91 318is rev limiter help!!

[dwf08]

I've had this car for about 6 years and haven't had much problems with it but I just recently started to drive it again on a daily bases and it used to hit the rev limiter around 6 or so and today I noticed it acted like the rev limiter was around 4300 to 4500 the only thing I've done to the car recently was change the speedo cluster it came out of a 1990 325 any help would be thankful.

[Nelson_40]

Isn't there a coding plug that might be needed to get the signals right? This may not be quite right, but I remember something about that. Further, does your engine FEEL like it is not reaching the proper rev limit?

[dwf08]

feel like its just starting to pull good and hard then it hits it. if that makes any sense to you what would i look for on that coding plug?

[Geoff]

I think you should remove the coding plug from your original cluster and plug it into the new one.
                                                        Geoff

[Nelson_40]

feel like its just starting to pull good and hard then it hits it. if that makes any sense to you what would i look for on that coding plug?

Sounds like business as usual for a stock M42. The fun comes on hard and hits a brick was just as hard. I suppose if you really needed to you could hook up an induction

Quick and incomplete coverage of this topic on M42 Club, but it does show coding plugs. http://www.m42club.com/forums/showthread.php?t=10006

And more coverage from M42 club. http://www.m42club.com/forums/showthread.php?p=65964

[DesktopDave]

Definitely the coding plug in the front of the cluster.  Swap it out and you'll be fine.  Your tach is misreading the coil signal input from the Motronic ECU.  The tach sweep calibration is determined by a number burned into that chip (also the speedo, fuel tank level and coolant temp range).  

So the cluster is assuming that you're firing six spark plugs every other crank rotation.  Our M42 only fires four plugs every two rotations.   Thus your tach will read exactly 2/3rds of the actual engine speed...given that Motronic kicks on the rev limiter at 6300 on a stock M42, you should feel it cut out at 4200rpm indicated.

Why it doesn't read off the crank wheel or one specific plug is totally beyond me (likely a fail-safe design or due to the COP setup), but that's the way it was made.

[dwf08]

Thanks for all the replys i never would have thought of something like that but i geuss thats what this site is for thanks guys

[dwf08]

Ok so I changed the coding plug and tach is working but the gas gauge is still not reading right but did before I changed the cluster Ido wats going on anyone got any ideas

[DesktopDave]

Some of the gauge clusters are set up for the larger 66L fuel tank's dual senders.  Only the late 325I and 325IS models had those tanks here in the North American market.  IIRC you should swap the fuel gauges from one cluster to another.  I think the gauge's resistors are different so it'll read incorrectly with a single sender tank.  They're plug and play - take out the screws and then just wiggle them out of the circuit board from the front.

I don't think the clusters have any other major differences.  FYI some early clusters use a different style of coding plug and all the eta's have a low-RPM tach.  M3 clusters have an oil pressure gauge instead of the MPG meter.

While you're in there you should definitely check the SI board batteries and maybe test all the light bulbs.

[dwf08]

Would the si batteries make the oil change lights not be on? Or what do they do is what I guess I'm trying to ask

[monty23psk]

The gas gauge is independent from the tachometer circuit. You might have a loose ground nut on the back of the gauge.

[dwf08]

the gauge works but was jus reading half a tank when about empty