Ok, this is probably something basic, and since I'm swapping my new engine in over spring break, I probably don't even need to worry about it, but.....

I have a '91 Civic std with the d15b1 and 4-speed, the only thing I've done to the engine is an MPFI swap, the swap's been in for almost a year now. before the swap, I was getting almost 40 mpg, after I did the swap, I was consistantly getting 30-35 MPG, no problem. But I've noticed lately I'm only getting 20-25 MPG. It's still running strong, no loss of power. With the future swap in mind I haven't been doing a whole lot in terms of maintenence, but I know the fuel filter and air filter are clean. and there's no fuel leaks anywhere. It's always smoked a little (250k motor) and doesn't seem to be any worse than before.

any Ideas?

 

yeah same here. when i bought the car it was super good on gas. then lately $10cdn won't even last me a week. by the way we buy in liters not gallons. so i changed the plugs and plug wires with NGKs and still barely any improvement. and i drive normally within speed limits all the time during winter sometimes even slower and i dont see an improvement.

but on my first car it was the same thing when i bought it. so i changed the fuel fliter and plugs and then i changed the O2 sensor and that's when everything changed. $25 cdn would last me over 400kms that's a full tank.

try the O2 sensor.

 

try 16-17 mpg on premium...thatll get ya...
for a honda at least.

 

Well, I already have a brand new O2 sensor, which is mounted to my brand new header, which is mounted to my brand new engine, which is being installed over spring break. I guess I'll just tough it out until then. I don't want to dirty up that nice new sensor in my old, worn engine.

 

PCV valve. easy to replace, or try cleaning first. cheap anyway. will help with the oil consumption as well. located on the intake manifold webbing between the 1st and 2nd intake tubes, has a right angle bend. just pop it off.

 

I put a new PCV valve in when I did the MPFI swap, but the breather chamber is all plugged up so I start smoking after 4k rpm. But it was this way when I was getting 35 mpg too.

 

tough call. i was at 42mpg, im at 28.8 currently on 93 octaine. still beats a lincoln tho
could be an o2 sensor... mine last a week at most before i ruin them


[Modified by limoZeen, 1:41 AM 2/3/2003]

 

Maybe you hittin it w/ the gas more often? Not really sure what would cause this. I think that the 02 would contribute to the problem. Try setting the valves, that should help some and restore some lost power.

Blaze

 

so if i replace the pcv valve and te o2 sensor, my mpg will improve?
would it help smog tooo?

 

yes it would.... IF your breather chamber isn't all plugged up.

 

how is your breather chamber all plugged up? i would seriously fix this if youre looking for better mpg.

 

I've been told that it's very common with the older civics... when I went to replace my PCV, it was all gummed up with crap, so I looked at the hose and it was all gummed up with crap. I know the breather chamber that the other end of the hose connects to is just as bad. My pcv is doing no good, any time i get the rpms over 4-5k, there's so much pressure in the crankcase that it starts pushing oil out through the rings and around the rear main seal. (Nice slipping clutch and smoke screen action)

I figured I'd just limp along until I get my new engine in because you have to pull the intake mani to get to the breather chamber, and even then it's a pain to get to with the engine in the car. And I was getting 35 mpg WITH this problem.

 

thumper77,
there's so much pressure in the crankcase that it starts pushing oil out through the rings and around the rear main seal


does that mean that u burn oil, cus i didnt have a breather for like 3 month and now my friend told me my car is burning oil, onil when i rev high tho. when i shift under 3 maybe 4k rpm there will be no blue smoke.

 

and also will it affect the idle? cus my idle is at 1200 rpm now, and i need it under 1000 to pass smog. or else it is automatic not pass

 

You could try changing the fuel filter, spark plugs and also the air filter.