VEMS EFI

[silverfrost]

Hi all,

As most of you are aware i also have a mutant G shaped esprit, things have been moving on and its coming near the end

of the build, well sort of

As i used the same sort of engine as HILLY i.e the modern audi V8 although different engine cc i.e hilly been 4.2

mine is a mere 3.7 but still good for a few bhp, Hilly as a sensible option chose VEMS versatile engine management

systems it runs everthing with suqential spark and injection and has a massive scope for tuning and also features

wideband o2.

The bonus side of this system is the cost it a hell of a lot cheaper than the off the shelf systems that are nearly 1500plus

but the down side is its not easy to use if you dont know custom efi systems and thats me

As Hilly had sorted my wiring loom i.e introduced the vems loom into the audi loom, and he has also put most of the settings

on my ECU, however im using this project thread to pick his brains and help me finish the tuning data, also it

will give other people a bit more insight into VEMS as im sure there are many more engine conversions on the

books out there on this forum

Andy, looking at the data Andy from what i can see there only seems to be two bits missing or am i wrong it would

not be the first time,

I have looked on the wiki but its not the easyiest thing to drag info from!

The first one is the inj opening time, not sure where to get this data from and how to put it down in data form

on the settings page!

The second one is the primary trigger tooth page, it has a bit missing that just says trigger tooth

need some help! regards danny

[hilly]

I suggested to Danny to open up a thread about his ECU as I am sure a few of you out there are interested in what these systems can do and how they work.

Not sure if this should be in the tech or project section, I am sure a Mod will move it if needed.

The reason we need to use a after market ECU with the Audi engine is that the OEM unit will go into limp home mode (reduced rev limit, ignition timing pulled right back) without the auto gearbox, which is not much use for a performance car.

Therefore a configurable ECU is required to allow the operation parameters of the Audi V8 to be dialled in and get the most out of it.

These after market ECUs can be use by anyone running a efi Esprit or one which has been converted if they are fed up with the carbs.

The after market ECU business is quite large and varied with offerings rangine in price from a few hundred pounds up to thousands.

The VEMS ECu is based on another DIY system called MegaSquirt (which is what Punky used on his V6) except it has more features.

So a quick run down of what VEMS is: -

It is a stand alone engine control unit which will control both fuel delivery and ignition timing, you program it using a laptop.

It also has a number of general purpose output which can be used to control stuff like radiator fans, boost controllers, idle valves and such like.

On top of that it also has a built in Wideband Lambda sensor control which allows full time on-the-fly afr closed loop control.

It is totally DIY, you buy the ECU, wire it up to your engine, tune it and then drive.

Now the beauty of these systems are that they are totally configurable to fit any engine, however it also means that there are a lot of setting to enter and if you get them wrong you could melt your engine.

So what I'll do is run through how a system is set up for an engine, in this case Danny's 3.7 V8.

If no one is interested then we'll take it off line and do it via PM.

OK so with all the hundreds of different setting where do you start ?

Well there are some basic parameters which can be worked out just using data about the engine.

First is how big do the injectors need to be.

A basic rule of thumb is: -

Injector Flow Rate (lb/hr) = (Engine HP x 0.5) /( Number of Injectors x max Injector duty cycle)

You don't want to drive the injectors more than 80% as a safety margin.

In Danny's case it would need to be (230bhp x 0.5) / (8 x 0.8) = 18lb/hr (188cc/min)

Now Danny already has his injectors and they are 225cc/min which is plenty good enough for upto 280bhp.

Now we have the injectors we now need to tell the ECU how big they are.

This is done by working out how long the injector needs to be open to give enough fuel to fill 1 cylinder at 100% volumetric efficiency (required fuel)

req_fuel = 6.49 * (D / N / I)

D engine displacement (cc)

N number of injectors (eg. 4 for a 4 cyl port injection)

I injector flowrate (cc/min)

Again in Danny's case

= 6.49 * (3700 / 8 / 225)

= 6.49 * (462.5 / 225)

= 6.49 * 2.06

= 13.3msec

So this info goes into the basic screen

The TPS high/low are to get the max and min positions of the throttle position sensor.

The MAP range is to tell VEMS what air pressure sensor you have fitted, 250kPa in this case and you can calibrate the sensor to get the correct reading using the offset.

The rev cut is a hard rev limiter, set it to where your engine rev limit is.

Same goes for overrun.

More soon...........................

Hilly

[silverfrost]

Andy,

Have put the 13.4 in on that page but will not let me enter anything in the bits high lighted red i.e MAP RANGE UNIT and

TABLE KBA UNIT!

any clues!

regards danny

[hilly]

Andy,

Have put the 13.4 in on that page but will not let me enter anything in the bits high lighted red i.e MAP RANGE UNIT and

TABLE KBA UNIT!

any clues!

regards danny

Set those to the defualts using the arrow to the righthand side of the box.

Next it is time to tell the ECU what type of engine you have i.e.

8 cylinders (bvious)

Type of injector scheme (4 stroke, even fire)

Lambda sensor type.

The RPM constant relates to the trigger wheel being used, so for a 60-2 you need to enter 1500.

The Battery calibration is for fine tuning the Voltage measurement, 192 is a good starting point here and then just fiddle till it is correct.

Don't worry about the Baro correction as we are not using it.

Hilly

Edited February 11, 2008 by hilly

[silverfrost]

Yep done that, so whats next!

regards danny,

[peter_england99]

Hilly,

Please keep it coming. I personally would love to understand more about ECU's.

Regards,

Peter.

[Splashout]

Hmm interesting read will keep an eye, would like to ask one question though.

How does the cost of this relate to something like an emerald system where usually there is a rolling road set up session included in the price?

Can this reliably be set up on the fly i.e. road driving or would it also need a rolling road session at a cost?

[silverfrost]

Andy,

the rpm is just about moving,

Also getting a reading at the bottom of the page saying TRIGGER ERROR

any ideas regards danny

Edited February 11, 2008 by silverfrost

[hilly]

Coolant Bins

This table is used to alter the fuelling at different engine temperatures, the default values are fine (on the left hand side) so if yours are different then make them the same.

Now we are getting into the nitty gritty part of engine set-up.

Injector settings

We need to tell the ECU what type of injectors we have and how you drive them.

There are 2 basic types of fuel injectors, Saturated and Peak-Hold.

They differ in the type of solenoid coil they have: -

Saturated have a high resistance coil which means you just put 12V across them and they open, however they don't do it very fast.

Peak-Hold have a low resistance coil and hence you can dump energy into fast to get the solenoid to open quickly, however if you just put 12V across them the coil will overheat in short order.

These tend to be for high flow rate injectors (300cc/min and above) and what the ECU can do here is apply 12V for a short period to whack it open, then lower the voltage to keep it open, but not overheat the coil.

This is done with a method called Pulse Width Modulation (PWM) where you apply 12V, but turn it off/on very quickly. Altering the ratio (%) of off against on time effectively reduces the voltage "seen" by the injector, i.e. 0% is off, 50% would be 6Volts and 100% would be 12 Volts.

All these settings are done on this screen.

For Saturated injectors (what you have Danny) you just turn on the injector for the amount of fuel you need and therefore don't need PWM (hence it is set to 100%).

Now we come to how you operate the injectors. There is no reason why you can't fire all the injectors at the same time for each engine cycle.

The fuel hangs about in the inlet and gets sucked in as the valve opens. Now this may sound a bit crap and the fuel would disappear or dribble out the bottom or something.

However even when the engine is running at idle the longest time it would be hanging about before getting sucked in would be 0.1 seconds, so no big deal.

There is very little gain for sequential injection (injecting as each cylinder needs it) except for emmisions reason, as far as power output there are no proven gains.

VEMS does have 8 injector drivers so you can do sequential injection so you need to tell it that you have 8 injectors and what order to fire them in so that is what this screen is for.

This is set up your the specific firing order of the particular engine, this is the Audi V8.

Hilly

Edited February 11, 2008 by hilly

[silverfrost]

Spot on Andy, keep it coming! how long before i can turn the key

Have input all data so far, regards danny

[talon]

facinating thread!

[hilly]

Easy Tiger, you may end up blowing it up!!!!

Now come to the important bit, ignition timing and triggering.

As most modern engine have no provision for a dizzy you can't just slap one on and hope it will start.

This is what gives most people a headache when trying to get them to run.

The ECU needs to know at what point the engine is in the cycle so it can fire the spark plugs at the right time.

This is done with a trigger wheel on the crank shaft.

There are a number of different trigger schemes used by various manufacturers and you will often see stuff like this thrown about 36-1, 60-2 etc

This relates to the number of teeth on the trigger wheel.

The ECU counts the teeth as they pass a sensor and for a 36-1 wheel that is every 10dge crank rotation.

However a whole bunch of pulses is no good as it needs to know where Top Dead Centre (TDC) as this is when the the spark is needed .

So the trigger wheel has a tooth(teeth) missing which it can use as a reference point, hence 36-1 (35 teeth and one missing tooth or gap), 60-2 (58 teeth and 2 gaps).

You tell the ECU where the missing teeth are in relation to TDC.

As the engine is rotating it sees the gap, then starts to counts the trigger teeth to find where TDC is and then fires the spark plugs, simple

Now as there are so many different trigger wheel set-ups out there this is a complex aspect to set up and hence a lot of variable to get right, if they are wrong it won't work right (hence the trigger errors you are seeing Danny)

Here is the screen for the crank trigger

As you can see there are a lot of numbers to enter any of which if wrong will screw it up.

A fair few are not used, but the important ones are: -

TDC after the trigger ( this tells the ECU where the missing teeth are)

Number of teeth (58 for a 60-2 trigger wheel)

Next trigger tooth (this is defined by the number of coils you have, in the Audi V8 case there are 8 coil packs, 2 engine rotations =120 teeth/8 coil packs =15)

Trigger tooth (this is where the ECU starts counting from to work out where TDC is)

This is where much of the head scratching starts.

On top of all the variables above you also have the problem that the crank trigger sensor and the wheel can be anywhere, it all depends on the mechanical set-up of the engine.

The best way to do it is to set the engine to TDC, then align the the missing teeth to be 40 - 60 dge be AFTER the sensor.

This allows the ECU time to see the missing teeth then workout the ignition advance required (whilst counting teeth) and then fire the spark. This isn't always possible so you can tell the ECU to use a specific tooth on the trigger wheel as the trigger. The teeth on the trigger wheel are numbered starting at 0 and counting up from the missing teeth.

Now in Danny's case he fitted the trigger wheel/sensor without doing this alignment, but luckily he wasn't far out.

From memory your tooth zero is at 38dge BTDC so you need to set "TDC after the trigger" to 38 and "Trigger tooth" to be 0

You MUST check this with a timing light once the engine is running though because if it is wrong you will quickly melt your engine as soon as you drive it.

All the other entries just copy as they will work for a V8 with a 60-2 trigger.

Now that the ECU knows where TDC is we have another problem.

Each cycle on a 4 stroke engine take 2 crank revolutions. The crank trigger can't give you this info as it won't know if the engine is on the compression or exhaust stroke.

A way around this is to use something called a "Wasted spark" coil.

This works on the theory that on the exhaust stroke there is no fuel to ignite so if you fire a spark it won't do anything. So what happens is that when the engine is running it always fires 2 spark plugs, one cylinder on the compression stroke (this is the one you want) and one on the cylinder on the exhaust stroke, but this spark is "wasted" as it doesn't do anything.

The ignition coils for this need to be twice as big as it is doing double the work, but the advantage is that engine sensors are more simple.

This system is what is used on the 4 pot SE/S4/S4S/S300 etc.

Unfortunately you can't do this for coil on plug set-ups (well you can ish) so you need to know what the engine is doing to know what plug to fire.

This is done with the cam (secondary) trigger as the cam shafts turn at 1/2 engine speed.

The Audi V8 already has this fitted and the VEMS reads this sensor to know what to do.

Here is the screen to set up the cam trigger.

These numbers define how the cam trigger resets the spark firing order, so just copy these Danny.

NOW I HAVE JUST REMEMBERED DANNY THAT I DIDN'T TELL YOU THAT YOU NEED TO ADJUST THE AUDI CAM TRIGGER WHEEL TO WORK WITH VEMS.

This is why you are getting trigger errors. I need to modify the cam trigger wheel, but the pic is at home so I'll post that when I get there.

Hilly

[hilly]

More on the cam trigger.............

What it does is just makes sure the correct spark plug is fired when needed.

It can (and often is) just a simple pulse when cylinder 1 is at top TDC and this is what VEMS uses.

However there is a problem with this in that depending on where the engine stops last time it was run it can take up to 2 whole revs on start-up before the cam pulse appears and the ECU knows where everything is.

Audi got around this by having a complex trigger wheel with different sized teeth which it not only counts but also looks at their length to work out position, enabling engine sync within 1 rev.

VEMS can't cope with this so you need to hack off some teeth to make it work.

Danny, if you are typing in these numbers and then cranking the engine over to see what happens make sure you pull out the 20A fuse (it is the supply for the coil packs) in case it fires up and with the wrong settings and then goes bang!!!!

Now that the ECU knows what the engine is doing you need to tell it how to operate the ignition coils.

You need to define the number of coils, coil charge time (dwell) and voltage correction.

Next you define the coil (spark firing order), this is defined by the engine.

This order looks a little odd, but it is due to the way the cam trigger on the Audi is positioned (too complex to go into here).

Now with these settings and the cam trigger wheel "adjusted" you should now be able to turn the engine over (with the 20A fuse removed) and the tacho on the laptop (the tuning software) should read about 200 rpm and there hopefully are no trigger errors.

Still not ready to start it up just yet, but you are close.........

Edited February 11, 2008 by hilly

[silverfrost]

Andy, All is well and i have input the data, the cam sensor has been altered with the teeth now removed, have read through all the

system checks so far and everthing is spot on, however i have not tried to turn it over yet!

Just bare with me as my wireless does not work that well in the garage regards danny

[hilly]

Getting close to getting is running now.

Initial start-up

Starting a car requires extra fuel as the engine, oil etc is cold and hence the efficiency goes down, in the old days this extra fuel used to be added by pulling on the choke lever.

ECUs know the engine temperature so therefore can work out the extra fuelling needed for you, but you have to set it up first and this is done here.

Priming just turns on the injectors for the time specified when you first turn the key, this is to get an initial amount of fuel into the system.

You tell the ECU the amount of fuel needed to get it to start at a very low temperature, again at operation temp and it will work out everything else in between.

The above is the settings are for my engine, but yours will be slightly different, so the first thing to set up is cranking.

The -40 C cold cranking pulse length needs to be roughly twice your required fuel value so go for 22msec.

Warm cranking needs to be about 40% of reqfuel so set that to 5.5 ish.

The cranking threshold is the rpm at which the ECU thinks the engine is running so if your cranking rpm is 200 (what mine is) then set this value 50% above it ie 300.

Cranking advance is the ignition advance used to start the engine, 10 is a good initial number.

Once the engine catches and starts to run it still needs more fuel than normal to keep going, this is called after start enrichment.

This adds a percentage of your normal running fuel to keep the engine running, this enrichment tapers away for the number of engine revs entered, 400-500 is a good value.

Now we need to define how much electronic "choke" is needed to allow the engine to run until it us up to operation temperature, called warm-up enrichment.

This is just a table of temperatures and the corresponding amount of extra fuel needed.

This can take a bit of working out as you only get one shot at testing this each day.

The last things to do is enter the fuel and ignition maps.

We don't really need these to be accurate to get the engine idling, just rough numbers will do.

This is a fuel map

Now this is a 3 dimensional map made up of rpm along the bottom, inlet manifold pressure up the side and fuel in the z axis.

This is expressed in Volumetric Efficiency (VE) which is basically....... in an ideal engine, 1 cylinder would require the reqfuel amount of petrol and air to give max power.

Now this not the case with an NA engine as you never get the 100% VE across the entire rev range so the numbers are normally less than 100.

In a turbo car it is different as you have the air being forced into the cylinders, so when on boost the VE value is well above 100 depending on the amount of boost.

As it isn't important right now I'll go into these numbers later.

The ignition map is similar except you change fuel for ignition advance.

This is a very basic ignition map with no vacuum advance, again not really needed right now to get it started so we will come back to this later

Now with this lot all done your car will probably attempt to start.

Before we get too far, have you got the temperature sensor fitted?????

If you haven't then you are stuffed as the ECU won't know how much fuel to inject.

Hilly

Edited February 12, 2008 by hilly

[silverfrost]

Andy,

I always seem to be beaten at the last post, im affraid the temp switch is still the original its a blue one though and not the

black one! not sure if this would of worked, but its going to be a long while until i can try and start the car.

Cheers for the help hilly this thread has given me a lot of info and made me understand if not completly but has given

an easier understanding of how to set the car up and what things do, a lot easier than the wiki from which it is

hard to gather information in a mine field like this if your not efi minded and seem to need a degree in physics!

As the posts have said a lot of people will be interested in the VEMS for more esprit mutants and general upgrades

on the lotus 4 pots, It was a good idea of yours to give a bit of an insight to the custom ecu background,

Cheers Hilly your a top man

regards Danny

[hilly]

The blue one it the sensor you need, the black one is for the VDO dash and is too low resistance.

If you plug it in the blue connector up at the front of the nearside cylinder head you should get a reading on the laptop.

Hilly

[silverfrost]

The blue one it the sensor you need, the black one is for the VDO dash and is too low resistance.

If you plug it in the blue connector up at the front of the nearside cylinder head you should get a reading on the laptop.

Hilly

Yes i get a reading on the laptop i just though it was the wrong switch in the first place but hey presto if its alright then its alright

regards danny

[fjmuurling]

Very interesting, keep it going.

Freek

[Splashout]

Hilly or Danny

I would still be interested in your opinion of cost and set up in relation to a setup system such as the emerald system where it comes with a basic setup allowing the car to be run but their price includes a rolling road session to set up the system or at least it did when I enquired a few years ago. This looks interesting but does it really need a rolling road session to set it up correctly or can it be done properly on the road and does the cost and buggeration after all this still make it better value for money that a setup system?

Glyn

[hilly]

Sorry Glyn for the lack of reply yesterday, I have still got keyboard rash from all the typing......

The Emerald system is quite good and Dave Walker is a master with all things rolling road and mapping.

It is all a matter of what your priorities and wants are of the efi conversion.

If you are a total techno novice then the turn key Emerald type of solution is the way to go, you cough up your money (

[Splashout]

Cool thanks for making your fingers bleed a bit more for a response.

Reading that it seems that the VEMS system is a far superior system for your money but you have to invest the time to learn it and without access to someone who is experianced such as yourself you could possibly stand the risk of getting something wrong and ending up with a melted engine.

Intersting for sure.

Thanks

Glyn

[hilly]

Cool thanks for making your fingers bleed a bit more for a response.

Reading that it seems that the VEMS system is a far superior system for your money but you have to invest the time to learn it and without access to someone who is experianced such as yourself you could possibly stand the risk of getting something wrong and ending up with a melted engine.

Intersting for sure.

Thanks

Glyn

That pretty much sums it up, however I am biased about VEMS as it was the only DIY ECU which could run the Audi V8 properly.

To be honest you only risk melting the engine if you run lean when at full power, most other times you will know something is up before destroying it.

All the DIY systems are like this including Emerald if you don't get it mapped by them.

If you take your time (and do a bit of research about DIY EFi, the MegaSquirt forum is good for this) pretty much anyone should be able to get an engine up and running.

Hilly

Edited February 13, 2008 by hilly

[hilly]

As Danny is back from his travels for the next few days and is keen to get his V8 engine up and running it is time to kick this thread back into life.

It was left a few weeks back with engine temperature sensors.

The ECU uses 2 sensors to adjust the running of the engine.

Manifold Air Temperature (MAT)

The temperature at which the air used by the engine is important as it defines how much fuel is used and ignition timing.

Cool air is more dense and therefore holds more oxygen which means you have to add more fuel to compensate.

This is a good thing as it means you get more bang out of it and hence the whole point of intercoolers/charge coolers on forced induction engine as the process of squeezing more air in raises the air temp.

The ECU has a correction map which it uses to adjust the fuelling against MAT, so as long as the temps being read by the ECU are correct then everything works fine.

Coolant Temperature (CT)

This is the running temperature of the engine (water temp) and controls a bunch of stuff.

Cold engines are nowhere as efficient as hot ones and hence need extra fuel to make them run, this is what is done by the choke on carbs, it just throws in an extra amount of fuel.

The ECU looks at the engine temperature and adjust the fuel above the standard fuelling map accordingly giving max extra fuel whan very cold and zero when up to temp.

It also adjust the acceleration enrichment according to temperature as well.

The ECU can drive a relay to control the radiator fans (mine does this which meant I could junk the Otter switch) and CT is used for this.

A load of other functions such as boost control, water injection can also be set up from this, but we won't be using this on a NA engine.

As you can see it is important to get these sensors working correctly.

So before you can get any further you need to check these are OK which is fairly simple.

If you just power up the ECU and look at the home screen on Megatune it displays both MAT and CT assuming they are plugged in!!!).

The reading you should get will be ambient temperature. It doesn't matter if they are not spot on (+/- 10

[silverfrost]

Hi Andy,

Cheers for starting up the thread again, hopefully this time round i will get the beast fired up! just to hear it choke and spit would

would do me for the time been

Right last time round we had the dramas of the temp switch, to be on the safe side i have bought a new one from audi,

its green and was the sameas the one to fit the temprature gauge sensor into! so im going to pop this new one in to save

any dramas, i still need to double check everything again that we went through last time as i just have had no time yet,

Also still need to check that the trigger error red warning light has gone! will try and check everthing today and

hopefully will get the ball rolling again!

Takeit easy regards danny

Hi Andy,

checked all the VEMS stuff that we have done so far and all is well, still a little concerned with the trigger errors though, the dial

on the megasquirt instrument gauge is red as is the voltage gauge! it worked before now for strange reason it dont!

THE NEW TEMP SENDER NOW GIVES ME A READING OF 16 TO 17 DEGREES,

Regards danny