Bad Gas Mileage - Honda Prelude Forum

1992H23A3 · 01-13-2010, 11:32 PM

my car eats gas. i don't understand it because it is a new engine.
my guess is the knock sensor?
but not sure.

minilogoguy18 · 01-14-2010, 08:14 AM

Knock sensor has nothing to do with gas mileage, check your EGR system and your O2 sensor.

kurt2191 · 01-14-2010, 09:33 AM

my o2 went out and i got around 12-15 mpg so thats gotta be it... unless your losing backpressure

minilogoguy18 · 01-14-2010, 07:14 PM

Back pressure is bad.

1992H23A3 · 01-14-2010, 11:59 PM

i feel really dumb, but the o2 sensor on the exhaust's catalytic converter or is there another sensor like by the intake?
i have a catback exhaust with the original headers, downpipe, and cat so i don't think i'm losing any back pressure.

another stupid question,
whats an EGR system?

minilogoguy18 · 01-15-2010, 09:03 AM

The O2 sensor is a sensor on the exhaust system, it's on the collector right before the cat. The EGR system is easy enough to spot, look at the intake manifold and its the large sensor closest to cylinder 4. There are even stickers on the underside of the hood pointing out the EGR valve.

1996PreludeVTEC · 01-28-2010, 07:40 PM

The EGR system is a son of *****! i have a cel on for the EGR insufficient lift. my car would have black smoke coming from the exhaust under power and it smelled bad. took it off cleaned it with throttle body cleaner (it was bad) most of the black smoke went away but after about 30 mins of driving the cel came back on with same code. took it off cleaned it again almost all smoke/smell went away. but after 2 days the cel came on again. i took it off a third time and this time sprayed the valve and the passages. if you do the passages make sure you dont put way too much and make sure you let it air out for at least 20 mins before replacing the valve because if you leave too much in there and it cant get out it may explode when the hot exhaust goes through

Thurmont · 02-01-2010, 12:53 PM

A similar problem but probably not the cause of what you're experiencing since your gas mileage drop is WAY more severe...

Once I noticed my gas mileage drop from its normal 27MPG down into the low 20's and the car smelled like gas alot. Problem was solved with a new set of gaskets that sit between the injectors and fuel rail. Seems I was leaking gas down the side of my engine while I drove. Luckily, no fire.

Rasmusm · 02-01-2010, 03:29 PM

Well i noticed that i have bad milage aswell.. around 7.8km/l - 8.2km/l on my h22 - but its cuz of the winter :/ usualy i drive 9.5-10km/l
Its kinda expensive in fuel when one gallon (3.78liter) cost 40$ sucky Denmark..