E30 rev problems and back box blown!

[ThreeDLee]

My car will not rev over 4,500 revs, I thought it might be a blockage so I kept the revs up and it ha blown a massive hole in the side of the back box! And it's like new, still not reving over 4,500 revs either! What would cause it to blow a hole. I'm thinking there is a air of petrol problem restricting it from building up the revs.

Help

[Grrrmachine]

Some idea of what engine you have would help the diagnosis considerably.

[ThreeDLee]

M20 320i 1984 auto

[Speedtouch]

My first E30, a 1984 320i, had the same problem after I got Halfords to fit a new cambelt - I think they accidentally fitted it one tooth out, so check your timing.

Also check the rotor arm, which has a built-in centrifugal rev-limitter underneath - if the spring has gone weak, it will cause such an issue.

It can, in any case, be dispensed with, since the ECU has it's own built in rev limitter which operates in a smoother manner.

[ThreeDLee]

Hi, thanks for your help, I understand the first two points but not the ecu bit, should I unplug the battery to reset ecu? And if I get a new rotor arm will it have that spring you talking about?


Thanks

[Speedtouch]

No, the pre-facelift 320i had the analogue L-Jetronic ECU, so no need to disconnect it and reset it like a later facelift digital Motronic one.

However, check the rotor arm - just pull it off and check the operation of the spring switch underneath.

A new rotor arm should have the spring; you only need to replace it if the contact tip is badly eroded.

But like I say, the spring switch can be discarded, since the ECU already has a built in rev limiter, which cuts in at around 6,250rpm, and doesn't brutally cut the power at 6,000rpm like the rotor arm centrifugal rev limiter does.