Econometer

[amiller360]

Trying to workout some gremlins while my car is sitting in the garage. Currently working on cruise control and cleaning up engine bay.

Right now trying to get the MPG gauge to work properly. I believe there is a signal going to the OBC and then feeding to the gauge on my cluster since the gauge will move from 40 to 0(ish) when the car turns on. It will also spike to 40 and go back down to 0(ish) if I get close to killing the car.

The OBC reads 5.9 MPG (doesn't fluctuate at all). If I stop moving (at idle) and hit the OBC AVG MPG reset it will go to dashed lines. As soon as I start rolling it will jump right back to 5.9 MPG.

I've looked into the fuel signal converter that SeattleCircuit offers (http://www.seattlecircuit.com/fuel_signal.htm). Is that all I need to make this work? Or are there more pieces to the puzzle? Any thoughts or insight is appreciated.

[justin_l_]

Pretty sure that is all you needed. I bought one a while back and still haven't installed it so I'm not 100%

[Coupelx]

it should function normally with a 24v swap, it just wont be accurate.

[nando]

www.seattlecircuit.com is owned forum member hoveringuy.

buy the convertor, enjoy perfectly accurate OBC/econometer.

of course, yours should read a little better than that. are you sure you hooked up the MPG signal from the DME to the car? it goes through the C101.

[spiftacu1ar]

are you sure you hooked up the MPG signal from the DME to the car? it goes through the C101.

This. The behavior you describe is exactly what I experienced before I added the necessary wire. For mine, I had to go from c101 to a 3 pin connector above the glovebox. Now it works, but not accurately (17lb vs 14.5lb injector). You need to buy that device if you want it to be accurate.

[amiller360]

So the swap was done in 1997. I'm still working out all the gremlins from over the years. I got behind the OBC and this is what I found.

I found the 3 pin connector with the yellow/white wire.


It leads to another 3 pin that's above the ECU (labeled 83)


Here's a yellow wire pin that comes out of the OBC that's not connected (is this what I'm looking for?)


Also an interesting find. A purple/grey wire spliced to a black/purple wire via a white/painted yellow wire. This one is coming from the DME.


Been trying to make sense of some wiring diagrams, but would like some outside input. Thanks for your responses so far.

[e30rapidic]

pick your year

http://wedophones.com/BMWManualsLead.htm

[amiller360]

Thanks! I've determined that the yellow pin on the back of the OBC is the econometer input. I feel like I've gone over the 95 525i DME wiring chart and can't seem to find the fuel rate output anywhere.

The 3 pin yellow/white wire simply pegged the MPG gauge to 40 and the OBC to 99.99...

[nando]

The econometer input goes to the cluster, not te obc. The cluster sends a signal to the obc.

[amiller360]

Okay I pulled the cluster and found the yellow/white wire coming out of the back of the cluster. Still leaves me a few questions:
1. It seems odd that when I connect the yellow/white wire to the back of the OBC to that yellow plug that BOTH the MPG gauge and OBC change readings. Unless it's just 12v that would cause that it's the only wire I've been able to get any movement out of.
2. If the econometer signal needs to come from the DME to go to the cluster (to that yellow/white wire) I'm still unable to figure out what wire that signal comes from out of my 95 e34 DME.

[e30rapidic]

Unfortunately you have different colored wires spliced in making it tougher but this is how I wired mine - 87 325i with a 95 S50

fuel rate output is white/black (pin 24 on the e36 connector), goes to the red/yellow wire of the c104
pin 14 on the e36 connector (black/white) goes to the black wire of the c104
pin 20 of the e36 connector (black) goes to the wire on the back of the instrument cluster in the circuit board with the green covering that snaps onto the cluster.

[amiller360]

I tried many different combinations of pins and connections and none seemed to work.

I ended up just splicing a wire from the yellow/white wire in C1 on the back of the cluster to one of the negative leads of an injector. Works great now!

Thanks for all your input.