I noticed my fuel mileage dropped a lot, like 10 miles per gallon. I also noticed I can smell gas when my car is full to as low as about a half tank. I haven't run a diagnostic check yet but a guy at work told me it sounds like the rear fuel vent canister. I looked it up and there are two solenoids back there and seems one opens and lets the tank vent to the engine to burn fumes instead of just fuel. If that isn't working that is likely why I smell the fuel, right ? I know I have no leak, already checked. I cleaned the EGR system when I did the head gasket replacement last year. It was totally clogged. Anyway, as I said, the engine runs perfectly smooth even though the check engine light is on. I'm almost certain when I run the diagnostics it will pull an HVAC code. I also read about the smoke test but I cannot do that, don't have one. Thanks.

 

I would run a scan and see what the O2 and other items looks like, sounds like a car running really really rich, spark plugs in bad condition, check tire pressure, burning oil maybe,or something like that. That seems like an excessive loss of mileage, one that I don't think a failed vent canister would produce.

Maybe it's in a limp home mode...report back what the engine light is telling you after scanning it.

 

I replaced the head gaskets a year ago along with all the top end gaskets. Spark plugs, wires and distributor cap were replaced then also. It doesn't burn oil. Engine runs perfect. I will get a scan and see what it.brings up. I'm almost certain it's the vent solenoid and likely O2 sensor(s). I know there is an up stream and down stream.

 

I'd guess your CEL code would be a P1457. That's what I had on mine and discovered the fuel (and brake) lines were bad. They were replaced about a year ago. I think the downstream line actually had a couple holes. I recall I could smell gas at times - but I don't think MPGs went down significantly.

Once you get it repaired it may take a while for the code to be considered cleared. If I understand correctly the whole process is a few cycles - and it takes a couple of cycles with good results to reset the code. In my case that was about a month since I don't drive the car much.

 

I run an obd on it today and got the code p1457 evac canister leak. It's the only code that come up. So I ordered a complete canister with both solenoids. I don't have a gas leak so what is happening is the valve is stuck open letting fumes out.

 

Good you don't have a leak in the lines - and that the parts are still available.

 

That will be very interesting if that brings the mileage back up, I'd have to say I've not heard of a loss of mileage in that range. I replaced my canister about a year ago, but never saw a reduction in gas mileage at all. Venting fumes just normally is not significant enough to drop 10 MPG. But it's a very interesting symptom. Hope that's all it is, you barely even get dirty changing it out!

 

If that doesn't help the fuel mileage then I will be clueless. If an O2 sensor was bad it would throw a code.