Speedo Calibration...

[Commsman]

Hey, good point Alex. I didn't think of checking it with the Cipher cable. My guess is the ECU reads real speed & modifies the speedo to be wrong.

I have a similar question about intake air temp. Cipher was saying 38 deg when outside was 14 deg as displayed on the dash.

I'm starting to get the feeling our cars are telling us lies the whole time, lol.

[PN-Mad]

Ummm... shouldn't be that wrong. I have mine after the turbo, after the I/C and smack bank in the engine bay (I'm sure you've seen where) and on cruise it only ever reads a few degrees above ambient.

Yours being smack bang at the front sucking what I thought would be cold air, I figure would be pretty close to ambient.

Maybe get a pod filter like me....

[Commsman]

  On 06/06/2012 at 9:25 AM, PN-Mad said:

Ummm... shouldn't be that wrong. I have mine after the turbo, after the I/C and smack bank in the engine bay (I'm sure you've seen where) and on cruise it only ever reads a few degrees above ambient.

Yours being smack bang at the front sucking what I thought would be cold air, I figure would be pretty close to ambient.

Maybe get a pod filter like me....

LOL, no thanks. It's nothing to do with the filter. Probably some weird correction table at work if you ask me.

If there's only one air temp sensor in the airstream, then why the 2 different readings. Remember, the in car display reads accurate....

[PN-Mad]

Should read identical unless there is some funky in plenum sensor or something. Haven't got it in Fahrenheit have you? Just thought I'd ask!

Ill stick it on Craig's car sometime, and get a reading.

[scotty nm35]

The ecu is reading spot on in mine, according to the Informeter and GPS. The intake sensor is located in the afm and is close to the exhaust so temps can get up there, if the car was cold then perhaps the sensor is out?

[Daleo]

On my informeter, the intake temp is always at least 10 deg above ambient.

Obviously it will be higher when sitting in traffic.

Averages around 10 above when at steady cruise on the motorway.

[Commsman]

  On 06/06/2012 at 11:18 AM, PN-Mad said:

Should read identical unless there is some funky in plenum sensor or something.Haven't got it in Fahrenheit have you? Just thought I'd ask!

Ill stick it on Craig's car sometime, and get a reading.

I just had a oh-oh moment, but then checked the data logs. The column header says 'INTAKE AIR TMP ©' & the temps on that particular run were 26-28 deg C. I know the ambient air was ~14 deg C so maybe that is about right - 12 or 13 degrees above ambient??

When you have it near Craig's car, it would be interesting to see if it's similar.

  On 06/06/2012 at 11:29 AM, scotty nm35 said:

The ecu is reading spot on in mine, according to the Informeter and GPS. The intake sensor is located in the afm and is close to the exhaust so temps can get up there, if the car was cold then perhaps the sensor is out?

Yep, I agree that the ECU knows the correct speed. If Alex or I get a chance to use the Cipher cable & it supports that statement (& it will), then it will be conclusive - Nissan engineers are treating us like idiots by building the optomistic speedo error into the CAN bus.

Re the air temps - where does the dash display get its temp reading from? It can't be the same one co-located with the AFM or they'd be the same (see my findings above).

And sorry to hijack the speedo thread with all this talk of temps.

[Commsman]

  On 06/06/2012 at 12:34 PM, Daleo said:

On my informeter, the intake temp is always at least 10 deg above ambient.

Obviously it will be higher when sitting in traffic.

Averages around 10 above when at steady cruise on the motorway.

OK, so that supports my Cipher readings. In the larger scheme of things, I don't suppose it really matters where the dash display gets its data....

[scotty nm35]

There is a sensor in front of the intercooler for outside temp, it heatsoaks off the radiator when you are parked. I would say it's only for the display or perhaps the climate unit?

The speedo error will be inside the dash, there will be some way of adjusting it but without translated schematics it would be difficult to find. I was hoping the Nismo dash would be more accurate, it isn't. I just use the informeter now.

[Commsman]

Ahh, OK, I didn't know there was a temp sensor there. I always figured the heat soak when parked was because it was under the bonnet.

The way to adjust the speedo is with the Jaycar kit & intercepting pin 27 at TCM (same one as used by the cruise control) so it's modified before it gets sent to the CAN.

Two things worth noting:

1) The adjusted output will be a compromise, ie fix it at 100km/h & it may read a bit low at 50km/h

2) Because the signal is changed before getting to the ECU, the ECU won't know exactly what speed you are going so it could affect the odd map table & things like the Informeter will read different (wrong). I doubt that there will be anything too noticable going on though.

[sav man]

I tested the speedo on my car and found it was pretty much perfect to 80km/h, above that it reads 10% fast. Cause it's not a linier fault, i'm guessing the ECU is being gay.