Gas, oil and engine problems

OK, heres my deal. I own a 1991 acura integra ls. when i bought the car is had a blown head and i repaced it and all the seals, set teh timing and agian and i was good for awhile. Now no matter how conservatively I drive I go through gas and oil like nothing. And also ever since i got the car after its been driving a litle bit (like 5 minutes) The check engine light goes on after it warms up. If you have any idea of what it might be then reply back and let me know your diagnosis. I have an intake and exhaust and performance plugs and wires so I should be geting at least average gas mileage(around 30 ) instead of 18 liek im getting now. I really need help so please leave a reply.

91 integra, factory spec is 25 mpg combined city and hiway. Considering your car is more than 10 years old, and you added some performance parts, I think 18 mpg is really not that unreasonable.

Of course, it is pretty much impossible to get EPA mileage figure in real life. Lay off the gas a little and see what happens.

If the check engine light goes on, scan it for codes.

When some parts of the engine aren't function properly and if the OBD throw a code, sometimes the ECU sends more fuel to save the engine of more damage (some security mode). Scan it, that's why they did the OBD (on board diagnostic).

88-91 = Non OBD (unless converted)
92-96 = OBD1
96+ = OBD2

I beileve you will not be able to use scan tool. check code by counting amount of times LED on ECU flashes.