2000 Esteem Running Lean?!

[sblrog]

Hi all,

I got a few things going on that could actually be multiple issues, but all happening over the last 1/3 tank of gas. The only thing I did differently was vacuum out the air filter a bit... I know that's a bit of a no-no, but it was really dirty and I couldn't wait a couple of weeks for my K&N (I know, another can of worms) to arrive in the mail. And I was careful about the vacuuming, only really going after the big stuff (leaves, feathers, etc.).

Since then, I've had a three things happen. First, the fuel economy went through the roof. I've been running consistently at an average of 33 MPG for the last 5 fill-ups (roughly 50% city, 50% highway). However, I could tell that the needle was hardly moving the last few days. After using about a quarter tank, I had gone just over 300 km ~ 190 miles.

During this time, the check engine light also came on. I found a P0451 code (Evaporative Emission Control System Pressure Sensor/Switch Range/Performance). I reseated the gas cap, and cleared the code. It hasn't come back yet. However, after taking the car out about 5 times, the EVAP monitor, catalyst monitor and EGR monitors have yet to run their programs (the others HAVE).

Concerned that my car was running lean, I went to fill up today to see if was just the fuel gauge going wonky. However, the gas station pump kept shutting off, right from the start. This has happened to me a few times in the past, and seems to be a common problem on the 2000, as documented here: http://www.suzuki-forums.com/suzuki-...-fill-ups.html. So I couldn't really tell when my tank was full, but the needle ended up being pretty much where it is after a fill-up. And my gas mileage came out to 41.6 MPG (compared to the usual 33)! I realize that there is some variability, especially due to the pump shutting off, but I don't think it would account for an improvement of 26%.

So here are my questions:

1) Can vacuuming out the big debris from the air filter lead to such a dramatic improvement in fuel economy, up to 42 MPG (50/50 city/highway)?!

2) If not, can I be running lean without the oxygen sensor monitor detecting/reporting it

3) I realize that the problem causing the gas station pump to shut off could be tripping the P0451 code. Could it also be causing my gas needle/fuel level sending unit to read inaccurately?

Thanks for bearing with me

[sblrog]

I forgot to mention that it was 42 miles per US gallon (obvious?), and that the car is automatic transmission. So that seems unusually high to me, even though I've heard about fuel economy awards and stuff.

[jim_naisium]

That does seem awfully high, my 1999 1.6 liter Esteem has only done 40 mpg once in the 137,000+ miles that I have owned it, and to do that I bought gas at a freeway gas station drove for hours then pulled off the freeway and bought gas again.

I would have it scanned for codes it might be recording some codes that haven't tripped the check engine light yet.

[sblrog]

I've been scanning after every time I drive the vehicle... no pending codes. Although there ARE the 3 programs that have yet to run.

As long as I'm not running lean, I'm okay with it. Worse case would be a faulty fuel gauge reading. Best case would be some kick-a** fuel economy. Back in this thread, http://www.suzuki-forums.com/suzuki-...o-you-get.html, sd_read talked about an average (over 220,000 km) fuel economy of 45.34 miles/imperial gallon = 37.8 miles/U.S. gallon. RebelPC' talked about 39 MPG hwy & 35 MPG city on the 1.8L with the A/C running. Mxz-man talked about Google turning up 37+ MPG for the Esteem (I didn't do a Google myself, but fueleconomy.gov turns up similar numbers to yours (Jim_naisium).

Anyway, as long as I'm not running lean...

[jim_naisium]

Yeah, the only benefit to running lean is you get great gas mileage, on the other end of things you can warp your head, blow a head gasket, melt holes in your pistons, and melt your valves.

I'm not sure how you would go about testing them but I would have both of your oxygen sensors tested or replaced.

[sblrog]

Just an update here. Apparently, the gas station pump shutting off early is common on the Esteems, and is related to the P0450/P0451 codes. Too much vapour pressure in the gas tank causes the pump to shut off. I'm suspecting the tank pressure control valve, but it could be something upstream as well (EVAP canister & purge valve).

Apparently, Suzuki has a recall for the pressure control valve. However, I couldn't get any satisfaction from my local dealer. They wanted to plug in a code reader for $55 CAD. Forget that! I sense that something wasn't on the up-and-up. When they ran my VIN, one service manager started telling me that the gas pump shutting off is common for ALL cars in hot weather, when the tank is empty. However, it hasn't happened on any of my other cars, but it's happened on me Esteem when it's cold. Another service manager came over and looked at the computer screen and exchanged some glances w/ the original guy. I suspect that the valve on my car had already been replaced under recall by one of the previous owners at this dealership. Does anyone know what recall policy is? If they've replaced it once, is the owner out of luck?

Anyway, I doubt that I'm running lean, but rather the fuel gauge isn't reading accurately. But as far as I know, the fuel sending unit should not depend on the vapour pressure. Is that correct?

Thanks

[sblrog]

Actually, I'm not sure if what I wrote above makes any sense ("Too much vapour pressure in the gas tank causes the pump to shut off.") When you take off the gas cap, the tank would pretty much vent to atmospheric, wouldn't it? Back to the drawing board.

[sblrog]

Got some more info. Apparently I don't have an EVAP canister. I remember seeing it on my sister-in-law's Esteem when I bought it, and wondered, "What is THAT?" But there's no big rectangular box under under my hood, neither beside the throttle body nor the master cylinder.

[sblrog]

If I AM running lean, will this show up on the spark plugs in time to do something about it?

[sblrog]

I'm itching to get at this issue, but I'm down-and-out w/ a nasty flu. But I think I might have a clogged fuel tank breather tube which leads to:

1) Premature shut-off of some gas station pumps, i.e., the ones with the larger diameter pump tubes, which won't allow the air being displaced by the gas to escape, thus creating back pressure

2) A vacuum in the tank until the fuel level drops enough to expose the tank-end of the filler pipe, thereby releasing the vacuum through the gas cap. While the vacuum exists, the car may be running lean

3) A tripping of EVAP codes P0450/P0451 due to abnormal pressure conditions in the tank (these codes tend to show up after fill-ups, and goes away by themselves).

Sound reasonable or am I blowing hot air? I guess I'll have to wait until I feel a bit better