Activa Rev Limiter

[CitroJim]

I rarely take my Activa anywhere near the redline as frankly there is no need to. All the power and fun is there between 2000 and 3500 rpm for me and besides it spends most of its time tootling around town drinking petrol and warming the planet

This evening I got the in me on our local dual-carriageway bypass and gave into the temptation. Second gear exiting a roundabout, foot flat down, lag, boost, surge forward at a fair rate of knots, tacho needle speeding toward the rarely visited redline and then bouncing off the rev limiter.

When I say bouncing, that is precisely what it felt like. Not nice at all. I was expecting a gentle cut but no, it seems that it reaches just under 6500 rpmand then cuts and then goes, then cuts, then goes and so on like a very violent misfire. Is this right? Right up to this point it is smooth, lusty and even.

I noticed the oil temperature went from 80 to 100 degrees pretty sharpish but soon dropped back when sanity won over. Does it ever go though!

So is the rev limiter behaving normally? I presume it is doing an ignition cut at this point.

[DickieG]

Whilst I've never bounced mine off the rev limiter your desciption is typical of petrol engine limiters whereas diesel ones are generally very smooth to the point where the car just stops accelerating.

Have you tried super unleaded in yours yet Jim? Tesco's sell 99 RON unleaded, try it and you'll notice quite a difference

[AndersDK]

Cant believe its the oldfashion style ignition cutter. That would emit clouds of unburnt fuel.
Must be the injectors restricted against fuel admission.

I clearly remember the VW transporters we had in the danish RAF. They had the limiter to protect againts overreving. I believe these were simple ignition cutters.

[CitroJim]

Have you tried super unleaded in yours yet Jim? Tesco's sell 99 RON unleaded, try it and you'll notice quite a difference

Yes I've been running nearly exclusively on Shell V-Power for several months now and the difference both in economy and performance is very noticeable. Well worth the few pence price premium in my opinion.

An igniton cut makes sense in a turbo engine as if you cut fuel at full boost and wide-open throttle you risk running a lean mixture which would lead to possibly damaging detonation. The unburned fuel would serve to cool things down a bit perhaps?

Thinking on, My GTi does the same, it appears to misfire violently but then it runs very primitive (by Motronic standards) injection and ignition.

I just thought the Motronic on the Activa would have done it with a bit more finesse.

I won't be going there again for a good while!

[Sl4yer]

So is the rev limiter behaving normally?

I think so. All the petrol rev limiters that I've come across do this.

James

[AndersDK]

Any defintive answers on the ignition or fuel cutting method ?

[deian]

It will do this... my old bmw used to do the same, and i thrashed to daylights off that quite often. I've had it happen once in my V6 when i planted the gas in 1st position.

They will just bounce from a range of 6150 and 6250 very smoothly and very quickly, sounds like an alarm if you keep it going. And I do believe half the injectors are starved of fuel, in the bmw i think it was half the spark that was cut.

On older cars (ford sierra 1.8 it was) ... the rev limiter was in the rotor arm, the link between the middle (where the feed was) and as you all know rotor arms just spin and share out the current to the spark plugs, but if the rotor arm span too fast the force would pull a connection inside the rotor arm and it would no longer make a connection to provide the spark plugs. The limiter on these as you can imagine were a bit sudden and you just lunged forward, not nice, but fun.

[xantia_v6]

The rev limiter must cut the petrol, as on a catalyst equipped engine, just cutting the ignition would send unburned fuel into the catalyst which would very quickly cause a melt-down, especially with the rate of fuel used by an activa at full throttle.

I know that some BMWs actually restrict the air (via the throttle) to provide a smooth rev-limit. I knew someone who had one of these (M5) with a fault such that it limited at about 2000 RPM, and then when he was at this limit in second gear, it suddenly let go with full power.

[deian]

Coooool!!!

[CitroJim]

Thanks Xantia_v6 That makes very good sense! I guess there is a vast difference between running a slightly rich mixture under "limp home" mode to protect the cat and dumping lots of raw petrol into it which will go BANG in a bad way as soon as ignition is restored

[LeeDJC]

My 309 GTi used to do the same thing. When you accelerated hard and hit the limited it felt like hitting a brick wall! When it cut out, it wasn't smooth, just bounced on and off the limiter. Like a series of bangs(!)

Also it's the only car I've ever had that bounced off the limiter in 5th! (on my private runway of course!!)

Never did it with the Activa though!