Re: Not trying to pile it on but I believe if you go the remove the exhaust manifold route...

I've got a problem...

Originally getting codes:
P1124 Manufacturer Controlled Fuel And Air Metering
P1126 Manufacturer Controlled Fuel And Air Metering
Other symptoms: unsteady idle, Stalling suddenly when HOT (like after several autocross runs) but starts right back up. Otherwise running really well. No drop in gas milage. No driveability issues
Checked ICV- seems good. I had already bought an AOS and gas filter so went ahead and replaced them with no change. Checked for air leaks by using engine starter spray to see if get reving- nothing. Fuel pressure at 49PSI at idle & steady
Now getting above codes with 2 additional codes and still same symptoms:
P0130 Oxygen Sensor Circuit Bank 1 Sensor 1
P0150 Oxygen Sensor Circuit Bank 2 Sensor 1

Any thoughts? Could the O2 sensors be going bad (All 4 have been in the car for 170,000 miles)

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Ollie
I've got a problem...

Originally getting codes:
P1124 Manufacturer Controlled Fuel And Air Metering
P1126 Manufacturer Controlled Fuel And Air Metering
Other symptoms: unsteady idle, Stalling suddenly when HOT (like after several autocross runs) but starts right back up. Otherwise running really well. No drop in gas milage. No driveability issues
Checked ICV- seems good. I had already bought an AOS and gas filter so went ahead and replaced them with no change. Checked for air leaks by using engine starter spray to see if get reving- nothing. Fuel pressure at 49PSI at idle & steady
Now getting above codes with 2 additional codes and still same symptoms:
P0130 Oxygen Sensor Circuit Bank 1 Sensor 1
P0150 Oxygen Sensor Circuit Bank 2 Sensor 1

Any thoughts? Could the O2 sensors be going bad (All 4 have been in the car for 170,000 miles)

Air/fuel mixture so lean DME at its enrichment limit at idle: rpms below 880.

You did all the right things but you overlooked one thing: Did you check if the oil filler tube cap is leaking? (Failing to catch this on my car caused me to replace a perfectly good MAF.)

Another possible cause is the injectors are contaminated (carbonized). Unless you've been running really really crummy gas and driving short trips, not likely.

Let's look at the P0130/P0150 codes...

P0130 - Oxygen sensor for converter cyls 1-3 short circuit or limited voltage increase.

P0150 - I do not have anything on this but I suspect it is the same error but for the other bank, cylinders 4-6.

Neither of these codes point to a sensor aging problem. There are codes specifically for that. But they do point to the sensors not working properly. The sensor heating is active, the sensor is active, the sensor after the converter's voltage is > 350mV, tank vent system diagnosis is not active, secondary air injection system not on, and neither system has any faults.

If you have a scan tool (and you should) get the engine up to temp -- my info is this is best done on the road with the engine under load -- and check the voltage levels of the sensors ahead of the converters. The voltage should fluctuate between 100mV and 800mV.

I can speak from experience though that unless the sensor has completely failed it is hard to catch a sensor not working properly. I drove around with a code reader/data viewer hooked up and showing sensor voltages in real time and only after I had developed a sense of when the error was going to occur did I see the voltages not fluctuating properly and sometimes the misbehavior was short-lived. It might have been due to the DME compensating somehow which helped the sensors resume working. Also, shutting off then restarting the engine the sensors were ok. Until the next time. It took about 30 miles of driving before the sensors would act up enough to trigger the CEL.At some point I was looking at the voltages and noting they were not changing and concurrent with this behavior the CEL came on. I replaced both #1 sensors shortly thereafter.

So, check the oil filler tube cap. But at 170K miles if those are the original sensors I think they are high on the suspect list. I had to replace the #1 sensors at around 100K miles, then the #2 sensors at between 100K and 150K miles... I do not recall the mileage but it was a number of miles after the #1 sensors were replaced. I've never had to replace or even clean the injectors.

Sincerely,

MarcW.

Should have mentioned I checked oil fill cap by taking it off car ran crummy- put it back on ran fine.

The P0150 is same as P0130 except for Bank 2- I am leaning toward O2 sensors are on their way out/close to dead.

Only thing I hesitate on is the idle hunting, can an O2 sensor cause this? Could bad/dieing O2 sensors cause the P1124 &1126 codes? (Seems likely to me as O2 feedback will effect rich/lean mixtures)

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Ollie
Should have mentioned I checked oil fill cap by taking it off car ran crummy- put it back on ran fine.

The P0150 is same as P0130 except for Bank 2- I am leaning toward O2 sensors are on their way out/close to dead.

Only thing I hesitate on is the idle hunting, can an O2 sensor cause this? Could bad/dieing O2 sensors cause the P1124 &1126 codes? (Seems likely to me as O2 feedback will effect rich/lean mixtures)

All you did was confirm that if you created an intake leak the engine reacted by running 'crummy'. Had you waited the DME would have adapted and the engine would have run better. Then when you put the cap back on this would have of course eliminated the air leak and the engine would have reacted until the DME could once again adapt.

What you need to do is with the engine idling wiggle the cap to see if you can create an air leak. What you will hear, if of course the cap is leaking, is the sound of an air leak, and if you leave the cap in this position the engine will likely react to this leak.

Another possible leak in that area is the oil filler tube.

The hunting idle could be caused by bad sensors. The DME monitors the #1 sensors to verify it has control of the fueling. It does this by swinging from adding just a tiny bit more fuel than is called for to subtracting a tiny bit of fuel that is called for. Adding/subtracting is done by lengthening or shortening the time the injectors are open. You can get some idea that this is occurring by observing the short term fuel trims.

If the sensors are particularly bad the DME will increase the amount of fuel it adds then of course subtracts and this could cause the engine rpms to rise and fall.

The sensors could contribute to the P1124/P1126 codes if the sensors as they go bad develop a bias in their readings. For instance if they have a failure mode that has them over reporting the amount of oxygen in the exhaust gases the DME will add more fuel to try to get the oxygen content down. This then can result in the DME going too far and reaching its enrichment threshold.

Sincerely,

MarcW.

I checked the oil cap as you suggested- no real help. I think at this point given 170K miles on the O2 sensors I am going to replace all of them even if they are not the cause of my issues (although I strongly suspect they are).

I will post back after I change them and let you know if they fix. Will pick up new oil cap also even thouigh does not seem to be issue as it is also the original oil cap. I still have a lot of original stuff on the car...

Thanks for the help and I will let you know how it turns out with the O2 sensors.

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Ollie
I checked the oil cap as you suggested- no real help. I think at this point given 170K miles on the O2 sensors I am going to replace all of them even if they are not the cause of my issues (although I strongly suspect they are).

I will post back after I change them and let you know if they fix. Will pick up new oil cap also even thouigh does not seem to be issue as it is also the original oil cap. I still have a lot of original stuff on the car...

Thanks for the help and I will let you know how it turns out with the O2 sensors.

were I in your shoes that's probably what I'd do, too.

While you might be premature in replacing the sensors, you can spend no little amount of money and time in trying to eliminate the sensors and of course you have to elevate another hardware item to account for the behavior. There are more expensive hardware items than the sensors. So you are throwing relatively inexpensive parts at the symptom.

Handle those new sensors with extreme care! Touch the tip and you might render the sensor bad.

Be mindful of the electrical connectors. While you are replacing the sensors, and they'll come with fresh wiring/connectors, the car's wiring harness connectors are old and a bit fragile.

The hardest part of replacing the sensors I encountered was figuring out how to get the connector 'latch' to release and separating the sensor connector from the wiring harness connector without subjecting the wiring harness connector to excessive movement or strain.

Oh, and note the routing of the sensor wiring. IIRC the wiring runs close to the exhaust and it must be properly routed and secure to avoid any contact of the wiring with the hot exhaust.

Sincerely,

MarcW.

Biggest issue I am having is actually getting the sensors off- 170K miles of heat on the exhaust has them locked in there good.

especially since my car spent the 1st couple of year and nearly 80K miles driving in all kinds of weather in the midwest, including on snowy/salted roads in the winter.

I bought a very nice properly sized crows foot wrench -- the brand name I do not recall, but I have a lot of Snap-On tools -- but I do not recall encountering any difficulty unscrewing the sensors.

However, your car has covered double those 80K miles mine had covered when I needed to replace the #1 sensors.

Sincerely,

MarcW.

Yup- those 170K miles are all in NH. Car stays on the road year round so sees lots of salt...

Thinking of taking the exhaust out and hitting with my impact wrench, these suckers are not coming out otherwise. If I rip the bung out weld a new one in... LOL

I have changed many O2 sensors before all have come out with a little muscle- not these. Heated then hit them with cold water several times, lots of Freeze Off, even put a pipe wrench on the sucker and refuses to move

you'll have to deal with one or more stuck exhaust manifold fasteners. Or worse, one or more will break off.

When I got a quote on having one of my car's exhaust manifold/converters replaced the tech told me the shop always adds in some extra labor to cover this because it almost always occurs.

Now that I think about it, when he had to remove one exhaust manifold to fix the passenger side VarioCam solenoid/acuator one fastener snapped off but with the manifold off he was able to grip the end enough to unscrew it. Just my luck though that the exhaust manifold he removed was not the side the bad converter is on. I was hoping he'd remove it, address any broken fasteners, then I could pick up a salvage exhaust manifold and replace it myself with a high degree of confidence I'd encounter no broken fasteners.

Sincerely,

MarcW.

I wouldn't take the exhaust manifold off- disconnect at the flange between the header and the cat- 3 bolts each side and who cares if they break off, cheap and easy. I agree if try taking the manifold off studs may well snap... not good

For what it is worth -I just replaced the two pre-cat O2 sensors on my soon to be 14yr old BMW E46. They were easy to get off, not as their brothers behind the cats done last year. In the end, on those I stripped both bungs, but luckily left enough material to re-tread. Had the car on stands for a week while i struggled with this so feel for you.
Now, the pre-cat O2's did improve the milage by 9% so hopeful you will also see some payback in the wallet as well.
Good luck!