84-89 Digi Dash solutions.
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5th Gear
Joined: Apr 2011
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84-89 Digi Dash solutions.
With 84-89, the Digi dash gets gas mileage, average and momentary fuel consumption and odo trip from ECM; the ALDL line does 4-byte stream at 160 bits per second for that.
Now, the ECMs from that era have the limitation of measuring and calculating air only up to 255 grams per second.
Is there someone out there that has solved the Dash challenge; ie. hacked $8D (1227727 or 1227730) software to output dash 160 bps stream, or done a separate VSS+injector scanning microcontroller to feed the dash with that stream?
I know of some earlier MAP based software, that does dash data, but if I recall right, it could not do 8192 bps ALDL stream at all.
If someone already has this solved, I'd appreciate if you could share it.
Now, the ECMs from that era have the limitation of measuring and calculating air only up to 255 grams per second.
Is there someone out there that has solved the Dash challenge; ie. hacked $8D (1227727 or 1227730) software to output dash 160 bps stream, or done a separate VSS+injector scanning microcontroller to feed the dash with that stream?
I know of some earlier MAP based software, that does dash data, but if I recall right, it could not do 8192 bps ALDL stream at all.
If someone already has this solved, I'd appreciate if you could share it.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
It's not clear what you're trying to accomplish here.
The '84 was TBI so its ECM is unique among the C4s. The '85 ECM was GM's first attempt at PFI. The ECMs that came after were much improved. The '86 - '89 1227165 will do 8192 baud out of the ALDL. I'm not familiar with the later ECMs that came after GM switched to MAP in 1990.
The '85 MAF was Bosch frequency output and had limited maximum flow rate (I don't remember off hand). The '86 and up MAFs were voltage output and did go to 255 grams/second (that's a theoretical maximum and can't be achieved in reality - it's limited by the ADC in the ECM).
The injector pulse widths are calculated from a combination of TPS readings, MAF flow rate, engine speed and O2 sensor readings. There's more involved (like coolant temperature, knocks, etc.), but those are the major contributors.
VSS goes from the transmission to the dashboard and then to the ECM.
The '84 was TBI so its ECM is unique among the C4s. The '85 ECM was GM's first attempt at PFI. The ECMs that came after were much improved. The '86 - '89 1227165 will do 8192 baud out of the ALDL. I'm not familiar with the later ECMs that came after GM switched to MAP in 1990.
The '85 MAF was Bosch frequency output and had limited maximum flow rate (I don't remember off hand). The '86 and up MAFs were voltage output and did go to 255 grams/second (that's a theoretical maximum and can't be achieved in reality - it's limited by the ADC in the ECM).
The injector pulse widths are calculated from a combination of TPS readings, MAF flow rate, engine speed and O2 sensor readings. There's more involved (like coolant temperature, knocks, etc.), but those are the major contributors.
VSS goes from the transmission to the dashboard and then to the ECM.
Team Owner
Joined: Mar 2000
Posts: 83,383
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From: Boston, MA
Melting Slicks
Joined: Aug 2003
Posts: 3,399
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From: Lakeville MI
Sure the ecm is still limited by the 8 bit A/D converter, however with the appropriate sensor, a 0-5 Volt signal into the 8 bit A/D can support as much airflow as required for almost any application up to approx. 1,200 hp.
Due to the parabolic nature of a typical MAF transfer function, the 8 bit A/D still provides reasonable signal resolution for the idle and cruise airflow region, while still supporting maximum airflow up to 1,020 gm/sec or so.
I'd say this is about the practical limit for 165 ecm, assuming 80 lb. injectors are used.
