How to megasquirt a Vauxhall engine, with MS2 v3
Hello everybody. Since noticing more and more people are interested in going down this seemingly dark and troublesome route of Megasquirting their engines on here, I have decided to write up a rough guide, as well as providing a thread for everybody to come to and share their knowledge and help each other.
This ‘guide’ is really more an account of what I found doing it for my c20xe, with my Megasquirt II, V3 board, and a collection of links to the most useful pages when doing this.
As with anything to do with cars, try to do as much as you can yourself, and take time studying diagrams, reading pages thoroughly, making notes, organising your parts. The more you learn the less complicated it will become, this will save time in the long run. If you skim read a page now and just pick the information you need, you may have missed something vital, and you’ll only need to go back to the same page later. So it will just cost time in the long run, see!!
Megasquirt, what it is and why everyone who want to use it, fear it, and the ones who have it running, love it.
It started off as an educational project by mr Bowling and mr Grippo, for people who want to learn about electronic fuel injection (EFI from now on).
Since then it has evolved and become THE choice ECU for peeps who either fancy a challenge, don’t want to spend big money, or both.
It’s easily up there with the best programmable management systems in terms of what its capable of, its hardware, and software (with new firmware such as the Extra codes), but unlike pro ECU’s, if you want to have fancy features like idle valve control, boost control, launch control, you have to put in the time researching and experimenting (and sharing your results – its how it got so far in the first place ).
And since we can all share our research and results, the diy-ness of it is now becoming less of an issue .
First things first:
Which megasquirt (MS from now on) you need, is up to you. I’d suggest going for the Megasquirt 2 V3. The V3 is a name for the most recent board layout and component set. The V3 board has been developed to be more fool-proof, more reliable, better in most ways than the previous boards.
As for the processor – there is the MS1, and MS2 chip. MS1 (the 68HC908) was the original chip brain of the whole party. The MS2 is a daughter-board which replaces the MS1 chip, and on it contains a more modern processor that’s faster, supports higher resolution tables, has more accurate interpolation between the table sites, amongst other things. More on that is here:
Up until recently, there was a very strong following of the MS1, as it had the Extra code written for it, which is firmware which allows the hardware to do more things (read on), but now that Extra code has been written for the MS2, it really makes sense to go for the MS2, also makes you more future-proof.
Megasquirt comes with the original B&G code, which supports all the standard stuff to make your engine run and live happy ever after.
There are however other firmware versions such as the MSnS Extra code, which you flash your ECU with yourself, via a little program you download. The extra code supports many additional features such as boost control, launch control&flat shift, switched maps, nitrous control, knock control, tach output, idle valves and others.
Lots of good info here:
Ooodles of good reading:
MS1 Extra and MS2 extra manuals
Megatune is the default program to tune MS with windows, or Megatunix if you run linux. This allows to change the configuration, tune, and datalog your engine.
Megatune is now getting really out of date, and most folks now prefer TunerStudio. The Lite version is free and gets you going, the premium version allows you to design your own gauge clusters etc. TunerStudio is awesome!
There is now MSDroid as well, which is a really nice looking Android app, which is fairly capable and you can tune/tweak with it. Great for permanent dash-tablet installs!
Specific info for the Vauxhall engines (c20xe, let, ne, seh, most other 4 pots)
What megasquirt needs to know (sensors):
RPM’s – easiest way is to use the Vauxhall crank angle sensor (called the VR sensor from now on, for Variable Reluctor). The trigger wheel for the xe/let/se/seh is in the crank case, and is is a 60-2 type, meaning it has 60 teeth and 2 missing. No extra hardware is needed to make this work. Some people get VR conditioning circuits as an extra (google it), but the V3 has all the necessary circuitry to accept the sensor’s signal and interpret it into RPM’s.
You can also use the xe/let’s hall sensor which is in the dizzy housing instead of the crank sensor, with the appropriate modifications to the jumpers on the V3 board (more info on jumpers later).
NOTE:Injection modes that Megasquirt supports are batch (all injectors fire at once) and bank (2 at a time). If i got these the wrong way round, let me know. The point is, MS doesn't yet do sequential injection (each injector individually) - so this is why you don't need to run the hall sensor AND the crank sensor. On Motronic standard management, crank sensor sees revs, hall sensor sees 'phase' ie which cycle the engine is at, and works out which injector needs to fire next.
Throttle position – any linear potentiometer sensor should work. The throttle position sensor (TPS from now on) needs to have 3 wires, and resistance between 2 of these should change as you move the throttle. LETs have this sensor, also ne/seh engines I’ve been told, and many other non-vauxhall engines. Early xe TPSs are a switch, not a sensor. They go click at wide open throttle (WOT from now on), this sensor will not work.
Coolant temperature – this is done by a coolant temperature sensor (CTS from now on), and GM sensors are spot on for megasquirt. MS comes calibrated for GM sensors out of the box. The xe/let sensors are roughly there already.
Manifold pressure – or manifold absolute pressure, MAP from now on. This sensor is built into the MS ecu, and you run a vacuum line to this from anywhere between your throttle body and inlet valves.
Additional sensors that help:
Manifold temperature – or manifold absolute temperature, MAT from now on. This is a sensor similar to a CTS, but for air temperature. You don’t need it, but with this sensor you can tell MS to pull ignition timing to compensate for higher MAT, which is essential for a thorough map on a boosted engine. By not pulling timing when things get hot, you’ll get det/knock/pistons melting, which is very bad. The LET sensor is spot on out of the box, well, they’re about 10ish degrees out, but it’s all relative so it will be fine if its mapped and used with the same sensor. Other sensors can work, you just need their temperature vs resistance tables to calibrate them properly in megatune.
O2 sensor – or lambda, oxygen sensor (hence O2). A wideband system helps, but megasquirt doesn’t use it to control fuelling directly unless you set this up. A wideband with a display is pretty much essential if you’re mapping it yourself. Alternatively you can feed the o2 data from the controller to the megasquirt, and see the value on the Megatune screen. This means it will also be present when datalogging, which is very useful, but more on that later. The Innovate controllers work beautifully, and I have nothing but good stuff to say about the JAW system, this is what I assembled and use. I heard AEM stuff is very good too.
Knock sensor – if you can get it to work. Megasquirt doesn’t have any circuitry to deal with a knock sensor directly, so you need a controller such as Boris’s Knocksense, the Phormula KS3, the SAAB APC, or other systems. These then need to be calibrated for correct sensitivity, and can then tell MS when it’s knocking, and MS will tell you on the screen, or pull timing (much like motronic does).
A few options. You can get Megasquirt looms from DIY-autotune and other places, make your own loom, or modify the motronic loom.
Megasquirt looms purchased:
Advantages – most straight forward. Good insulation, good quality well chosen cabling, new cables will last longer.
Disadvantages – cost, lengths of cabling may need to be modified for whatever layout you choose on your car, if you bought it because you hate electronics then you’ll be lost if/when you need to fix it or find a fault.
Advantages – Can tailor it to your own car, you’ll know it inside outand where everything is, learning potential.
Disadvantages – cost of cabling, connectors, insulation, cost of time, quality (if your soldering isn’t exactly **** hot)
Advantages – quick if you know what you’re doing, cheap as you already have it, all the connectors are already there, its already ideally laid out, standard ‘look’
Disadvantages – can be a pain trying to trace cables, can have worn/broken wiring as they’re old, can get complicated when trying to trace wires.
The neatest option is probably to use a spare ECU and use it for the loom connector. This is the best option if you’re leaving your engine standard. Get a spare ecu, leave the wiring loom alone, but take apart the spare ecu and gut it. Then solder cables to the inside of the connector, and run the cables out the other side of the ‘fake’ ecu and to the megasquirt/relays. Or you can house your relays inside this fake ecu, or even the megasquirt itself! The advantage of this method – is that you can just plug your original ecu in and drive, if you haven’t messed around with the loom/configuration of your engine too much.
There is more info on this here:
Also, this chap has done it, its very neat check it out:
Also here is what I was talking about by gutting the spare ECU.
Whichever option you choose, you’ll probably benefit from a decent multimeter, so even if you’re not going to make your own loom, budget a multimeter in anyway.
Rapid will have most the bits and pieces you'll need to do your wiring:
I strongly recommend either buying a relay circuit pre-built, or making your own separate relay board. Trying to use the motronic fuel pump (FP from now on) relay, is not a great idea. There are a few reasons for this:
> the FP relay actually houses 2 relays inside, this means it’s very diffucult to understand how to run them separately, let alone wire them up for megasquirt.
> the GM FP relay costs about £30, versus £1 for an automotive relay from Rapid.
> it will be old, and they don’t last forever.
Ignition, what where how?
Direct coil control – megasquirt comes ready to rock, using this system.
Advantages – simple in theory, you just run a wire from the ECU to the negative of the coil, power the positive and MS does the rest.
Disadvantages – not simple in practice. I never got mine to work this way. Many many people get issues with the coil producing too much electrical noise, and making their MS ‘cut out’, or ‘reset’. I’m not sure if I was just unlucky, or if it’s something that is characteristic to xe’s/let’s. Also your keeping mechanical, wearing parts.
Coilpack (wasted spark) – in my opinion the best way to run, using a Ford or Vauxhall coilpack (non-amplified type – 3 pins).
Advantages – more reliable as no mechanical parts to wear out, less electrical noise, no distributor means more space for tight conditions especially RWD engine position, better performance with better coilpacks – stronger longer spark, more control of timing.
Disadvantages – need to purchase ignition driver chips, ecu needs small modifications. Have to run the Extra code (iirc).
Megasquirt to existing ignition amp to coil – It is possible to use the low-current signal from megasquirt to trigger the ignition amplifier which is normally mounted on the coil bracket next to the coil, on the distributor early c20xe’s and lets (motronic 2.5). I haven’t tried this system, but apparently it works. This would be less prone to cause electro magnetic interference, as the signal is amplified right at the end. Also the wiring is already there on the loom, so it’s more or less a straight install.
Ford EDIS system – many people run this system but it’s not really practical for an xe/let, as fords use 36-1 trigger wheels, and you need many ford parts, it’s extra wiring, messy, and pointless as you have all you need on your Vauxhall engine.
If you want to run 4 cylinder wasted spark and have a standard MS ecu, then you need 2 ignition driver transistors (field effect transistor - FET from now on) which you can buy on ebay here
or on here:
You need 2 FETs because a 4 cylinder coil pack has 2 coils inside. Megasquirt comes with one driver installed, so you can re-use this one, but I don’t recommend you do this. Its best to install the 2 FETs and leave the original in peace, in case you want to revert to direct coil control at some point.
Also, if you’ve bought your megasquirt a couple of years ago, you’ll have a VB921 (iirc) coil driver FET, which are no longer made. The best equivalent to use is the Fairchild FET on diyefi (link above), these run cooler and are more efficient, so you’re going an upgrade aswell with the new FETs.
Where i located mine (you must make sure they are mounted on a heatsink):
Some people mount them to the top half of the enclosure, but this will be problematic when you'll need to upen up the ecu again.
Why do I need ignition drivers?
What happens is – megasquirt supplies a small electrical pulse at each ignition event. This small pulse is not strong enough to drive a coilpack directly. It needs to be amplified to a couple of amps, from a few milliamps that megasquirt squirts out.
These FETs do just that, and drive a NON-amplified coilpack.
Again, you can use most 3 pin coilpacks just fine. I use a Ford fiesta rs coilpack and it works beautifully. Apparently Ford coilpacks run a stronger spark, and also allow to run a longer duration, and overheat less which is just what everyone needs.
Information on how to wire up the new ignition driver FETs, look here.
Lets get started:
Use this diagram here to work out the wiring:
This diagram contains all you need to know regarding the wiring.
You need to look at it and understand what it all means, if you don’t, ask here and we’ll help .
I will describe in words what this all means, some people understand better by looking at pictures, some by reading words.
We start from the ignition switch.
> You switch ignition to switched live (2nd click).
> [+] is given to both relays, but only the main relay energises at this point, as its grounded. This relay powers the MS, injectors, and idle valve (if you run one).
> Megasquirt primes the fuel pump for a second or 2, switches off.
> Megasquirt is now ready to receive RPM signal (as this is how it knows whether engine is running).
> You crank the engine, MS sees RPM signal, and energises the FP relay, which powers the fuel pump and heated o2 sensor. Engine is running, megasquirt is now controlling injectors and ignition coil/coilpack, according to inputs from all it’s sensors. See, simple! .
When you have finished wiring it, switch on ignition, fuel pump should prime. If there is no prime, then check the wiring and make sure it’s as per diagram.
Jumpers and optional components
This is a very important step. When you receive megasquirt from whoever built yours, it will have been built ready for a specific configuration – ie what RPM signal it uses, how it’s conditioned, where the ignition signal goes, et cetera.
There are a number of jumpers and ‘flying’ leads that must be set the correct way for your setup to work.
For the VR sensor:
> Jumper VRIN to TACHSELECT on the bottom side of the PCB (near the DB37, opposite the heat sink.)
> Jumper TSEL to VROUT (Or VROUTINV if you want the VR input to be inverted) on the bottom side of the PCB, near the center.
OR (Do NOT install both sets of jumpers, chose one set or the other!)
For the Hall sensor, optical sensor, coil negative terminal or points:
> Jumper XG1 to XG2 on the bottom side of the PCB, near the 40 pin socket,
> Jumper OPTOIN to TACHSELECT on the bottom side of the PCB, near the DB37 connector, opposite the heat sink.
> Jumper TSEL to OPTOOUT on the bottom side of the PCB, near the center.
All the above info and more is on the V3 assembly page here
With the Vauxhall crank sensor, you need to adjust the 2 VR potentiometers on the megasquirt board, if they have not been adjusted already. These adjustments are part of the VR conditioning circuit, and you need these adjustments well sorted if you want a solid RPM signal with no drop-outs.
All the info is here:
I found that the best way to control the idle, is to get rid of the Vauxhall ICV, and use a mechanical plumbing valve from B&Q. This allows you fine control over how much air is allowed to bypass the throttle, and you need very fine adjustment to get a reasonable idle (lower than 1000 rpms).
Or, blank off the ICV pipes and adjust the throttle stop, so the throttle never fully closes.
You now need to set up the megatune configuration.
You should now follow this page:
when most things are configured, follow the tuning guide:
Rough plan of action:
> Download and install the latest version of megatune. If you want the Extra code, download the megatune Extra releases, which are on the MS1 and MS2 manuals pages linked above.
> Flash the MS ecu if you want Extra code.
> Use the megatune configurator to set all the basic settings and activate a ‘profile’ for your car.
> When this is set, your megatune should have the correct menu sets for your firmware and everything will run silky smooth.
> Now you should have readings for your temperatures, battery voltage (in the real-time thingy menu), the MAP sensor should read about 100, and TPS gauge should react to throttle presses. If it doesn’t – run the TPS calibration.
> Set all the engine constants by following the link above. Info on trigger wheel settings was on the vaux-extreme forums somewhere but I cant find the page, by they way which is an awesome forum for information for megasquirting our engines. The main value that is important is the Trigger offset, which is 21 for the Vauxhall 60-2 trigger wheel. The others are in the megatune configuration page (above)
> Generate some rough VE and Ignition tables, these should get you started. Don’t worry about the AFR table yet.
If all your engine constants are roughly correct, engine should start.
WARNING!! BEFORE ATTEMPTING TO START YOUR ENGINE, MAKE SURE THE OIL PUMP IS PRIMED!! If your engine has sat for a while whilst you did all the work, prime the oil pump and make sure its getting good pressure while cranking. There is a possibility of the revs shooting up the first time you start it, and xes and lets don’t instantly have pressure. Trust me, this is what ruined my engine. Running ‘dry’ at 3k rpm for 5 seconds will hammer some nails in its coffin, and you’ll have to change big ends.
> If engine starts, but dies, then watch at which part of the megasquirt starting sequence it dies – the ‘states’ are shown at the bottom of the main screen of megatune.
> It will probably die at After Start Enrichment phase (ASE from now on), during which you need to watch the o2 gauge to see if its rich or lean, and tune it. Remember, when engines are cold they need to run quite rich.
> If it lives long enough for the ASE indicator to go out, time to tune the Warm Up Enrichments.
This will take a while, as you tune for the correct amount of fuel at each temperature level all the way up to operating temp, whilst trying to keep a solid idle around 900 rpm.
> When you get it idling itself through the entire temperature range, its time to tune the VE table.
It is here that you can fine-tune the idle, by playing around with the VE value and idle valve position.
> When idle is good, you can take it for its first gentle drive! I richened all the sites up by 5% just to be safe.
> Watch gauges, drive and tune. (or get a mate to help)
> Drive and datalog (after making sure your wideband o2 sensor is reading correctly).
Analyse datalogs, and tune accordingly.
Repeat the above step many many times!.
I don’t feel like I’m expert enough in this field to really talk much about it, as I never perfected my map before it all got taken apart again.
But ill give it a bash.
Tuning means different things to people, in this context tuning is modifying the tables and settings, to obtain maximum performance/fuel efficiency/whatever you’re after, from your engine and its configuration. Not sticking bits of chrome on your window wipers, LED wiper jets, or tattoo vinyl’s on your bonnet. That’s not tuning.
You start off by generating base tables to get you going in the right direction, forward or sideways whichever you prefer :P.
For ignition, use this spreadsheet to generate a good starting point of an ignition map and enter it into the megatune table:
OR obtain an ignition table from a person running a similarly specced engine to yours. You can import MS1 tables into MS2 (it will do the interpolation), and you can also ask people to kindly export their table into a format you can understand, and enter the values into megatune yourself. It’s not that difficult really, just time consuming. This means a table from ANY programmable ecu is fine, as long as you can read it.
OR you can get megatune to generate you a very rough table to get you started, by entering some basic information.
Similar applies to the VE table, but the VE table will REALLY vary between engines. Even if the engines are the same down to the very last detail, is the person you’re getting the map from is running REQ-FUEL values that differ to yours (just 1 example), the map will be very different. Basically it’s just best to do it yourself, is what im trying to get across!
You have 2 options at this stage.
1# You can use the megatune's table generators to plug in some details about your engine and generate a starting point map. As suggested by peeps it can be way off, so be very wary. It will probably be literally enough to get your car to move, not much more. Just as a precaution, richen your generated map at the start by 5-10% just to be on the safe side. Remember Forrest Gump - rich and retarded (i didnt come up with that lol).
#2 Obtain a VE table from someone running similar spec to your engine (.vex file), plug this into your table, use as starting point. Make sure you have similar injector settings and the fuel requirement value is similar, otherwise once again it could be too lean for your engine and therefore dangerous.
Both of these methods will give you a rough map.
Also, I’d suggest staying clear of the set of default MSQ files megatune comes with. MSQ's are a file which contains the whole set-up including maps, settings, etc. It is NOT just a map. VEX files are the maps. Anyway, dont use these pre-set MSQ's - you may be running different software versions than the author, you may have more/different parameters that need entering, and without a doubt different spec engines, again its asking for trouble.
Ok, so you have a map, I would richen it up by 5% or %10 just to be on the safe side.
Assuming the engine starts and idles OK now, we can progress!
There are a few ways to do the tuning:
#1 – take it to the RR and get someone who likes MS to map it.
#2 – map it as you drive.
#3 – drive with your bumcheeks clenched and datalog the drive, then analyse it and tune later.
I prefer to drive with the o2 gauge in front of me, a boost/vacuum gauge and a rev counter to start with.
I will explain the driving and mapping process:
Pull off. As you pull off, watch the o2 gauge. Make a mental note of what is happening, then stop, and adjust the map. So if you’re idling at 10:1 AFR, and pull off and the AFR doesn’t change, its waay too rich, lean it by lowering the VE values in the ‘pulling off’ section of the map. If you’re idling at say 10:1, and you pull off and as youre pulling off it leans to 16:1 then the idle part is fine, but the lower MAP section needs richening. If it dies when you pull off, it’s far too lean.
Somewhere around here it will help if you populate your AFR table. The AFR table is a load of ‘target’ AFRs which ‘autotune’ in megatune can aim to achieve if you use it, together with EGO (exhaust gas oxygen) correction set up and working. I won’t go into this, but basically, set up the AFR table to the AFR’s you want under each condition. Generally you want to be leanest you can get away with on cruise, and richer on the power (specially turbo engines).
The AFR table will not be used by megasquirt to directly adjust the fuelling mixture, unless you use autotune. Also, make sure EGO is off.
Lets carry on!
When it’s moving, drive slowly (on a private track of course), and again, mental notes on what’s happening. If its driving smoothly at constant revs, no jerking, no coughing, then just adjust the VE according to the wideband gauge once again.
Basically, you keep driving and populate the table from the bottom left part (which is probably where a road car spends most its time), and make your way diagonally across to the top right.
The more you progress with the map, the more spirited you will have to drive, therefore you will want to do concentrate more on the driving, less on the tuning, which is when datalogs become very useful.
Basically log every journey, every style of driving, and name them by date, so you see progression.
Then, you can feed your .MSQ (megatune configuration file, which contains all the maps) and appropriate datalog file (.xls I think) into this little program called MegaLogViewer to automatically compare your ACTUAL afr’s from your datalog, to your TARGET AFRs in your .msq file, and adjust the VE for you!! It’s a lifesaver, use it! (thanks NICK )
Modifications, additional features:
Megasquirt shift lights how to:
Launch control wiring, flat shift, water injection control, boost control, loads of other info.
Terms and abbreviations
(I tried not to use abbreviations without explaining them but what the heck)
Cruise – low MAP, cruise RPM.
Idle – low MAP, low RPM
WOT (wide open throttle) on naturally aspirated engine can only get be atmospheric pressure – 100ish kpa.
Power – WOT, revs increasing.
Boost – MAP over 100kpa (atmosphere)
AFR – air/fuel ratio.
VE – volumetric efficiciency
MS – megasquirt
MSQ – megatune map
MAP – manifold absolute pressure
MAT – manifold absolute temperature
ICV – idle control valve
IAC – idle air control
DET – google ‘engine detonation’
Knock – google ‘engine knock’
EGO – exhaust gas oxygen
LED – light emitting diode
EFI – electronic fuel injection
CTS – coolant temperature sensor
TPS – throttle position sensor
AFM – air flow meter
AMM – air mass meter
O2 – oxygen.
VR – variable reluctor. A device which creates an AC pulse when ferrous metal is passed by it.
FET - field effect transistor.
Engine does not start, what do I do?!
Does it crank? If not, then battery is probably flat. If it cranks, and doesn’t start, does the fuel pump relay come on?
If yes, check to see if you have fuel/spark. If FP relay doesn’t click, then check the RPM display in megatune, remember you need RPM’s for megasquirt to energise the FP relay (if you’ve wired it as per diagram)
I have no RPM’s
Check to make sure the TACHSELECT jumper is soldered to the correct position – VRIN for crank sensor, OPTOIN for hall sensor.
Adjust the VR pots on the main board as per instructions here:
Try swapping the wires around on the VR sensor (as per link above)
I have fuel and spark and RPM signal, but still doesn’t start
Did your engine start happily before this project?
Check to make sure your ignition leads are the correct way round. If the engine backfires when trying to start, swap the leads going to the coilpack (if running wasted spark). You may be getting spark at the wrong stroke (phase), ie firing order may be opposite.
Megasquirt cuts out when engine is cranking, the moment I turn the key.
Check to see where you’re taking your main megasquirt power from. In newer cars, there are 2 types of switched live, one that cuts out whilst cranking (to help the starter), and one that doesn’t. You need to use the one that stays live while cranking. These are normally available on the stereo plug, and directly from the ignition barrel.
You may have a weak battery - check with multimeter to see how much the volts drop when you crank (accross battery terminals)..
If you relocated the battery, you may have used too small gauge a cable. There would be too much voltage drop when engine is cranking. To check voltage drop, measure voltage while cranking across the battery terminals, then take reading from the point where megasquirt is powered and chassis. Then compare the 2 readings.
It kicks to life but all the gauges go blank on megatune as the engine cuts out, then they come back again.
You may be getting resets. Very common, there are disruptions in the megasquirt main power feed. This may be interference from non-resistance spark plugs, bad grounds, ignition components causing EMI (electro-magnetic interference), or bad/worn alternator brushes.
Some info here:
watch the grounding and noise elimination videos on this page (lots more info on this site)
Google is your friend, there are many stressed out people on the net with megasquirt reset issues. I had these issues, and it’s why I ditched my coil and went wasted spark, which fixed everything.
My mouse in megatune goes all sluggish
Check to make sure the baud settings are correct for the serial port – its all on this page
AFR values on my wideband display and megatune don’t match up
Check to make sure you set the correct wideband controller in the megatune configurator, and your car’s profile. If the megatune configurator does not have your particular brand of wideband controller, google it or ask here. To get my JAW to read close to true, I had to connect to the JAW controller, and change the VOUT tables to values that matched the megatune configurator values.
I can’t get my idle low enough, no matter what I do.
You (or your idle valve) is probably allowing too much air to bypass the throttle. Reduce this air, and you will find it easier to get a low, solid idle. I had this problem, lowest I could get it was about 1400 rpm, no matter what I did. Then I ditched the ICV and put a mechanical tap valve which did the trick. When I finished tuning my idle, it was more solid than it ever was on Motronic. Remember, light flywheels=difficult idle.
I can’t get my idle to stay solid; it hunts all over the place by itself.
It may be your idle valve playing up (if you’re using one). If you’re not, it’s down to the VE and Ignition map. Different engines like different levels of ignition advance at idle. Best to leave the ignition map alone at this point though, and fine tune the idle on the VE map. Harsh changes in values will cause the revs to bounce around the map. Best is to ‘box in’ the idle section, making it very rich at the lowest RPMs which will let the engine recover from near death, and lean it right off at high vacuum (low MAP), which will mean the revs will be quick to come back to idle after you’ve ‘stabbed’ the throttle. Then make sure there are no harsh transitions between map sites.
The car drives very jerky, my MAP gauge bounces up&down, and my datalogs look spiky.
The MAP sensor on the ecu is very sensitive, and the ECU is very very fast, which means it reacts to changes of it’s sensor values like it’s on speed. If you run lairy cams, or rely heavily on helmholtz resonance in your inlet system, then instead of seeing a solid pressure the MAP sensor is seeing a very quickly fluctuating manifold pressure, and acting on it. You need to increase the lag in the megatune lag settings, which means megasquirt will average these values more, or make a little damper out of a small fuel filter or similar. Or both, the combination of the 2 make huge improvements to the driveability of the car. More on the damper here:
Tigra c20xe to turbo on Megasquirt wip - lots of pics!
Also, make sure your EGO correction is off. EGO correction is a function designed to allow closed loop control of a mixture. This is not really needed as we have mapped it! It will influence your fuelling amount according to the o2 sensor values, which can be prone to electrical noise, be laggy, or inaccurate. For these reasons I don’t recommend running it.
How to wire my TPS?
Read this part of the external wiring page:
I am using my c20xe loom, and want to use an IAT sensor, the Vauxhall loom doesn’t have one, how do I wire it?
Either run the 2 cables from the IAT sensor to the MS,
Use 2 of the pins from the AFM plug (as megasquirt doesnt need an afm), then find them on the ECU plug end and run them to the MS ecu. Just make sure the wires you use aren’t power feeds, etc. Avoid black, red and blue cables generally :P..
So there we go, it’s a long old read, but I think I’ve covered most bases. I will add stuff as we all go along , hope this helps !!
lets make this thread live !!
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