Engine and Transmission Tech

The VE Analyzer feature is a very helpful tuning aid and it's great fun to play with too... but I was getting a little frustrated because its results seemed to vary with weather and specifically with temperature. I think I've identified two root causes. Thus these two tips, below. (You're invited to add more!)

1) don't forget to calibrate "BattV"

Most of the sensors and sensor wires in a fuel injection system are pretty conspicuous. Before you try to start your engine for the first time, it's fairly obvious that key sensor inputs (e.g. your throttle position sensor) need to be calibrated. But one key input isn't external and therefore isn't wired at all, and thus is easy to forget or ignore. MegaSquirt senses battery voltage on its main power feed and uses that measured value in its calculations. So, I've learned it's good practice to compare your MegaSquirt computer's measurements with a reliable voltmeter, and make sure they match.

How do you read and adjust voltage in Tuner Studio? First click on one of the gauges in the Gauge Cluster screen. Then pull down the "File" menu and select "Gauge Cluster", which will bring up a second level menu where you can select "Sensor Inputs 1" and then "Battery Voltage - Voltmeter". The gauge you clicked-on back in step one will now function as a voltmeter. Incidentally, you can of course also eyeball BattV in MegaLogViewer. If you discover a discrepancy, go to the "Tools" pull-down menu and select "Calibrate Battery Voltage". That'll bring up a window with two adjustment fields. My MegaSquirt seemed to reading voltage low by 0.4V in all cases. Raising the "supply voltage at zero ADC count" setting from 0.1 to 1.3V has MegaSquirt matching my Fluke meter.

2) consider tweaking the "Air Density MAT Correction" curve.

As you probably know, colder air has more oxygen per unit of volume. Whilst ingesting cool air, your engine needs more fuel to maintain parity. So EFI systems typically have a Manifold Air Temperature sensor mounted somewhere. Typically, it's on the intake track not too far from the air filter. The thing is, there could be quite a lot of difference between air temperature sensors and certainly a lot of difference between where they're mounted so it makes sense that there should be some sort of calibration. There's a thermistor calibration option under the Tools menu, or alternatively you can play with the Air Density MAT Correction table under the "Basic/Load Settings" menu. Per advice on the MSExtra bulletin board here, I've adjusted my curve to look like this. Seems to have helped a little.

By the way, you might want to think a bit about where you're drawing your air from. If you're drawing hot air from inside the engine bay, its temperature is likely to vary over a much wider range than if you're drawing air from ahead of your radiator or from the cowl area.

A background on my project: '97 Ford Explorer 5.0, Comp Cams XE264HR, 1.6 roller rockers, custom top half intake plenum, AFR 165 heads, Patriot "pancake" headers, 24# injectors.
In regard to MegaSquirt, do those who have installed the system recommend MS III over MS II even if there are no plans to upgrade to sequential injection or individual spark? Is data logging significant? I have in mind an EDIS spark on the Ford, and utilize the existing fuel rail in batch injection.
How about Tuner Studio? Do you recommend the Lite version or register for the advanced?
Is use of the stimulator advantageous?
So many questions, and feeling overwhelmed!
Thanks,
Dennis

I think MS3 is a good value and it gives you more room to grow.

Since I figured my vehicle would be traveling a long way from home on all sorts of roads, at night, and even in bad weather, I wanted the peace of mind that the professionally-assembled "plug-and-play" MS options give... professionals in a factory setting should certainly be able to solder more consistently than I can. MS3-Pro features significantly more modern electronics - machine assembled surface-mount components in a hermetically sealed enclosure! - and thus MS3-Pro should prove the most reliable/robust MegaSquirt computer by far.

I think the Stimulator is only useful if you're assembling your own ECM and want to test it.

Fuel rail is the same for batch-fired and sequential injection. You will however need some sort of cam position sensor for sequential.

There's an SD card inside my MS3-Pro, but I haven't yet bothered to turn-on its built-in data-logging feature. For general tuning, I find it more convenient to simply set my laptop in the passenger seat and datalog over a standard USB cable. That way, the logs can be as large as I like and I can start and stop them at will - for example, before and after tune changes. BUT I can imagine that SD-card datalogging could be useful feature if for example I were autocrossing. I could download a log after each run. My laptop stops logging if I close its screen.

You can start with the Lite version of TunerStudio... but you'll want to upload to the registered version. The advantages of doing so are listed here: [tunerstudio.com] Of them, difference reporting is a very good feature. I've used VE Analyze Live quite a bit and found it to be useful and fun to play with... but I don't think I really need it. As I've learned more about tuning, I've come to appreciate the scatter plot features of MegaLogViewer. If I had to choose one tool over the other I'd certainly take scatter plots. Note: the registered version of TunerStudio is included free with MS3-Pro.

I hope that helps!

Thanks Calvin, I appreciate your insight. I have the cam position sensor, as it was part of the Ford system, but had found the EDIS in Pick 'n Pull, and thought it simple enough. I have looked at the MS II and MS III in pre-assembled versions, as that would reduce the chance of errors. Well, I'll think some more on this, and decide. I sure would like to get to Indianapolis, I saw the cars at Omaha in '13, and they fill up my "I wonder if I could do that" pretty well!
Thanks again.
Dennis