FAST/C-Com Sensor definitions - what do they all mean?

[carbuff]

Hi guys,
First, I'm going to post this question in a few places, so if you see it more than once, I appologize!

In my quest to get my motor tuned, I started data logging yesterday. I collected a lot of information, and now I have to decipher it. The FAST documentation doesn't explain what all of the sensors available in the dashboard represent, so I thought I would ask the question here...

So, with that said, can anyone tell me what exactly the following sensors are representing:

- HR RPM
- Scaled RPM
- Aft Corr(%)
- Atm Corr(%)
- Grs Corr(%)
- Inj. Offs mS
- BPW (mS)
- HR BPW (mS)
- Inj. DC (%)

I have guesses for some of them, but I'd rather know what they really mean. For example, what is the difference between RPM, HP RPM, and Scaled RPM? What is the difference between BPW and HR BPW? And what parameter tells me exactly how long my fuel injector is being told to fire?

In addition to the above, does anyone know the rough delay in response time of the Wideband O2 sensor? In looking through my logs, I see what looks like about 1/2 second from the time a TPS or other change occurs to a change in the O2 readings. That seems reasonable to me, just want to see if others agree...

Hopefully this information will be helpful to others beside myself!

THANX!
Bryan

PS: The C-COM feature of overlaying a log onto a 3-d table is awesome! I walked through a 10 minute log last night, and it really helps get a feel for what is happening...

 

[Craig Smith]

HR RPM - High Res RPM. This is the exact RPM count straight from the crank sensor.

Scaled RPM - This is a calculated RPM number and the calculation is based on table cell width. I don't remember exactly how it gets calculated though.

AFT Corr. - After Start Correction. This is how much after start enrichment fuel is being applied.

ATM Corr. - Atmospheric Correction. This is only used in Alpha-N mode. It is a percentage of fuel added or removed based on a generic barometric compensation curve, as the MAP sensor is used to measure ambient air pressure in Alpha-N mode.

GRS Corr. - Gross Correction percentage. All this tells you is the sum of the CTS and ATS enrichment percentage values.

Inj. Offset - this is the value you enter for the injector opening time.

BPW and HR BPW - Base Pulsewidth and High Res Base Pulsewidth. On a sequential system, these two values will be the same, but on a bank to bank setup one will be half of the other as the injector fires twice per combustion cycle. I believe the HR BPW will be the smaller of the two, but I'm at home right now and I forget.

 

[carbuff]

Craig,

Thanx for the definitions. Here's one last one...

The Inj. DC (%) sensor. This does not appear to report the exact injector offset that you enter to define the injector. I just assumed it was a percentage of the BPW that was due to the Inj Offset entry. However, that doesn't appear to be the case either.

At idle, my BPW is approximately 4.0mS. The Inj. DC (%) sensor shows 5.6. As the BPW goes up with RPM, the Inj DC (%) goes up also? Another data point is with BPW of 9.something, the Inj DC(%) shows 12.something (can't remember the exact numbers). So my percentage theory doesn't work?

Also, do you have any feel for the delay in the wideband sensor response to input changes (TPS, MAP, etc)?

Thanx Craig!
Bryan

 

[Craig Smith]

Duty cycle is a ratio of the time that the injector is firing vs. the time available to fire. So, if at a particular RPM there is 15 mS available to fire the injector, and the injector pulsewidth is 7.5 mS, the duty cycle is 50%. Piece of cake.

As for the wide band deal, it can vary greatly. Most of it depends on the airflow signal across the sensor. I really couldn't say that the delay is of any particular value, but I would say that 1/4 to 1/2 second is typical in a good working system. Basically the changes need to happen inside the motor and that "new" air needs to find its way across the sensor. I think the sensor itself is rather fast. I suspect the delay is in the changes in the combustion process itself and getting an airflow signal representative of that change to the sensor element. Don't accept this as a fact yet - it's my own personal theory. It gives me a chance to use big words when addressing a worldwide audience though.

 

[carbuff]

DC = duty cycle! Ahh, the brain clicks, the gears turn...

Thanx Craig, both explainations make perfect sense now!

From all the corrections, is there any one which tells you the total amount of correction that is being applied at any given time? I know there are several listed below, as well as O2 correction, Battery Correction, etc... You said Grs correction was only the combination of ATS and CTS. So is there any sensor which puts it all together to show total correction?

Bryan