2000 S70 Base Getting 12mpg

[rspi]

[thankswww]

I've spent several hundred dollars trying to track down the source of my car's horrible gas mileage.

I've now:

1. Replaced spark plugs with OEM parts.
2. Located two cracked vacuum hoses and replaced them.
3. Fixed a fault airbox thermostat.
4. Replaced O2 sensors front and rear (car still throwing O2 sensor codes for Christ's sake!)
5. Replaced the evap system purge valve because ECU said it was faulty (still getting the code!)
6. Checked tired pressure.
7. Checked brakes for stuck calipers.
8. Checked intake manifold for leaks.

I've got a few more hoses to replace back near the evap canister.

Car is also throwing a knock sensor 'no signal' code but at this point I hesitate to replace it because thus far, the hundreds of dollars spend on replacing sensors has gotten me nowhere.

[osman]

I always thought it was the inline six cylinder that Porsche and Volvo designed together.
1. Carfax is a website you pay $30 and enter your vin # t get all available (keyword:available) info on said car.
2. NEVER replace o2 sensors without reading the waveforms in real time (elm 327 and torque) as you have found out many things can set off o2 sensor codes including misfires, running rich or lean, vacuum leaks.
3. If you are getting mpg that poor you should be seeing quite a bit of unburnt fuel (black smoke) in you exhaust.
4. You mentioned your MAF might have failed (which would definitely explain both poor mileage and o2 codes) but havent tried to replace or disconnect to see if that is your problem.
I had a 97 850 GLT LPT that was pouring black smoke and getting 12 MPG after trying everything an ECU from a junkyard for $20 set everything right.
6. In our cars which are designed to run on premium but can use lower octane fuels because of said sensor, a bad knock sensor will not affect anything as long as you use premium fuel and your timing is correct, their sole purpose is to alert you to pre-ignition/knocking which only happens with aforementioned symptoms
7. I would hypothesize that your ECT or MAF is at fault.
8. Good Luck.

[ChiNorm]

There is a rubber to metal fuel line connection imediately on top of the valve cover. I had a leak there, but it was real hard to spot because the fuel would imediately evaporate on the hot valve cover. My IM spotted it.

+1 for 'it might be the MAF'.

Good luck.

[precopster]

I have a friend with a recently purchased 2.2L '02 Subaru. His car recently ran llike crap until his knock sensor was replaced however his fuel mileage was OK because it was intermittently calling the knock sensor code.

Porsche helped with NVH and final power delivery recommendations such as port shape and flow characteristics of the B6304S. Volvo then merely cut this engine down to 5 & 4 cylinders for other models. For most owners the inline 5 is a great success.

Don't know how this equates to Volvo engine control but it would be worth a try. Knock sensors RARELY fail so a used one would be fine for small change.

Cleaning injectors would be my next step as they would easily cause O2 codes and the car may have never had injector cleaner in its life. Sometimes the only way to test them is on the bench and preferably by someone who knows what they're doing.

[rspi]

I thought a o2 sensor code meant the car had a bad o2 sensor. I stopped by a shop today and a guy that has been a Volvo mechanic for 30 years said that these sensors RARELY fail. He claims that one needs to do a hard reset of the system before replacing an o2 sensor. Check for vacuum leaks, make sure fuel system is in good shape, clear the code then reset the computer by disconnecting the battery for several minutes.

The guy claimed that he changed maybe 10 sensors in 28 years. Said that the only bad sensor is one that has the pre-heat function bad.

[difflock54]

Have you tried rechecking your codes using a different code reader?
Might be interesting to see any variations in results.
Are you noticing any improvement in fuel economy as youve fed new parts into her?

[thankswww]

@difflock54:

My cheapo code reader is getting the same codes that the dealer got when they hooked it up two months ago, so I have reason to believe the reader is accurate.

The only thing that has improved mileage thus far was fixing the airbox thermostat (it was stuck open to the hot side) and changing the spark plugs (previous owner installed wrong plugs!).

I changed the fuel filter last weekend. It looked as if it had never been changed.

I'm stumped as to why replacing the evac purge valve did not resolved the 'evap purge valve faulty' code. As this item is related to fuel and emissions and was suspect.

[precopster]

O2 sensors that are 4 wire technology have a typical life of 200, 000kms or 120, 000 miles. They are a wear item. They may not totally fail but will read the mixtures at out of tolerance ranges and result in excess fuel usage. They can be cleaned GENTLY if excess unburned carbon is deposited on them due to the vehicle running too rich.

[thankswww]

UPDATE OCT 29 2013:

After having spent more money than I want to calculate, replacing cracked hoses, sensors, etc. Still no joy.

2000 S70 Non-Turbo

The Trouble Codes:

P0505 -Air assisted control valve (AACV) Flow too low **This is the air valve connected near the fuel rail, right? Flow too low? Where would this be leaking from? I wonder if I should just replace it...though replacing valves thus far has done absolutely nothing.

P0327 -ECM-3400 Knock sensor (KS) Signal too low.

P0443 -ECM-4000 Canister purge (CP) valve Signal too low or too high **Thought it was maybe the valve malfunctioning. Replaced it this week. The code pops up again and again after a hard reset, and after clearing the codes with a code scanner again and again. What gives?

P1671 ECM-6400 Camshaft reset valve Signal too low/high **Awesome! While dealing with all of the other codes, this one now pops up, and refuses to go away!

P0135 ECM-2110 Front heated oxygen sensor (HO2S), preheating Signal too low/high **Oh really? I replaced it two days ago, how can the O2 sensor already be bad? Obviously something else is causing this, but what?

P0141 ECM-2210 Rear heated oxygen sensor (HO2S), preheating Signal too low/high **Again, it was just replaced, so please enlighten me, what other problems will cause an O2 sensor fault code on a BRAND NEW O2 sensor? Massive vacuum leak? WHERE?

Symptoms: Car drives fine, no hesitation or stuttering, or strange smells, or leak spots on the garage floor. Idles perfectly, starts up from cold without problem. I hear what SOUNDS like a vacuum leak coming from the area around the oil cap or spark plug cover. At first I thought it might be the oil cap. I removed it and covered the opening with the palm of my hand, sealing it completely, and the sound didn't change. The leak sound is not coming from the oil cap. The only actual symptom was the horrible gas mileage. I don't know what it is currently getting because I just reset the ECU yesterday after replacing the fuel filter, 02 sensors, and evac purge valve. Last week and the week before, it was averaging 14-15mpg under light driving conditions in the city, no AC on, no lead foot. This is up from the 11-12 mpg it was getting when I started replacing cracked hoses. Oh yeah, and it keeps throwing codes!

Strange: I went to replace the j-hose on the charcoal canister, only find that is there NO charcoal canister, at least not anywhere NEAR the fuel filter, where I assumed it would be, and where I have seen it on other S70 models. Hmm... this is strange. Perhaps this is because I have a non-US car, that didn't have to pass strict emissions tests? I know my Porsche has 2 catalytic converters instead of the US required 4, because it was originally sold in Japan. My Volvo was originally sold in Korea, so perhaps it also doesn't have the emissions control systems the US models have? But seriously? No charcoal canister at all? Did the thing fall off? Was it removed? Why do I have a charcoal canister purge valve if I don't have a charcoal canister? I had the car up on a lift last weekend, literally no trace of any charcoal canister, or any such hoses. What gives?

What I have now done up to this point:

1. Both 02 Sensors are brand new, and correct
2. Changed spark plugs with OEM parts
3. Replaced vacuum lines going from manifold to evac purge valve and check valve (both in radiator area)
4. Fixed airbox thermostat
5. Changed air filter
6. Changed fuel filter
7. Replaced charcoal canister purge valve
8. Cleaned throttle body

Some people pointed to the MAF sensor as being the culprit. The car runs very smoothly, starts and idles perfectly, and is not throwing a MAF code, but I'm open to the idea that this needs replacing. But, since the car runs well (other than poor mpg) already, how can I test this?

I started the car, let it idle. While idling, I sprayed carb cleaner all around the intake manifold where it bolts to the head. No drop in RPMs. I sprayed around the outside of the MAF sensor area; same thing, no drop in RPMs. I sprayed carb cleaner on every area I thought might be leaking, but nothing; no carb cleaner got into the intake manifold.

My gut feeling is that this car has a fairly large air leak somewhere that is not readily visible. I've already checked the PCV system and it is alright, no problems with that.

My main questions after all of this are:

1. Aside from what I have mentioned above, where else in the engine bay could a fairly large vacuum leak occur?

2. Why doesn't my car have a charcoal canister near the fuel filter like every other S70 I've seen pictures of online? I ask this because the car is throwing a P0443 canister purge valve code, which seems strange for a car that seemingly does not have a "canister" to being with, at least not in the area where one would expect it to be.