spirited driving. im not looking to get 50+ mpg but i sure as heck should be getting more than 25. i would be happy with anything more than 35.

who knows, if i cant get the engine running right, i might sell the whole VX swap to the right person, with them knowing that it needs to be rebuilt.

[Matt Timion]

it's possible the previous owner tried to modify some stuff. Ensure your ECU is a p07. Also ensure that the EGR valve is plugged in. If it isn't, it's possible a previous owner put a different engine/transmission in there.

[theclencher]

Matt's alive! Where have you been?