Road Speed Signal

[e30sh]

I know it is needed on OBD2 M44 and OBD1 M50's to control vannos, Does it control upper RPM maps or do anything other than control top speed on an e30 M42?

[bmwman91]

Motronic 1.7 does use road speed as an input to make some switches related to idle, O2 feedback and (I think) some amount of map selection. As far as top speed limiting, I am not sure if that is a thing in these cars.

[e30sh]

Sounds like I should wire that in. My car was an early 6 cylinder car when it started life and that wire is missing in C101. Can I source any port on the green cruise control add on plug to get a speed signal to the DME?

I was hoping all it did was limit top speed.. From other sources, the late e30's did have a top speed limiter. The 525 i DME comes to mind.

[bmwman91]

I am not super familiar with the signal routing, but the wiring diagrams on this site have decent detail which shows the connections form the speed sender to the cluster, inside the cluster, and from the cluster to the DME.

http://www.armchair.mb.ca/~dave/BMW/e30/

It seems to be down now, hopefully temporarily. If you tell me what year(s) you need diagrams for, I can try to attach the copies of the PDFs I have.

[e30sh]

I use the ETM from a 92 318 vert. The 91 318 version online is a preliminary copy and is missing some bits.

The 92 318 copy shows C2 pin 10 to C101 pin 14 to DME pin 73. I haven't pulled my cluster yet to see if C2 pin 10 is even in my harness (87 e) I would rather use the green add on plug for a speed signal versus fishing in a wire to C2 pin 10. All I own is a DVOM. No scope to see if the C2 pin 10 signal is the same as the green add on plug.

[bmwman91]

The green connector is C3, for the OBC correct? If so, then you are fine pulling the speed signal from there. Page 6210-0 of the 1992 ETM shows that the speed signal output from the cluster is all from the same source for the DME and OBC, so tapping into the OBC signal would be fine.

[e30sh]

The green connector is C3, for the OBC correct? If so, then you are fine pulling the speed signal from there. Page 6210-0 of the 1992 ETM shows that the speed signal output from the cluster is all from the same source for the DME and OBC, so tapping into the OBC signal would be fine.

I know cruise taps into that green plug because my car has it. It only has the 6 button OBC so no need for a speed signal on that. Not sure if the fancy OBC taps in there.

I just wasn't sure if the green plug output signal was identical to C2 pin 10 since I am scopeless.

[bmwman91]

C2.10 and C3.26 are on the same line inside the cluster, so it seems fine to use either one for the DME.