A COMPLETE Guide to Megasquirt on the 2002

[Colin]

Which unit are you using? Could you post pics of your PCB front/back? I've got MS1 with the green PCB, but I bought it off a volvo guy a while ago with the understanding it was ready to go. I noticed it's been modified though, I believe just a boost related modification, but I'd like to get it back to OEM if possible for one less possible problem.

I am using MS2 so I am afraid my photos would not be helpful.

[Colin]

Here is the correct part number for the in tank fuel pump with the feed and return line.

16141181075

[zinertia]

Colin

Did you leave all of the arrays (12X12 and 16x16) with their initial data values?

thanks

Dennis

[Colin]

Sorry, I have been quite busy and have not updated this. Here are my Fuel VE, Spark, and AFR tables. All of these are pretty "mature" at this point and work quite well. I did not go as crazy with super lean cells on my AFR table as some people have, but I do have "fuel cut over run" on and that makes quite a big difference on the mileage.

This spark table is also the best one that I have had. It works smoothly with good power throughout the rev range. I have a low RPM timing bump to smooth out the idle as well.

[zinertia]

Colin

Thank you! Your posts will enable me to move much more easily into the conversion that I will be starting in a month or so.

Dennis

[Colin]

Here is my new spark map that I have been working on for the past two weeks.

I like this one better than any of the others that have been floating around for M10s.

It follows the stock Tii advance curve but with about +2 degrees of advance throughout.

It goes "all in" at 4k and provides good resolution in the lower RPM range for smoother throttle response.

I have added in more advance at low load settings for better mpg.

Try it and let me know what you thinK!

[Colin]

Here is more info about the PID settings for EGO control. Again, I have found that this is one aspect of tuning that is VERY worth investing a lot of time into. I am still tweaking mine as I am getting oscillation around my target AFR, although it clings quite tightly to the target. Correction is quite quick, which has made for smoother running, better mileage, and more precise tuning.

From miataturbo.net:

if your I is causing oscillation, it's too high.

basically:

I makes sure you hit target. the longer you're away from the target, the stronger it wants to hit the target.

P is how strongly attracted to the target you are. the bigger the deviation from target, the stronger P gets

D is like the bouncer. when a big P drives the value toward the target really fast, D puts on the brakes and slows it down as it approaches the target.

So in short, to tune EGO (which is a pretty slow system in my opinion), you should run as much I as you can without going beyond the stability limit... so if you see it oscillate, back off 5%. Then crank up P until the correction overshoots from a transient event (blip of the pedal eg) and back it down so there is almost no overshoot.

leave D at zero because it's too hard to tune. D is generally used to allow a higher P value and improve response time. With a well tuned PI and D system, you can tune P to a value that would overshoot and use D to slam on the brakes at the last second. You reach your target faster (though maybe with minor overshoot and oscillation).

[Colin]

I have updated my PID EGO control setting and have arrived at a much better configuration.

One of the biggest issues I've had is that as I would approach a stop and engage the clutch, my RPM would drop below IDLE. As it turns out, this was due to an over correction of the EGO control. The following settings have seemed to correct it:

P: 10

I: 50

D: 20

The "D" setting is higher than many people recommend, but for me, it was crucial for eliminating any "over shoots" which is what I believe I was experiencing as I approached stops.

I also dialed out any "averaging" on my lambda lag (so it is now at 100). This made it much more responsive but did require the totally different PID settings listed above. I am very happy with how it responds now and I notice much less EGO correction is required, the idle is finally stable and VE Tune Live now was able to very quickly generate a smoother VE table.

Accel is smooth and responsive. I feel pretty good about the whole tune now and am much happier with my new spark map.

[Colin]

After years of messing about with the IAC and never really perfecting it, I believe I have honed in on some reasonably good settings, but what's more, on an effective technique for adjusting it.

The manual is not very clear when it comes to idle control, so I will attempt to explain it the best I can here.

The key factor is the "Start Value" under "Idle Control." This sets the baseline number of steps that the stepper motor uses to go from fully open to fully closed.

I have found that the default values are much too high. The megamanual recommends trying to remove the housing and stepper motor and observe it's movements on a running engine. For obvious reasons, this is simply not practical.

What I have found is easier, is to set up a digital readout in Tuner Studio that displays the current number of steps (or you may do this in the Realtime Display) and start by setting the "Start Value" at a rather high value, say 200 steps. Keep trying to do cold starts (this may take many days) and observe the steps readout as the car warms up. Note the step value at which the engine no longer seems to respond to a change in the IAC steps.

So, for example, you set the "Start Value" at 200, and the RPM goes to 2000 rpm, and as the steps decrease, the RPM eventually reaches your normal IDLE speed.

If the idle steps display is still reading 110 steps at the moment that your motor reaches it's normal idle RPM, that probably means that you have 110 steps more than the stepper motor is capable of providing, so some simple subtraction gives you 90 steps of resolution.

Next time, try a cold start with the "start value" and 90 steps and go through the whole thing again until you feel you have the best resolution that the IAC can provide.

To make this work, you will need to adjust your "IAC Steps Bin" table (see below) to reflect the current start value, so, in other words, if you set the start value at 200, your curve in your table will need to go from 200 on the cold end to 0 at the warm end.

Each time you change the start value, you should adjust your table accordingly.

[Colin]

Other key values:

Algorithm: I, and several others have found the most consistent results come from setting this at "IAC" always on.

Time Step Size: I have found inconsistent IAC operation if this is set lower than 3ms. The lower you set this value, the more responsive the IAC is, so I set it to 4ms as a safe compromise.

Minimum Steps to Move: This is the resolution at which the IAC will move. 1 is obviously ideal for smooth operation.

Start Value: See above post. With the 02again.com housing and the OEM jeep stepper valve, I have found 90 steps to provide the most consistent operation.

Crank-To-Run Taper Time: This is how long the IAC waits before transitioning from the "Cranking Steps" setting (per the Cranking Steps table) to the "Idle Steps" table. It basically gives the engine a little extra throttle after you turn to key to insure that it gets going ok.

Hysteresis: This is the amount of change in temp degrees that megasquirt needs to see before it will respond to a change.

For the time based after start, the megamanual recommends disabling it unless you are driving in some cold as a dog's ball sack conditions, which, I am quite sure none of us are as we are all battling off rust.

To disable it, as per the megamanual, set "Cold Temperature" to -40.

[Colin]

This is fairly self explanatory.

This table sets the number of idle steps vs coolant temp.

You'll have to play with these settings to generate a curve that allows your engine to run smoothly during warm up.

[Colin]

The Idle Cranking Steps table sets the IAC position during cranking. This allows you to provide some more air during cranking without having to press the throttle pedal.

I set mine to the maximum open position for all temperatures, in this case 90.

[Colin]

While going through some logs, I realized that my mapDOT signal and thus my MAP signal were both a bit noisy. This led me to investigate ways to clean it up in the box.

I run a fairly long hose from the port on the passenger side of the 318i manifold in through the cabin to where my megasquirt sits on top of the trans tunnel. I believe (as do others) that a long hose is actually good as it can have a bit of a dampening effect on the signal, thus smoothing it out.

After some research, I discovered that the "map sample angle" should be set to 90 for a 4 cylinder. The engine immediately idled smoother after I changed this (from 40). I played around with this value a bit more, but it seemed best at 90. I also upped the "No. of map sample events" to 2 with a positive effect on the map signal.

I did reduce the "Map Averaging Lag Factor" down to 85. This takes out some of the small spikes in the signal and truncates some of the peaks, but I do not feel that this is the best solution as it slightly reduces engine response and does not fully solve the problem of noise in the signal.

In the coming days, I will explore physical filtering options. My plan is to run some sort of a restriction in the line that will hopefully act as a low pass filter and remove some of the bigger spikes.

Having said all that, I have posted my current settings and I do endorse them!

[M3M3]

great info colin!

have you tried going a bit richer on the afr above 60% tp? i run 12.4 up in that range on my AN. more power.....

[Colin]

great info colin!

have you tried going a bit richer on the afr above 60% tp? i run 12.4 up in that range on my AN. more power.....

Thanks! I will try that. FYI I am not using AN so that axis is actually KPA.