3rd piston shut off

[lolsteve]

Am I correct in understanding the solenoid on top of the fuel pump shuts off the 3rd piston when on cruising speeds to help with mpg?
If so what rpm/mph does it activate at? so im not finding myself cruising a bit above or below the optimum speed

[Piggy]

never heard of this

[RJDubya]

What pump are you running, never heard of this but I do know the solenoid on the Lucas pumps stops the fuel altogether, it's used as part of the immobiliser and to stop the engine when powers cut off...

[Piggy]

thats what the solenoid is for... to stop fuel . . . thats it. v simple system

[lolsteve]

standard hdi pump. it's the bit ontop of it held in with 3 screws

http://www.tdocuk.com/viewtopic.php?f=7&t=1155

"Teh 3rd piston is used for many things - controlling overtorque, anti stall and to provide enough fuel when required. This is in situations like going up hills, overtaking in top gear etc"

[Tom]

Sounds like cack to me.

Also RJDubya this is the hdi section.. whole different set up compared to the xud

Edit: Just read that link, makes a bit of sense i suppose but i dont see the point of it lol

[RJDubya]

Sounds like cack to me.

Also RJDubya this is the hdi section.. whole different set up compared to the xud

Edit: Just read that link, makes a bit of sense i suppose but i dont see the point of it lol

My bad, just reading new posts, didn't see which section it was in... Sorry.

[Poodle]

I haven't got any specific info for the third piston shut-off, but i didn't notice any real difference when i unplugged mine. If it's going to be active for cruising i should think it'd be set with similar parameters to the egr, so part-throttle conditions at 60-70mph.

Tom, the main point of it is to reduce pumping losses at low engine load, pressurising fuel to over 1000bar is no small job, uses a fair bit of torque to run the pump. In theory, if you can shut down one of the pistons when it's not needed you can reduce the load on the engine and therefore save fuel. Allegedly, that is... As said on TDOC, it's probably 50% gimmick, but it may be possible to discern its effect - if any - with empirical testing, anyone fancy giving it a go?

[Piggy]

no...be a waste of time...loada rubbish

[cully]

2 - Deactivator of the 3rd piston of the high pressure fuel pump
2.1 - Role.
Role of the deactivator of the 3rd piston of the high pressure fuel pump :
To reduce the power absorbed by the high pressure pump if the vehicle is used at low load.
To limit the high pressure quickly in the event of a problem.

When the 3rd piston deactivator is not energised :
l The fuel suction valve is held against its seat by the spring .
l The cylinder is closed.
l The action of the pump shaft cam leads to a pressure being created.
l The fuel pressure lifts the delivery valve .
l The fuel is directed towards the high pressure outlet of the pump.

When the 3rd piston deactivator is energised :
l The push rod raises the suction valve from its seat.
l The cylinder is open:No pressure is created.
l The fuel is directed towards the low pressure part of the high pressure pump.

Control : injection ECU.
Type : "all or nothing" control through earth.
When the 3rd piston deactivator is energised:the pump operates on 2 pistons.
When the 3rd piston deactivator is not energised:the pump operates on 3 pistons.

[Piggy]

sounds like a lot of gumf to me

[lolsteve]

Interesting stuff, sounds like it could be a nice little gain for the engine

Different to what I orginally thought it was though, thought it shut off the 3rd engine piston at cruise speeds so only firing on 3 cyclinders to reduce fuel injected still all learning at the end of the day

[Poodle]

Thankyou for you constructive input piggy, we get your point now.

Steve, if you want to test it you can unplug the orange plug on the top of the pump, thatll render it inactive in the same way you can unplug the egr solenoid.

[Ruan]

sounds like a lot of gumf to me

Do you fancy keeping a little quiet? Theres people providing genuine info which people are more than capable if coming to their own conclusions about without you expressing your (rather naive...) opinion on the matter...

The 3rd piston deactivator as said is to reduce pumping losses when under cruise conditions etc...

[Mr Whippy]

It does help, but I'm not sure how much by.

You have to remember at a cruise condition at say 45mph the gross power losses might only be about 25bhp.

So your engine needs to make only 25bhp. If the 3rd pump deactivation can save you a 'small' 0.5bhp even, then that is a whopping 2%, which in fuel economy terms is quite significant for a simple switch... not sure what the exact figure are, but clearly they were worthwhile for the investment in having it.


I've tested with it on/off in the past and noticed no absolute changes in accelerative performance. However, along with de-EGR, I do believe there may be some element of 'lag' when it changes state from off to on... like the throttle is a bit more docile at lower speeds and then flooring it vs with it unplugged. I'd have to do more testing to be sure.
I was doing that testing about 6-7yrs ago now so can't remember for sure on the qualitative stuff, but in quantitative terms it generally seemed best to leave it plugged in on the grounds that there was no clear benefit to de-activating it... unlike with EGR which is easily noticeable and logically beneficial to remove for 'performance' purposes.


Dave

[Piggy]

sounds like a lot of gumf to me

Do you fancy keeping a little quiet? Theres people providing genuine info which people are more than capable if coming to their own conclusions about without you expressing your (rather naive...) opinion on the matter...

The 3rd piston deactivator as said is to reduce pumping losses when under cruise conditions etc...

yeah sorry chaps...bad week...just sounded like the french trying to sound smart...but be curious if this was realy a working system....?

[Jonny81191]

Of course it's a "working system"

The question is, does the system have any advantages as far as we're concerned. As far as I can see, there's no harm in keeping it plugged in, unless we can prove it makes a noticeable difference to the throttle response, without any performance downsides. As far as MPG is concerned, it would appear it's useful, albeit possibly a little bit un-needed.

[Piggy]

yeah I meant more worthwhile I guess than working...

could it even be exploited further for further mpg gains?

[Poodle]

Now that was my thoughts piggy, maybe expand the operating parameters a little so its active for more time. It certainly seemed like it made a difference to throttle response, at least when changing from cruising to hard acceleration. It also causes a slight hesitation when it engages, barely noticeable, but again, certainly there. Maybe I should do some testing with it once the project is on the road again...

[Piggy]

problem I get with such small changes is placebos or nocebos....

is it really affecting it or is something else making the diff!! or am I just imagining it!!

[Poodle]

Yeah, that's the issue alright. I'd be more dubious about my perception of the throttle response, but i wasn't expecting that particular change so it wasn't placebo in that case. It was the same with the hesitation problem, i didn't disconnect the tpd to stop the hesitation, but it stopped when i disconnected the solenoid, QED...

With regards to the mpg it's easier, as i can do some definitive testing, got some more ideas on the subject so will be doing so in the near(ish lol) future.

[Mr Whippy]

Now that was my thoughts piggy, maybe expand the operating parameters a little so its active for more time. It certainly seemed like it made a difference to throttle response, at least when changing from cruising to hard acceleration. It also causes a slight hesitation when it engages, barely noticeable, but again, certainly there. Maybe I should do some testing with it once the project is on the road again...

I was gonna say the same.

I tested this years back (as per my post above), and found the same kind of results.

http://www.tdocuk.com/viewtopic.php?f=41&t=399&start=15


I also did these acceleration tests for seeing if there was an outright difference.

http://www.tdocuk.com/viewtopic.php?f=41&t=714



So plenty to be having a think about I'd say.


Reading back it seems I concluded there were probably no overall gains, but there is certainly something going on at lower rpm's where throttle response seems better and perhaps that improves the low-end fuelling/boost cycle giving a fraction more power in transient conditions.


A bit like EGR I suppose, no outright benefit, but it's clearly noticeable when off > on throttle and the boost cycle too is impacted by EGR (ie, lower transient power gradient)


Dave

[cully]

whippy i wonder if you can see in the map if there is a set ruleset the 3rd pump valve follows
like 2 valves below 2krpm 3 above or is it dependant on throttle responce?

as this might be a way of mapping for better economy say at 80mph as this is just the other side of the 2.25k switching point in the map which i belive the 3rd piston valve shuts for full pumping

[Poodle]

Hadn't seen that second one before, thanks, makes for interesting reading.

That was one of my thoughts also, Cully, particularly as the R70 pumps should be that bit more capable of maintaining flow with only two pistons active.

[Mr Whippy]

What you really need to do is cruise at 50mph and, if you can, log the throttle input vs rpm.

Then cruise along with the orange plug unplugged, thus running on 3 pistons vs 2 pistons.

Then log again.

You'd need to run over say 5 miles, three times. Get a baseline/average for unplugged then plugged in.


Who knows if there is much in it.


Cully, as per my post two posts back, 3rd piston de-activation makes a difference when the parasitic losses are a high percentage of the total engine output required for the current cruising speed.

If by my figures at 45mph you are needing 25bhp from the engine, and you can save 2% in those cases by de-activation, then great.

But at 85mph you are needing about 60bhp from the engine and if the 3rd piston deactivation now saves you 0.5bhp, or even 1bhp at these speeds, then you are gonna struggle to see 1.5% down to 0.75% improvement.

It's at these levels that no test gear will show the difference alongside statistical noise, bar an engine dyno which is what the manufacturers will have used to determine the duty cycle for the 3rd piston de-activator.
It will work, it'll be slight but valid.

But I really don't think there will be any benefit at 85mph cruise speed. The engine speed itself is so high at that speed, the pump speed so high, that parasitic savings from de-activation will be tiny vs the power needed to cruise at that speed (60bhp+)

You honestly will find more saving by cruising at 84mph than at 85mph hehe, than you ever would tinkering with a control map for the 3rd piston deactivation!

Or just 1psi more in your tyres. Or better eco tyres.

Or a better engine/gearbox oil with lower frictional losses.


Not wishing to put you off, tweak the control map by all means. I've done stuff like that for years out of interest but it all comes down to usually being below the sensitivity of very well orchestrated on-road testing. Ie, results just mix in with statistical noise, thus in my view they are pointless to worry about as they might cost you a slight bit of power more than gain it.

Only when you see a clear benefit should you pursue it to get net gains in power/economy.


As said, the test at 50mph doing a run plugged/unplugged would be interesting. If you can see a benefit in those cases above statistical noise then it might be worth pursuing, but I think you'll just see noise even at 50mph... if it's not clear at 50mph it certainly won't be clear at 85mph

Dave

[Poodle]

I was going to test at 60 over 20 miles, as that is how ive done my mpg testing before, so ill have some easily comparable data. I wanted to ask you about recommended data logging progs actually, ive got pp2k, galetto and kwp leeads, so anything that works with those would be great.

[Mr Whippy]

For this task I've been using rpm vs throttle position, via ELM and logging in PCM Scan.

I can write a script which basically watches the values and fills each entry block with an average value.

So I have say 25rpm blocks from 2250rpm > 2750rpm, drive at 2500rpm in 5th, and log the throttle input value and put it in the right block. The table is then averaged over time, and I take the central blocks around 2500rpm (say 8 each side of 2500rpm and plot a little graph of average throttle vs rpm)

I then do that three times over a route that I can drive smoothly (say a quiet 5 mile run of motorway or dual carriageway) and go the same direction along it each time.

I then make my change, and then run again.

Since per-run correlations are well within 1-2%, any significant change should stand out if you average the three runs...

If the average of the after runs combine to one line that sits within the ranges of the original three runs then you can probably argue it's statistical error you are looking at.

If the average after is better than average before, then maybe it is better. But I'd want to do 5 before/after runs to try remove as much error as possible and resolve the actual result.

Since throttle and rpm are logged at a high resolution (1000 intervals for throttle iirc, and 500 intervals between 2250-2750rpm say), then you can get pretty good quality data.

Downsides are that the more you test you might just see more variance in natural variances like wind changing, air temp changing, tyres hotter/cooler on road, fuel tank going down = less tyre drag etc etc...

That is why if you generally can't see an average trend improvement within the error range evident on any given 'before' run, chances are you won't get results that are gonna stand out within the error your measurement technique offers.
Ie, your improvement might just be a few runs that were preferential.

Doing 6 runs before/after might improve things but this is where you get into statistical analysis and doing clever averaging of the before/after runs, otherwise your stat method might just be introducing more error to make spotting improvements even harder.


Needless to say, there isn't much you can get from these cars bar the obvious stuff. Drive slower, drive smoother, better tyres, clean aero surfaces, good oils etc... even a remap is struggling to boost steady state economy in all my tests... the only improvement a remap seems to offer is in 'driving style' improvements in all the transient phases.

But I'm testing lots of stuff actively.

I might do a test on this orange plug next time I do some testing if my test subject is happy to. Probably do some in January!

Dave

---

I was going to test at 60 over 20 miles, as that is how ive done my mpg testing before, so ill have some easily comparable data. I wanted to ask you about recommended data logging progs actually, ive got pp2k, galetto and kwp leeads, so anything that works with those would be great.

Is that just doing brim to brim method?

All these techniques are just open to error really. Brim to brim is ok as a rough guide but still might give decent sized errors for all sorts of reasons.


I've taken the usual 'claimed' economy boost remaps and not seen anything is steady state driving. My error is ~ 3% and if there is an improvement it's in the 0-3% range hehe...

However, customers always say their mpg is better, and so I guess that is noticed in transient driving benefits, ie, better gear choice, better use of revs/torque combo with more power on tap etc...
But that is REALLY tough to measure hehe... all you can really do is do brim to brim and drive as you feel fit.
In my car I saw no benefit on brim to brim mpg but then other people do on essentially the same remap files.

Dave

[Poodle]

In the past I actually isolated the lift pump from the fuel tank and used a separate container, made it much easier to get precise results. The testing is done along a bit of motorway between two jumctions that are almost exactly ten miles apart, made for very convenient testing lol. The section had two hills, so the tests should be representative of real-life driving, and running in both directions eliminates most intereference caused by prevailing winds. All twst runs were done with the engine up to temp and tyre pressures at exactly 33psi. Id also make a note of the ambient temp for each run and general weather conditions to try and account for most external variables.

I did go as far as calculating the std deviation to make the tests as scientific as possible, my main issue was keeping my driving style consistent, some decent data logging kit would make that so much easier. Will look into sourcing pcmscan, already got an elm on order.

I did see a measurable improvement on a stage 1 map, but as you say, I think it was down to better tractability at low revs and the mildly increased rail pressure below 2k rpm, which meant I was able to shift up earlier without straining the engine.

[lolsteve]

This is why this a good forum because people have decent discussions now and try to get the best from their cars.
Poodle i have a bluetooth elm reader which you can borrow if youd like, and ful torque on my phone so i could try and run some tests too

[Mr Whippy]

I did see a measurable improvement on a stage 1 map, but as you say, I think it was down to better tractability at low revs and the mildly increased rail pressure below 2k rpm, which meant I was able to shift up earlier without straining the engine.

I've boosted rail pressure at specific cruise rpm, and done movements of injection advance/retard at the specific injection amounts at the specific cruise rpm too, and in all cases of steady state testing my results all seem to sit in the 0-3~4% error that comes up due to testing any way.

In many cases I think, hmmm, more advance = better torque, but higher EGT maybe, which increases temp of intake charge on a HDi90 especially = lower power again.
High rail pressure by 10%, great, 5% better fuel burn, but 5% of the 30bhp needed at a 60mph cruise is about 1.5bhp, so you can trim throttle a bit, but the rail pressure boost of 10% might cost you 1bhp? So all in the benefit might not be there?!
Really we are talking very small benefits that culminate to a reasonable amount all working in unison. But until you can really see the benefits in an honest statistical way, reproducible again and again, then you can't really make any useful changes in my view.
There is a good chance you make 2% somewhere, worth doing if it's there, but another tweak might cost you 1.5% and you'd never really know it.

That isn't to say we shouldn't look for the benefits, but it's REALLY hard when our gear is gonna be nowhere near as sensitive as OEM's with engine dynos and controlled environments


I do keep thinking of ways to improve accuracy but it's all subtle stuff. Ie, 10% better accuracy is still 2.7% noise magnitude rather than 3% noise magnitude in my results.



PCMScan and ELM are deffo good tools for this job though!

As long as you do a baseline before any mod, and then mod it and repeat the test afterwards, things should show up in the results if they do make real net benefits!

You don't even have to run both ways down a road to account for wind. As long as you always do the same thing, or as close to it each time, your results are as good as you will get them in real world testing!


Ie, these are some G-tech results from my 306 HDi FMIC tuning development. Ignore the values, they are not really relevant as this is before/after testing, the important thing is how consistent my 'before' tests were... that is easily as good as a dyno imo!

Imo if you can get a grouping that tight for mpg over 5 runs, and then do something like drop tyre pressures 10psi and run again (something you know will make a difference), and run again, and see a grouping of 5 standing distinctly apart, you know you are gonna have a chance of seeing these subtle changes you are trying to find!


I think it'd be interesting to test before/after with the spoiler on the 306 for example, or that front splitter, or the splitter/under-tray combo. I bet these things could be surprising when it comes to economy at a 60-70mph cruise!

Dave