M42 will not rev above 4500rpm

[firstE30]

1992 318ic.
car starts and idles fine. Drives beautifully around town. When I try to wring it out, it hits a clean cut out (like a rev limiter) at 4500rpm indicated on tach. Does this in every gear. This is very frustrating since the power is all up top in these cars.

my research suggests this is an ignition cut out due to a fault in Crank Pos sensor or DME.

Please help me get this sorted. Thanks.

[fresh_TD]

Try swapping in, another working DME. "Passion is timeless"

[bmwman91]

Could be crank position sensor, failing rubber bond in the damper ring, wear in the AFM's carbon track, dead/dying ignition wires and/or coil. Do you get any codes with the stomp test?

https://sssquid.com/v3/bmw-stomp-test/

[firstE30]

Update:
I have confirmed that I can hit almost 60mph in 2nd gear. Gear calculator says at 57mph i should be at 6500rpm in 2nd. This suggests the tachometer is at fault not the drivetrain. Any thoughts?

[fresh_TD]

Update: I have confirmed that I can hit almost 60mph in 2nd gear. Gear calculator says at 57mph i should be at 6500rpm in 2nd. This suggests the tachometer is at fault not the drivetrain. Any thoughts?

You do have a 7k tach in there, correct? Can you post a Picture of your cluster "Passion is timeless"

[roguetoaster]

Yes, nearly 60, but never hitting 60 in 2nd is about right with a 4.1 rear end, but you'll probably be just a bit above 6500 in reality.

[firstE30]

4.27 LSD in this car. Yes can confirm its a 7k tach. Could incorrect coding plug be the issue? What else could cause tach to read low?

[firstE30]

So pulled the instrument cluster to find it has been been swapped previously (and poorly). The coding plug I have is “BMW17”
1 385 468
7/87. 002

which appears to be a 6 cylinder coding plug. Is anyone willing give/trade/sell me an m42 coding plug? Thanks.

[bmwman91]

Good catch, that would definitely explain why the tach reads only 2/3 of what it is supposed to lol. I'll try to dig around my parts pile when I get home from work....I know I have some OBC plugs, and I might still have one for the cluster.