e30 tach with s50 engine

[TWRViper]

Hey guys,

I need some input. I bought e30 325 with a s50 swap from a 1995 m3. However, the instrument cluster is from a e30 m3 (it says m3, and has the oil temp instead of the mpg), but the tach face (paper markings) looks like it is from an 325i since it goes to 7000 with a redline at 6500.

When i got the car it had a 4 cyl code plug so the tach would go much higher than redline. I swapped to a 325i 6 cyl code plug and it works much better.... However, the revlimiter is set between "6500" and "6700," depending on the gear, according to my current tach setup.

The car might have been chipped. What should be the stock and chipped redline and revlimiter for an s50? Somehow I got the impression it was 7000/7200rpm?

Does it sound like my tech is reading too low? Do I need to get the m3 8k tach faceplate to replace my 7k faceplate?

Thanks
Tom

[1990m3]

don't know about stock but with my conforti chip the redline is 7000RPM. I have a 318is with a 6-cylinder coding plug and the tach is accurate.

Good luck

[TWRViper]

Anyone do a swap to a e30 m3 cluster? Did you have to swap code plugs and tach faces?

[TWRViper]

what is the revlimiter on the s50? stock and chipped? (probably depends on the chip, but it would give me a ballpark of what to look for)

[TWRViper]

Are the 318i code plugs interchangible with the e30 m3 code plugs?

[Rev Engineer]

Stock s50 redline is 7200 in 1st gear, but otherwise 6500. Conforti chip redline is 7000rpm (I assume it allows 7200 in 1st?). I think the dme uses the road speed signal to control the 1st gear rev limit.

I'm using the stock e30 m3 cluster in my conversion. I'm working on a converter to down convert the tach signal from 6 cyl to 4. I actually just got to test it out today and it's working great off idle, but the tach jumps around at idle. I probbaly need to tweak the software or cirucit and it should be working better. If there is any interest in this, I can post some more details and/or offer to sell a few circuit boards once I get it tweaked a little better.

[Rev Engineer]

Are the 318i code plugs interchangible with the e30 m3 code plugs?

I imagine they are not. I believe the coding plugs sends out a blurp of data about the tach range and the number of cylinders- among other things. If the tach range of the 318i is the same as the e30 m3 than it proabbly will work, but I think they are different.

[TWRViper]

Stock s50 redline is 7200 in 1st gear, but otherwise 6500.

When you say redline at 7200, do you mean rev limiter? My Mazda MX6 has a redline at 7000 but the revlimiter doesn't kick in until ~7500. (I try not to take it up that high)

[Rocla]

Plug from a car with right amount of cylinders will give right tach reading. A plug from a car with same cc/m injectors will most likely to give right MPG reading.

[TWRViper]

Plug from a car with right amount of cylinders will give right tach reading. A plug from a car with same cc/m injectors will most likely to give right MPG reading.

But I have a e30 m3 cluster with a 325i 7k faceplate and a 325i codeplug. 7k on the e30 m3 faceplate and the 325i faceplate are slightly different. If I remember correctly I think that 8k on the e30 m3 faceplate is in the same location as 7k on the e30 325i faceplate.

So I'm trying to figure if I need to swap back to the 8k m3 tach faceplate?

Thanks

[Rev Engineer]

Coding plug alone does not necessarily work. I tried a 6 cyl coding plug from a 325e and the tach was way off. I've heard people comment that the 325i coding plug in the e30 m3 cluster works ok, but it is still off. I have to think that the tach units between the 325i and e30 m3 are the same, but the faceplates are different.

FYI - The tach in the late model e30's use some type of quadrature pwm. The entire tach range is divided into four quadrants/coils and a chip on the SI board modulates one of the four tach coils at a time. ie - one coil is pwm'ed up to say 2000rpm and after that a second coil starts being pwm'ed up to another rpm and so on. I looked at this as a possibility to correct the tach, but it would extremely difficult to modify the signal between the SI board and the tach. The same also applies to the late model coding plug. It would also be extremely difficulty to modify or reverse engineer the coding plug. Best bet for us e30 m3 folks to have an accurate tach is to modify the signal from the engine to the cluster.

I should comment that our tachs are not necessarily accurate. I've been testing mine on the bench and found it to be a few hundred rpms off between ~1500 and 4000. At around 5k it's very accurate and falls back off a couple hundred rpms around 8k. I suspect every tach is a little different.

[Rev Engineer]

When you say redline at 7200, do you mean rev limiter? My Mazda MX6 has a redline at 7000 but the revlimiter doesn't kick in until ~7500. (I try not to take it up that high)

I ment to say revlimit.

[X2theZ3]

Yes,

the problem here (with the e30 m3 cluster) lies in the different faceplates. Swapping the coding plugs help a bunch but doesnt make the tach completely accurate.

[Van Westervelt]

Has anyone tried like an e28 or e34 m5 plug? That would be a coded plug for a 6 cyl and a 7k redline on an 8k tach would it not? That plug if it fits should make the e30 m3 tach accurate. Right?

[X2theZ3]

Has anyone tried like an e28 or e34 m5 plug? That would be a coded plug for a 6 cyl and a 7k redline on an 8k tach would it not? That plug if it fits should make the e30 m3 tach accurate. Right?

Yeah,

that idea already crossed my mine. I looked it up, and I believe that the coding plug won't fit in an e30 tach.