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      04-13-2010, 02:10 PM   #1
OpenFlash
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Exclamation Reading DME Data

Originally posted by Mike@n54tuning in this thread.
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Originally Posted by shiv@vishnu
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More misleading info. None of those parameters are read by the jb3. DME actual boost is not read either. What is read by the jb3 is the desired MAP voltage output it is sending to the dme. The actual voltage being fed into the dme and what boost actual reading the DME translates this voltage to is NOT read by the jb3. These values are all internal to the DME. Reading with an external device (jb3) is only possible by reading data off of the CAN network.
Shiv you're getting pretty ridiculous now. The JB3 is generating the voltage signal, so of course it knows what voltage it is creating. It's loggable in the JB3 interface as ECU PSI. The DME itself converts that voltage to kpa. Since the V4 logs PSI like the JB3 instead of kpa it must not be reading the value either right? Pretty silly argument.
I don't know why that thread was closed. I thought the purpose of this forum was to discuss tech.

So here goes:

No, Mike. I'll try to explain it in another way. When a piggyback feeds a MAP sensor voltage to the DME, the DME interprets the voltage as a certain MAP/boost reading. I think we can all agree on that.

However, the voltage that is being fed to the DME is not measured/interpreted equally by the DME and Piggyback. For these next scenarios, let's say the piggyback wants to output 2.5v to the DME.

Due to calibration/hardware differences between DME units, some DMEs may measure this as low as say 2.45v while others as high as 2.55v (just estimates).

Similarly, due to calibration variance between different units of that same piggybacks, the actual voltage output will naturally have an output variance range as well of say, 2.45 to 2.55v (again, just estimates).

This measurement variance is normal for such electronic devices. This is also the same reason you can measure the same signal on 3 different voltmeter and see 3 slightly different values.

So when you factor in that no two piggbacks units (of the same type) will, despite the same mapped output, give exactly the same voltage AND that no two DMEs will measure the same input signal to be the exact same voltage reading, it's a fact that you are going to see cumulative differences of a fraction of a volt. And each tenth of a volt is 0.75 psi. This is not an insignificant increment.

The reason we know this is because we saw this first hand. When we were in the early development stages of v4, we were only testing on my car. And, in doing so, the tune would perfectly satisfy the DME's boost target requirement. This means that DME boost target and DME boost actual would be right on top of each other as one would want. This was great.

However, we we tested the same exact map/firmware another car, we noticed that there was measurable negative boost error. So much, in fact, that we would through an underboost code during sustained load.

And then we tested in another car. This time it would show a positive boost error and trigger throttle closure and an overboost error during sustained load.

Then we looked at the actual DME readings for boost actual and we noticed that they weren't the same for the reasons mentioned above.

To solve this, we had to develop an auto-calibration routine that start every time you start the car. It compares the boost value that the Procede *thinks* it is outputting to the CAN DME boost actual that the DME is seeing. And applies a running average correction to keep the two within a hair of each other. You can view both the instantaneous voltage error and the average average voltage error in the datalogging system.

This is why I take objection to suggesting that the JB3 can read DME boost actual. Because it doesn't/can't. The JB3 only knows the voltage that it is mapped to output. The actual voltage AND how that voltage is interpreted by the DME are unknowns. The latter will always be unknown until it is read off the CANbus.

I hope that explains things...

Shiv

PS. Mike, you are more than welcome to post in this thread.

Last edited by OpenFlash; 04-13-2010 at 05:10 PM.
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      04-13-2010, 03:09 PM   #2
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wow... so these tolerance stacks can they apply to o2 sim voltages?
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      04-13-2010, 03:13 PM   #3
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Originally Posted by zsapphire7 View Post
wow... so these tolerance stacks can they apply to o2 sim voltages?
Absolutely. And o2 voltage is only 0-1v and not 0-5v (like the map sensor) so it's going to be much more sensitive to to this voltage variance. This is why there is such a large range in o2 sim/o2 modifier settings between different cars with the same set of mods.
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      04-13-2010, 03:19 PM   #4
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What the Hell does DME mean. I give up. I have been trying to figure it out so I dont look like an ASS but I give in can someone please just tell me. LOL
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      04-13-2010, 03:21 PM   #5
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Originally Posted by marinellie View Post
What the Hell does DME mean. I give up. I have been trying to figure it out so I dont look like an ASS but I give in can someone please just tell me. LOL
Digital Motor Electronics.

"BMW E90 models are equipped with digital motor electronics(DME), also known as Motronic. In these systems, fuel injection and ignition are controlled by an integrated engine control module (ECM)."

- Bentley Manual

The DME engine managment system on the N54 manages and monitors Air, Fuel, Ignition, Emissions, and Performance controls.

Last edited by scottp999; 04-13-2010 at 03:31 PM.
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      04-13-2010, 03:46 PM   #6
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sort of calling the kettle black aren't we
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      04-13-2010, 03:58 PM   #7
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Quote:
Originally Posted by scottp999 View Post
Digital Motor Electronics.

"BMW E90 models are equipped with digital motor electronics(DME), also known as Motronic. In these systems, fuel injection and ignition are controlled by an integrated engine control module (ECM)."

- Bentley Manual

The DME engine managment system on the N54 manages and monitors Air, Fuel, Ignition, Emissions, and Performance controls.
Thanks a Million
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      04-13-2010, 03:59 PM   #8
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The only difference between CAN actual boost and voltage fed to the DME is a conversion formula that must be the same in all N54 software versions.

So, in the considered scenario, the only significant variance is introduced by the piggyback voltage output.

The Procede is able to verify through the CAN variable if the voltage it is actually feeding to the DME is coherent with the 'designed' value and, in case, adjust the gains applied to the MAP readings.

So, in this case, the correction is performed in order to solve a hardware problem related to piggyback quality control... and it's unnecessary in case all JB3 (or V4) are created equal.

P.S.
5% of variance can be accepted between gauges (pressure sensors), but IMHO is quite strange in case of electronic devices such as piggybacks.
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      04-13-2010, 04:13 PM   #9
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Interesting info ..subscribed ...

good luck Shiv with your development ..
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      04-13-2010, 04:16 PM   #10
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Quote:
Originally Posted by Prince ///M View Post
The only difference between CAN actual boost and voltage fed to the DME is a conversion formula that must be the same in all N54 software versions.

So, in the considered scenario, the only significant variance is introduced by the piggyback voltage output.

The Procede is able to verify through the CAN variable if the voltage it is actually feeding to the DME is coherent with the 'designed' value and, in case, adjust the gains applied to the MAP readings.

So, in this case, the correction is performed in order to solve a hardware problem related to piggyback quality control... and it's unnecessary in case all JB3 (or V4) are created equal.

P.S.
5% of variance can be accepted between gauges (pressure sensors), but IMHO is quite strange in case of electronic devices such as piggybacks.
The same voltage fed to the DME of different cars generated slightly different DME boost readings. Which suggests calibration variance, either software or hardware induced, between different DMEs. Easy to test if you have access to a stable voltage generator, a bt tool and a couple test cars. Explains why different cars react to the same tune very differently. We figured this out with v4 which explains the newly-found car to car consistency when all other things are held equal.

Shiv

Last edited by OpenFlash; 04-13-2010 at 04:24 PM.
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      04-13-2010, 04:24 PM   #11
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Originally Posted by scottp999 View Post
Digital Motor Electronics.

"BMW E90 models are equipped with digital motor electronics(DME), also known as Motronic. In these systems, fuel injection and ignition are controlled by an integrated engine control module (ECM)."

- Bentley Manual

The DME engine managment system on the N54 manages and monitors Air, Fuel, Ignition, Emissions, and Performance controls.

Thank you! I've been wondering about that too!

Just so everyone here knows, Motronic is the widely accepted name for this. DME, from my experience is used only in BMW world....
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      04-13-2010, 04:28 PM   #12
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Quote:
Originally Posted by shiv@vishnu View Post
Absolutely. And o2 voltage is only 0-1v and not 0-5v (like the map sensor) so it's going to be much more sensitive to to this voltage variance. This is why there is such a large range in o2 sim/o2 modifier settings between different cars with the same set of mods.
...but that does not matter much...

My understanding is that the O2 sim is a replacement for the actual O2 sensor that is for checking that the catalytic converters are up and running. The O2 sensor that is responsible for the fuel mixture adjustments is not removed, correct?

...so for as long as the ECU *thinks* that the catalytic converters are doing there job, it really makes no difference...
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      04-13-2010, 04:33 PM   #13
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It really makes me sad that you even have to clarify this.
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      04-13-2010, 04:35 PM   #14
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there are 2 O2's .. the primary one which before the Catalytic and the secondary one after the catalytic .. the primary one is responsible for the fuel mixture ..

the secondary one is to make sure the catalytic is doing it's job ...

the primary one can't be removed ... but the secondary ones can be replaced by the o2 sim + some resistors for complete ... but i have no idea about the 02 sim which is built in in the procede ..so Shiv should give u some info ..
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      04-13-2010, 04:39 PM   #15
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Quote:
Originally Posted by vasillalov View Post
...but that does not matter much...

My understanding is that the O2 sim is a replacement for the actual O2 sensor that is for checking that the catalytic converters are up and running. The O2 sensor that is responsible for the fuel mixture adjustments is not removed, correct?

...so for as long as the ECU *thinks* that the catalytic converters are doing there job, it really makes no difference...
Not quite. An o2 sim is a device that manipulates the output signal of the rear o2 sensor. Typically, they reduce the max and min swings to a range the DME would associate with a fully catted exhaust system.

And while the front o2 sensors are the primary lambda sensors that influence fuel trims, the rear o2 sensors do indeed effect fueling as well. You can see this yourself by monitoring short and long term fuel trims while adjusting the o2 sim strength (or, in the case of Procede, the o2 modifier setting).

Which is why we are developed a CAN based "o2 sim" that doesn't adjust the rear o2 signals but rather just keeps the DME from completing its catalytic inefficiency test routines.

Shiv
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      04-13-2010, 04:40 PM   #16
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Quote:
Originally Posted by ehssan_alkhiyami View Post
there are 2 O2's .. the primary one which before the Catalytic and the secondary one after the catalytic .. the primary one is responsible for the fuel mixture ..

the secondary one is to make sure the catalytic is doing it's job ...

the primary one can't be removed ... but the secondary ones can be replaced by the o2 sim + some resistors for complete ... but i have no idea about the 02 sim which is built in in the procede ..so Shiv should give u some info ..


Exactly what I thought!

I guess what I did not understand is why Shiv was talking about O2 sensors and their voltage? What does that have to do with the piggybacks?
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      04-13-2010, 09:12 PM   #17
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I so want to get into this discussion but need to generate a proposal so I am subscribing as a reminder.

That said, I have some input on this matter as I was just dealing with a similar matter but in a more significant environment.
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      04-14-2010, 07:32 PM   #18
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Thanks for the info. It explains a lot why there are so many variations between cars even though they are running the same maps and tunes.

Sad to say, I feel the majority of the people don't really care about the technical superiority of your engineering and hardware; they only care about the price point and whether they can make their cars run faster. They don't care about the way to go about making a car go faster.

It's still perplexing to think people buy a tune that can't control timing... All the great cars out there with tunes, regardless whether it's a piggy or flash, have timing control to some degree.
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      04-14-2010, 08:35 PM   #19
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There are multiple error possibilities in play here. Without a routine calibration scheme, which is common in the industrial world, one has to assume things are correct. But in reality, there are always errors and they vary from car to car.

From the factory, you have the following error points.

TMAP sensor - they are not all the same. I doubt this one is even 0.5% full scale. Meaning, that if the full scale range is 35 PSIA (Absolute range), 0.5% is a potential error of 0.175 PSI out of the gate.

A/D resolution - I do not know the A/D resolution of the DME but it is at least 12 Bit. That is 1 step in 4096 or that same 35 PSI / 4096 = 0.008 PSI which is minimal.

But this is assuming the barometric pressure is the same. The DME knows this. The piggybacks can only guess at start up and that does not remain the same for many reasons. More on that in a moment.

When you add piggybacks into the equation, they add the following errors:

A/D and D/A - Both have 10 Bit A/D which is 0.034 PSI on the input. The PROcede uses 10 Bit D/A (true analog) so that double to let’s say 0.07 PSI. Still less than the sensor potential error but this error needs to be looked at as a summation and worst case.

The JB3 does not use D/A, it uses a duty cycle signal and relies on the DME reading it as an RMS. This inherently reduces the accuracy. This is due to the time offset incurred with a duty cycle signal. The frequency rate, which from what I recall was not high, will create the first error component. The second is the non-linearity of an actual RMS reading; 50% duty cycle of a 5 VDC signal is not read as a DC voltage at 2.5 VDC, it is 2.7 VDC. A rough calculation of error would be conservatively in the 0.5% range. That is 0.175 PSI, potentially more but I would have to test further on the bench. And BTW, my test equipment is significantly better than the $10 Harbor Freight multimeters BMS has shown to use in the past to test and calibrate with. I do have $2500 Fluke calibrators and handheld scopes that are calibrated annually so I trust mine better than theirs.

Now back to ambient or barometric pressure. Both the previous iterations of the PROcede and JB3 could look at the TMAP signal the moment they come on and try and determine barometric pressure. There are several ways this could cause an additional error such as slight throttle change at start, simple pressure variances due to temperature differential, etc. This could be worth 0.25 PSI alone. Not to mention a change in altitude while driving or a front moving in which can change barometric pressure 0.5 PSI in certain cases.

In all, we have a simple variance potential more than what Shiv has stated seeing. But that is really the maximum potential error and most of the time no one would ever see it.

Now, with the newer logic, it is essential calculating an error correction, or near calibration (can’t be full as at least two discrete points are needed) is occurring with the PROcede. Shiv can correct me where I am wrong, but the new logic looks at the perceived error by the DME, via the CANBus interface, and creates a corrective multiplier to fix much of the potential error. This is where the difference comes into play.

Granted, the JB3 works well. But so does a Mustang GT. Both vehicles can get down the strip in similar times and speeds. But what separates them; technology and overall refinement, as well as price but there is a reason for the later which refers back to the former.

It is my understanding that BMS is now moving to interfacing with the DME as well as surface mount technology as opposed to assembled in a garage. I applaud them for that and wish them the best. I can also suggest a great place to purchase quality test equipment too.
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      04-14-2010, 08:51 PM   #20
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      04-14-2010, 08:56 PM   #21
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Quote:
Originally Posted by scalbert View Post
Now, with the newer logic, it is essential calculating an error correction, or near calibration (can’t be full as at least two discrete points are needed) is occurring with the PROcede. Shiv can correct me where I am wrong, but the new logic looks at the perceived error by the DME, via the CANBus interface, and creates a corrective multiplier to fix much of the potential error. This is where the difference comes into play.
Correct. we basically compare the DME boost signal the DME is reading and compare it what the Procede thinks it is putting out. The error is the difference. We keep track of this difference via a running average computation and apply it as a real-time offset. Which is why we know our "model" of DME boost is the same as the actual DME boost.

And thanks for taking the time to explain all that calibration info. There is a lot of slop in there and would surprise a lot of people who never bothered (or couldn't) measure themselves. It certainly surprised us when we discovered this issue ourselves.

Shiv
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      04-15-2010, 12:58 AM   #22
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Quote:
Originally Posted by shiv@vishnu View Post
Correct. we basically compare the DME boost signal the DME is reading and compare it what the Procede thinks it is putting out. The error is the difference. We keep track of this difference via a running average computation and apply it as a real-time offset. Which is why we know our "model" of DME boost is the same as the actual DME boost.

Shiv
So would it apply the difference in an variable load real-time or just on a sustained load for a specific amount of time?
Do I make sense or I'm I not following correctly.
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