OK couple of teething problems

[Ellisd]

Gauge is installed and I think working correctly.  However a couple of reading seems slightly out.

AFR - On idle and cruise the AFR jumps around between 14.7 up to 15.3 and watching it on mega tune it almost looks like 15 is the target instead of 14.7.  Is this just a calibration problem of the narrowband signal?  (i'm using VEMS to control my stock lambda.

RPM - the RPM is roughly double what the rev counter on the dash shows.  again i'm hoping this is becuse it needs setting up in megatune. i've messed about with the values in the RPM menu but i don't really know what i'm adjusting.

UPDATE

battery went flat on my laptop, now megatune won't connect to the gauge.  Mentions something about not being able to connect to the com port.  I've tried all the setting in windows and megatune, still no joy.  Is there a way of resetting the gauge?  I've checked that it's not set to off line.

[rob@vems.co.uk]

I'd not be supprised to see readings around 14.7 and 15.3, it is best to look at Lambda values.  A normal ECU uses the fact that the narrow band switches at lambda 1 (14.7) to control the closed loop fueling - when the lambda sensor reads less than 1 it reduces the fuel, over and it increases the fuel.  So you see rich, lean, rich, lean, ... , rich, lean.
On average you should see 14.7, but as has been discussed the Bosch is a Lambda sensor, and AFR is a multiplication of Lambda.

Connection problems are a pain in the arse to sort out, are you using a USB to RS232 adaptor?

[Ellisd]

The lamda value is slightly over 1.  Of the top of my head it swings around 1.02, so on cruise or idle it swingts down to 1.00 and up to about 1.03/4 (so follows the same pattern as my AFR).  I was just wondering if the Narrow signal getting sent to the ECU was a tiny bit high and if their was a way of reducing it slightly?  The free air is spot on, and if i remove the narrow band signal to the ecu it richens up to around 13:1  AFR. Sorry i didn't think to take down the lambda value  .

I am using a USB adaptor but it was working prior to my laptop going dead.  I borrowed a friends laptop which has a com port and i still couldn't connect again.  I'm going to re-check my wiring as i had to extend the PC cable to get it to the centre console.  Could you tell me what colour cables go to pins 2,3& 5?  If memory serves me white went to 5 but i can't remeber the other 2

[rob@vems.co.uk]

It is possible that the voltage is a little high - we are talking millivolts here, on this graph you can see how the narrow band switches from a ~900mV to below 200mV at Lambda 1.0 (stoichiometric burn)


You can pull-up/pull-down your narrow band output following the Analogue output connection section of the User Guide:
http://www.vems.co.uk/VEMSWB/UserGuide/README.html
It might be an idea to try pulling it down at first with a straight ground to ground connection (pin 9 to ground wire), then pull-up tests should be started with a very large resistor, or trim pot.

As for the serial port looking on an old dead gauge I have:
Pin 2 - Red
Pin 3 - Green
Pin 5 - White (Note that the shield wire is twisted onto the white wire).

[Ellisd]

Thanks mate i've sorted the3 connection problem, a soldered joint had broke.  I'll have a go at adding the the ground wire to pin 9. 

Any idea on what i should do with thr RPM issue?

[rob@vems.co.uk]

The RPM divider is the next thing to look at.

[Ellisd]

Hi, Rob, i've had a play about with the RPM settings and got it somewhere near (but not spot on).  The lambda reading are better now i've grounded pin 9, thanks .  I'm going to have a go at wiring in boost at the weekend.  When i 1st tried, it sent the gauge funny so i've got a variable resistor to have a go with.

[rob@vems.co.uk]

Good stuff, I hope you have fun with it.