[SuperHatch]

Well, I finished a VX conversion on my father's 91 CRX HF. After troubleshooting some check engine lights, distributor related, we got the car running great. Everything functions as it should, and there are no codes. The questions I have is this...

After running two full tanks of gas through the car, my father is only getting 45MPG. This is the exact same mileage he got with the original HF engine in the car. It is summer time, 90-100 degrees, and he is using the air conditioning consistently.

Would using the AC cause the car to get 45MPG, as opposed to the expected 55-60MPG?

Can the LAF sensor be "bad" without causing the Check Engine Light to illuminate? He says he can "feel" the slight stumbling at cruise from what I assume is the lean burn kicking in.

The enigne is very healthy, runs excellent, has had a full tuneup, timing is dead on, spark plugs are new OEM NGKs, fuel filter is new, air filter is new, etc. The car runs as if it were a very well maintained VX Civic.


When I had my HF, I got between 49-55MPG, my father never crossed the 51MPG mark, usually aroun 48-49MPG without AC. I tell him he needs to drive gingerly to get the great fuel economy numbers, but he says "I'm not going to drive like grandma", and "sometimes I need to use the throttle to avoid being a hazard pulling out in traffic."

I almost want to ask him to trade vehicles for the week to see what kind of numbers I can pull out of it... just as a sanity check. Suggestions?