Inexpensive way of converting to better flowing MAF, or from AFM to MAF
11-21-2005, 10:17 PM
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Originally Posted by toofast928
sjsj,
Mapping out the AFM signal voltage per 500 RPM increments and match it to the conditioned MAF signal is a base. After that we need a dyno to fine tune.
Mapping out the AFM signal voltage per 500 RPM increments and match it to the conditioned MAF signal is a base. After that we need a dyno to fine tune.
* Yes, a dyno could allow you to fine tune it, but dyno time and cost take the project into $$$ amounts I prefer to avoid.
My choice for fine tuning is using data acquisition. Only proviso here is converting say the distributor spark (a frequency) into a voltage to give RPM, though it can be done.
A practical how fine tuning could be performed is shown the URLS below. Simply monitor find a secret location hill, unplug the o2 sensor so you are in open loop mode, monitor the RPM, MAF signal into the ECU vs o2 sensor signal.
http://cyberdave.org/CarTest.html
http://cyberdave.org/carwb.html
Use shareware/freeware to be used with the DataQ data aquisition device is available at
http://www.ultimaserial.com/
http://groups.yahoo.com/group/ultimaserial_group/
Then make adjustments to the tunable MAF at the RPM points which under analysis show are running rich or lean using the handheld controller in RUN mode while holding the accelerator RPM.
Just need a good guide on tuning. Heard 12.0:1 is good up top for performance, leaner is good for take off, but engine runs hotter. Advise good coolant and good oil.
Key guide here too is the O2 sensor voltage to air/fuel ratio http://wbo2.com/sw/20-tables.xls. "Nbsim" is the O2 sensor output voltage for row for corresponding Lambda and AFR presented. The NBsim worksheet providing a at a glance representation.
sjsj
11-21-2005, 10:31 PM
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What is nice about the L Injection is its simplicity. Two dimensional analog ECM. Once the AFM is at its full door sweep (around 3000 RPM WOT) then the ECM main input is RPM. Modified by o2 (untill the o2 cut off switch is activated) and of course IAT and ECT. Lets not make it any harder than it has to be.
11-22-2005, 12:23 AM
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Originally Posted by toofast928
What is nice about the L Injection is its simplicity. Two dimensional analog ECM. Once the AFM is at its full door sweep (around 3000 RPM WOT) then the ECM main input is RPM. Modified by o2 (untill the o2 cut off switch is activated) and of course IAT and ECT. Lets not make it any harder than it has to be.
< 3000 RPM = AFM signal + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: can use tunable MAF to modify as outlined above.
> 3000 RPM = RPM and o2 signal mainly + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: could be triggered by a reed relay to move stoich point of O2 sensor as per http://better-mileage.com/memberadx.html to richer or leaner (probably richer? fro 14.7:1). The MAF sensor voltage which indicates the airflow at > 3000 RPM (or any other voltage based signal that could tell us when it is > 3000 RPM.
Makes sense, as at > 3000rpm the exhaust fumes evaluated by the O2 sensor would flow quick enough for real-time correction back to stoich point 14.7:1.
Brilliantly simple and effective.
sjsj
11-22-2005, 12:36 AM
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I think were on the same page. L Injection uses no TPS input for driver command. Engine demand only, = CFM.
The AFM works on a 3.2 v idle speed sweep to 7.5 v at predetermined x value of engine CFM. No one that I know of ever measured it. Easier to say AFM door maxes out around 3000 RPM, WOT
The AFM works on a 3.2 v idle speed sweep to 7.5 v at predetermined x value of engine CFM. No one that I know of ever measured it. Easier to say AFM door maxes out around 3000 RPM, WOT
11-22-2005, 02:15 AM
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Originally Posted by toofast928
I think were on the same page. L Injection uses no TPS input for driver command. Engine demand only, = CFM.
The AFM works on a 3.2 v idle speed sweep to 7.5 v at predetermined x value of engine CFM. No one that I know of ever measured it. Easier to say AFM door maxes out around 3000 RPM, WOT
The AFM works on a 3.2 v idle speed sweep to 7.5 v at predetermined x value of engine CFM. No one that I know of ever measured it. Easier to say AFM door maxes out around 3000 RPM, WOT
11-22-2005, 08:10 AM
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TPS - Throttle Position Sensor
CFM - Cubic Foot Minute
AFM - Air Flow Meter
WOT- Wide Open Throttle
ECM - Engine Control Module
sjsj pick up the Bosch book "L Injection"
The 944 is a good reference to AFM operation but bases on the Motronic ECM. Motronic is little more advanced than 928 ECM.
CFM - Cubic Foot Minute
AFM - Air Flow Meter
WOT- Wide Open Throttle
ECM - Engine Control Module
sjsj pick up the Bosch book "L Injection"
The 944 is a good reference to AFM operation but bases on the Motronic ECM. Motronic is little more advanced than 928 ECM.
11-23-2005, 12:26 AM
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Originally Posted by sublimate
Based on what you say it doesn't sound like it'd work.
A maximum of +50% correction would adjust the .8v of the MAF at idle up to only 1.2v, which is nowhere near the 3.2v that the L-Jet is expecting to see from the AFM at idle.
A maximum of +50% correction would adjust the .8v of the MAF at idle up to only 1.2v, which is nowhere near the 3.2v that the L-Jet is expecting to see from the AFM at idle.
It works, I've done it.
11-23-2005, 12:37 AM
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Originally Posted by sjsj
Lots of acronyms there. Just as a courtesy to other forum members wondering if you would volunteer explanding on their meanings?
11-23-2005, 07:07 PM
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*******************************************
So as a summary for AFM folks, here is how we could tune
the air/fuel ratio without changing the stock ECU
*******************************************
< 3000 RPM = AFM signal + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: can use tunable MAF via say a the Digital Fuel Adjuster to modify as outlined above.
> 3000 RPM = RPM and o2 signal mainly + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: could be triggered by a reed relay to move stoich point of O2 sensor as per http://better-mileage.com/memberadx.html to richer or leaner (probably richer? from 14.7:1). The MAF sensor voltage which indicates the airflow at > 3000 RPM (or any other voltage based signal that could tell us when it is > 3000 RPM.
OR
- Digital Pulse Adjuster (DPA). Using the same handheld controller as for the DFA, it allows the the duty cycle (eg: 0->100%) to have delta correction values added or subtracted again along 128 load poits. (not sure on the limits of the correction though, coz never used one). Details at http://autospeed.drive.com.au/cms/A_2471/article.html . This is directly modifying the fuel injector duty cycles!! Presumably at say 4000rpm, the fuel injector duty cycle may be 65%. So at the load point that corresponds you could simply add duty cycle such as 10% to richen the mix or say subtract 10% to lean out the mix.
Available at Jaycar:
[US/Canada]
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$51US
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$38US
[AUS/NZ]
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$80AUD
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$60AUD
* Further reading perhaps? *
Well worth getting is Silicon Chips's "Performance Electronics For Cars" , reviewed at http://autospeed.drive.com.au/cms/A_2457/article.html . It explains the basics of car electronics then gives and explains a stack of electronic circuits kits to modify the car operations to bring up to your needs and the 21st century. Jaycar stock the kits mentioned in the book and the book iitself. This is worth it's weight in gold IMHO, but what makes it extra nice is its pretty inexpensive. See below:
[US/Canada]
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$15US
[AUS/NZ]
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$20AUS
NOTE: not affiliated with Jaycar or any other products suggested here.
sjsj
So as a summary for AFM folks, here is how we could tune
the air/fuel ratio without changing the stock ECU
*******************************************
< 3000 RPM = AFM signal + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: can use tunable MAF via say a the Digital Fuel Adjuster to modify as outlined above.
> 3000 RPM = RPM and o2 signal mainly + ECU lean-out/enrichment for air temp (provided by Internal Air Temperature sensor within the AFM itself)
- ie: could be triggered by a reed relay to move stoich point of O2 sensor as per http://better-mileage.com/memberadx.html to richer or leaner (probably richer? from 14.7:1). The MAF sensor voltage which indicates the airflow at > 3000 RPM (or any other voltage based signal that could tell us when it is > 3000 RPM.
OR
- Digital Pulse Adjuster (DPA). Using the same handheld controller as for the DFA, it allows the the duty cycle (eg: 0->100%) to have delta correction values added or subtracted again along 128 load poits. (not sure on the limits of the correction though, coz never used one). Details at http://autospeed.drive.com.au/cms/A_2471/article.html . This is directly modifying the fuel injector duty cycles!! Presumably at say 4000rpm, the fuel injector duty cycle may be 65%. So at the load point that corresponds you could simply add duty cycle such as 10% to richen the mix or say subtract 10% to lean out the mix.
Available at Jaycar:
[US/Canada]
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$51US
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$38US
[AUS/NZ]
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$80AUD
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$60AUD
* Further reading perhaps? *
Well worth getting is Silicon Chips's "Performance Electronics For Cars" , reviewed at http://autospeed.drive.com.au/cms/A_2457/article.html . It explains the basics of car electronics then gives and explains a stack of electronic circuits kits to modify the car operations to bring up to your needs and the 21st century. Jaycar stock the kits mentioned in the book and the book iitself. This is worth it's weight in gold IMHO, but what makes it extra nice is its pretty inexpensive. See below:
[US/Canada]
http://www.jaycarelectronics.com/pro...Max=&SUBCATID=
$15US
[AUS/NZ]
http://www.jaycar.com.au/productView...Max=&SUBCATID=
$20AUS
NOTE: not affiliated with Jaycar or any other products suggested here.
sjsj
11-23-2005, 09:03 PM
#25
Drifting
I think sjsj would make a far better legal assistant than a mechanic/engineer. Willing to do tons of research and provide sources of who said what. There... I said something nice.
