Hello fellow Honda Techies! I have a problem going on with my wife's 1991 Honda Accord EX Wagon 5spd. Right now off the top of my head, I will try to list everything I've done to this engine-I've done so much it should be a freakin brand new car!
The problem she is having now is poor gas mileage-around 20mpg city/hwy. That being stated, when she first got the car, about 4-5yrs ago the car averaged around 32hwy/30city.

The last problem the car had was an awful surge when warmed-we're talkin 1,000rpm spiking to 3,000rpm and I couldn't get the car to idle less than 1050rpm- the screw was all the way in. So of course I did the usual procedure-IAC(EACV) cleaning and remounting, FITV clean and adjustment, checked Idle Adj Screw for leakage, PCV valve, purged any air from coolant, etc.... The end resultant of that problem- LEAKING IM-found with a can of carb cleaner. So I pulled entire IM and IM gasket was in two at no.3 & no.4 cylinders.

Here's the kicker, even with all that surging going on and air leaking into the Intake Manifold, the car avg about 27mpg!! Now after fixing the surge problem, and not to mention I bought a new FITV from Honda, she's getting avg 20-22mpg, WTF!
Also no codes present on ecu

Details on the work done to engine:
Engine-F22A6 w/5spd
Mileage- Approx 386K mi LOL!
I overhauled the engine around 50k-60k mi ago and installed a LUK pro gold clutch at the same time-the block I used was from a low mileage F22 so non-original (to the car) block
Standard rings, bearings, seals, etc cylinders reamed and honed
The head was rebuilt by a machine shop around 80k-90k mi ago which at that time they replaced a couple of burnt valves but otherwise a standard job
Timing belt/wtr pump all done at engine overhaul
rebuilt pwr steering pump w/ new pressure line
new TPS sensor and adj to .45v @ close to 4.5v< @ WOT
new Speed sensor
new coolant temp sensor to the head
new distrib (TD-31U) now has about 100k on it but just replaced cap & button
new OEM denso O2 about 60k on it
new Vac tank with new solenoid valve-on bottom of IM since I broke it
new Alt about 3mos ago which is about the 3rd or 4th one on it since we bought the car
new harmonic balancer that broke on us on vacation and a used one was installed there
new FITV-Fast Idle Thermal Valve
replaced all vacuum lines except for line that goes to reservoir inside left frnt fender
rebuilt starter with new magnets from Alt shop
even switched out old ECU with replacement from ebay
new fuel filter, main fuel relay, pump screen, fuel press regulator
the dessicant in the carbon canister was used up so I grabbed one out of a sedan-which is noticeably different- that was good and installed it

Everything else has been taken off and cleaned up at least like IAC, Air Boost, EGR, throttle body, Intake Manifold, Injectors-with all new seals too and I also spray tested them when I had them out.

I also installed a cold air intake about 2yrs after she bought it, so no OEM air intake.

So are there any techs here that could tell me where to start with the fuel mileage problems? Is it possible to lean the car out any? There's no reason for this car to get as crappy gas mileage as it's getting! When a 1985 chevy caprice estate wagon can get the same gas mileage as her accord wagon, there's a problem!

Carbon/charcoal canister maybe?
P.S. The reason I laugh at the mileage on the car is because my wife thinks it should run just like a brand new one! I just don't think that's possible

Any input is appreciated

 

i just sold an 91 ex wagon with the same problems . the guy i sold it to was an mechanic . he looked at the car and got back to me and said it was an bad cylinder. the car was running on 3 out of 4 . the #3 valve was stuck open and dumping fuel out the exhaust. that the car needed an head replacement . if i wanted it back .