Erratic tick-over

[macdeb]

Classic Chim said:

macdeb said:

I had a helluva game with the stepper, wouldn't go back to rest at same point etc. Did away with it completely and had the start up map changed. OP, have you checked plugs? I changed down a grade and it smoothed out the idle perfect at 650 rpm.

That’s exactly how mine works. And the grade down too which does help keep things smoother.

GOG Dave.
My scatter spark is switched off. It’s just fuelling and timing that maintains idle. Cold start map etc.

I agree the 14CUX is very sophisticated and when working is all but as good as any.
If reliable steppers etc can be found there’s a good case for keeping it. Tvr engine bay heat is probably what starts the faults not the system. If we could control the heat better they’d still be fairly reliable.
Things like AFM do last well considering it’s proximity to the exhaust if you think about it.

^^^^Absolutely, one of the very first things I did when I got a TVR was to shield the AFM from the radiant exhaust heat, it's the anorak in me.

[ChimpOnGas]

Classic Chim said:

My scatter spark is switched off. It’s just fuelling and timing that maintains idle. Cold start map etc.

Surely that's a contradiction Alun, 'Scatter Spark' is dynamic idle management using ignition timing

My understanding is the MBE from Powers Performance uses no idle air control valve whatsoever, to be honest if they can genuinely deliver the idle speed increase required during cold start using ignition timing alone I'd be very impressed indeed, because the truth is there's only so much you can do with ignition timing when it comes to raising or lowering idle speed.

My experience is 'Scatter Spark' is a fantastic feature for fine trimming idle speed when the engine is warm and ideally should only be used as such, asking it control more than +/- 100rpm either side of the predetermined idle target is pushing 'Scatter Spark' to the edge of its useful abilities, and because timing changes affect more than just idle speed if you add or subtract lots of timing you enter a world of other compromises that are less than ideal.

However it does depend on where you start, if your base idle timing is set at 12 degrees then yes you could add a whopping 6 degrees of timing using 'Scatter Spark', and that may deliver as much as a 300rpm increase during cold start. I suspect this is how Powers do it or they would definitely struggle to raise idle speed sufficiently during cold start without the help of an idle air control valve. Actually I've heard tale of people having an idle air control valve retro-fitted to their Powers Performance MBE installation as their cold starts on this system suffered low idle problems, like I say there's only so much you can do with ignition timing ('Scatter Spark').

My experience is you only really want the 'Scatter Spark' feature adding 2 to 3 degrees either side of your base idle timing an absolute maximum, and mostly just a one degree shift either side of the target is the ideal, running a lazy responding 'Scatter Spark' calibration is also preferable if a hunting/surging idle is to be avoided. Where idle air control valves score is where more than a 100rpm correction is required to meet the idle target, if you need to add say 300rpm during cold start or 200rpm rapidly to catch a stall then the only truly practical solution is to lob in a slug more air using an idle air control valve.

But if you add air you better match it with fuel or the very stall you're trying to save may even be worsened by the ensuing lean condition, it makes sense the AFM on the 14CUX responds accordingly when the stepper is instructed to add air, but exactly how fast can the old Lucas ECU respond?

If this is genuinely how it works the Lucas system certainly has quite a chain of commands, so it better be able run them quickly.

1. ECU detects a stall
2. ECU tells stepper to add air
3. The rather slow responding stepper motor adds air
4. AFM detects this additional air
5. ECU responds by adding additional fuel to avoid a lean condition
6. The rather slow responding narrow band closed loop lambda tries to trim to 14.7:1 which is actually a very lean idle AFR for old Rover

My Canems system for instance draws a faster straighter line to achieve the same end:

1. ECU detects a stall
2. ECU rapidly instructs the superior and faster responding infinitely variable Bosch rotary idle air control valve to add just enough air
3. At the same time and directly linked to idle valve duty, fuel is instantly added following the idle valve fuel correction calibration
4. Super fast wide band lambda closed loop rapidly trims any remaining discrepancy to hit my far more suitable 13.5:1 AFR idle target

But mostly my 'Scatter Spark' holds the idle target perfectly anyway so idle air control valve activations will be far less frequent than the 14CUX stepper activations in the first place, because for obvious reasons the Lucas system can't offer ignition timing idle management.

Fundamentally adding air to manage idle speed is not an ideal solution as you are just introducing an ECU managed vacuum leak, but given you can only do so much with ignition timing an idle air control valve becomes a necessary evil. To me the ideal arrangement is you can get 'Scatter Spark' to manage idle speed for 99% of the time, the idle air control valve then only comes into play during cranking, cold starts and to catch a stall.

If both the 'Scatter Spark' & idle air control valve calibrations are configured correctly they should work hand in glove to deliver the ultimate rock solid idle management strategy that covers every scenario and maintains the target engine speed perfectly.... no matter what!

[Classic Chim]

macdeb said:

^^^^Absolutely, one of the very first things I did when I got a TVR was to shield the AFM from the radiant exhaust heat, it's the anorak in me.

Just the technician in you bloke, bit like your axe,,, A1
Richards super charged car has lots of this he cut and shaped himself,,, looks awesome and more to the point does a really good job.
It’s probably why the splitter was added as much as any handling as it helps throw cold air up there.

[Classic Chim]

For some I can understand why they add an idle valve to MBE
On a very cold morning once engine fires it idles to low at 600 revs but I have thick cold oil st this point, so I introduce a very light throttle setting to increase air intake and the cold start map does the rest. I artificially hold a high idle with my right ft, using different plugs increases the engines ability to hold a steady side within about 20/30 seconds.
The idle will now be around 700/750 from then on with no issue.

Depends on cam etc
There maybe some timing changes added to the cold start map but Jason told me Scatter spark wasn’t needed and is turned off.

I’ve read up and like all you say about the use of it though Dave and I’m glad you are using and explaining it. A very useful tool.

For me cold starts are just that and I like being the responsible part that controls how fast the engine picks up on initial firing. I slowly raise it to about 1100/1200 so I don’t get follower rattle.

It works for me.
I get a thrill out of and still like toe and heel and when it’s cold you defo need to employ this to get smooth gear changes.
-10 d I used it,,,, Mad but you have to back up the talk,,, thing is it’s warn enough within a few minutes even in that weather to drive seemingly unimpeded. It’s just like when it’s warm. Incredible as without an idle valve you’d expect it to struggle.

Anyway.
CUX,,, I m coming to the conclusion my afm was half my trouble, I had 3 steppers and some days they all worked so now we talk of it, always when it was hot, idle problems have you scratching your head with engine running and no air flow which adds to the heat ! so I should have looked more closely to the afm readings... hmmm.

Live and learn

[ChimpOnGas]

Classic Chim said:

For some I can understand why they add an idle valve to MBE. on a very cold morning once engine fires it idles to low at 600 revs but I have thick cold oil st this point, so I introduce a very light throttle setting to increase air intake and the cold start map does the rest. I artificially hold a high idle with my right foot, using different plugs increases the engines ability to hold a steady side within about 20/30 seconds. The idle will now be around 700/750 from then on with no issue.

Understandably when a customer pays upwards of £4k for an engine management upgrade he might reasonably expect to turn the key and let the system do the rest, after all the 14CUX does exactly that if it's working correctly, and that system comes in £4k cheaper because it came with the car for free.

Surely one of the very benefits of engine management is you don't have to mess about holding the throttle open with your right foot? The whole point behind engine management is it's meant to be turn-key spot-on under all conditions, anything less is therefore room for improvement. The challenge for the MBE is during cold start as you're very unlikely to achieve the required idle speed increase using ignition timing alone, for that you'll need an idle air control valve of some sort..... which of course is the very reason they exist.

On the other hand if you implement a drive by wire throttle system as we see Lloyd Specialist Developments are doing with their new Wildcat engine, an idle air control valve becomes redundant because the throttle butterfly rest position/gap can be dynamically adjusted in line with coolant temp. Basically it's exactly like you holding the throttle open for the first few minutes Alun, except rather than you having to think about it the ECU does it all for you. Actually my Canems ECU & Bosch idle air control valve works in the same way, but the drive by wire idea is even better in my opinion as you are only modulating the air allowed into the engine from one point, ie the same point you use to control engine speed with your foot.... the throttle butterfly.

You might assume an engine doesn't mind where it gets it's air from, but that's not really the case, airflow is an exact science, adding some air via the throttle butterfly is fine but if you then add some more via the back of the plenum as with the standard arrangement it may potentially cause weird turbulence issues. It's far better in my opinion to only add air at one point, the same point where the designer of the plenum and inlet manifold intended it to come from, the throttle butterfly.

Irrespective of whether the ECU is adding the air via an idle air control valve, or the MBE people need to add it with their foot to manually open the throttle butterfly, our big challenge will always be the original plenum and inlet manifold design. Revealingly Lloyds not only went drive by wire throttle but they also developed a far superior plenum and inlet manifold design like you see on most modern V8s, their cross over exhaust manifold may help a bit too. Finally they topped it off by running fully sequential injection which is known to deliver a better idle than batch fired semi sequential systems like ours.

With fully sequential injection, drive by wire throttle, far superior airflow from the Wildcat heads, and the better inlet and exhaust arrangements, one can only imagine this must all add up to deliver a beautiful idle (with the right cam), and devastatingly good throttle response compared to anything achieved before on the Rover V8?

Edited by ChimpOnGas on Thursday 21st June 13:14

[Classic Chim]

if I go start my car now from cold it will idle instantly.
We are talking about very very cold and damp,weather.
It’s a sportscar so how often are you starting up in those conditions.
The Ecu was made with mostly racing or performance in mind so less than 1 minute to warm your engine is no hardship to me. I’ve known people with Bosch and after market to have idle problems, usually an air leak but in one case the valve was capput. Probably a one off!

Removing the problem for good and a few seconds bringing my car safely upto temp is my preferred choice. If people want to fire it and ignore it while it warms up then fair enough but raised idle is lazy driver input in a performance car and I don’t need or want it.
I have heard people who are not happy with idle so maybe they should have chosen a different system but for me it’s not a problem and only needed a few times a year anyway.
You can just set the base idle higher if this bothers you but to me a very small detail I can happily live without.

This is also why it runs so well low down, you hit the nail on the head, the air comes via the throttle butterfly, good air and no turbulence or loss of pressure from air coming in from the back end of the Plenum.

As many will say, you can do anthing if your prepared to spend enough. Dom stopped all this a long time ago, this leaves the door open for others to fill. Lloyd’s are doing a fine job.

But my engine has the best manners I could ever imagine so what they do works as it’s still way up there and returns proper fuel returns. 300 hp 28 mpg
I don’t need an idle valve I can tell you

Edited by Classic Chim on Thursday 21st June 13:53