Secondary Air Injection Mass Air Flow

Background:
2008 E90 M3, ~125k, failing smog due to secondary air system not ready. Getting codes 27C5 and 2739.
Checked fuses/relay, replaced inlet hose/mini HFM with new OEM, pressure tested pump outlet Y-hose for cracks, verified air pump runs, replaced air pump just for fun, replaced control valves, replaced pre-cat O2 sensors. No changes. Took the control valves back off, scoped/cleaned the injection ports that run the length of the head, they had some buildup but were open all the way back.

I took the car to a bmw shop because I was out of ideas and they said they'll pull the engine for $3k and check to see if the air injection ports are clogged, but I'm hoping there's a way to verify that's the problem before they start experimenting on my dime...

Question: When I check "Secondary air mass from Lambda Bank 1/Bank 2" using Bimmerlink I get values between 11 and 13 kg/h, does anyone know what this value is supposed to be for a car that does set ready/pass smog? Alternatively, does someone want to go do a cold start and check these values for me so I can compare?

Any help is greatly appreciated, trying not to ride my motorcycle through the winter!

Dropping the motor would be the "nuclear" option if there is a way to avoid that.



I wonder if there is a panel in ISTA for the SAI MAF. If there is, then I can help check this for you.
Did you check to make sure the MAF sensor is clean?
Did you use a "smoke" machine to check for leaks too? I know you said you checked for cracks.

Doing some quick-math, 13kg/Hr is about 3.61 g/s. Usually a MAF on an engine for quick-logical numbers should correspond to a fully warmed up, idling engine (no load) of about the engine displacement per 500 rpms. So in this case, if the car is idling at 500 rpms, it should be about 4 g/s of air intake since these are 4.0L engines. Maybe this makes sense of 3.61 g/s on the SAI MAF? That definitely seems within the ball park, but I would wager the SAI needs to overcome the exhaust pressure to blow air into the exhaust.

I'd guess there is something similar in ISTA but I'm not versed in it so I couldn't tell you.
Assuming you mean the mini HFM, yes it's clean/new.
I pressure tested the Y-hose, and seals look and feel tight. I didn't use a smoke machine tho.

Not sure where you're going with your mass flow rate calcs, I don't think there's any relationship between intake mass flow rate and secondary air mass flow rate?

you said you replaced the inlet hose on the airpump? the fresh air hose with the airflow sensor on it?

after the inlet airflow sensor there is not another sensor but carbon blockage in the cylinder head of this car is not likely unless the pump was pushing alot of moisture rich air, not saying its impossible but its unlikely.

theres a couple of things to look at here, if your primary o2 sensors are not reading accurately or are slow to respond to the air injection cat warm up curve it will pop an electrical diagnosis code because thats what the dme perceives is going on not enough air so I would suggest you look at the o2 sensors or use ista and see what the egt reading is from a cold start.

can you also confirm how long the pump is running for when you start the car cold in the morning, when the relay for the pump goes bad the dme still sends the signal but you get an "performance" diagnosis fault for this.

your specific codes are relating to the airflow sensor specifically so if you didnt replace the inlet pipe with an oem piece I would suggest you start with that first. if this was replaced with an oem part then you will want to check the continuity of the wires of the sensor. I have the wiring diagrams somewhere if you need them I can try to locate them.

B228 Secondary air injection (AIR), mass air flow (MAF) sensor
M73 Secondary air injection (AIR) pump
K152 Secondary air injection (AIR) pump relay

letsgopaddle wrote

I'd guess there is something similar in ISTA but I'm not versed in it so I couldn't tell you.
Assuming you mean the mini HFM, yes it's clean/new.
I pressure tested the Y-hose, and seals look and feel tight. I didn't use a smoke machine tho.

Not sure where you're going with your mass flow rate calcs, I don't think there's any relationship between intake mass flow rate and secondary air mass flow rate?

The relationship between the two are suppose to correspond to logical values. -- Do they make sense? I've used "off-brand" MAFs before that would report erroneous values and wasn't fixed until I used the actual OEM brand.

amrazM wrote

you said you replaced the inlet hose on the airpump? the fresh air hose with the airflow sensor on it?

after the inlet airflow sensor there is not another sensor but carbon blockage in the cylinder head of this car is not likely unless the pump was pushing alot of moisture rich air, not saying its impossible but its unlikely.

theres a couple of things to look at here, if your primary o2 sensors are not reading accurately or are slow to respond to the air injection cat warm up curve it will pop an electrical diagnosis code because thats what the dme perceives is going on not enough air so I would suggest you look at the o2 sensors or use ista and see what the egt reading is from a cold start.

can you also confirm how long the pump is running for when you start the car cold in the morning, when the relay for the pump goes bad the dme still sends the signal but you get an "performance" diagnosis fault for this.

your specific codes are relating to the airflow sensor specifically so if you didnt replace the inlet pipe with an oem piece I would suggest you start with that first. if this was replaced with an oem part then you will want to check the continuity of the wires of the sensor. I have the wiring diagrams somewhere if you need them I can try to locate them.

I was suspecting the same thing if MAF if ALL ELSE is good, aka, the hoses are not leaking, etc.

Now that you mention it...checking the wiring can be a very important thing, too! A bad ground can skew the reading to the DME, as well as bad O2s when they are going to "verify" the performance.

OP:
At any rate, here's another look for the wiring. The ground is "spliced" and shared among the other sensors in the system. That splice X6464 is located inside that plastic "junction box" by SAI pump. You can simply disconnect the X60105 on the DME and disconnect the X13937 of the MAF and test the ground via resistance then a load test. Then you can also test the signal to the DME on X6011 and the DME X60101. Lastly, the proper 12v from the relay, also mentioned above.

If that checks out well, then I would look at the O2 monitors next like mentioned above--are they logical?

Thanks for the responses.
Yes I replaced the inlet hose/mini HFM with an OEM part.
I also replaced the air pump, no change (as expected). I'll time it later tonight and update with how long it runs.
I checked the signal and ground wires and they seem to have continuity.
I don't know how to check the O2 sensors. I haven't replaced them since it seemed like I'd be getting an error specific to them if they were the issue. Might be the next thing to try tho since I don't have anything better to try.

I'm still looking for the target value for the "Secondary air mass from Lambda Bank 1/Bank 2", anyone know?

Searching the forum it looks like a bad HFM points to the problem. Perhaps you need a good drive cycle?

Here it seems to suggest that one of the forum users needed to click a connector in all the way...

https://www.m3post.com/forums/showthread.php?t=1060963

Agreed, I was bummed when replacing it didn't change anything. Since this is cold start related it only needs two cold start sequences to check function. It consistently pops a code on the second start.

Yes I've seen that thread, wish that was my problem...

Have you searched what ISTA D says?

Are you positive you are on stock tune?

Update on the above: air pump runs for 25-30sec

I do not have ISTA D, so no I have not.

Haha I thought of that possibility the other day, but I flashed back to stock when this started, so the only way that's possible is if my tuner provided a modified stock tune. I don't think they would do that without telling me.

I just went on something similar with this, twice...

It turned out to be the Secondary Air Pump (SAP) MAF sensor, again. As you, I got a new OE one from the dealer, but it failed after only 4k miles, so I need to buy a new one, again.

If you don't have ISTA-D, get it, there are multiple sources, even older versions will work for this. There is even a diagnosis process on ISTA that starts "listening" for a signal from the SAP MAF sensor when air goes through it, ie, it will read its voltage and tell you it's ok or not. So ISTA will let you know if it's getting a signal from the SAP MAF or not.

You can even turn on the SAP through the relay to test it, or blow air through the plastic hose that connects to big rubber hose between the airbox and intake plenum.

I was hesitant to believe the newish SAP MAF would be bad after only 4k miles, so I swapped it from a running car with no SAP issues and viola, no more codes and the smog monitor for it got into "Ready" status immediately after starting the engine.

So if I were you I'll find a "victim" with a local donor car that lets you use its SAP MAF to test yours and maybe pass emissions once you do the driving cycle and get all the required monitors in ready status, which BTW, I can get all these monitors ready except EVAP in around 15 min doing it, and I've done it several times... In CA you can pass smog with the EVAP monitor in not ready, but all the other relevant ones need to be ready.

Here are the two detailed error code you'll get using ISTA-D

Thanks for posting that. Lets hope the OP can use your experience and apply it to his own. I think that's the closes we're going to get for the metered readings as your fault code memory suggests.

For parenthetical info, the 78.1 kg/hr is roughly 21.7 grams/sec, and the 12.8 kg/hr is 3.56 grams/sec--just for a "pulse check" on the MAF reading. Kinda interesting...

Thanks for the response Evo, I was hoping not to have to learn any new softwares but it's looking more and more likely. I guess it's possible the brand new part I put in is also bad, but that seemed pretty unlikely to me. Would need to test it to verify.

I'm assuming those fault codes are what you had when yours was bad? The 12.8kg/h secondary air mass is very similar to mine... Still looking for what it should be in a properly functioning system.

I had the hose with a sensor fail after a few months as well. I also forget to completely connect the hose to the plenum in the back right. corner so I've had the code because of that as well. I'd take it apart to see if all of the connections are secure.

Hey Ximian, yeah I saw your posts and I've had my system apart several times now to check and double check, everything is connected as it should be.

I've updated my original post to include replacement of O2 sensors with no change in behavior/codes.

Hey All, still stuck on this. Anyone in the Orange County area with ISTA-D want to come hang out for an hour?

So from the 2nd air valves you scoped and cleaned the main runner but what did you do to clear the ports that run from that main runner down to each exhaust port? If you remove the headers you will see a tiny hole that goes from each exhaust port up to the runner. Clear each (8) of them with a clearing tool or a wire hanger. ISTA & INPA both have test plans for secondary air systems but you can only run it once the car is completely cold. In my case the air flow was and still is low.

I did nothing to clear the ports that come off of the main runner, however I did verify that each one does flow air. I'm guessing they are all partially blocked based on how the main runner looked. I'm after the target airflow numbers through the system so I can verify that pulling the headers/engine to clean these ports would actually fix this. Would hate to do all that and find I'm still getting the same codes...

I don't think letsgopaddle problem is related to where the SAP injects the air into, which is what I believe you're referring to. It's related to the two same exact codes I had, which are 100% related to the SAP MAF sensor not working properly since the DME cannot get the signal it's expecting from it.

As for the test plan in INPA, I didn't see it, I only saw the one in ISTA. Can you please share where in INPA is it ? ie, menu options sequence / navigation ?

As I mentioned earlier, I figured out this since I have two E92 M3s, so I can / did swap parts including the SAP MAF, which is what I did, but I still have to buy a new for my race car, which is still registered for street use since I drive to / from the track.

If the exhaust ports where the SAP gets injected are clogged, I would assume the O2 sensors might not see the additional air being injected, which might triggers a code, although different to the OP due to O2 sensor readings being out of bounds, which is what I believe you're suggesting.

Scrippy wrote

So from the 2nd air valves you scoped and cleaned the main runner but what did you do to clear the ports that run from that main runner down to each exhaust port? If you remove the headers you will see a tiny hole that goes from each exhaust port up to the runner. Clear each (8) of them with a clearing tool or a wire hanger. ISTA & INPA both have test plans for secondary air systems but you can only run it once the car is completely cold. In my case the air flow was and still is low.