You sure it's "g" and not "kg".
Does your scan tool actually tell you in "g"?
As you can see my scan tool says kg.

I found this online calculator.

I just typed my parameters in at idle and the result suggests that my scanner should be reading in grams not kilograms.

You could give this a go see what comes out the other end.

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yes i made sure it's correct, i converted it from lb/min which is what my scanner reads

 

That idle data from the MAF is correct.

 

Yes. I know. But it is still confusing as to how it is arrived at.

I actualy went through this calculation manually a couple of weeks ago on here but can't find the thread.

 

Here is a screenshot of my info at idle from a 320i 2.2L (m54b22) after warm up.
Hope it can be helpful in some way

 

Input your details into this webpage and see what it spits out.

See if it comes out with 3.57 g/s

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here's a few more screenshots... and i lie i just found a higher reading...

 

here's a few more screenshots... and i lie i just found a higher reading... View attachment 924439 View attachment 924440 View attachment 924441

The 698 RPM value is 16 Kg/hr which is 5 Kg/hr more than mine. Mine has always been around the 10 or 11 mark at idle as far back as I have had it. My LT fuel trims are fine. Nearly zero. I clean the MAF element regularly and have no reason to believe it is problematic. I get 27 MPG with almost entirely urban driving and we have ridiculously slow 20 MPH speed limits here.
What size is yiour engine?

 

nobody? sorry i just haven't found any info on to why it'd be so high i figure it's a faulty maf. It's the original MAF and this car is 18 years with 200k+ miles old so i assume it's time for a change 🤷🏿‍♂️ but i just want to be sure there could be nothing else that could cause it to read so high

 

See my last post.

 

If you look at Cruz's 8.5 lb/min that's 3.85554Kg/min @ 3487 RPM

Or 3855.54 g/min

Or 3855.54 / 60 = 64 g/s

So your 59.7 g/s isn't far away from that.

Bear in mind air temperature and pressure make a big difference and can account for these variations.

 

I was just schooled on this a week ago. Temperature and pressure don't affect mass.

 

he lives in south africa, I would be suprised if its colder there than the UK where you live.

 

Not a lot of difference at the moment. 13C there and 11C here.

 

The BMW software uses kg/hr for the MAF
OBD2 software uses g/s for the MAF

The conversion is:
g/s = kg/hr x 0.28

The only sensible data you have posted is the data at idle.

• You have 4.5g/s on the MAF
• Bank 1 total fuel trims of -9.3%
• Bank 2 total fuel trim of -11.8%

Your car is running very rich.
Rich is caused by:

• Too much fuel
• Not enough air
• Bad sensor fooling the DME into thinking that one of the above is occurring
• Blocked cat's.

A over reporting MAF will give you a rich condition. The DME thinks that there is more air coming in than there really is. The DME injects the right amount of fuel for the reported air and causes a rich condition.

Old tired pre-cat O2 sensors can cause a rich condition.

As you have a high mileage car, If it is still running on the original MAF and Pre-cat O2's, just change them. VDO for the MAF and Bosch for the O2 sensors. Aftermarket MAF's have very mixed reputations. Some are very good, others are very bad. VDO is very good.

 

The BMW software uses kg/hr for the MAF
OBD2 software uses g/s for the MAF

The conversion is:
g/s = kg/hr x 0.28

The only sensible data you have posted is the data at idle.

• You have 4.5g/s on the MAF
• Bank 1 total fuel trims of -9.3%
• Bank 2 total fuel trim of -11.8%

Your car is running very rich.
Rich is caused by:

• Too much fuel
• Not enough air
• Bad sensor fooling the DME into thinking that one of the above is occurring
• Blocked cat's.

A over reporting MAF will give you a rich condition. The DME thinks that there is more air coming in than there really is. The DME injects the right amount of fuel for the reported air and causes a rich condition.

Old tired pre-cat O2 sensors can cause a rich condition.

As you have a high mileage car, If it is still running on the original MAF and Pre-cat O2's, just change them. VDO for the MAF and Bosch for the O2 sensors. Aftermarket MAF's have very mixed reputations. Some are very good, others are very bad. VDO is very good.

Perfect, i've replaced only one O2 sensor that being on bank 1 due to the P0171 error i have... see that's where ive been confused is i see my cars more running rich than lean yet i'm getting a P0171 code for bank 1 system too lean (still have the code and ses light) I bought a VDO MAF and will buy another O2 sensor to replace the Bank 2 sensor. If i figure out how to post a video on here without having to have y'all press on a link i will post a video of me recording my dashboard with all the fuel trims and everything.

 

Air volume in liters. It's use in Liters per second.
Air Mass in grams or kilograms. Its use in grams per second or kilograms per hour
They are different. One is a volume that is dependent of atmospheric conditions. The other is a mass/weight that is not dependent on atmospheric condition. The volume of air to provide a set mass will change for atmospheric conditions but a kilogram of air will still be a kilogram of air.

Inlet air temp, yes, there is a sensor
Barometric pressure, no, I have not yet seen this sensor on the E46. There is no MAP sensor. From the testing I have done, the OBD2 PID 04 Calculated Load%, which is correlated to atmospheric conditions, appears to use the throttle position as an indication of air volume changes. If you have a stuck Idle control valve and the DME is using the throttle body to control the air at low loads, then the calculated load % values are zeros. This is because the DME thinks that the air is so thin that it needs a very large volume of air to get the required air mass as reported by the MAF.

 

The other is a mass/weight that is not dependent on atmospheric condition.

Incorrect. See attached chart.

The volume of air to provide a set mass will change for atmospheric conditions but a kilogram of air will still be a kilogram of air.

Correct.

Note that my scan tool datastream includes barometric pressure. It's getting it from somewhere and it's not being measured by the scan tool itself.

First, in the calculation of MAF the volume parameter is fixed. It doesn't change because it is determined by the displacement of the cylinders and that never changes. But the density does. Hence the weight fluctuates with time. The weight, as I explained earlier, is entirely dependant on temperature and pressure at any point in time. (see chart)

Second, I think you are losing sight of the purpose of this control system. It's to ensure, as far as possible, that there are no unused O2 atoms or unused fuel molecules in the exhaust gases after combustion. The combustion process is just an exothermic chemical reaction and like all chemical reactions the objective is to provide exactly the right proportion of reactants to produce a reactant free product. The product being the exhaust gases in this case. That's what these controls attempt to achieve. That ideal proportionality of reactants is refered to as the stoichiometric ratio and stands at 14.7 : 1 air:fuel. It is impossible to achieve that without considering the density of the air molecules entering the cylinders when calculating the amount of fuel to inject into the cylinders along with the air.

So,in conclusion, when calculating the MAF the air and temperature do matter. Two very important parameters.

 

Hey Big Bopper, I'm enjoying our discussion.

I don't know where your scanner is getting that ambient pressure number from. I've been through the E46 wiring diagrams and not found a sensor. It may be a calculated value from other PID's. I don't know. Please direct me to the sensor, so I can go find it on the car.

The Air mass temp/pressure chart is for a set volume of air and how the air mass changes relative to the temp and pressure of that set volume of air. It does not show that a set Air Mass changes relative to temp and pressure.

You are correct in that the volume of the cylinder does not change, but the mass of air going into the cylinder for each compression stroke is different. It is the throttle that limits the amount of air that enters the cylinder. The driver limits the air supply with the throttle. The DME uses the MAF signal (air mass not volume) to inject the right amount of fuel(14.7:1 air/fuel ratio) to produce the correct amount of energy to do the work required by the driver. So for the same rev's, you can get a wide range of MAF values. A high value means the driver wants to accelerate or hold speed going up a hill. A low value means that the driver want to slow down or coast down a hill. A medium value means the driver want to maintain the current speed.

My proposition is that Air Mass is not affected by temp and pressure. The DME manages temp and pressure changes (air volume changes) by the throttle opening more for high temps and less for low temps in order to consume the same mass of air.

 

Hey Big Bopper, I'm enjoying our discussion.

I don't know where your scanner is getting that ambient pressure number from. I've been through the E46 wiring diagrams and not found a sensor. It may be a calculated value from other PID's. I don't know. Please direct me to the sensor, so I can go find it on the car.

I have no idea where it is and I don't care. But it's not in the scan tool or in my hand as I'm holding it so it's got to be the car. Right?

The Air mass temp/pressure chart is for a set volume of air and how the air mass changes relative to the temp and pressure of that set volume of air. It does not show that a set Air Mass changes relative to temp and pressure.

As previously indicated the MAF calculation uses a set volume of air. It's called the displacement. So imagine a chart drawn spefically for that set volume of air. The profiles will look exactly the same as the one I have posted. Just with different values.

You are correct in that the volume of the cylinder does not change, but the mass of air going into the cylinder for each compression stroke is different. It is the throttle that limits the amount of air that enters the cylinder.

Yes. That's true but the volume will still be the same. The density will change again as the throttle opens and closes. So we are back to density. Right?

My proposition is that Air Mass is not affected by temp and pressure. The DME manages temp and pressure changes (air volume changes) by the throttle opening more for high temps and less for low temps in order to consume the same mass of air.

You can propose that by all means but I am going to disagree with it. I posted a link earlier to a webpage which purports to calculate the mass air flow from 6 parameters. When I use that calculator I get pretty much the same result as when I do the calculation manually. Two of the mandatory parameters on that webpage are air pressure and temperature which tends to suggest that your earlier assertion regarding those paremater to be unneccessary is erroneous.

Here is the webpage:

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Yes I have seen that MAF flow calculation website before. In order to calculate the Mass, the calculator needs to know the volume of air. As air volume is dependent on temp and pressure, the calculator requests those numbers.

Our BMW's have Mass Air Flow Sensors not Air Volume sensors. Think about how a MAF works. It has a hot element with a targeted temp. The air passing over that element cools it. The MAF increases the current through the element to maintain the target temp. The amount of current used to heat the element is the basis of calculating the air mass. On a mid summers day, the air is thin/light (low density). It takes a lot of air (increased air volume) to cool the element to measure the a set MAF value. On a mid winters day, the air is thick/heavy (high density). It takes less air (lower air volume) to cool the element to measure that same set MAF value.

What the engine wants is oxygen. A known consistent amount of oxygen so the DME can inject the right amount of fuel. As Air Mass is independent of temp and pressure, the BMW engineers have selected air mass as the basis of measuring the incoming air. It avoids the need to measure temps and pressure that you would have to do if you used an air volume meter, to determine the amount of oxygen.

It's 10:40 am Tuesday morning here. I have to go and fit a couple of pre-cat O2's to a M52TUB20 engine. I'll be away from the computer for a while.

 

well I replaced my MAF and i'm still getting the same readings, same power loss but i did just notice something... when i press on the gas i hear a whistling sound accompanied with a weird rattling sound (not the disa) here's a video of that issue. Also here's some screenshots from a hot idle, acceleration, and at a cruise.. Picture 1 is at hot idle, pictures 2,3,4,5 are during acceleration and pictures 6 and 7 are at a cruise.

 

3.6g/s at idle is normal for this engine.

 

Alright, I still get the P0171 code but i've been doing more reading and have noticed that a lot of the symptoms i'm having could be due to the Camshaft sensor (intake side).

My car sometimes does not start (crank no start) it has power loss, and it's stalled on me twice after trying to accelerate from stops... when going up hill my car gets stuck above 4000+ rpms (until i reach the top) and it still does not gain any speed only maintains the speed even if i press the gas a little harder but i prefer not to to prevent in fear of it stalling.

I used to have a camshaft code when my crankshaft sensor went bad but when i replaced the CPS and cleared my DTC codes on BMW Scanner I no longer get the camshaft sensor code. Only codes that pop up is P0171 and sometimes P0306.

 

Wait ... the SAP? It's only active for 90 seconds at most on start up, and that's if it's really cold out. Usually it runs for much less time. And with a 2004 you have the newer style SAP with its own mini-MAF sensor and completely electronic control, so you don't have any of the vacuum lines running around the back & exhaust side of the engine from the vacuum ports at back of intake.

In other words, I'm not sure how the SAP would cause power loss issues after engine is warm and SAP is inactive.

Maybe if the sap valve is stuck open somehow, and it being in the exhaust stream, after combustion chamber causes the O2 sensor to see a "lean" condition .... ??? I would think you could test the valve after car arms up by removing the sap hose at the check valve to see if it is closed ... ???

Fwiw, I'm just thinking out loud here trying to understand how the SAP might cause a power loss ...

Was the replacement pre cat O2 a Bosch 17215? What brands were the fuel pump and filter?

Also, try swapping bank 1 and bank 2 pre cat O2 sensors to see if the high fuel trims follow the sensor.

 

Maybe its time after 51 posts, to get some data to look at. It seems that you have OBD Fusion on your smart device. Make sure it is set up as per these instructions. 5 second refresh/snapshots for the data logger is good. OBD Fusion

Run the 3 diagnostic logs described in the OBD Fusion thread:

• Cold Start
• Highway cruise
• Hot Idle.

Also do the Rev Rise Test as detailed below

Run your normal OBD Fusion log. Hot engine and Cat's, stationary car. Slowly raise the rev's of the engine up from idle to around 3,000 rpm. I mean slowly. It should take you 3-4 minutes to do this test.

It takes some skill to do this test due to the lightly loaded engine. A little throttle change results in a large rev change. If you stuff up the first part of the test getting used to controlling the small rev changes, then redo the test.

Post all 4 logs in Drop-box and we'll have a look at them.