2000 S70 Base Getting 12mpg

[precopster]

You haven't seen the charcoal canister near the fuel filter because it's located near the front left wheel very close to the fender.

To view MAF readings you can go into live data using most scanners and view the MAF flow rate. It should be reasonably steady at between 14 and 18 kg/hr or g/min depending on the scanner.
I still believe you may have leaky injectors. These would cause high O2 sensor readings as exhaust gas temperatures climb.

[thankswww]

@Mike: I think you may be on to something because:

1. The hissing/air leak sound is coming from the general area of the fuel rail.
2. Before I replaced my fuel filter, I pressed the pin in the schrader valve on the fuel line near the filter, and nothing happened, indicating that perhaps the fuel system is not maintaining pressure.

I will pull the plugs next weekend and see if one looks different from the others.

[osman]

Your EVAP system is technically part of the fuel/air delivery system , especially with a failed check valve.
I bought a 850 wagon once that did not have a charcoal filter, just the j-hose and the straight one staring down at me from under the battery tray, front of the left tire on left hand driver vehicle.
So there is your massive vacuum leak and the reason for code p0400 constantly recurring.

[precopster]

A vacuum leak will not be related to lack of fuel line pressure. They are 2 very independant systems. Another cause of O2 sensor flagging is LACK of fuel pressure resulting in poor spray pattern at the injectors.

As the OP is looking for the charcoal canister in the wrong location we haven't yet established it isn't present.

If fuel doesn't squirt out of the shraeder valve with great force I believe you've found the problem.

[osman]

Does the evap cannister not attach to the throttle body with a hoses through a check valve. If it attaches to the throttle body and can leak, that is unmetered air and a vacuum leak.

[precopster]

No it doesn't attach directly to the throttle body. In the non turbo versions they use a simple ribbed rubber plenum which attaches directly to the MAF sensor then directly to the throttle bore. Behind the large plenum hose is another hose directly attached to the vacuum system. If this lets go there can be a vacuum leak but this is easy to spot as it's a 20mm hose.

[oragex]

Update: OCT 28

Replaced both O2 sensors. Unhooked battery, touched cables together to reset ECU.

Cleared codes with scanner. Ran the car for a bit, drove it around for about 40 minutes in various conditions.

The two O2 sensor codes are "cleared" but have popped back up under the "pending" category, meaning the ECU has received the fault codes at least once again, and is waiting to see if the code comes up again before displaying it as a permanent fault.

This car is infuriating. Why in the world would two correct, brand new O2 sensors be throwing error codes in the ECU????

I thought working on my Porsche was stressful, but it turns out that the S70 is a much, much bigger money pit and nightmare of a car. Life isn't fair; I always wanted a Lamborghini, but instead I got a volvo that gets the same gas mileage as a Lamborghini.

I don't believe in 'touching' the battery cables to reset ECU. Unplug both battery terminals for the whole night. When you put them back you will notice even the ventilation settings on the center console are reset to a default.

I would stop replacing parts. It will get expensive, plus chances are you're replacing several still working parts.

Clean the MAF sensor, it's easy access and I would clean it gently with a q-tip with water, unless you want to buy a CRC maf sensor cleaner.

Check ECU grounds and interior for corrosion, and check cables under the hood. How is transmission fluid level?

Does the car easily accelerate until 6000 rpm? Run a finger inside the exhaust pipe, does it get really black or just a little?

[abscate]

All that fuel (roughly 2x normal) is going somewhere.

Pull plugs, take pictures and post
Inside of tail pipe - black or grey?

It could be you have a fuel leak that is evaporating but usually you will smell that.

[ChiNorm]

+1 for does it rev smoothly to 6K?

I had a fuel line, in the fuel tank, with lengthwise cracks. So the fuel pump pumped most of the gas right back into the tank. If floored, the motor stumbled, coughed and died, owing to fuel starvation. And, the mileage sucked too.

If it revs to 6k, you don't have this problem.

Good luck.

[thankswww]

Update: November 1

@ chinorm, oragex: Yes, the car easily and smoothly revs to 6k without any troubles. Additionally, there is no fuel smell.

There is no colored smoke coming out of the back, even during startup. I've had someone else drive the car under a variety of conditions, while I followed behind in another car to look for smoke, etc.

Last weekend, I replaced the evac purge valve, and the vacuum hoses going to that, and the check valve that is on the radiator shroud. I also replaced the fuel filter. After this, I reset the ECU. Since then, after topping up again and driving under a variety of conditions (mostly city though, stop and go), I've been averaging around 17 - 17.5mpg.

I still hear a "hissing" sound coming from the fuel rail area.

@Mike, I changed the fuel filter after the car had sat for approximately 2.5 to 3 hours. At that point, there was no pressure coming from the fuel line pre-filter schraeder valve. Should the system maintain great pressure for that long? I was bothered by the fact that there was no pressure. There are no visible fuel leaks, nor is there a fuel smell, or any signs of a leak around back.

Would a leaky injector make a "hissing" sound? I'm going to pull the plugs tonight or tomorrow. I'll photograph them. The plugs are less than 4 months old. They were changed out by my mechanic before I got a chance to look at the old plugs. He was changing the timing belt, and I hadn't instructed him to change the plugs, but he did so after pulling one of them and realizing that the previous owner had installed the wrong plugs.