Duty Cycle on Boost controller - doesn't make sense to me

I have read and linked to some external sources that the search/similar threads results threw up but I am non the wiser and some had complicated looking calculations!

Been out for a steady drive this morning with no traffic. You can hear the whistle of when turbos start to spool at around 1,200rpm with the minute-ist of feathering on the throttle. This usually was the case at around 1,800rpm on inclines and around 2,200rpm on flats. With the same thing happening pretty much from idle, my car is guzzling fuel when I am just trying to potter about.

I think my duty cycle on my Gizmo MS-IBC may be set too high and I need to have a go at reducing it (hoping this may make the whooshing sound of the turbo spooling to come in a little later rather than react to nearly every throttle movement of my right foot).

However, I fudementally do not understand what the duty cycle is. Can someone please explain in plain simple english what the duty cycle is, and if I was to reduce it or increase it what actually happens?

hoping this may make the whooshing sound of the turbo spooling to come in a little later rather than react to nearly every throttle movement of my right foot

Go TTC, comes in much later then or eTTC like me, and if you dont like it... switch it back....

... awaits abuse

Been out for a steady drive this morning with no traffic. You can hear the whistle of when turbos start to spool at around 1,200rpm with the minute-ist of feathering on the throttle. This usually was the case at around 1,800rpm on inclines and around 2,200rpm on flats. With the same thing happening pretty much from idle, my car is guzzling fuel when I am just trying to potter about.

Righto, we'll have a bit of turbo basics

The turbos can spin up and whistle but still not spin fast enough to produce a higher air pressure than atmospheric - which is what "boost" is. If you produce positive boost, the engine power will go up as the higher pressure air is measured and fuelled for by the ECU. If engine power goes up, your car will accelerate and go faster. If you're accelerating, you aren't pottering or cruising at a steady speed and I think you'd notice Ergo, if you aren't accelerating, you certainly aren't on boost, in fact I'd wager your engine is seeing a vacuum to the order of probably -5 to -7psi.

If you are hoovering up more fuel than you think you should be, chances are your oxygen sensor is dirty or just plain failed, which means the ECU is fooled into running the fuel mix too rich all the time.

I think my duty cycle on my Gizmo MS-IBC may be set too high and I need to have a go at reducing it (hoping this may make the whooshing sound of the turbo spooling to come in a little later rather than react to nearly every throttle movement of my right foot).

While a good stab at thinking through what's going on, this isn't correct. The boost controller controls the wastegate, which is the flap that opens to vent exhaust gas and control how much gas the turbo sees and therefore how fast it spins (and therefore how much boost it produces). Keeping the wastegate fully closed is the way to build up boost the fastest, as the turbo sees all the exhaust gas all the time. This would be 100% duty cycle (more on that in a bit). But, you need to be producing boost in the first place and as explained above you aren't The duty cycle affects how much boost you produce, and to a degree, how fast you make it. It can't change when your turbo starts making boost (known as the boost threshold).

However, I fudementally do not understand what the duty cycle is. Can someone please explain in plain simple english what the duty cycle is, and if I was to reduce it or increase it what actually happens?

There is a solenoid that is activated by the boost controller, and this controls a valve that is either open or shut (kind of like a fuel injector). This valve, when shut, stops pressurised air from the turbo from passing, and when open it allows it through. This air, when allowed through, activates the wastegate by pushing on a diaphragm. If the solenoid was either simply open or closed it would be pretty useless as the wastegate would either never open (runaway boost and bang goes turbo/engine/both) or start to push open as the boost built up (wastegate creep), which makes boost pressure buildup quite slow as exhaust gas is bled off well before you reach your target boost, and also means your maximum boost is limited to the pressure needed to fully open the wastegate.

Phew, big bit of text there, sorry. So, the solenoid is pulsed. It alternates between open and shut many times a second. The time it stays open compared to how long it stays closed is your duty cycle. How many times a second it opens and closes is irrelevant, it's the total amount of time this averages out to that matters. So if it's open for 0.5s and closed for 0.5s, your duty cycle is 50%. If it's open for 0.7s and closed for 0.3s it's 30%.

(tl;dr)

What that boils down to is that the higher the duty cycle, the longer the solenoid is closed per second, the less pressurised air gets to the wastegate diapraghm, the less the wastegate opens, and you get higher boost.

-Ian

Moved to tech

Thanks for this Ian_C :thumbsup

After reading this I think I'll let the pro's handle sorting it all out.

For the info, the car was 100% before and was BPU'd last week. On full chat it feels great and very powerful, but seems to lack low down torque and has started guzzling fuel since BPU even when I am trying very hard to feather it about. Prior to BOu I could get from Nottingham > Leicester, go for some high speed overtakes, enjoy the waft of torque etc and the car's fuel gauge would barely move.

For the info, the car was 100% before and was BPU'd last week. On full chat it feels great and very powerful, but seems to lack low down torque and has started guzzling fuel since BPU even when I am trying very hard to feather it about. Prior to BOu I could get from Nottingham > Leicester, go for some high speed overtakes, enjoy the waft of torque etc and the car's fuel gauge would barely move.

Something's up then. Check the voltage on your OX1 pin in the diagnostic port while the car is idling with a warm engine. It should fluctuate aroun 0.5v (I think, I've done an FAQ on it somewhere)

Many thanks.

The 2nd O2 sensor was unbolted to remove the CAT but was then bolted straight back into the de-cat pipe. Not sure how how this could just stop working but will ask the garage to test.

Many thanks.

 

The 2nd O2 sensor was unbolted to remove the CAT but was then bolted straight back into the de-cat pipe. Not sure how how this could just stop working but will ask the garage to test.

Get them to check your emissions while you're there, see if you are running rich

After the work was completed and the car started up, I could smell it was quite rich but this was intially put down to a cold start.

However over recent days I have noticed that it now always smells rich (prior to the work and BPU and it smelt fine). During set-up of the boost controller they had fitted an AFR (air/fuel) gadget to the exhaust and relaying it to a computer inside the car to run higher boost. No issues to indicate a weak fuel mix were reported. However I think from the smells its fair to say I am running rich.... but why/how is the question?

If work has been done around the O2 sensors it's most likely that. Step 1 though is to diagnose it as far as possible, which you can do one of two ways.

One, get the garage to stick a wideband sensor up your zorst while warm idling. Anything under 14:1 is too rich.

Two, get a multimeter and check pin OX1's voltage in the diagnostic port.

You can find what to check here:

http://www.mkivsupra.net/vbb/showthread.php?t=35940&highlight=oxygen

-Ian

Thanks Ian_C.

The 2nd 02 bolts were rusted and had to be cut off with a grinder. It was then mounted into the de-cats with new bolts.

I will get this tested on Saturday. I will also print off your link. Thanks.

Great information Ian

DSK may be of no use but I've gone half BPU (Decats) and I think the Supra is drinking slightly less fuel. I went from London to Leicester & back on about £60 fuel, that included a couple of times hitting triple digits. Though also think my car could be running rich since BPU. Does smell like it but then I put it down to having no cats.

Keep us updated DSK.

BPU should take around the similar amount of fuel unless you hammer it, in which case it should obviously take more.

I got mine from Aberdeen > Nottingham on 1 tank of fuel. Driving sensibly with the odd bursts. Whilst trying to be as gentle as possible (which I did not have to do before), its taking over twice the amount of fuel it should! Very strange how such an alarming amount of fuel is suddenly being used.

Going in tomorrow to have the 02 sensors tested and looksee over all the work that was done on the off chance something is spotted and then take it from there......

If it cannot be solved then unfortunately I will no longer be able to keep the car as I'm already taking a taxi to work as it works out far cheaper!

BPU should take around the similar amount of fuel unless you hammer it, in which case it should obviously take more.

 

I got mine from Aberdeen > Nottingham on 1 tank of fuel. Driving sensibly with the odd bursts. Whilst trying to be as gentle as possible (which I did not have to do before), its taking over twice the amount of fuel it should! Very strange how such an alarming amount of fuel is suddenly being used.

 

Going in tomorrow to have the 02 sensors tested and looksee over all the work that was done on the off chance something is spotted and then take it from there......

 

If it cannot be solved then unfortunately I will no longer be able to keep the car as I'm already taking a taxi to work as it works out far cheaper!

I need to check the O2 sensors on my car too I think (also BPU'd) as it's also using bucket loads of fuel at the moment. Barely get 200miles to a tank now even when driving like I am trying to win the worlds slowest driver competition.

New O2 sensors @ Toyota are around £150+vat So hoping if 1 has been damaged its just the one!

I never doubted Ash's mechanics workmanship, only reason I went for the repairs and trusted them with BPU is they get things right first time everytime!

Comprehensive testing of the 02 sensors along with a trip to an MOT station for a detailed emissions test all indicated VERY positive results so its not the 02 sensors. All pipe work is in tact as before etc. So I went on my way and after work decided to increase the gain on my boost controller. Here are the results;

Previous Settings;

Duty Cycle = closed loop > 45

Gain = 10

Boost = 1.25 bar

The Duty Cycle was set with the addition of fuelling and other computer equipment and this was the highest I could run. So I left that as is. The manufacturer stated that the gain should be generally 10 points less than the duty cycle.

TEST RUN 1

Duty Cycle = closed loop - 45

Gain = 19

Boost = 0.9 bar

RESULT = much more torque, closer to what it was like standard

TEST RUN 2

Duty Cycle = closed loop - 45

Gain = 26

Boost = 0.9bar

RESULT = even more torque, just ever so slightly less than standard Despite a few carrigeway sprints just seeing what the revs are like, how its changing gear, hows its pulling etc, my fuel gauge HAD NOT moved and the car drove as it did prior to the upgrades

TEST RUN 3

Duty Cycle = closed loop - 45

Gain = 33

Boost = 0.9 bar

RESULT = much more torque! Simply stupid bang as soon as the trubo's are in you're off, no f*cking about, no spooling just plain performance. Oh and my fuel gauge still hadn't moved!

So despite the wet conditions, I tried played exiting a few roundabouts seeing how brave I was and how the car handled them on/off power. Have to very very careful in the wet, you can still push it but there is NO room for error. The wollop the moment the sligest hint of pressure is applied and the car shoots forward rather than a simple strong satisfying surge.

TEST RUN 4

Duty Cycle = closed loop - 45

Gain = 34

Boost = 1.42 bar

RESULT = mental so eased it upto 130mph and floored it to simulate some motorway my c'cks bigger than your c'ck stuff. Simply instant and savage to the extent it made me feel comfortable whilst deploying power, so first time in history - I backed down whilst swearing at myself.

Drive Home

Duty Cycle = closed loop - 45

Gain = 33

Boost = 0.9 bar

Car now drives like it did before the upgrades, silky smooth perfect gear changes, correct reaction to throttle inputs, lots of low down torque (at least the same as standard but feels stronger), absolute no lag on the turbos, just instant take off, car pulls itself along as effortlessly as it did before so now I am always pretty much just covering the throttle rather than having to press it at all. FUEL ECONOMY is about normal!

There is no way on this earth that changing the duty cycle on a boost controller affects the fuel economy of a car when it's at cruise off-boost. All your previous comments indicated that you were cruising around off-boost, but this testing appears to be "nailing it at WOT"?! And your testing is "has the fuel gauge moved?". Sorry my man but that's really no test whatsoever.

I have to comment on this as someone could search in the future for fuel economy issues and read this as a happy result. I also suspect you'll be back on here after a couple of tanks, realising the problem is still there.

Switching the Gain from 33 to 34 should also in no way change the max boost from 0.9bar (wastegate pressure) to 1.4bar!(practically runaway boost and a death sentence to the engine) The gain is the speed at which the controller tries to achieve max boost, it's the duty cycle that controls the actual boost level you want to get.

Something is deeply wrong with the config of your boost setup, with results like those. We can either discuss it and try to work out what's going on, or you can continue to think changing the gain 1 point on your boost controller doubles your fuel economy In which case I wish you well and can only assume you steer with the aircon controls, for they are as connected

-Ian

PS what was the lambda reading at the MOT station?