DWake

iTrader: (1)

So I regularly get about 18-19 mpg from regular driving, and sometimes a little lower if I get on it, but I seem to have dropped down to 12-13 mpg out of nowhere. Car has felt the same as far as response and power go, and I am not sure where to begin looking. Smells a bit rich sometimes but I have been chalking that up to no cats and the muffler being dumped before the axle. It has been getting very cold here in NC and my tires might be a little bit low but I assume that wouldn't cause such a big drop. Any help would be much appreciated.

Mods:
Lid
Wires/plugs about 20k miles ago
Lts/ory/dumped bullet muffler w/ new 02's
Tune by frost
Stock 3.23s

LS6427

iTrader: (2)

Classic Oxygen sensor issue. Even though they are new, lots of NEW dudds are sold. I got a bad new one just two months ago. Get a scan if you can with an OBDII scanner...AND by someone who knows what they are looking for. See how the 02 sensors are switching with a running engine at operating temp.

You probably have a bad sensor.........just change that one.

Rockauto.com usually has the best ones....Denso sensors for like $37.00-$40.00 each.

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LS6427

iTrader: (2)

Oh.....if its not the 02 sensor......it could be a terribly leaky fuel injector dumping tons of gas into a cylinder. But they are rare.

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DWake

iTrader: (1)

Thanks, what's the best way to check if it happens to be an injector? Also wouldn't the car definitely run weird if it was dumping that much fuel?

LS6427

iTrader: (2)

A leaky injector will show itself more at idle.....it will be a constant, but very hard to feel/hear rough idle. But under acceleration and just driving around with the throttle off idle, the piston can eat up the extra fuel and spit it out the tail pipe, so you won't feel/hear anything. Only at idle. Only way to check them is to remove them and have them checked. Usually they charge like $5.00 per injector on some kind of machine/tool.

Or I think you can just remove the fuel rails and injectors, put them all back into the rail and leave them in the rail and turn the key on and see if any of them drip after the fuel pump primes.....

I would say its a bad 02 sensor.......when they start to fail they run pig rich and you smell a ton of gas all the time. Plus the loss in power, misfiring, hesitation.

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9T8Bird

1:How does your Mass Airflow sensor look?
2:Any vacuum leaks around in the PCV system or intake manifold? I ask because cold cold weather tends to bring out the worst in PCV lines, elbows and fittings. they like to crack and leak unmetered air, which causes a false lean and adds more fuel than necessary.
3:Any excess idiling since the temperature dropped?
4: Any loose intake clamps, bellows, boots, etc after the MAF?

DWake

iTrader: (1)

Thanks again guys, gonna borrow a friend's scanner and see if I can find out if it's the 02 sensors today. If it's not obviously the sensors then I'm gonna try the leak test on the injectors.

9T8:
1) cleaned it about a month ago
2) have to check
3) sits around 550-600, might idle a little rough in the morning, but not high, I also have almost every bushing/mount as poly so I can't tell if it's the cold poly or if it's actually rough
4) I will go over them again but when I cleaned the maf I made sure they were all tight

ss performance

iTrader: (17)

If you are an A4 are you going into lock up? IF going into lock up does the rpm actually drop?

Just some thoughts.

LS6427

iTrader: (2)

You might have a PCV leak somewhere....but that would make the engine run lean, not rich. So the smell of fuel is from something else.

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9T8Bird

Right, but wouldn't the 02s see lean and the computer add too much fuel to compensate, especially at idle or open loop on a cold start?

And when I mentioned excess idling, I meant it in the respect that since its been cold, do you let the car idle to warm up before you drive it? As in using more fuel at idle when its cold and you would see a MPG drop since its not moving...

Carguy8888

iTrader: (1)

Great thread, I'm in the same boat too.

DWake

iTrader: (1)

Nah I haven't been letting it sit to warm up, maybe one or two mornings where it was 25 or below when I was leaving for work. It's an a4 but I have not noticed any higher rpms during my daily driving to indicate the converter has not been locking up. It would be good to mention I keep rpms around or below 2500 like 90% of the time.

9T8Bird

I guess i would really look it over for vacuum leaks and exhaust leaks (ahead of front 02s).
And go from there whether or not you need 02s.

ss performance

iTrader: (17)

You can check for vacuum leaks using propane. Use a small propane bottle the type used for soldering pipes. Open the valve and hold the nozzle close to where you think there might be a leak. If the motor revs that is where the leak is. I have never done it on an EFI engine but I have with great success on carb engines.

Good luck

DWake

iTrader: (1)

What am I looking for on my friends scanner to see if I have bad 02s or any other symptoms? Its this one:

http://m.advanceautoparts.com/mt/sho...chTerm=scanner

9T8Bird

you want to see that B1S1(bank 1 sensor 1) and B2S1 (bank 2 sensor 1)
are switching rich lean rich lean rich lean etc.. when the car is running in closed loop. if one or both are lazy or not changing much, there is your problem.

also look at LTFT(long term fuel trim and see if it is more than +/-5% and post your results

LS6427

iTrader: (2)

The way I've learned it from tuners over the years......until the coolant temp sensor reads temps of 122*F and above, the 02 sensors are not doing anything, the MAF is doing all fuel metering. After its warm then the 02s join in and start reading exhaust gas to then help the engine run as perfect as it can. And as I understand it when the 02s take over the MAF doesn't really do much until you go close to or go WOT. But it helps the 02s a little bit all the time. I've unplugged my MAF after my engine was warmed up and it runs 100% identical in all rpm ranges, except if I go WOT.....then it feels a little strange and a little less power. Plug it back in and WOT is strong and smooth.

That's why cold starts have a lot of issues, but after its warmed up a lot of engines run fine. Then when it's cold again on start up, same problems begin until its warm again.


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LS6427

iTrader: (2)

Is that just a code scanner?

You need an OBDII scanner to look at 02 sensors switching while the engine is running......I think those scanners cost a few thousand $$$......

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9T8Bird

Some of the cheap ones do show data stream, but I agree with what your saying, I usually use my Tech 2