Oil Leaking Onto Downstream O2 Sensor Connectors

[X5Cat]

While under the X just now, searching for the upstream O2 connectors so I can replace them (just the upstream O2 sensors), I found the downstream connectors drenched in oil (as shown in photo) from a slow, but long-term leak. Wondering if this could possibly be responsible for or contributing to my performance problem.

I've had this issue for quite some time where, once the vehicle warms up after the first mile or two, it jerks and stumbles when I accelerate or when there is a demand for power, like going uphill. Pulled the codes and got the P0430 (Cat Bank 2, I think). Bought replacements for the upstream sensors a good while back, since they were overdue for replacement anyway. But, due to some health and other issues, have just now gotten around to attempting to install them.

Guess I'll know pretty soon if I'm extremely lucky and it turns out the upstream sensors do the trick. Feel like I won't have that sort of luck, though. So, I'd really be interested in knowing what you guys think the chances are that all that oil goo could be throwing off the downstream sensors enough to cause my issues.

One more thing -- I saw in a post somewhere some guy saying I had to clear the DTC's before installing the new sensors. I have a little trouble believing that is necessary. Thoughts on that also, please?

Thanks!

[ard]

you have to clear the codes at some point!



Do NOT think oil on the wires or even in and around the connectors is causing your issue
Id look at air leaks, cracked hoses, fittings.... really really hard to chase down, but as these cars age (ie ALL BMWs) it seems to be common

[andrewwynn]

Downstream O₂ are really only to tell you when the cats are with out I'm not aware of any other function they are not in the feedback loop for performance.

The pre cat are the main sensor dirt feedback for the air fuel mix and if they are reading the wrong info it will definitely affect performance! The engine for example will think it's sending the feedback for exactly 14.6:1 air: fuel butt in reality it's sending 16:1 and you'll get terrible power.

A big incorrect feedback will show up as too rich/lean on the post cat however as the cat won't be able to scrub the poison as it should

Get those new O₂ in and there is a trick on older cars to reset the O₂ heater calibration: run the car With both O₂ precat unplugged for one or two starts ( I would start the car and run for 3-5 minutes twice). You do not need to clear any codes before changing and you should not need to reset the heater calibration unless you get an O₂ heater related error.

Oil on an O₂ sensor lead can really mess them up however; they get their reference O₂ level from the atmosphere through the wiring jacket that's why there's specific notes on not using silicone sealant on the wiring to O₂ sensors. However the post cat are not used for engine performance so that's a different issue.

[X5Cat]

Got the new upstream sensors in. I didn't clear any codes. The little orange engine light is still burning. Drove it about 9 or 10 miles tonight while we had an ambient air temp of 57 degrees. First 4 or 5 miles no issues, then it started the stumbling and chugging whenever I accelerated hard or went uphill. It may just be because we're having a relatively cool night here, but it still seems about 90% better than it was before. Time will tell with that I guess. I will clear the DTCs and rescan. Maybe possibly it needs a chance to learn the new sensors. If this doesn't cure it, I guess I'm on to checking for vacuum leaks, VANOS issues, or the (don't wanna say it) CAT. I'll disregard the oil on the post CAT connectors, since as Andrew says they don't affect performance. Thanks guys.

[ard]

Andrew-


OP says it runs OK on cold start, but then when it warms up it runs poorly.... when cold the DME ignores AF readings from the (cold) O2 sensors, and instead runs a 'rich' map.... then, when it comes up to temp, it then uses the o2 sensors.


If the car has an air intake leak, this 'cold start rich period' would be fine...then when the DME uses the O2s, he is now lean. (becuase air is getting in that the DME doesnt know about...)


OP, dont look at CATs yet, lots of stuff can fool the DME into thinking cats are bad

[X5Cat]

Originally Posted by ard

Andrew-


OP says it runs OK on cold start, but then when it warms up it runs poorly.... when cold the DME ignores AF readings from the (cold) O2 sensors, and instead runs a 'rich' map.... then, when it comes up to temp, it then uses the o2 sensors.


If the car has an air intake leak, this 'cold start rich period' would be fine...then when the DME uses the O2s, he is now lean. (becuase air is getting in that the DME doesnt know about...)


OP, dont look at CATs yet, lots of stuff can fool the DME into thinking cats are bad

Yeh, I've been thinking about this very thing about how the O2 sensors don't get factored in until warmed up. Thought about the intake or vacuum leak thing too. Seems like intake manifold leaks are usually worse when cold and often close up a bit as the engine warms up. But then, I know every situation can be unique. Hmmm, guess it would have to be a leak in cylinders 4, 5, or 6 (Bank 2, per the P0430 code).

One thing I do need to do is pull the codes again, since I haven't yet after installing the new sensors. Probably nothing's changed, but it still seems prudent to do so.

[X5Cat]

I am thinking this is not likely an injector issue, unless injectors have been known to get sluggish after an engine warms up.

I have a vacuum gage, if I can find a way to plug it in. Not sure if it will show up such a leak. I certainly don't hear an air leak.

Some shots of the old Bank 2 sensor removed:

[pshovest]

Sounds like a lean condition. Use the live data in your scanner to check the ST & LT fuel trims. Is the DME is adding fuel?

[ard]

^^ im going to add a kinda out there observation...


On another BMW engine, we would see air leaks causing rich conditons and fouling of cats.


The DME would see a small air leak, ramp up fuel...but when the engine then moved to higher RPMs the amount of air leaking in was less, in terms of a % of airflow- the DME would back off. After a long time of this sub-criitical abuse, the excess fuel would load the cats with hydrocarbons, you would get cat codes. The air leaks and the fuel trims never reached the level that triggered a DTC code...but the trims were always moving around.


It was a wierd thing.


I also personally had a sluggish VANOS solenoid that caused rich running but only at some RPM bands. After a while, id get a cat code. Id get tell-tale speckles at the rear bumper due to unburned HCs. Finally overhauled the vanos solenoids, afetr 2 years of chasing that beatch... perfect. Interstingly it only impacted the one bank. (whereas most intake air leaks will not be an 'only one bank issue...)

[X5Cat]

Currently distracted again from this project by career and family, but I'll be pulling some data and posting soon. May look for some vids on overhauling the vanos. Thanks!