What causes only ONE cylinder to run rich?

[nimski62]

This is a v8 s4, but nobody over there seems to know. The cars cams were misaligned when I bought the car, but that problem is fixed now.

Cylinder 1 runs rich as HELL. no other cylinder is like that.

Swapped injectors AND coil, same problem. any frickin ideas? from a mechanics perspective?

code -bank 1, 02 sensor #1 running rich

[Smiley]

how do you know Cylinder 1 is running rich?

[nimski62]

how do you know Cylinder 1 is running rich?

Pulled plug, black and gunky as fuck.

All the rest of the plugs were perfecto

[A4ringedONE8T]

Thats not signifying only one cylinder is running rich, that is showing that wideband sensor #1 is running rich. Most likely there are two, one on each bank of 4 cylinders. #1 is probably the drivers side, #2 the passenger side, then there are also narrowband post cat 02 sensors which verify cat efficiency (presence) typically labeled bank 2, sensor 1 & 2. Normally with any wideband sensor codes, the sensor itself is bad and/or giving faulty readings. Locate the the plugs for the two sensors, most likely found attached to the firewall in a plastic holder underneath the coolant bottle. Verify which ones run to the two front (or wideband/pre cat) 02 sensors. They will be the same plug, normally 6 pin, just a different color. Switch the harness plugs left to right, right to left, and clear the code. Start the car and drive until the code reappears. If the sensor is bad, the code will follow it will then say bank 1, sensor 2 running rich. If the code remains bank 1 sensor 1, then it is something in that bank of 4 cylinders, again not signifying cylinder #1 specifically

[A4ringedONE8T]

BTW is this a FSI 4.2 from the B7 or normal fuel injectors in the intake mani from a B6 S4? What plugs and at what gap?

[nimski62]

Thats not signifying only one cylinder is running rich, that is showing that wideband sensor #1 is running rich. Most likely there are two, one on each bank of 4 cylinders. #1 is probably the drivers side, #2 the passenger side, then there are also narrowband post cat 02 sensors which verify cat efficiency (presence) typically labeled bank 2, sensor 1 & 2. Normally with any wideband sensor codes, the sensor itself is bad and/or giving faulty readings. Locate the the plugs for the two sensors, most likely found attached to the firewall in a plastic holder underneath the coolant bottle. Verify which ones run to the two front (or wideband/pre cat) 02 sensors. They will be the same plug, normally 6 pin, just a different color. Switch the harness plugs left to right, right to left, and clear the code. Start the car and drive until the code reappears. If the sensor is bad, the code will follow it will then say bank 1, sensor 2 running rich. If the code remains bank 1 sensor 1, then it is something in that bank of 4 cylinders, again not signifying cylinder #1 specifically

Yeah but the 02 sensor is right! it is running rich on that cylinder bc when i pulled the plugs, that one was the only one running rich.. black gunky ass buildup. no other plugs were like that.

[nimski62]

BTW is this a FSI 4.2 from the B7 or normal fuel injectors in the intake mani from a B6 S4? What plugs and at what gap?

normal injectors. plugs are the 4 point bosch ones.. no gapping required. i think if it had the normal gap type plugs, it would foul in a few miles!!

And b6/b7 has same motor.. (regular fuel injection.)

only rs4/s5/q7 has the FSI!

[A4ringedONE8T]

I gotta run out so wont be able to check back until later, but if what I said doesnt get you anywhere. Switch that cylinder #1 plug and coilpack (untouched, changed, cleaned, etc) to a cylinder on the opposite side of the motor. Run the car and then check both plugs and see what they look like. See if the bad one cleans up on another cylinder and if the #1 fouls up. If #1 continues to foul the plug, then the injector might be at fault. Start with the 02 sensors though

[A4ringedONE8T]

Yeah but the 02 sensor is right! it is running rich on that cylinder bc when i pulled the plugs, that one was the only one running rich.. black gunky ass buildup. no other plugs were like that.

Each cylinder does not have an 02 sensor, it has one sensor for a bank of cylinders. So the 02 sensor is saying that particular bank is running rich, not a specific cylinder

[A4ringedONE8T]

normal injectors. plugs are the 4 point bosch ones.. no gapping required. i think if it had the normal gap type plugs, it would foul in a few miles!!

And b6/b7 has same motor.. (regular fuel injection.)

only rs4/s5/q7 has the FSI!

Might possibly be an injector then, do everything as I described in my other responses, that should point out what your problem is.

I thought later B7's had FSI, sorry. Dont study up much on the 4.2, worthless motor IMO when my 4 cyl makes more power

[nimski62]

Each cylinder does not have an 02 sensor, it has one sensor for a bank of cylinders. So the 02 sensor is saying that particular bank is running rich, not a specific cylinder

yeah its saying the bank is running rich.. i know and understand that.. so i took the 4 plugs out of that bank, and out of those 4 plugs, only one plug was black. signifying that was the only cyl running rich. the rest of the 3 are good.. like new after 24k.

ill give the 02 sensor thing a shot.. and my cars exhaust smells like SHIT after i go WOT. and my oil gets black as fuck in 200 miles and my exhaust tip gets BLACKKKK after 25 miles.

[nimski62]

Might possibly be an injector then, do everything as I described in my other responses, that should point out what your problem is.

I thought later B7's had FSI, sorry. Dont study up much on the 4.2, worthless motor IMO when my 4 cyl makes more power

but i swapped injectors!! from cyl 1 to 2. sme problem!!

[20vturbo]

do a compression test on that cylinder

[A4ringedONE8T]

but i swapped injectors!! from cyl 1 to 2. sme problem!!

As he said, do a compression test and also a leakdown test. Compression test can still show correct results even with burnt rings.

[trexturk]

if its only gunky on cyl. #1, you might have some issues with oil entering the cylinder.
you might have a vacuum leak causing it to say too lean. I would prolly check the intake manifold around cyl 1

[mike-2ptzero]

Any sign that some air might be leaking out from where the injector goes into the seat? That or like the others said, the CR might be low in just that cylinder.

[nimski62]

do a compression test on that cylinder

Okay so I forgot to tell you that it also burns oil on that one cylinder.. uh oh. im guessing that low compression on one cylinder means the car would run richer??

[cjonesgo]

have you tried cleaning up and moving that plug to a different cylinder? unlikely, but it could just be a faulty plug. no spark = no fuel burned.

[sambrody44]

If it's burning oil then you have a leak.

[nimski62]

If it's burning oil then you have a leak.

But how does burning oil constitute to running rich?

[nimski62]

have you tried cleaning up and moving that plug to a different cylinder? unlikely, but it could just be a faulty plug. no spark = no fuel burned.

yeah i did that.. got all new plugs actually.

[sambrody44]

But how does burning oil constitute to running rich?

Maybe it's not running rich, just burning oil, which could gunk up a spark plug to make it look like it's running rich.

[nimski62]

Maybe it's not running rich, just burning oil, which could gunk up a spark plug to make it look like it's running rich.

Nasty cat smell?

[sambrody44]

Nasty cat smell?

Your burning oil. It could be that you were burning oil, but now it's clogged up your plug so bad that it won't fire anymore. Therefore your injector is still spitting into the cylinder and the oil and gasoline is being pushing into the manifold where it combusts from radiant heat.

[B6Lovin]

But how does burning oil constitute to running rich?

if you burn enough oil through that cylinder your o2 sensor could be just as gummed up as that plug.

have you sniffed the plug to see if it's oil or fuel residue on the plug? i'm willing to bet it's not running as rich as you think 99% of the time and that the o2 is the problem there.

Your burning oil. It could be that you were burning oil, but now it's clogged up your plug so bad that it won't fire anymore. Therefore your injector is still spitting into the cylinder and the oil and gasoline is being pushing into the manifold where it combusts from radiant heat.

that's also a very real possibility, and something to look in to.

the BIG problem though is the oil burning in that cylinder. if my hunch is right you probably have cooked rings on that piston, low compression/lots of blowby into the chamber. the half burned oil is fouling out the plug and o2 sensor - as well as what's making your exhaust black. the car is probably running rich, but again, probably not TERRIBLY rich. so you're getting a nice oil/gas smell after going WOT and burning all that off.

when you say the car had misaligned cams do you mean that the car wasn't timed properly? or the cams were just straight up put in wrong? furthermore - why the hell were the cams out of the car to begin with? most people don't fuck with that motor... they just assume replace it rather than try to remove it and do any real work on it.

seems like all the pieces just fall into place.

[nimski62]

When I bought it, flood car, out of warranty, the car wasn't running right due to the common problem of camshaft adjuster gone bad.. and that was replaced and now is fine. The car NEVER miss fires. When I turn it on in the morning, it is a really gas smelling mixture.

Somebody told me that it could also be running so rich on that cylinder causing cylinder 'wash' or carbon in the ring for cyl 1.

Do you think that if the problem wasn't in the rings but rather in the intake compression being low would cause it to burn oil?

[dirtybrd]

Do a compression test on that cyl, dry then add a little oil to the hole and test again. If your compression psi increases you have bad rings. You might also have a very lightly bent valve, reducing compression thus running rich.

[nimski62]

Do a compression test on that cyl, dry then add a little oil to the hole and test again. If your compression psi increases you have bad rings. You might also have a very lightly bent valve, reducing compression thus running rich.

What about cam timing being SLIGHTLy off?

[s4clone]

is there any way you can take a pic of the plug. it definately sounds like oil fouling the plug it could be because of the rings but also can come from the valve stem seals does it smoke in the morning when you first crank it after its been sitting for a while. also how many miles is on the car

[nimski62]

is there any way you can take a pic of the plug. it definately sounds like oil fouling the plug it could be because of the rings but also can come from the valve stem seals does it smoke in the morning when you first crank it after its been sitting for a while. also how many miles is on the car

Nope. it only has 23k. ive changed the plug.. and it gets gunky again.

It does not smoke at all at idle.. but if i let it idle, for 20-30 mins, adn then rev it up, whatver smoke has built up will come out.

[dirtybrd]

That sounds like a valve seal. I'd still run a compression test to be sure.

[nimski62]

Do a compression test on that cyl, dry then add a little oil to the hole and test again. If your compression psi increases you have bad rings. You might also have a very lightly bent valve, reducing compression thus running rich.

Compression test results: 1=130 2=150 3=130 4=140 5=145 6=140 7=150 8=150

Cyl 1 with problem/leak down results = 4%

Shop cant figure it out either. Go figure.

All spark plugs okay, except cyl 1 plug which is gunked up badly. The other plugs look like new the shop said.

[nimski62]

bmp.. help!!