DASH2 Boost Conversion - Autronic SM4
Posted: Thu Jul 22, 2021 6:39 am
Greetings...
Apologies in advance for the long-winded explanation...
I have the DASH2 linked up to an Autronic SM4 ECU (v1.09).
I have everything working fine, all the data channels passing data through from the ECU to the DASH2. However, I have an issue with showing the correct boost pressure. I'd like the DASH2 to show the psi, but the ECU outputs pressure in Kpa (absolute).
I've seen another forum post (viewtopic.php?f=2&t=3656&p=13813&hilit=boost#p13813) which details how to convert Kpa to PSI via an equation in the DASH2 config software. I can see I can enter the equation via the ECU Interface option against the Boost pressure data channel. The equation is in the format (<value> x input) + <offset>
So in the above forum example, this would be... (0.145 x input) + 0
So...
10 Kpa converts to 1.45psi
45 Kpa converts to 6.5psi
70 Kpa converts to 10.2psi
100 Kpa converts to 14.5psi
170 Kpa converts to 24.7psi etc...
I think this assumes you are converting atmospheric pressure in Kpa to PSI.
However, the Autronic ECU measures the absolute pressure in Kpa... so ~100Kpa above atmospheric.
So if I use the above conversion, on testing the actual outputs from the ECU and DASH2, I get the following...
@45 Kpa ECU absolute pressure (car idling), I see ~0.06 (psi) on the DASH2
@170 Kpa ECU absolute pressure (~10psi shown on the mechanical boost gauge), I see ~0.2 (psi) on the DASH2... so not what I need.
Now if I do a manual conversion of absolute to atmospheric and then apply the Kpa to psi conversion (using the tested pressures above), I get the following...
@45 Kpa ECU absolute converts to -55Kpa atmospheric, which converts to -8psi
@170 Kpa ECU absolute converts to 70Kpa atmospheric, which converts to 10.2psi ...which is correct.
So the conversion I need is, ((input - 100) x 0.145)
Is there any way of defining this format for the equation?... essentially subtracting a 100Kpa offset before doing the Kpa to PSI conversion?
Many Thanks!
Mick
Apologies in advance for the long-winded explanation...
I have the DASH2 linked up to an Autronic SM4 ECU (v1.09).
I have everything working fine, all the data channels passing data through from the ECU to the DASH2. However, I have an issue with showing the correct boost pressure. I'd like the DASH2 to show the psi, but the ECU outputs pressure in Kpa (absolute).
I've seen another forum post (viewtopic.php?f=2&t=3656&p=13813&hilit=boost#p13813) which details how to convert Kpa to PSI via an equation in the DASH2 config software. I can see I can enter the equation via the ECU Interface option against the Boost pressure data channel. The equation is in the format (<value> x input) + <offset>
So in the above forum example, this would be... (0.145 x input) + 0
So...
10 Kpa converts to 1.45psi
45 Kpa converts to 6.5psi
70 Kpa converts to 10.2psi
100 Kpa converts to 14.5psi
170 Kpa converts to 24.7psi etc...
I think this assumes you are converting atmospheric pressure in Kpa to PSI.
However, the Autronic ECU measures the absolute pressure in Kpa... so ~100Kpa above atmospheric.
So if I use the above conversion, on testing the actual outputs from the ECU and DASH2, I get the following...
@45 Kpa ECU absolute pressure (car idling), I see ~0.06 (psi) on the DASH2
@170 Kpa ECU absolute pressure (~10psi shown on the mechanical boost gauge), I see ~0.2 (psi) on the DASH2... so not what I need.
Now if I do a manual conversion of absolute to atmospheric and then apply the Kpa to psi conversion (using the tested pressures above), I get the following...
@45 Kpa ECU absolute converts to -55Kpa atmospheric, which converts to -8psi
@170 Kpa ECU absolute converts to 70Kpa atmospheric, which converts to 10.2psi ...which is correct.
So the conversion I need is, ((input - 100) x 0.145)
Is there any way of defining this format for the equation?... essentially subtracting a 100Kpa offset before doing the Kpa to PSI conversion?
Many Thanks!
Mick