944 turbo DME full throttle operation?
11-04-2002, 01:50 AM
#1
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944 turbo DME full throttle operation?
I'm wondering if the DME in the 944 turbo scans the values taken from the air flow meter at full throttle.
I'd appreciate any responses.
Ahmet
I'd appreciate any responses.
Ahmet
11-04-2002, 02:29 AM
#3
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Rage, I would agree with you but then how do all these piggy back computers give you the ability to adjust air/fuel ratio at full throttle?
What's most frustrating to me is that I can't find any info on this for sure. All sources I came across give vague answers and thus most of us 'think so'...
Ahmet
What's most frustrating to me is that I can't find any info on this for sure. All sources I came across give vague answers and thus most of us 'think so'...
Ahmet
11-04-2002, 03:05 AM
#4
Nordschleife Master
Here's my think so...
O2 sensor is ignored above X rpm, I think its 3500rpm.
The AFM: It isn't ignored, but rather it is maxed out above I think 4000rpm, which is why fuel controllers have an effect.
BOOM BABY! (emperor's new groove)
O2 sensor is ignored above X rpm, I think its 3500rpm.
The AFM: It isn't ignored, but rather it is maxed out above I think 4000rpm, which is why fuel controllers have an effect.
BOOM BABY! (emperor's new groove)
11-04-2002, 04:24 AM
#5
Race Director
You have to distinguish WOT/full-load operation from open/close-loop mode which are actually two inter-related but distinct conditions (they are not one and the same).
Yup, the O2-sensor input makes a correction to the fuel-amount only under closed-loop operation. However, closed-loop mode can extend all the way from idle to redline. The triggering event that throws the DME into open-loop mode is a sudden opening of the throttle-plate over 60-degrees in less than a preset amount of time. So you can be in open-loop operation without ever hitting full-throttle. Or conversely, you can also be in close-loop operation at full-throttle as well.
"I'm wondering if the DME in the 944 turbo scans the values taken from the air flow meter at full throttle."
"It isn't ignored, but rather it is maxed out above I think 4000rpm, which is why fuel controllers have an effect."
Yes and the effect of signal-massagers depends upon your airflow patterns. If you refer back to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002522" target="_blank">VAF-conversion chart</a> I had drawn up, the air-flow meter voltage is always used to arrive at an injector duty-cycle figure (therefore fuel-volume amount).
However, depending upon the mods you have, this can throw the air-flow signal up into the edge of the map where values are no longer changing.
One part of this issue is the chips that are being used. There are two distinct types of chips in use today. One for AFM and one for MAF. AutoThority did it correctly with their MAF kits in that they have a specific chip mapped for the particular voltage-response curve of their MAF. So an 80% of max air-flow signal will point to an 80% on the fuel-map which then has a pre-programmed amount of fuel that's correct. Anyone notice that AutoThority MAF kits don't require a signal-massager/interceptor/adjuster?
However, if you use their AFM chip or any other AFM chip with a MAF, then try to make up the difference with a intercepting signal-massager, there's a mis-match. An 80% signal from a MAF will correspond to a point on the AFM chip that's too lean. So you increase the voltage from the MAF (80% output from MAF, 90% sent to DME) and 'fool' the computer into thinking there's more airflow moving than is actually occurring. That then points to a 90% point on the fuel-map to give more fuel.
However, you run into a problem when the MAF reaches 90% (4.55v) which is massaged into a 100% (5.0v) signal is sent to the DME. You'll be right up to the edge of the fuel-map and further increases in fuel is not possible from that point on. However, that's typically not what usually happens.
The second, more common problem is that the AFM or MAF maxes out too early (before redline). For example, if you have a stock AFM that's maxed out @ 4000rpm because you've turn up the boost, or a too-small MAF that puts out maximum-voltage of 5.0v too early, say around 5000rpm. Once those devices are at maximum, no amount of after-the-fact signal-massaging/intercepting can help. Sure you can lower it down a fixed percentage to say 4.75v @ 4000rpm, but it will then hold that voltage all the way to redline because the signal-source is stuck at 5.0v, which won't help any. Or you can increase it to 5.25v all the way from 5000rpm to redline, which is off the edge of the fuel-map anyway.
In both these cases, the air-flow signal going into the DME no longer is an accurate depiction of actual air-flow patterns. But the DME will still use it and give inaccurate fuel-metering as a result. But most people don't have a read-out of their air-flow signal at the dyno to verify its validity. They just turn ***** on their air-flow signal-massager and get no change in the air-fuel ratio curve. People aren't able tune out a high-end lean issue, thus they think that the DME is using some 'chip-only' look-up table and ignoring air-flow the air-flow signal. However, they don't realize that the DME IS using the air-flow signal, it's just that the air-flow signal they're sending it is erroneous.
One little unknown tidbit is that our MAP-sensor can ALSO function as a digital signal-massager like UniCHIP with 3D RPM vs. loaded-based mapping (at least the early boxes). What has really help us in developing our chips and MAP kit is the readouts provided by the hand-held Tuning Module:
The display above shows the AFM input and resultant output to the DME. This allowed us in the beginning to accurately datalog a stock AFM and determine its 3D output curve (with the serial adaptor). It also allowed us arrive at a 3D fuel-map that we programmed into our chips to get a perfectly flat air-fuel ratio curve. Additionally, the unit also outputs a digital O2-sensor voltage accurate to 0.01v that can be datalogged with a laptop:
The O2-sensor output can then be graphed in Excel and the resultant curve looks darn close to the chart that the dyno generates:
Yup, the O2-sensor input makes a correction to the fuel-amount only under closed-loop operation. However, closed-loop mode can extend all the way from idle to redline. The triggering event that throws the DME into open-loop mode is a sudden opening of the throttle-plate over 60-degrees in less than a preset amount of time. So you can be in open-loop operation without ever hitting full-throttle. Or conversely, you can also be in close-loop operation at full-throttle as well.
"I'm wondering if the DME in the 944 turbo scans the values taken from the air flow meter at full throttle."
"It isn't ignored, but rather it is maxed out above I think 4000rpm, which is why fuel controllers have an effect."
Yes and the effect of signal-massagers depends upon your airflow patterns. If you refer back to the <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002522" target="_blank">VAF-conversion chart</a> I had drawn up, the air-flow meter voltage is always used to arrive at an injector duty-cycle figure (therefore fuel-volume amount).
However, depending upon the mods you have, this can throw the air-flow signal up into the edge of the map where values are no longer changing.
One part of this issue is the chips that are being used. There are two distinct types of chips in use today. One for AFM and one for MAF. AutoThority did it correctly with their MAF kits in that they have a specific chip mapped for the particular voltage-response curve of their MAF. So an 80% of max air-flow signal will point to an 80% on the fuel-map which then has a pre-programmed amount of fuel that's correct. Anyone notice that AutoThority MAF kits don't require a signal-massager/interceptor/adjuster?
However, if you use their AFM chip or any other AFM chip with a MAF, then try to make up the difference with a intercepting signal-massager, there's a mis-match. An 80% signal from a MAF will correspond to a point on the AFM chip that's too lean. So you increase the voltage from the MAF (80% output from MAF, 90% sent to DME) and 'fool' the computer into thinking there's more airflow moving than is actually occurring. That then points to a 90% point on the fuel-map to give more fuel.
However, you run into a problem when the MAF reaches 90% (4.55v) which is massaged into a 100% (5.0v) signal is sent to the DME. You'll be right up to the edge of the fuel-map and further increases in fuel is not possible from that point on. However, that's typically not what usually happens.
The second, more common problem is that the AFM or MAF maxes out too early (before redline). For example, if you have a stock AFM that's maxed out @ 4000rpm because you've turn up the boost, or a too-small MAF that puts out maximum-voltage of 5.0v too early, say around 5000rpm. Once those devices are at maximum, no amount of after-the-fact signal-massaging/intercepting can help. Sure you can lower it down a fixed percentage to say 4.75v @ 4000rpm, but it will then hold that voltage all the way to redline because the signal-source is stuck at 5.0v, which won't help any. Or you can increase it to 5.25v all the way from 5000rpm to redline, which is off the edge of the fuel-map anyway.
In both these cases, the air-flow signal going into the DME no longer is an accurate depiction of actual air-flow patterns. But the DME will still use it and give inaccurate fuel-metering as a result. But most people don't have a read-out of their air-flow signal at the dyno to verify its validity. They just turn ***** on their air-flow signal-massager and get no change in the air-fuel ratio curve. People aren't able tune out a high-end lean issue, thus they think that the DME is using some 'chip-only' look-up table and ignoring air-flow the air-flow signal. However, they don't realize that the DME IS using the air-flow signal, it's just that the air-flow signal they're sending it is erroneous.
One little unknown tidbit is that our MAP-sensor can ALSO function as a digital signal-massager like UniCHIP with 3D RPM vs. loaded-based mapping (at least the early boxes). What has really help us in developing our chips and MAP kit is the readouts provided by the hand-held Tuning Module:
The display above shows the AFM input and resultant output to the DME. This allowed us in the beginning to accurately datalog a stock AFM and determine its 3D output curve (with the serial adaptor). It also allowed us arrive at a 3D fuel-map that we programmed into our chips to get a perfectly flat air-fuel ratio curve. Additionally, the unit also outputs a digital O2-sensor voltage accurate to 0.01v that can be datalogged with a laptop:
The O2-sensor output can then be graphed in Excel and the resultant curve looks darn close to the chart that the dyno generates:
11-04-2002, 06:43 AM
#6
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I'm sure some of the aftermarket providers (lindsey) use generic (pro-flow)MAFs. One that's correctly sized(mustang MAF), along with a device that can modify the signal (apex-i)at multiple points (higher the resolution, the better) would work fine. I'm going to guess that there's no free lunch and the output of a generic MAF is not compatible with the 951 DME, I should do more research before getting ideas...
I have a question for you, where did you find out about this DME info? Is it through experimenting, and monitoring values from various inputs/outputs realtime? I ask because I just spent about 3 hours looking into the factory manuals, 'the bosch bible' (the blue book), searched on the internet, and looked through all my 944 specific books as well. They all mention how the non turbo 944 goes into open loop, but nada on the 951. This ofcourse talking about the AFM not the oxy sensor.
Eitherway, thanks for the information you've provided, if I had more money I wouldn't be doing this!
(It was actually out of curiosity)
Ahmet
I have a question for you, where did you find out about this DME info? Is it through experimenting, and monitoring values from various inputs/outputs realtime? I ask because I just spent about 3 hours looking into the factory manuals, 'the bosch bible' (the blue book), searched on the internet, and looked through all my 944 specific books as well. They all mention how the non turbo 944 goes into open loop, but nada on the 951. This ofcourse talking about the AFM not the oxy sensor.
Eitherway, thanks for the information you've provided, if I had more money I wouldn't be doing this!
(It was actually out of curiosity)Ahmet
11-04-2002, 07:11 AM
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Reading over your post, I see that you've already answered my question...
Anyway, it looks like you did your homework with this one. Plan to have a sale anytime soon?
Ahmet
Anyway, it looks like you did your homework with this one. Plan to have a sale anytime soon?
Ahmet
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11-04-2002, 07:16 AM
#8
Race Director
"I have a question for you, where did you find out about this DME info? Is it through experimenting, and monitoring values from various inputs/outputs realtime?"
All the above and more. Datalogging is really important in correlating what's happening inside the DME based upon sensor inputs, and the results you're seeing. Good example is injector duty-cycle, how many people monitor that? Also the DME/KLR Test Manual really helps, as does Probst's book on the Motronics. Finally, find a brilliant computer-programer, take the program-code from the Intel CPU in the DME, run it through a disassembler and see the step-by-step algorithm that the computer runs... ... heh, heh.. the Bosch programming is actually quite good.
All the above and more. Datalogging is really important in correlating what's happening inside the DME based upon sensor inputs, and the results you're seeing. Good example is injector duty-cycle, how many people monitor that? Also the DME/KLR Test Manual really helps, as does Probst's book on the Motronics. Finally, find a brilliant computer-programer, take the program-code from the Intel CPU in the DME, run it through a disassembler and see the step-by-step algorithm that the computer runs...
... heh, heh.. the Bosch programming is actually quite good.
11-04-2002, 11:38 AM
#9
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[quote]Originally posted by over1g:
<strong>I have a question for you, where did you find out about this DME info? Is it through experimenting, and monitoring values from various inputs/outputs realtime?</strong><hr></blockquote>
Once upon a time, there was a little program called DME Editor...
I actually played with making my own chips using DME Editor and a EEPROM burner before I jumped onto the standalone bandwagon. Tuning the factory ECU was very educational (but time consuming)
.
<strong>I have a question for you, where did you find out about this DME info? Is it through experimenting, and monitoring values from various inputs/outputs realtime?</strong><hr></blockquote>
Once upon a time, there was a little program called DME Editor...
I actually played with making my own chips using DME Editor and a EEPROM burner before I jumped onto the standalone bandwagon. Tuning the factory ECU was very educational (but time consuming)
.
11-05-2002, 02:21 AM
#10
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Me and my roommate played around for a little while with DME editors, but didn't find anything specific to a 944 turbo. Then I got interested in it again when I was thinking about making my own map sensor conversion about 8 months ago but with school, parents moving out of the country, me moving to another apartment, selling cars, etc. etc. never got back to it. Hopefully I'll have more free time in the next few months and get interested in this stuff again.
Thanks for the replies guys, and the detailed illusturations.
Ahmet
Thanks for the replies guys, and the detailed illusturations.
Ahmet
11-05-2002, 09:38 AM
#11
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Hi, I see that you talk about DME edit, anyone knows how to get a copy of it ? I've been searching for it for a while now without results.
Maybe some friendly soul can send me a copy of it. fredrik.nielsen@fasetten.se
// BR Fredrik N
Maybe some friendly soul can send me a copy of it. fredrik.nielsen@fasetten.se
// BR Fredrik N
