E30 Wheel speed input

[SamE30]

Hey guys,

I have a brand new VEMS unit. I took the wheel speed signal from the instrument cluster to the cruise control, and wired it into the VEMS wheel speed input. It works and is accurate, but intermittently it will cause a no-start, the VEMS display turns on but goes blank, no COM, and no fuel pump prime.

I have measured 5v with no wheel speed at the output from the cluster. I believe it is taken from the rear diff as a VR sensor, and then converted to a digital signal and sent to the cruise control (which is where I'm picking it up).

Should I grab it from the sensor itself, or am I missing something?

Thanks,

Sam

[DevInAz]

Did you run a separate wire? I've installed many vems on e30s and haven't had a problem using the speed sensor wire that's already wired into the dme wiring harness. off the top of my head I believe is a small all blank wire, the speed sensor wire is a direct output from the cluster. I've never experienced a no start condition because of this though.

Devin

[SamE30]

It's a blue with yellow trace.

It's from the cluster solid state to cruise control unit. I don't know why, but the 5.0v input seems to be making the VEMS unit not happy.

I'm currently getting the signal from here:




Should I get it from here, as it will just pull to ground?



Thanks,

Sam

[DevInAz]

Is your car a 85 like the pdf shows?  I didn't think about the age of the car.... The e30s I've done were later models with a vehicle speed output from the cluster to the dme itself, and that's the wire I've always used. I don't see why the cruise control wire wouldn't work though it its a digital signal. I don't believe you can use the wire from the differential unless you get a vr converter installed first. They do have the vr converters on the webshop:  https://shop.vems.hu/catalog/hall-p-162.html?osCsid=596cf40b6ed50de6007570215ac6005a

Maybe some one else like Gunni has run into this before.

Does everything work fine with that wire disconnected?

what pin did you hook to on your vems? does your vems have one or two speed inputs?

Devin

[SamE30]

Is your car a 85 like the pdf shows?  I didn't think about the age of the car.... The e30s I've done were later models with a vehicle speed output from the cluster to the dme itself, and that's the wire I've always used. I don't see why the cruise control wire wouldn't work though it its a digital signal. I don't believe you can use the wire from the differential unless you get a vr converter installed first. They do have the vr converters on the webshop:  https://shop.vems.hu/catalog/hall-p-162.html?osCsid=596cf40b6ed50de6007570215ac6005a

Maybe some one else like Gunni has run into this before.

Does everything work fine with that wire disconnected?

what pin did you hook to on your vems? does your vems have one or two speed inputs?

Devin

The car is an 85, I know the later models have a vehicle speed sensor to the DME. But from my understanding it's the same signal, if it's a pre 87 equipped with cruise control. I believe the cluster converts the VR signal to digital and sends to the cruise control.

Everything works fine with it disconnected, it will intermittently start and vehicle speed accurately will read in VEMStune. But most of the time it will mess with the ECU and not start.

My VEMS has 1 wheel speed input, it's connected at EC-18 Pin 8.

Here is a late model diagram. Only difference is there is another pin from the same solid state speed output for the on-board computer.



Thanks,

Sam

[VEMS]

Hello SamE30,

The speed input connected to the cruise control output on the e30 dash should work without a problem; Are you sure it is not providing 12v to the wheel speed input ? If so (but it is also a low-side switch) you could try adding an inline diode from rescuekit (stripe towards the dash side of the wire) to insulate the potential positive current inflow towards the v3.

Best regards, Dave

[SamE30]

I have measured 5.0v with the key on, and no wheel speed input. to the cluster. I don't know if the voltage increases as the frequency changes, but it shouldn't. I will add a diode and reply back.

[gunni]

It should be 5v if its between to ECU boxes. i.e speedo to cruise control or ecu.

I would ideally try and scope the signal to see whats happening,

[SamE30]

I wired the diode with the stripe to the dash side of the wire, when connected the ECU turns on no problem, but it doesn't read wheelspeed.

Sam

[SamE30]

Is there some sort of current flow towards the VEMS from the speed sensor?

Anyone else have any ideas?

[gunni]

Is this for launch control?

If so I reccomend a ABS sensor up front and a VR converter from the store then wire to ECU, this way you are never reading wheelspin just actual road speed

[SamE30]

Is this for launch control?

If so I reccomend a ABS sensor up front and a VR converter from the store then wire to ECU, this way you are never reading wheelspin just actual road speed

It's for boost by gear. I can't wire up front ABS sensors, my car is a early model without them in the front.

I'm pretty set of getting this to work, does anyone else have any ideas?

[gunni]

Can you scope the output from the dash by any chance to see what its spitting out?