Adjusting MotoMeter speedo without the square wave generator

[estoguy]

Hi guys and gals,

Is it possible to just just adjust a MotoMeter speedo by turning the trimpot and going by trial and error with GPS, instead of the square-wave generator. I had read a post somewhere about this, but can't find it anymore.

Does anyone know which direction adjusts the speedo up/down when you turn the trimpot? Knowing this would make the job easier.

Right now, my speedo is showing 15-20KM/H faster than actual speed.

Thanks!

[IS300E30]

Bump.

Would like to know as well

[nando]

I'm sure it's possible just a lot more frustrating.

you could just adjust it one way and see how it responds, 50/50 it will be up/down.

[crazyman]

Is the needle itself lined up correctly with the stop mark?

[bmwstudent]

Are you sure the sending unit isn't faulty?

[crazyman]

It sounds like the needle was taken off of the gauge and not lined up properly when it was put back on. Cus if the sending unit in the diff is bad the speedo will not work. I thought I had a bad one as well and BMW technician I called and talked to said: the e30 speedometer signal system in short is so simple that it'll go from working perfect to nothing at all, no intermittent BS stuff, and because it's a simple setup very rarely do they actually fail. That's what I was told, almost to the point.

[FLG]

I made a simple circuit and adjusted mine using a computer. I offered a service and there was no interest, ill PM you with how to do it yourself. Ill prob just make a DIY cause it looks like i wont be making any business LOL

[bmk]

bumping this old thread. Doesnt anyone have expierence with adjusting the trimpot? Is R or L turn the speed down. Mine it probably around 10mph off it not more

[estoguy]

Well, I did mine by just adjusting the trimpot, then going for a spin and using my phone's GPS and the MyTracks app (Android). Now I am running slightly smaller tires than stock - 185 65R14. I have found that after my adjustments, the speedo is accurate up to around 105 km/h. Once I hit 110, I'm about 5 KM/H over. 120 is closer to 130, but I rarely get up to those speeds, unless I'm in a hurry, and if I am, I'll flip on MyTracks to double check my speed to avoid getting a ticket. I'm guessing that the tire size is throwing off the speedo at the higher speeds.

I forget the directions for adjustment now... but its easy enough to figure out.

[guibo09]

I haven't done it myself yet, but plan to at some point.

Theoretically you should have two errors to correct, offset and bias. Offset is needle placement and is corrected manually by moving the needle. Bias is the multiplier that converts the sensor signal to speed and is corrected by the trim pot.

Proper way to adjust would be to take several readings at different speeds with your gps. Then plot that in excel against the speedo reading. Fit a linear curve to it and get the equation which will be y = bias*x + offset.

Then I would straight away correct the offset error based on that value. Then tweek the trim pot for bias correction. To reduce trial and error, you can measure pot resistance and plot that against your bias error. After a few tries, a trend line through this data will show you which resistance is correct.

The reason your speedo is still off at higher speed is because you are correcting both error types with only bias adjust. Will never be right.

[FLG]

It's really simple to do at home. I wrote up a pm to someone I'll try to find it. All you need is a cap, multi meter and a set of decent speakers.

[guibo09]

It's really simple to do at home. I wrote up a pm to someone I'll try to find it. All you need is a cap, multi meter and a set of decent speakers.

Can't wait for this diy!

[rzerob]

I might try this, I am so use to my E30 speedometer being 10% faster, it doesn't effect me anymore.