apicia

Can the 99-04 Mustang instrument clusters be calibrated? My cluster tells me the car is going faster than it actually is. Also, the tachometer tells me there are less RPMs than the motor is actually seeing.

The computer is seeing the actual vehicle speed and rpms verified by SCT data logging, Dyno tuning, and GPS readings.

The problem is the instrument cluster. It is just not calibrated correctly. Even after the gear change, the SCT X3 compensated for the change and the vehicle computer is reading the actual vehicle speed. Again, the cluster is not reading actual vehicle speed and rpms.

cliffyk

There is no "calibration" available, however the indicator needles can be relocated--do you happen to have an aftermarket gauge overlay?

You can use the HEC diagnostic mode to read the digital values on the odometer...

apicia

The digital values are accurate. The speedo and tach gauges are not... Just checked... hmm.

cliffyk

Are they off by a fixed amount at any speed or RPM, or is it a percentage of the displayed reading?

If the former then relocating the indicators will fix it, if the latter then there is something else going on...

apicia

Yeah, they are off by a percentage. It seems like I need drivers for the tach and the speedo. My GPS says I am going 80mph and the self-diagnostic mode tells me the car is going 80mph. It only the gauge that is reading wrong.

Is the driver for the tach and speedo in the cluster electronics or the gauge electronics? If I remember correctly, you can pull the seperate gauges out of the cluster?

apicia

Dude, and that is BS what happened to your step-daughter. I checked out your website and that must have sucked. Sorry mate.

cliffyk

Thank you, it's been over 11 years now--still sucks big time!

The gauges are all (all 6) identical stepper motors that are driven by the instrument cluster (the HEC, Hybrid Electronic Cluster) micro-controller. The HEC controller receives digital sigansl over the SCP bus and drives the gauges.

This is all firmware AFAIK--I have never heard of any updates or hacks for the HEC...

How far are they off?

apicia

They vary. At 2.2k rpm, it reads 1.8k. Then at 6.5k rpm, it reads 6k. The ratio is off.

The speedo is the same. At 60mph, the gauge tells me I am going 80mph. Less discrepency at lower speeds and more at higher speeds. Again, the ratio is off.

The electronics that read the signals being sent to the cluster are where? In the gauge or the cluster that the gauge plugs into? Some Mustangs have 120mph speedos and others have 200mph speedos. There must be different drivers for the ratios. You say it is firmware?

Again, the self diagnostic readings are all dead on!

cliffyk

2.2k-1.8k = 500 rpm;
6.5k-6.0k = 500 rpm;

Depending on how much, this may be an offset issue as well--the speedometer is not that accurate, within 4-5 MPH between 60 and 100 would not surprise me.

The PCM tune has settings for tire revs/mile and axle ratio, and a sensor on the tranny output shaft--that's all it needs to calculate the vehicle speed. The value is sent digitally over the SCP (Serial Communications Protocol, the OBD2 J1850 signals) bus, to the cluster controller. The cluster controller then supples the appropriate 2-phase (IIRC) drive signals to the gauge motor, to position the needle--this is the same as servos used in model aircraft and RC cars/boats, etc.

The tach signal is easy, it's a scaled version of the pulse rate from the crank position sensor.

They will be because they are just digital the digital values the PCM is publishing on the SCP bus displayed on the odometer.

The tach is needle position issue, the speedometer may be as well depending on how far off it is--don't expect digital precision from the analog servo motor driven gauges.

apicia

Thanks. My tuner told me he has seen many Saleens where the speedo/tach were off. Mine is a 2000. I guess when they change the cluster and/or gauges, they were not right on. My outside worry was the cluster had gone bad at one time and they swapped it for a GT cluster, reusing the Saleen gauges. The GT has a 120mph? speedometer with a different ratio than the Saleen and the Saleen tach goes up to 7k and I have seen some GTs with an 8k tach. If someone put my gauges in a GT cluster, could that account for the inaccuracy? Or, is it just an issue with the gauges as seen by my tuner? Don't know exactly what to make of it. A good thing is the computer is seeing accurate tach and speedo data.