Reasons for low rev limit on M52?

[ste]

Hello chaps - my M52 swap is finished, apart from a niggly problem. The rev limiter cuts in at about 4,500 rpm. She pulls very well up to there, and just when she's starting to pull harder, (as if the Vanos switches there?) the rev limiter halts proceedings.

My Carsoft diagnostic threw up 'sticking vanos', 'MAF short' and 'Speed signal'.

I took the Vanos apart as per the TIS guide for 'sticking vanos'. There were no burrs and it operates very smoothly.

I replaced the MAF.

I also replaced the SI board as the NiCad batteries were dodgy and possibly cutting speed signal to ECU. I replaced with a newer style board with the Lithiums. This has been sat on my shelf for almost a year though - so it's possibly no better than the NiCad board I removed.

I took it out for a drive and it possibly idles smoother now, it still nuts the limiter early though. I did notice on this drive that the speedo was dropping out every so often. I possibly have a damaged speed signal wire from the diff, so I'll look at that.

Is there any other reason I could be getting an early 'limp home' rev limit though?

[Jhonno]

i was gonna suggest the speed signal...

cant think what it might be other than that atm.. try asking on the e36coupe forum maybe?

[Dan318-is]

Don't you have to reset the ECU or something to get it out of limp mode (if thats what its in)

[ste]

'Resetting' the ECU makes no difference.

[Brianmoooore]

A couple of points that may or may not have any relevance:
BMW refer to the rev. signal as a (engine) speed signal, as well as the road speed signal.
The problem with the earlier SI board is that the batteries go short circuit rather than just fail, and pull down the relevant supply rail in the electronics. They also leak, and damage other parts of the circuit.
The lithium batteries don't go short circuit, and don't actually do anything when the board is connected to a car battery. They are purely there for back up purposes.

I would imagine the rev limit is part of limp home arrangements. Do you have an engine fault light connected up?

[ian332isport]

Ste,

Have you checked the fault codes recently ?

If not, I can pop round in the week and see what it's currently showing, and clear any that are there.

Cheers,

Ian.

[ste]

No - I have a dedicated 'garage' laptop now that can live in my toolbox. It's a tiny old Toshiba that looks like it was built to withstand a direct nuclear strike. Being pretty old it has the full array of ports on the back, serial, parallel, Calais, Folkestone etc... so perfect for Carsoft.

Only problem is that Carsoft 6.14 CD I bought won't install on it, even though it installs on my other laptop fine. I need to d/load a better version. I think you had the same problem with my version didn't you?

I can do the pub tonight if you like - and we can go via my house? Should only take 5 mins to get the fault codes off? I could murder steak and chips actually...

[ste]

I would imagine the rev limit is part of limp home arrangements. Do you have an engine fault light connected up?

Thanks for the tips - I haven't got an EFL yet.

I do have a spare set of clocks so I may swap this lithium board into those and try that. As you say it's possible the NiCads that were in this set of clocks have caused some damage. Even with the lithiums in I still have the red service light stuck on, even when running. Next step after that I suppose I'm getting under the car tracing damaged speed signal wires...

Ian just a thought - do you remember you put a temporary loom in to put the E36 clocks in circuit when we were trying to re-align the EWS? I don't suppose any of that remains and the ECU is seeing that loom and seeing no speed signal from it?

[ian332isport]

Ian just a thought - do you remember you put a temporary loom in to put the E36 clocks in circuit when we were trying to re-align the EWS? I don't suppose any of that remains and the ECU is seeing that loom and seeing no speed signal from it?

Ste,

No, that literally only gave the E36 cluster power and data lines. It will make zero difference to the speed signal. I'm pretty sure you still have a dud SI board, and/or a dodgy connection on the diff speed sensor that's the cause of the speed signal error.

Cheers,

Ian.

[eternalife]

I have had a similar problem...

I was having a little problem with my Fuel Gauge and decided to get a spare set of clocks to fit in...
My car is a 318is Hybrid in a 4door shell.
My clocks are dated... 1990
The replacement clocks i bought were dated 1987,

The replacement clocks would show me hitting the limiter at 4500 rpm - however, eventhough the clocks were showing 4500rpm I know for certain that the revs were at just under 7000rpm. I know this as my speed at the time corresponded to hitting the rev limiter at just under 7000rpm on my old clocks.

Therefore, unless the replacement clocks i have got are faulty - I would be inclined to think that there is a difference in clocks between the generations of E30? Maybe someone can confirm?

Not sure if this helps - but your problem does sound extremely similar to mine.

[Andyboy]

Would it be related to the traction control? Or the ECU picking up on the lack of it (like when you try to give an E46 M3 full beans on a dyno?)
Does the M52 have the two throttle discs like the M62 V8??

Can't help thinking a non EWS M50TU loom would have been a shit load easier!

[stonesie]

Therefore, unless the replacement clocks i have got are faulty - I would be inclined to think that there is a difference in clocks between the generations of E30? Maybe someone can confirm?

Not sure if this helps - but your problem does sound extremely similar to mine.

In your case i think the problem lies with the codeing plug, the clocks you have now are probably from a 6cyl car, so you need your old 4 cyl plug

4500*1.5= 6750

[ian332isport]

Would it be related to the traction control? Or the ECU picking up on the lack of it (like when you try to give an E46 M3 full beans on a dyno?)
Does the M52 have the two throttle discs like the M62 V8??

Can't help thinking a non EWS M50TU loom would have been a shit load easier!

Andy,

Ste's engine was not fitted with the traction system, so won't be the problem in this case. Could be an issue if you did get an M52 fitted with traction control. I assume it was optional, or fitted on later vehicles, but certainly not on all of them.

When fitted with traction control, they do have two throttle discs (two complete throttle bodies actually). The traction control throttle is driven from a separate actuator that's driven by the ECU.

You may be right about using the M50TU loom, but wouldn't you need to get it mapped accordingly (assuming you also use the M50TU ECU) ? It's so easy to wire the EWS system into a car that doesn't have it (assuming you get the matching EWS components from the donor), that it's not really worth the bother of changing the complete engine loom. It's also quite a nice security feature as well. The M50TU loom may be a good option if you only have an M52 long block assy without any wiring etc.

Cheers,

Ian.

[dasparkybad]

Had the same problem with my m52 rev limiter cut in at about 5200 mine was because the vanos unit was not installed correctly was not actually sticking it was not located correctly in the camshaft causing it to reach its end stop early sounds as if you have the same fault with mine i could clear the fault and drive a short time with the correct rev limit until the fault re-occured then the rev limit would drop back again

[HairyScreech]

if its stoping just when you expect the vanos to kick it could it not be picking up on your sticking vanos and trying to prevent any damage to the engine?