S4 Digital boost gauge re-calibrating?

[merlin's S4]

Hi Guys!

I've just installed a remapped RS2 ecu into my S4 to complete my RS2 setup. The car seems to be going great however my digital boost gauge on the dash trip computer is now reading low (1bar max boost). I am assuming that having a 3bar map sensor now instead of the 2.5 has confused this therefore making it read low.

Is there anyway of recalibrating or modifying this function to be more accurate or will I just have to forget it and fit an analogue gauge?

[UrS4boy]

Hi Guys! I've just installed a remapped RS2 ecu into my S4 to complete my RS2 setup. The car seems to be going great however my digital boost gauge on the dash trip computer is now reading low (1bar max boost). I am assuming that having a 3bar map sensor now instead of the 2.5 has confused this therefore making it read low. Is there anyway of recalibrating or modifying this function to be more accurate or will I just have to forget it and fit an analogue gauge?

Ummm...I don't think an RS2 ECU works straight-up in with an C4 UrS chassis. The pin-outs are different = your gauge problem.

Normally if you upgrade your C4 AAN ECU with chips and a 3.0 Bar MAP, the digital boost gauge will "work", i.e. give a reading above 1.0 Bar (= atmospheric pressure) but it will not be accurate because the voltage signal sent by the MAP is different than the calibration of the boost gauge (which was based on the 2.5 Bar MAP). I don't think anyone has resolved this. BUT it *is* something that needs to be done. Electronics geniuses, this is your challenge.

[prj]

Ummm...I don't think an RS2 ECU works straight-up in with an C4 UrS chassis. The pin-outs are different = your gauge problem.

Incorrect, the ECU's are identical.

There's nothing to solve, the software in the cluster needs to be reprogrammed, as 5V=2.5 on dash. It's just an ADC, which is scaled.
I don't have a spare cluster, plus I have no idea if the program for the computer is in a processor with ROM or if it is on a separate chip.

Also, if it is showing "2.0" max on a non-stock ECU, then you have mechanical problems with your car, as that's "only" 1.4 bar boost.
Unless the ECU has a 4 bar MAP sensor in it, then that's 2.2 bar of actual boost.

[merlin's S4]

Ok thanks.

Just to confirm it actually reads up to 2.0 which is 1bar boost, except due to the bigger MAP sensor it's actually boosting more.

@prj - So a 2.0 reading should mean I have 1.4bar boost is that correct?

[prj]

Yes...

[UrS4boy]

Incorrect, the ECU's are identical. There's nothing to solve, the software in the cluster needs to be reprogrammed, as 5V=2.5 on dash. It's just an ADC, which is scaled. I don't have a spare cluster, plus I have no idea if the program for the computer is in a processor with ROM or if it is on a separate chip. Also, if it is showing "2.0" max on a non-stock ECU, then you have mechanical problems with your car, as that's "only" 1.4 bar boost. Unless the ECU has a 4 bar MAP sensor in it, then that's 2.2 bar of actual boost.

I thought before you said the RS2 ECU was different, i.e. there was a resistor or something that the AAN ECU does NOT have. No?

I am not clear why a reading of "2.0" is 1.4 boost. Isn't boost over and above atmospheric pressure (not engine vacuum) and therefore if atmospheric pressure is about 1 Bar, then a reading of 2.0 Bar = 1 Bar (14.5 psig) of boost. No?

[prj]

I thought before you said the RS2 ECU was different, i.e. there was a resistor or something that the AAN ECU does NOT have. No?

They are pretty much the same, the pinouts are the same, and for this case both will work the same.

I am not clear why a reading of "2.0" is 1.4 boost. Isn't boost over and above atmospheric pressure (not engine vacuum) and therefore if atmospheric pressure is about 1 Bar, then a reading of 2.0 Bar = 1 Bar (14.5 psig) of boost. No?

3/2.5*2.0

[UrS4boy]

They are pretty much the same, the pinouts are the same, and for this case both will work the same. 3/2.5*2.0

So "the ECU's are identical" is false. ("pretty much the same" is not identical.) Thanks.

In a discussion about the scaling of the 3.0 Bar and 2.5 Bar MAP sensors I once had with Kevin Day (the inventor/developer of the TDS-1, now marketed by Marc S. at EFI Express), Kevin said that the relationship between the 3.0 Bar and 2.5 Bar MAP sensor outputs at a given pressure input are NOT linear.

[prj]

So "the ECU's are identical" is false. ("pretty much the same" is not identical.) Thanks.

Okay, in that case no ECU is identical, because each of them uses different variable resistors.
Doesn't make any difference, when they all add up to the same value though, now does it? I mean 2+2=4 and 1+3=4, functionality wise identical. Component wise no... and then you could say there are tons of different ECU's, because some 80C535 chips are made by AMD, others by Siemens. I/O helper is made by Motorola and by Philips etc.

In a discussion about the scaling of the 3.0 Bar and 2.5 Bar MAP sensors I once had with Kevin Day (the inventor/developer of the TDS-1, now marketed by Marc S. at EFI Express), Kevin said that the relationship between the 3.0 Bar and 2.5 Bar MAP sensor outputs at a given pressure input are NOT linear.

Bosch 250kpa:
Ua = Uv/5 * (4.6*Pabs/230kpa - 0.2).
Bosch 300kpa:
Ua = Uv * (0.85 * Pabs/280kpa + 0.0193)

With Uv of 5 we get for 250kpa:
Ua = 0.02*Pabs - 0.2
With Uv of 5 we get for 300kpa:
Ua = 0.01518*Pabs + 0.0965

Let's put that into a chart:

Pressure	Voltage 300kpa	Voltage 250kpa	Difference mult
25	0.476	0.3	0.630252101
50	0.8555	0.8	0.935125658
75	1.235	1.3	1.052631579
100	1.6145	1.8	1.114896253
125	1.994	2.3	1.153460381
150	2.3735	2.8	1.179692437
175	2.753	3.3	1.198692336
200	3.1325	3.8	1.213088587
225	3.512	4.3	1.224373576
250	3.8915	4.8	1.233457536
260	4.0433	5	1.236613657

1.2* is a pretty damn good average. Considering 1 kpa is about 0.02 volts, and the measuring error is pretty much at least two times that at any given moment where it actually matters (>100kpa) and 4 kpa at 5V, then I'd say you can quite well apply a multiplier of 1.2 to it.

I wonder why you are being so **** lately about everything.

[UrS4boy]

I wonder why you are being so **** lately about everything.

The reason is, I don't like it when words like "All" and "identical" are thrown out and misused when the correct phrasing should have been more like "almost all" or "almost identical". "All" = everything. Identical = everything is the same (not just some things). Misuse and/or sloppy use of language can result in problems, sometimes serious, sometimes not so serious.

In the case of the comparison of the 300 kPa and 250 kPa MAP sensor outputs and scaling factor for the in-dash board computer boost gauge, a constant factor of 1.2 is not correct across the range of data. The best fit to the ratio (scaling factor) that I could do based on your calculations was a fourth-order polynomial, as shown below with and R^2 of 0.9965. Your "1.2" constant isn't too bad between 125 kPa and 260 kPa but otherwise, it is off significantly.

Now if there was just a way to fix the display with a magic 4th order polynomial resistor.

[prj]

Your "1.2" constant isn't too bad between 125 kPa and 260 kPa but otherwise, it is off significantly.

And that's the range it is important in, no? Considering the dash's accuracy is 0.1 bar, 1.2 is pretty good for the entire in-boost area. And that's what the average person here cares about.
Also, Motorola's 300kpa and 400kpa sensors are linear. These are used in VMAP's/as replacements.

Now if there was just a way to fix the display with a magic 4th order polynomial resistor.

There's likely no formula, it's probably just a lookup table.
3B clocks are scaled for 200kpa MAP, so just dumping both contents and comparing will show where the map is.