MAF voltages
05-07-2005, 02:15 PM
#16
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This is marc - the maf is fairly linear from 0-5 volts, then the curve goes flat. You can read higher, but if we are getting xKg of air at 2.5, and 2x at 5.0, then at 6 v, you may only see 2.1x and at 7 2.11x.
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
Hope this helps.
Marc
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
Hope this helps.
Marc
05-07-2005, 02:48 PM
#17
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Originally Posted by Susan K Thomas
This is marc - the maf is fairly linear from 0-5 volts, then the curve goes flat. You can read higher, but if we are getting xKg of air at 2.5, and 2x at 5.0, then at 6 v, you may only see 2.1x and at 7 2.11x.
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
Hope this helps.
Marc
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
Hope this helps.
Marc
Now are pulse width and duty interchangable terms or are they two differnt things?
A very shade tree mechanic here.
Ive seen the diagnostics diagrams in the shop manual representing pulse width so i assume its differnt.
How would could chart/plot that?
05-07-2005, 04:19 PM
#18
Rennlist Member
Hi Tony,
I expect Marc is busy with the new addition ! You may be able to measure injector on time with your data logger, the signal at the injectors goes low to ground while the injector is on. The rest of the time at +13v. If you can somehow measure the "low time" during each engine rpm, then you have it.
Does your logger have a timer that can be triggered by the rpm signal ?
Duty cycle is how long the injector is on during that 1 rpm. It is usually expressed as a %.
I expect Marc is busy with the new addition ! You may be able to measure injector on time with your data logger, the signal at the injectors goes low to ground while the injector is on. The rest of the time at +13v. If you can somehow measure the "low time" during each engine rpm, then you have it.
Does your logger have a timer that can be triggered by the rpm signal ?
Duty cycle is how long the injector is on during that 1 rpm. It is usually expressed as a %.
05-08-2005, 06:38 AM
#19
Rennlist Member
QUOTE: This is marc - the maf is fairly linear from 0-5 volts, then the curve goes flat. You can read higher, but if we are getting xKg of air at 2.5, and 2x at 5.0, then at 6 v, you may only see 2.1x and at 7 2.11x.
>>>>>>>>>>>>>>
Hi Marc/Tony,
This is partially correct, the MAF curve is a log law. However it doesn't flatten as much as you predict. There are still very useful reading to be had at higher powers than standard. The s/c guys have demonstrated this.
>>>>>>>>>>>>>>>>
QUOTE:
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
>>>>>>>>>>>>
This is partially correct. There is an rpm based map which is used when WOT is triggered, but this map just adds an enrichment value to the basic injector pulse time which is still MAF dependant. This is why an aged MAF will give low power at WOT.
>>>>>>>>>>>>>>
QUOTE:
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
>>>>>>>>>>>>
What this will show, when Tony gets over about 5.5v is that indeed the injector on time will flatten out. But this is due to a limitation in the LH hardware and mapping, not a limitation in the MAF voltage reading.
It is possible to remap up to 6.1v or so, using the standard hardware. We have done this.
Regards
>>>>>>>>>>>>>>
Hi Marc/Tony,
This is partially correct, the MAF curve is a log law. However it doesn't flatten as much as you predict. There are still very useful reading to be had at higher powers than standard. The s/c guys have demonstrated this.
>>>>>>>>>>>>>>>>
QUOTE:
AND at full Throttle, the LH full throttle map is used and it really does not matter what the maf is reading.
>>>>>>>>>>>>
This is partially correct. There is an rpm based map which is used when WOT is triggered, but this map just adds an enrichment value to the basic injector pulse time which is still MAF dependant. This is why an aged MAF will give low power at WOT.
>>>>>>>>>>>>>>
QUOTE:
This might be helpful to graph:
MAF volts
inj Pulse width
This tells the story.
>>>>>>>>>>>>
What this will show, when Tony gets over about 5.5v is that indeed the injector on time will flatten out. But this is due to a limitation in the LH hardware and mapping, not a limitation in the MAF voltage reading.
It is possible to remap up to 6.1v or so, using the standard hardware. We have done this.
Regards
05-10-2005, 09:33 PM
#21
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Originally Posted by Tony
Thanks Marc.
Now are pulse width and duty interchangable terms or are they two differnt things?
A very shade tree mechanic here.
Ive seen the diagnostics diagrams in the shop manual representing pulse width so i assume its differnt.
How would could chart/plot that?
Now are pulse width and duty interchangable terms or are they two differnt things?
A very shade tree mechanic here.
Ive seen the diagnostics diagrams in the shop manual representing pulse width so i assume its differnt.
How would could chart/plot that?
Pulse width is measured in milliseconds. It is the time that the injector is open.
Duty Cycle is the percentage of time that the injector is open.
05-10-2005, 11:27 PM
#22
Rennlist Member
John,
How have the sc guys demonstrated this?
This si what we did some time ago during stroker development. We scoped the injectors and perfromed this test: Using the same engine and two different injectors, a 30lb and 36 lb on a 400 rwhp stroker. We equalled the idling pulse width with fuel pressure, and then ran up on the dyno. Above 3500 rpm where we started the pull, the inj pulse curve was just about identical from that point to redline with both sized injectors. Power was also very similar! WE did not allow any remapping of the ecu/maf, ie: no close dloop operation. Start the engien and make a run.
Then we let the closed loop kick in, and the pw curve was different for both injector sizes!
From this we concluded that the an offset factor is applid to the full throttle map based on the closed loop characteristics of the engine.
Mike, nice PB blue GT for sale
, only needs power!
Marc
How have the sc guys demonstrated this?
This si what we did some time ago during stroker development. We scoped the injectors and perfromed this test: Using the same engine and two different injectors, a 30lb and 36 lb on a 400 rwhp stroker. We equalled the idling pulse width with fuel pressure, and then ran up on the dyno. Above 3500 rpm where we started the pull, the inj pulse curve was just about identical from that point to redline with both sized injectors. Power was also very similar! WE did not allow any remapping of the ecu/maf, ie: no close dloop operation. Start the engien and make a run.
Then we let the closed loop kick in, and the pw curve was different for both injector sizes!
From this we concluded that the an offset factor is applid to the full throttle map based on the closed loop characteristics of the engine.
Mike, nice PB blue GT for sale
, only needs power!Marc
05-11-2005, 09:10 AM
#23
Rennlist Member
Marc: How have the sc guys demonstrated this?
>>>>>>>>>>>>>>>
Several s/c guys have logged MAF volts while doing WOT runs. This shows the MAF volts climbing steadily. They have recorded peak values of around 6.5v.
The circuitry of the MAF means it is easily capable of going higher than this. The only concern of consistantly running high MAF voltages, above the design values is that MAF life will be compromised, due to the higher current through the hot wire. This can be corrected with a modification.
>>>>>>>>>>>>>>
Marc :This si what we did some time ago during stroker development. We scoped the injectors and perfromed this test: Using the same engine and two different injectors, a 30lb and 36 lb on a 400 rwhp stroker. We equalled the idling pulse width with fuel pressure, and then ran up on the dyno. Above 3500 rpm where we started the pull, the inj pulse curve was just about identical from that point to redline with both sized injectors. Power was also very similar! WE did not allow any remapping of the ecu/maf, ie: no close dloop operation. Start the engien and make a run.
>>>>>>>>>>>>>>>
The idling pulse is set on a seperate loop to anything else (triggered by closed throttle switch) and controlled by the ISV loop in the LH. This wouldn't effect the running off idle to any significant degree..
Clearly, with the fixed mapping of MAF volts versus rpm that you had in open loop, then the A/F ratio must have been 20% different between the two runs, certainly up to when the WOT switch closes at approx 2/3 throttle. Then at WOT, there is the extra enrichment (rather too much on some versions of 928 EPROM) so maybe that explains why the power at max wasn't much different betrween the 2 tytpes of injectors. Did you monitor A/F ratio ?
>>>>>>>>>>>>>>>>>>>>
Marc: Then we let the closed loop kick in, and the pw curve was different for both injector sizes!
>>>>>>>>>>>>>>>>>
The O2 loop would work out an outset to apply to the mapping to try and get to stoich under steady state (non WOT) conditions. Whether it was able to do this within the limitations of its adjustment range would be interesting to know. Did you read out any LH fault codes after ?
It may be that it could settle a value for the one size of injector, but not the other.
>>>>>>>>>>>>>>>>>>>
Marc:
From this we concluded that the an offset factor is applid to the full throttle map based on the closed loop characteristics of the engine.
>>>>>>>>>>>>>>>
The WOT map offset factor doesn't appear to be related to the other map values, other than adding a specific rpm dependant additional fuelling to the baisc pulse. However, the software is very complex and not easy to disassemble, and we are still on a learning curve !
In the instance you refer to, the basic pulse in closed loop would depend on whether the closed loop was still in control, or if it ran out of range, and defaulted to a mid range value. And also if one set of injectors was loop controlled and the other not.
It would be inrteresting to check LH fault codes ...especially for an O2 loop error code on some of the modified 928's. S/C and N/A.
Regards
>>>>>>>>>>>>>>>
Several s/c guys have logged MAF volts while doing WOT runs. This shows the MAF volts climbing steadily. They have recorded peak values of around 6.5v.
The circuitry of the MAF means it is easily capable of going higher than this. The only concern of consistantly running high MAF voltages, above the design values is that MAF life will be compromised, due to the higher current through the hot wire. This can be corrected with a modification.
>>>>>>>>>>>>>>
Marc :This si what we did some time ago during stroker development. We scoped the injectors and perfromed this test: Using the same engine and two different injectors, a 30lb and 36 lb on a 400 rwhp stroker. We equalled the idling pulse width with fuel pressure, and then ran up on the dyno. Above 3500 rpm where we started the pull, the inj pulse curve was just about identical from that point to redline with both sized injectors. Power was also very similar! WE did not allow any remapping of the ecu/maf, ie: no close dloop operation. Start the engien and make a run.
>>>>>>>>>>>>>>>
The idling pulse is set on a seperate loop to anything else (triggered by closed throttle switch) and controlled by the ISV loop in the LH. This wouldn't effect the running off idle to any significant degree..
Clearly, with the fixed mapping of MAF volts versus rpm that you had in open loop, then the A/F ratio must have been 20% different between the two runs, certainly up to when the WOT switch closes at approx 2/3 throttle. Then at WOT, there is the extra enrichment (rather too much on some versions of 928 EPROM) so maybe that explains why the power at max wasn't much different betrween the 2 tytpes of injectors. Did you monitor A/F ratio ?
>>>>>>>>>>>>>>>>>>>>
Marc: Then we let the closed loop kick in, and the pw curve was different for both injector sizes!
>>>>>>>>>>>>>>>>>
The O2 loop would work out an outset to apply to the mapping to try and get to stoich under steady state (non WOT) conditions. Whether it was able to do this within the limitations of its adjustment range would be interesting to know. Did you read out any LH fault codes after ?
It may be that it could settle a value for the one size of injector, but not the other.
>>>>>>>>>>>>>>>>>>>
Marc:
From this we concluded that the an offset factor is applid to the full throttle map based on the closed loop characteristics of the engine.
>>>>>>>>>>>>>>>
The WOT map offset factor doesn't appear to be related to the other map values, other than adding a specific rpm dependant additional fuelling to the baisc pulse. However, the software is very complex and not easy to disassemble, and we are still on a learning curve !
In the instance you refer to, the basic pulse in closed loop would depend on whether the closed loop was still in control, or if it ran out of range, and defaulted to a mid range value. And also if one set of injectors was loop controlled and the other not.
It would be inrteresting to check LH fault codes ...especially for an O2 loop error code on some of the modified 928's. S/C and N/A.
Regards
05-11-2005, 03:41 PM
#24
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Originally Posted by marc@DEVEK
Mike, nice PB blue GT for sale , only needs power!
, only needs power!
05-11-2005, 04:37 PM
#26
Rennlist Member
Hi Marc
I don't have an accurate graph, because I don't have an absolute calibrated flow rig. I have a curve with a few known points which appear to tally with the real world. You are welcome to a copy. Give me an email address I can send it to..
Regards
John
I don't have an accurate graph, because I don't have an absolute calibrated flow rig. I have a curve with a few known points which appear to tally with the real world. You are welcome to a copy. Give me an email address I can send it to..
Regards
John
05-19-2005, 01:53 PM
#27
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New Apexi AFC Select for euro cars: wont calibrate MAF's over 5v either
Nuts. I waited 6 weeks for this brand new unit from Japan: designed for European cars & even has wiring diagrams for other Porsches in the manual, but still, it cannot comprehend MAF voltages over 5v, so once I'm over 4k, my warning goes off that my MAF has reached 100% & I have to shut it down.
A 2v voltage reducer should work just fine...can anyone elaborate?
Mark
A 2v voltage reducer should work just fine...can anyone elaborate?
Mark
