Coding Plug Mod E30M3

[TSAF]

As the E30 M3 is a four cylinder car, the signal on my tachometer is all wrong with a 6 cylinder S52 engine. I swapped the coding plug for an e30 6 cylinder version easily enough, but these only have a 0-7000 rpm scale - so still isn't accurate with the m3 tacho.
I read somewhere that the e28 m5 uses a 0-8000 rpm tacho and of course this car has a high rev six cylinder engine. What I am hoping is to find an e28 m5 coding plug, remove the voltage-frequency converter, and fit it in place.
Has anyone bought an E28 M5 coding plug, opened the case and fixed the guts to the M3 cluster?
They say that this is the cure for accurate readings when you run a s52 engine and use the original E30 M3 cluster. But again there are rumors one guy says it works another says no.
Any ideas?

[UweM3]

just buy the DAKOTA unit as suggested on s14.net

[TSAF]

I already gave the order for the dakota digital but still I am not sure it will do the work properly.

[GeoffBob]

I read somewhere that the e28 m5 uses a 0-8000 rpm tacho and of course this car has a high rev six cylinder engine. What I am hoping is to find an e28 m5 coding plug, remove the voltage-frequency converter, and fit it in place.

TSAF,

There are a number of ways to skin this cat, but first you need to understand that a BMW coding plug is a device that outputs a voltage that is proportional to the number of pulses it receives per second from the ECU ignition output. The faster your engine spins, the more pulses it counts, the higher the output voltage. It is, effectively, a frquency-to-voltage converter. Your tachometer, on the other hand, is simply a voltmeter that is graded in RPM.

Now, with the four cylinder coding plug in place your tacho will read 1.5 times higher than actual because the frequency to voltage converter will "interpret" 4 spark events to indiate 2 rotations of the crank. Whereas the job of the six cylinder coding plug is to interpret 6 spark events to indicate 2 rotations of the crank.

One way you can solve this problem (at least in part) is to simply "scale down" the output voltage of the frequency to voltage converter using two resistors to create a 4/6 voltage divider. This will lower the voltage fed by the coding plug to the tachometer by a factor of 2/3, and the tacho will therefore read 4000 RPM where it would have previously read 6000 RPM.

While this solution is very simple, the coding plug "runs out of voltage" around 5000 RPM, causing your tachometer to have an artificial limit imposed upon it (even though you can hear your engine revs rising, the tacho appears "stuck").

So, another way to solve this problem is to use a standard six cylinder E30 coding plug, but this time to use two resistors to create a 8/7 voltage divider. Your tacho will then read 4000 RPM where it would previously have read 4570RPM.

Both solutions unfortunately require that you cut into the line that runs from the coding plug to the tachometer.

Of course you can always fit a coding plug from an E28 M5 if you can find one.

To learn more about frequency-to-voltage converters download the LM2907 datasheet here. See page 8 for a typical tachometer circuit. If push comes to shove you can just use an LM2907, but lets not go down that route unless you are proficient to do so.

Let me know if you wish to investigate any of the above options and I'll post further details. Fitting the coding plug from the M5 is, however, by far you simplest solution.

Hope this helps.
Geoff

[Jhonno]

I read somewhere that the e28 m5 uses a 0-8000 rpm tacho and of course this car has a high rev six cylinder engine. What I am hoping is to find an e28 m5 coding plug, remove the voltage-frequency converter, and fit it in place.

Of course you can always fit a coding plug from an E28 M5 if you can find one.

Hope this helps.
Geoff

£20 from BMW..

[TSAF]

Now its to late I placed the order to DAKOTA.

[GeoffBob]

I read somewhere that the e28 m5 uses a 0-8000 rpm tacho and of course this car has a high rev six cylinder engine. What I am hoping is to find an e28 m5 coding plug, remove the voltage-frequency converter, and fit it in place.

Of course you can always fit a coding plug from an E28 M5 if you can find one.

Hope this helps.
Geoff

£20 from BMW..

10p for two resistors. Do the math.

[Jhonno]

I wasn't knocking your suggestion, I was merely pointing out where you could find one..

[GeoffBob]

Understood. I apologise.

[TSAF]

The order has been placed. I will let you know about the result.

[billgatese30]

I used the e28 M5 plug, I think it was about £23 from the dealers,

Your suggestion sounds like an ingenious and cheap way around it Geoff, but for me it works out more cost efficient to go into work for an hour's overtime and spend half an hour fitting the M5 chip than spending 2 hours doing mods to the cluster.

[UweM3]

I used the e28 M5 plug, I think it was about £23 from the dealers,

Your suggestion sounds like an ingenious and cheap way around it Geoff, but for me it works out more cost efficient to go into work for an hour's overtime and spend half an hour fitting the M5 chip than spending 2 hours doing mods to the cluster.

you also have to decide what you really want. I precise working rev counter or guess work.

What I can't get it that he already has ordered the Dakota (after posting same question on S14.net with more or less the same answers/advise before posting here the same again) and still keeps going on about using a different coding plug.

[GeoffBob]

you also have to decide what you really want. I precise working rev counter or guess work.

No guess work in what I suggested Uwe. Don't knock what you don't understand. To learn more about frequency-to-voltage converters download the LM2907 datasheet here. See page 8 for a typical tachometer circuit.

[UweM3]

you also have to decide what you really want. I precise working rev counter or guess work.

No guess work in what I suggested Uwe. Don't knock what you don't understand. To learn more about frequency-to-voltage converters download the LM2907 datasheet here. See page 8 for a typical tachometer circuit.

pack it in please. Not all off us have the time to study electronics in the evening. Some of us have a busy live and enough on the cards already.

And I didn't knock anything. As long you don't understand electronics fully it's trial and error. In the time it takes me to read the datasheet and just to get all the components and solder something together I have earned more money in my job enabling me to buy one which works.

If you like to play and have some spare time, fair enough.

[GeoffBob]

Some of us are in this game for the pleasure of learning and doing, Uwe. It's not always about money. If all I wanted was to get my car fixed I'll pay a mechanic. If I want to learn something I'll do it myself.

And who the f*ck are you to comment on the quality of my posts. I answered the OP, not YOU. If you don't like what I have to say then ignore it or respond with a reasonable counter argument.

I suggest this: In future you refrain from trolling my posts and I won't feel the necessity to comment back when you describe my tachometer as "guess work".

[suzie650]

One detail, as I've looked into it as well for my car:

It seems that even with an M3 counter and a 6 cylinder plug, the counter is still about 10% off the correct scale. (source e30.de) Don't know about e28 m5 at all though. (does the coding plug even fit the e30 counter?)

Without looking at the datasheet, I suppose that the crank sensors are slightly different.
The dakota unit takes this into account. If you want to work out the difference between both yourself, you certainly can but the simple division of pulses is not good enough.

(Same problem with my car, divide the voltage by 2 from the V8 to a 4 cylinder plug doesn't work properly, I tried.)

Just my 2p.

[billgatese30]

does the coding plug even fit the e30 counter?

You have to remove it from the casing and just insert the PCB into the slot, carefully engaging the pins without damaging them, but its not too fiddly if you have a fair level of dexterity.

[UweM3]

Some of us are in this game for the pleasure of learning and doing, Uwe. It's not always about money. If all I wanted was to get my car fixed I'll pay a mechanic. If I want to learn something I'll do it myself.

And who the f*ck are you to comment on the quality of my posts. I answered the OP, not YOU. If you don't like what I have to say then ignore it or respond with a reasonable counter argument.

I suggest this: In future you refrain from trolling my posts and I won't feel the necessity to comment back when you describe my tachometer as "guess work".

where have I answered YOUR post??

just for the record, I have answered the OP before you showed up. So much for trolling. I am surprised that somebody with your integrity requires such colourful language to get his point across.

And if you can't stand some criticism then don't force yourself into each posting you can find.

I have an interest in this matter myself. Remember I am fitting an S50 and need to convert my rev counter as well. Where is your interest in this posting?

[taper]

I used the e28 M5 plug, I think it was about £23 from the dealers,

Your suggestion sounds like an ingenious and cheap way around it Geoff, but for me it works out more cost efficient to go into work for an hour's overtime and spend half an hour fitting the M5 chip than spending 2 hours doing mods to the cluster.

Have you the item number to buy one's?


Thanks

[suzie650]

does the coding plug even fit the e30 counter?

You have to remove it from the casing and just insert the PCB into the slot, carefully engaging the pins without damaging them, but its not too fiddly if you have a fair level of dexterity.

interesting! And the old M88/S38 uses the same crank sensor? (i.e. exact revs shown?)

And would you have a picture of the stripped PCB?
(i.e. wondering if the e34 one would work for my M60)

Cheers!

[billgatese30]

code is B62.11.1.377.657 Cost is £24.81

[suzie650]

star! Thanks.

[billgatese30]

Well, I'll have to give credit to theo325 for the picture, I just stole it from a PM he sent me a few weeks ago

[suzie650]

obviously serving other purposes as well on the e34!

RealOEM Linky, part N°16

[billgatese30]

It was never used on the E34

It was only used on the E28 M5 and the E24 M635CSi



http://www.realoem.com/bmw/partxref.do?part=62111377657

[TSAF]

I bought the SGI-8 Tachometer Interface Unit from Dakota Digital and now the tachometer (tis extremely accurate but the speedometer and the oil temperature are not. When I first bought the car the previous owner had installed the instrument cluster from a E36 M3 (attach #1) in order to avoid problems such the ones I am facing now. The point is that I didn't like the panel from the E36 therefore I found a 320km cluster from a E30 M3 dealer in Germany. Originally I was going after the original 260km but then I thought that since my car is a lot stronger and faster the 320 will look better. Yesterday I took the car for a spin on the highway. I was going next to my friends E46 M3 on 5th gear. His cluster was showing 140km/h and mine was showing almost 200 km/h. I called my mechanic and he started telling me the same things that I shouldn't have changed the cluster and there is nothing we can do. I believe that there must be a way to have accurate readings on the speedometer as well. How can I fix this kindly help me out over here because I am getting desperate and so far I have spent a lot of money for the instruments. PLEASE HELP ME OUT!!!!!!!!!!!!

[Theo]

Your speedo is probably inaccurate because it's a standard instrument with a silly 320km/h gauge face fitted, so the scale is all wrong.

[TSAF]

Your speedo is probably inaccurate because it's a standard instrument with a silly 320km/h gauge face fitted, so the scale is all wrong.

As you said the speedo is inaccurate at the moment. The gauge face though is not a sticker. The cluster is an original E30 M3 item. Any ideas what can I do?

[Theo]

Unless the speedo unit has been recalibrated, then it will not work accurately. The original gauge face goes to 260km/h this one is 320km/h, the difference in scale is why it's hugely over reading.

[TSAF]

How can I post a photo of the cluster in order to take a good look at it. How can I recalibrate it. I talked to my mechanic who is a BMW specialist and told me that there is no way to recalibrate it. Any ideas?
Cheers Dimitris

[suzie650]

320km/h on an E30 instrument cluster is just gay. When you drive over 230, it already feels like the car is going to take off.

That being said, this (or similar devices) might help you in this case.

[GeoffBob]

Speedometer circuit includes a trimpot for calibration purposes. Best adjusted with the instrument cluster opened with the car on a dyno. Not the sort of thing you want to fiddle with while trying to drive.

[TSAF]

Speedometer circuit includes a trimpot for calibration purposes. Best adjusted with the instrument cluster opened with the car on a dyno. Not the sort of thing you want to fiddle with while trying to drive.

Thanks a lot for the advise.

[eta]

I have fitted a 325i coding plug chip to an E28 coding plug and the guages work well (in an effort to get the OBC to read correctly which it didn't no matter what OBC coding plug I have used). I have used a widget from seattle circuit to calibrate the OBC and that works reliably too. So the reverse would have worked and E28 M5 coding plug chip on an E30 coding plug board.

[jaistanley]

I emailed Seattle Circuit but couldn't get a response... I'm after an OBC correction circuit so my OBC and swingometer work (I have an S50 engine in a 325iSE).

How did you get hold of them?

Jai