MegaSquirt EFI Dyno Tuning Help

A proper tune, on a proper dyno, can make a world of difference….

We’re all about you learning to tune your car yourself, and for fuel tuning that’s usually very attainable with a good wideband a fair amount of time.  However for the DIYer, ignition tuning is usually either guesswork, or blind trust in a map you pulled off of some forum on the internet, that is unless you have the help of a good steady state dyno and know how to use it.  Ignition timing what you want to get right too– that’s where 90% of the power is.

Your MegaSquirt or MegaSquirtPNP EMS does need to be mapped to your car to get you the best performance.  I’ve track tuned cars, pretty well actually, and then fully mapped the same car on a good steady state dyno, and there is a world of difference.  Better throttle response, better powerband starting from much lower in the rev range, higher peak torque and horsepower, better torque at part throttle and at cruise even.  And even more than that– all of this can be done without any guesswork at all when it’s done on a steady state dyno.  The car can be kept well away from the knock threshold, allowing you to make the most power possible without ever encountering detonation.  Do NOT add advance until you hear knock and then back it off– that’s a recipe for disaster at worst, and at minimum it’s very poor tuning technique that will likely leave you down on power.  There is a science to this, and it’s fairly easy to dial a well built engine in on the proper equipment, with the proper training and experience using that equipment.

There are steady state dyno’s all over the country/world.  The tuners may or may not have worked with an MegaSquirt or MSPNP before but the tuning software is easy to work with, you should bring your laptop already setup/configured to communicate with your unit as there are various flavors of firmware/hardware out there and you can’t expect the dyno tuner to be ready for every one of them.

You will want to find a steady state/load bearing dyno, not a simple inertia dyno.  Dyno Dynamics, DynaPack or Mustang are high quality steady state dyno manufacturers.  Inertia dynos are pretty much a waste of time when it comes to tuning, you can roughly map in wide-open-throttle (WOT), but that’s it, and you can’t even do that right as you can’t adjust the load to anything that’s realistic for the road.

Here are some links to locators and/or lists of owners of our recommended steady state dynos, we can’t personally vouch for any of these tuners, just that they have the right equipment.


Dyno Dynamics has a Dyno Locator


You can call around to a couple shops and see what they charge as it varies in different areas.  Also find out if they’ve worked with MS before, or if they’re willing to work with it even if they haven’t– the software is very simple to use, and most tuners love the newer TunerStudio MS Software.


Preparing to take your car to be tuned

You or your installer should insure of the following things before taking the car to be tuned.  Keep in mind that dyno time is not very affordable diagnostic time, you don’t want to be figuring out problems on the dyno.  The operator is more than likely going to have to charge you shop rates even if the dyno isn’t operating as you’re still essentially using the dyno and they can’t have any other cars on it until your car is off.

MegaSquirt EFI Dyno Tuning Information and Technical Help

Make sure your install is complete

You car should be running perfectly, just not tuned yet.  What does that mean?  It doesn’t mean you can drive your car at all…

  • Base timing should be set, nothing else matters if it’s not right.
  • The car should be starting and idling reliably at all different coolant temperatures that will be encountered.
  • All sensors are reading properly in the tuning software.
  • You’ve properly calibrated the coolant and IAT sensors if need be.  (GM Sensors read correctly by default, others need calibration, see the MSExtra Manual for the MegaSquirt version you are using)
  • Your TPS sensor is calibrated.  If you don’t have a usable variable TPS, then the TPS pin on the ECU should be pulled down to ground through a resistor to keep the TPS reading from floating around (this can cause a confusing no-start issue if you don’t)
  • You don’t have any strange ignition misses, etc.  If possible, do enough research on tuning the car yourself, and with the help of a wideband if available, free rev the engine a bit and keep the AFR in the safe zone by dialing it in (while free revving, for the purposes of this test, 14:1 is a good target AFR), you’re really just looking to see if the engine revs fairly well with no load on it to help ensure the EMS install is complete and free of issues you need to work out.  You should be able to free rev it through pretty much all of it’s RPM range.  You’ll be at zero load, just keep the AFRs safe (12.5 – 14:1) and the timing safe (most cars at no load 25-30deg will be fine, most likely more once tuned)
  • Make sure you’ve properly figured out your dwell settings and/or by use of a scope to check primary current– too little dwell can cause misfire, too much can burn things up.  The tuner is likely to guess at this number if he thinks it needs to be changed; you have the information needed in the MSExtra Manuals— you or your installer should have this right before the tuning session.
  • Your idle valve should be functioning properly, make sure you’ve tested it, have it running at the proper frequency, and that it controls idle speed when you increase/reduce DC control of the valve.
  • Forced induction cars– Your IAT sensor MUST be AFTER the compressor, and AFTER the intercooler.  Preferably just before the throttle body inlet.  It needs to measure the actual actual air temp that’s entering the intake manifold, hence the name intake air temp (IAT) or manifold air temp (MAT). If you are measuring ambient air temp just after the filter, then heating the air with a compressor (SC or turbo) then maybe you cool it with an intercooler, who knows what temp that air will be when it enters the intake?  The ECU surely doesn’t, and your fueling calculations will suffer badly.
  • If you have a wideband, make sure it’s reading properly (installed and calibrated properly), and preferably have it’s output piped into the MS where it can be datalogged.  Have MegaLogViewer loaded on your laptop for quick log viewing.
  • Your cooling system should be adequate– much of the time spent on a dyno is spent waiting for a car to cool down, the better your car manages heat, the faster your tuning session will go.  If your cooling system isn’t adequate you’d be better off spending a bit of money on improving it, then take the car to dyno and the session won’t take as long and you’ll save money there.  Wouldn’t you rather put that money into cooling upgrades instead of dyno time waiting for the car to cool off?

Make sure your car is well maintained

  • The spark plugs are in great condition, new is even better, and properly gapped.
    • NOTE:  If you’ve installed forced induction on a stock n/a car, or even if you’ve significantly increase the compression on an n/a car sometimes, you should go with a ‘colder’ plug, at least one step colder.  Also it’s likely you will want to gap the plug a few thousands less than stock unless you’ve upgraded your ignition system to jump the gaps under higher pressure.  For example if stock is .035 maybe go to .028, if needed later during tuning (misfires under boost) you could drop the gap a tiny bit more.  Check the plugs after driving the car a bit- if the plugs are too cold they’ll foul quickly, if they’re too hot (as stock n/a plugs may be with forced induction) then you could have pre-ignition/detonation.  Usually I start with 2 steps colder, then read the plugs, if they’re reading dark even though I know my fuel mixture is right then I’ll change to only one step colder than stock and that’s usually fine.
  • Make sure the rest of your ignition system is in great condition– wires, distributor cap, etc.
  • Make sure all fluids are fresh and topped off.  Oil/coolant/etc.
  • Make sure you have your wheel lock keys if you’re going to a hub dyno such as a DynaPack!!!  If the tuner can’t remove your wheels it’s a no-go…

Want to learn more about tuning EFI?

Pick up Matt Cramer & Jerry Hoffmann’s book, Performance Fuel Injection Systems TODAY!

HP1557 - Performance Fuel Injection Systems