E46 Fanatics Forum banner
1 - 20 of 61 Posts

·
Premium Member
2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
Joined
·
2,085 Posts
Discussion Starter · #1 ·
I need some help with a real head scratcher of a problem.

Working on 4 E46's each with unexplained rich conditions on both banks.

Almost all rich on both banks issues are caused by sensor failures. It's really hard to get a modern car to run rich on both banks by other means (yes fuel pressure, but that's been checked). They all have new VDO MAF's and near new Bosch pre-cat O2's. That just leaves the DME in the primary control loop.

3 are MS45's
1 is a MS43

2 are 325's (1 MS43)
2 are 330's

The logs from the various cars are consistent and show some interesting Calculated Load data. Below are typical logs from a Rev-Rise test for the condition being investigated. Load for this test should be stable in the range of 8% to 18% (+/-1.5%). The load is dropping from 14% to 3.8% at the same time as the MAF Error jumps from -25% to -2%. With the MAF returning acceptable values, the Load has unacceptable values. Thus I'm looking at the calculated load, OBD2 PID 04
calculation.

Barometric pressure is a fundamental correction factor in Calculated load. I am now wondering if the DME is using Barometric pressure in part of the fuel trim routine to correct for altitude?

Fundamentally the MAF should automatically correct for standard temp and pressure as the MAF measures air Mass and not air Volume. But the load calculations have me wondering.

The proposition is that if the Barometric sensor on the the DME PC board is faulty, that it impacts on the fuel trim calculations and returns rich fuel trims.

I do not have an MS45 on hand to test. I do have a MS43 on hand.

Barometric Pressure in the MS43:
  • Not available in INPA
  • Not available in OBD Fusion
  • Is in Foxwell NT530 with BMW software
  • Is in TestO for the MS43 but not for the MS45.
So, testing the Barometric sensor looks to be with specific scanners with BMW software.

What is everyone's experience on this?


Helpful links:





Rev-Rise Log

Rectangle Slope Plot Font Parallel

Above chart has time as the X axis


Rectangle Slope Font Plot Line

The above chart has RPM as the X axis.

Hot Idle Log
  • Load has lots of variability, on the extremes of acceptable figures
  • Total Fuel Trims are very Rich
  • Pre-Cat O2's are showing a lean off-set.
Rectangle Slope Font Plot Parallel

Rectangle Slope Plot Font Parallel

Rectangle Slope Font Plot Parallel



Cruise Logs

  • Load is showing a far higher variability when compared to the MAF than is accepted
  • Total Fuel Trims are still very Rich.
  • Pre-Cat O2's have a rich off-set.
Rectangle Slope Font Parallel Pattern

Rectangle Slope Font Plot Parallel

Rectangle Slope Font Plot Parallel
 

·
Premium Member
E30M3 Race F10 535 R1150Rt M Coupe
Joined
·
11,971 Posts
Sorry mate didn't read it all.
I've seen barometric pressure sensors kill a few E30 M3 with the S14 engine.

Pressure sensor was piggybacked on the AFM feedback wire to the DME. It was to alter the signal going from the AFM to the DME. In theory good. However some of them failed very badly and the signal was too far under-reported.

One thing a S14 does NOT like: High RPM and lean , can go pop at the track in less than 1 minute of WOT.
 

·
Super Moderator
2004 325i automagic
Joined
·
3,882 Posts
The thread below about p2227 codes and replacing the barometric sensor on the DME circuit board may be of some help. In post #38, Terraphantm mentions using Tool32 to check the data, although the output he included in the post did not give actual pressure data. What Paraklas mentions above might be more useful for data logging purposes.

 

·
Premium Member
2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
Joined
·
2,085 Posts
Discussion Starter · #7 ·
messages. send Robin at ms4x a message he can probably give you more info.
Hi

Thank you for the tip. Unfortunately I can't find anywhere on the MS4x pages to send a message or make contact. The join "Discord" process is broken and will not go past the hCaptcha

Do you have any contact information you can send me via a PM?
 

·
Registered
Joined
·
9,607 Posts
The sensor has an analog output voltage:
VOUT = VS x (0.009 x P - 0.095); where Vs supply typically is 5v., P is absolute pressure

So to verify, measure Vs from pin2 to pin3 and should be around 5v, then measure voltage on pin4 Vout which is the pressure in volt and use the equation above to calculate the pressure P, and verify of the value within the local atmospheric pressure.
The DME processor runs an A to D conversion and calculates the pressure.
Just turn the key to ON and as soon as Vs has 5v then the chip should output pressure value at pin4 which can easily measure with voltmeter.

Note; pin1 is the lower left pin and pin4 if on lower right, when the chip label oriented as normal reading.

Rectangle Slope Font Parallel Pattern


 

·
Registered
Joined
·
9,607 Posts
So at sea level of 101.3 Kpa, the output pin4 should be about 4.2V, and if you think the DME calculated too rich due to bad P sensor, then the measured pin4 would be much lower than 4v -- under reported -- to cause the rich mixture.
 

·
Premium Member
2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
Joined
·
2,085 Posts
Discussion Starter · #11 ·
Thank you @Sapote

Yes, I also have the sensor data sheet and have already worked out the test procedure. It's good to have yours to confirm mine against.

Before I send out a procedure to a person on unknown capability that requires them to open the top of the DME, power it up and go probing around with some test probes, I really want to know if the sensor is the likely cause. The risk of dropping something onto the live PC board or shorting something with the probes is a real risk that could kill the DME.
 

·
Premium Member
Joined
·
4,319 Posts
Hmmm....
I'd be very curious to see if the baro sensor is actually used to alter fuelling data.

The MAF compensates for bp by its fundamental design, so it doesn't SEEM like
it would need to be factored into any running corrections. Kind of like IAT is used
for starting, and then pretty much ignored...
The BMW literature says it doesn't use it, but that... can always be taken with a grain
of salt.

t
 

·
Registered
Joined
·
99 Posts
The IAT and MAP could well be used as a check for the MAF. If, however, they are used to make sure the MAF is sending data mirroring the MAP and IAT then you'd think you'd get some kind of code if any of the sensors aren't coming back with an in spec checksum.
 

·
Registered
Joined
·
9,607 Posts
Before I send out a procedure to a person on unknown capability that requires them to open the top of the DME, power it up and go probing around with some test probes, I really want to know if the sensor is the likely cause.
Personally I doubt even if a bad P sensor could cause that much of fuel trim offset that you reported. With the MAF sensor, the atmospheric pressure should only be used for a little fine adjustment and nothing like 10% or more on the TFT. If it is important factor in the sensor, then Vout should be included in the OBD2 PID.
First, find out if the chip pin3 GND is the same ground as the engine block. If it is then just use the engine GND instead.
Second, pin4 on the board has a large pad for testing so it is not too difficult to probe it. No need to have engine running, as if the DME has the 12v supply then the chip should output Vout for the pressure.
 

·
Premium Member
2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
Joined
·
2,085 Posts
Discussion Starter · #17 ·
Personally I doubt even if a bad P sensor could cause that much of fuel trim offset that you reported. With the MAF sensor, the atmospheric pressure should only be used for a little fine adjustment and nothing like 10% or more on the TFT.
I have pondered this question a lot.

Reading the data sheet:
  • The sensor is constructed with a Vacuum canister as a reference. Ambient air pressure is measured as the difference between the outside air pressure and this vacuum canister. Should the canister loose vacuum, then the sensor will read low, as the difference is less.
  • The Transfer function chart shows the range of the sensor as 15 to 115 kPa or 150 to 1150 hPa. Ambient air pressure at sea level is 1013 hPa, which is at the upper end of the sensors range.
  • If the vacuum canister has a leak, then there is a 863 hPa (1013-150) range for a low pressure reading. That's equivalent to 7,397m or 24,263 feet of altitude when you use a simple equation of air pressure changing at a rate of 3.5 millibar (hPa) per 30 m.
So the potential is there for a faulty Baro sensor to tell the DME that the car is at a far higher altitude than it really is.

The real question is, does the DME use Baro pressure in the fuel trim control loop? I don't know for sure. I suspect it does. That is why I've written up a test procedure and sent it out to a number of members on here who have the unexplained rich fuel trim problem.

Waiting on tender hooks until they send back test results to confirm the question or not.

Added test procedure to assist people researching this topic in the future.
 

Attachments

·
Premium Member
2000 E46 323i, 3.0L, 2.8L and 2.0L Z3's
Joined
·
2,085 Posts
Discussion Starter · #19 ·
Or lift up pin4 and solder on the the pad a variable pot within 0 to 5v, then watch the TFT when adjusting the pot.
I would, but don't have a MS45 powered car to play with.

But this is well within the capabilities of @OURMANDAN and he has a MS45. I'll ask him.
 

·
Registered
Joined
·
1,058 Posts
Now you are bragging with your fancy James bond cars. After I have the other tamed and when I have some money again I'm going to look around for one of those.. They are really cool. Your taste is excellent.
 
1 - 20 of 61 Posts
Top