revs topping out at (indicated) 5,500

[mgaut]

During some 'spirited' driving this morning, the engine seemed to be hitting the rev-limiter at an indicated 5,500 (or so) RPM.

It's been on the rollers twice, and whilst I can't put my hands on the graphs I'm sure it's been above that.

I can't recall which gear this was (possibly second), and I only did it once.

Do the PH masses have any suggestions; dicky rev counter, cam, or something ?


cheers

Mike

[Jasandjules]

Not 100% sure but I thought that some engines did indeed have a 5500 limit whilst others could go to 6250 or so, but quite honestly is there much power left over 5500 anyways which a nice upshift couldn't obtain?

[blitzracing]

The rev limiter is somewhat dynamic, and depends on more sensor inputs than just the actual RPM, so it may kick in ealier in lower gears. The nomal limits are 5200 - 5400 for the Range Rover map, and the TVR map is higher.

[spend]

blitzracing said:

The rev limiter is somewhat dynamic, and depends on more sensor inputs than just the actual RPM, so it may kick in ealier in lower gears. The nomal limits are 5200 - 5400 for the Range Rover map, and the TVR map is higher.

How does the ECU know what gear you are in then?

Dave

PS Mike, stick a noid light on and see if the ECU is cutting the fuel- else it will be an ignition fault.

[mgaut]

spend said:

noid light

DO WHAT DAVE ?

[E1DJH]

I hope you weren't chasing anything too quick Mike

Thanks again for your company, and here's to a speedy resolution to your car problems

[That Daddy]

I would not recommend an engine with a Noid light connected to be revved hardto see if the limiter is indeed cutting out the injectors firing(you have to unplug one injector to connect the Noid lamp)i have obviously misread your post though Spend

Edited by That Daddy on Sunday 11th November 17:00

[spend]

That Daddy said:

I would not recommend an engine with a Noid light connected to be revved hardto see if the limiter is indeed cutting out the injectors firing(you have to unplug one injector to connect the Noid lamp)i have obviously misread your post though Spend

Edited by That Daddy on Sunday 11th November 17:00

I don't know what you are on about? Noid is just a passive light - injector is still connected, I can only assume you have some archaic version if thats how yours work?

Dave

[blitzracing]

spend said:

blitzracing said:

The rev limiter is somewhat dynamic, and depends on more sensor inputs than just the actual RPM, so it may kick in ealier in lower gears. The nomal limits are 5200 - 5400 for the Range Rover map, and the TVR map is higher.

How does the ECU know what gear you are in then?

I suspect that is more a combination of throttle opening, air flow, RPM, and most of all road speed. Those parameters will will be different for each gear.

Mark

[spend]

blitzracing said:

I suspect that is more a combination of throttle opening, air flow, RPM, and most of all road speed. Those parameters will will be different for each gear.

Mark

I don't think the ECU knows anything about speed, AFIK it just senses if the car is moving or not

Dave

[GreenV8S]

blitzracing said:

The rev limiter is somewhat dynamic, and depends on more sensor inputs than just the actual RPM

That surprises me, and is the first time I've ever seen a suggestion that it works like that. Are you sure? Assuming the rev limiter works in the straight forward way I think it does, I'd be inclined to suspect a high rev misfire caused by a weak spark or badly wrong fuelling, if the engine won't pull cleanly up to the rev limiter.

[That Daddy]

spend said:

That Daddy said:

I would not recommend an engine with a Noid light connected to be revved hardto see if the limiter is indeed cutting out the injectors firing(you have to unplug one injector to connect the Noid lamp)i have obviously misread your post though Spend

Edited by That Daddy on Sunday 11th November 17:00

I don't know what you are on about? Noid is just a passive light - injector is still connected, I can only assume you have some archaic version if thats how yours work?

Dave

No Dave,mines a Snap on kit,its used to check injector duration on many many systems for non starting,your one is obviously more of a universal job,or possibly just for this system(and better obviously),as usual you have bitten which is the reason why i put the"misread your post bit"in my previous post shouldent have bothered, Charlie Big Potatoes!just in case the original poster dident understand i dident want him revving the nads of his car with one of the Noid lights i described above

[blitzracing]

spend said:

blitzracing said:

I suspect that is more a combination of throttle opening, air flow, RPM, and most of all road speed. Those parameters will will be different for each gear.

Mark

I don't think the ECU knows anything about speed, AFIK it just senses if the car is moving or not

Dave

Theres definately more to it that that, after all the 4x4 Rangie map is speed limited, so this is more than go - no go parameter. As for the "dynamic" bit Its what Mr Buxton told me when I was trying to pull the ECU map apart. I had visions of some hex values I could go ahead and change if I knew where they where located, but the ECU uses some clever algorithms to produce "load" figures, that it then controls the injector timing width etc. Still trying to get my head around it.

[GreenV8S]

blitzracing said:

the ECU uses some clever algorithms to produce "load" figures, that it then controls the injector timing width etc.

That sounds like the basic fuel mapping function, I'd expect the rev limit configuration to be quite separate (and much simpler).

[shpub]

The rev limit is exactly that and is the rpm limit at which the ECU starts to limit the engine speed. However... they are often hard and soft limits which can give rise to the idea it is dynamic as in some cases the soft limit may not be initially noticeable. In some cases the mapping/ignition is so out you get the equivalent of a rev limit as well.

The TVR Ecus have a variety of rev limits and indeed Mark Adams can reset them.

The RR versions may also have a speed limiter - the speedo pulse train is supplied to the ECU so that it can establish a road speed limit. This is disabled in the TVR ECUs.

The ECU however can't work out which gear you are in accurately - it can approximate it but the ECU doesn't know anything about ratios. Particularly true for automatics BTW. It also doesn't really know much about load. All it knows about is the amount of air flowing into the engine.

It doesn't have any real feedback to calculate loading etc because there are no sensors to give it that. It takes the AFM measurement and adjusts the fuelling to suit the air flow. It is effectively an open loop system. It goes into a closed loop system with the lambda sesnor at below 3000 rpm and so when getting to the rev limit, the ECU is running open loop and its fuelling is based on the look up tables that it has. Also the ignition at this point is also controlled by a set of mechanical weights and heavily reliant on sparks across the rotor.

The brain is not that smart as it is only a lickle micro. Your average MP3 player probably has 10-20 times as much processing power.

[mgaut]

All

thanks for all the info, but bar the Noid Light suggestion I'm not sure I've got much else to go on ?

I was thinking that if I warmed it up then repeated the high revs in 1st/2nd/3rd (on a private road of course) I would see if it's gear-specific ?

Does this sound like a good idea before I trundle off to the menders ? I'll reset the ECU before I start.

cheers

Mike

[PurpleV8]

Mine has always had the ignition cut out at an indicated 5,500ish RPM. Got it checked on a rolling road at the start of this year and found that the rev counter was reading low above about 5,000 RPM and in fact the 5,500 indicated when the cut out came in was an actual 6,250 RPM so the only fault was the rev counter. Now I know, I just change a bit sooner.
Would be worth comparing road speed and RPM at ignition cut out in say 2nd and 3rd gears with a known good car. Who would like to start with their figures?

[mgaut]

Well, that problem seems to have gone away. No issues today in 1st & 2nd.

Mike