Now that you have the car running (or at least starting and idling), here are a few basic tuning tips to help out. This is not a complete tuning guide, only a set of tips to make the process a little easier. It is suggested that you find someone with experience to help you through the rest of the process, because while the concepts are rather simple, it does take some experience an intuition to end up with a good tune. Remember: If you tune too lean under load, you will blow the engine!
Fine tuning the warmup enrichment cannot take place until the rest of the map has been tuned.
Once you have crossed 100KpA, you are now in boost. I would recommend running 12:1 until approximately 4-5 PSI (135KpA), then taper down to 11.5:1 and carry that all the way until about 15 PSI (204KpA) where you should start aiming for the high 10s. Overall I have found these ratios to be very safe with the timing I have provided in this writeup, and they will provide excellent power with great turbo response. As always, the ultimate deciding factor for your boost AFRs will be your car. If you find that running richer down low provides better turbo response, then by all means do it. If you are nervous about running into the 11s under boost, tune for 10.9:1.
Don't neglect the low RPM boost areas. This means finding a big hill (or using a dyno) and doing wide open runs starting from 1500RPM in high gear. That is a typically ignored area but makes a huge difference in how the car drives. Don't just start all your boost runs at 3500 RPM because that leaves all points on the map below probably far too rich. The last thing you want is to be in the wrong gear (for whatever reason) and have the car fall on it's face with a cloud of smoke if you get on the throttle.
Getting a smooth transition between vacuum and boost will take some time. Don't be over aggressive in tuning one point. Make sure to keep the map smooth around 100 KpA and make small changes. Additionally, tuning the car around the secondary injector stage point will require working a range of bins in that area all at once.
The overrun settings I have provided should be good for 99% of applications. The two settings you will likely tweak are the KpA and TPS activation points. Fuel will not be cut unless the Megasquirt is reading KPA and TPS position below those points so you will need to pay attention to both when tweaking the overrun. If overrun is not coming on consistently because your TPS doesn't fall below the activation point, lower the activation point. The same goes for the KPA point. You should not change the RPM cutoff point from 1500 RPM as lowering it will make the engine have a tendency to stall. Raising it will just waste fuel needlessly.
To tune the accelerator pump, start at idle and then stab the throttle slightly. From within the accel/decel window, observe the graph beside the bins to decide which ones need to be changed. If the engine hesitates for a second and sounds as though it is momentarily "stopped running", you will need to add fuel. If it falters and drops RPM, you will need to remove fuel. Minor changes can make big results, so work slowly. Gradually increase the amount of throttle you are using until you reach wide open. Essentially, you are sitting at idle and then flooring it while observing the result.
If you find that you need to add a load of fuel in the accell pump, revisit the VE table and richen up the bins directly above the idle bins a little. You will find that when you stab the throttle, the engine will shoot towards atmospheric/boost directly above the idle. It is important that these bins provide enough fuel with a smooth transition into the rest of the map.
It will take some time to get this right.
This may take days, or even weeks, to get right. Obviously you cannot tune temperatures lower then ambient when you cold start a car, so it may even take months until you have weather appropriate to tune the lower temperature corrections.
If you find that the car rarely goes into closed loop, you will need to determine which value keeps it out of range.
For MS1 people using the settings I have provided, this will be manifold pressure. I have set up 70 KpA as the cutoff point for closed loop, thus anytime the ECU sees over 70 KpA it will go back to reading only from the VE table. If you have as small turbo, or an aggressive port, your car may pull less vacuum then this on the highway. If that is the case you may wish to set the settings in "Open Loop Mode" to use the TPS as the determining factor instead. The only annoyance you will run into here is that you can end up with the engine spending too much time in closed loop while driving in the city in traffic, which makes for an anemic feeling car.
For MS2 users, it could be either TPS position or manifold pressure. You will need to observe both while driving to determine which is keeping you out of closed loop. You may need to increase the vacuum point in "EGO Control" to compensate. Likewise, you may need to adjust the TPS value if you find that you are consistently operating the car above that setpoint. Just be careful not to go too aggressive because you can then force the car into closed loop when you don't want it to be (ie. under moderate acceleration). The result is a car that feels weak.
MS1 people have a few more parameters to adjust then MS2 users. The "EGO Switch Point" represents the output voltage from the O2 sensor that the Megasquirt will seek to maintain. The settings I gave with the AEM UEGO I specify in this writeup, represent an AFR of about 15.2:1. A higher voltage is a leaner ratio and a lower voltage is a richer ratio. You will find these ratios on a chart in the UEGO Instructions (PDF). "Ignition Events" represent the number of ignition events between adjustments of the A/F ratio. Around 20 is a good number for 2 rotor and 4 cylinder engines. Another option (down at the bottom of the dialog box) is to use a fixed number of milliseconds between changes. However this can result in a rather choppy closed loop. I'd suggest leaving it as a function of engine speed. "Controller Step Size" determines how many percent the controller will alter the A/F ratio by at each change. 2 is about the limit. Any more and the change will be two great for the Megasquirt to handle quickly. If you find 2 leads to wild oscillation of the AF ratios, go down to 1. "Controller Authority" is how much the controller is allowed to alter the injector output to maintain the AF ratio. If closed loop is making more then 30% worth of changes, you need to dial in you VE table a little more!
The MS2 closed loop algorithm is far more sophisticated and has fewer parameters. The controller decides how it will go about correcting the AF ratio and you only need to tell it the ratio you wish it to seek and when you want it to activate. You can set an AF ratio in the "AFR Table 1" dialog. In theory you could change your closed loop settings to run closed loop over the entire VE table but the settings I have provided should only put you into closed loop at light loads. "Controller Authority" is the same as used in the MS1 (see above).
One thing to note for both MS1 and MS2 users with S4 narrow range TPSs is that you will likely have to set closed loop to come on via a manifold pressure set point only. This is because the TPS value will show near full throttle even at less then 1/4 pedal due to the fact that it is narrow range.
Closed Loop Idle Tuning For MS1 Users
Under closed loop idle, the Megasquirt is using the BAC valve to actively regulate the idle at a set RPM point. This is quite useful in that it allows a high idle when the car is cold and will keep a steady warm idle regardless of air temps, engine electrical load or other factors. Earlier in this writeup you set up the closed loop idle parameters, then set the BAC valve as "Warmup Only". Warmup only is a duty cycle only setting that opens the valve while the engine is cold and then gradually closes it as the engine warms up. This creates the high idle and makes starting/driving a cold car fare more pleasant. Now that you have a good VE table and your cold start enrichments are dialed in, the controller can be set to enable closed loop idle.
Note: Don't bother trying to set up closed loop idle until the VE table, warmup enrichments and idle are properly set up. It will be very difficult to get a stable idle if the BAC valve is trying to compensate for wildly wrong AFRs. If anything, tune the AFRs at idle and cold start slightly rich to start and then adjust them once you have closed loop idle set up.
To turn on closed loop idle, go back into the "Idle Control" dialog and set "When to use PWM idle" to "Closed loop only". A bunch of options will change on that dialog and when you burn the changes, you should notice an immediate change to the idle. The ECU will try to regulate your idle speed to 1000 RPM if it is at or below 1000 RPM. You can observe this action by switching one of the gauges in Megatune to "Idle DC". The more the duty cycle increases, the more air the ECU is letting in to increase idle speed.
Tuning closed loop idle involves adjusting how the BAC responds to engine changes to achieve the most stable corrections. Everything in the "Idle Control" dialog should be fine for most engines. We'll cover the "Dashpot Settings" a little later. Most of your tuning will take place in the "Idle Control (Closed Loop Settings)" dialog. The "Deadband Range" sets an RPM range close to the set idle speed at which the ECU won't bother correcting changes. 40 RPM is a good place to start. If you are tuning for lower idle speeds, you will want to lower this value a little. The upper and lower RPM limits tell the Megasquirt when to recover the idle quickly (if the difference is at the upper limit or above) and when to recover it slowly (if it is near the lower limit). The lower limit should always be around the deadband range, and the upper limit tends to work best when it is double the lower limit. Much of your tuning will be in adjusting the "Fast recovery" and "Slow recovery" times.
If the idle is unstable (hunting or oscillating) when the RPMs are far away from the target idle (for example, if you accidentally almost stall the engine when coasting down) then you need to increase the fast recovery time. If the opposite is true, where the engine lazily returns to the correct RPM, then you need to decrease this time. The numbers I have provided were obtained with a considerable amount of experimentation and should be a good place to start.
Slow recovery is used basically only when the engine is already around the idle speed. For example, if the electric fan switches on and tries to drag down the engine while idling, slow recovery will be used. If you slow recovery number is too large, then the engine will tend to hunt for a second or so to find the idle. If this is the case, decrease the slow recovery time a little and try again. If the slow recovery time is too short then the ECU will overcompensate and the idle will bounce.
As you can see, most of the problems will result in a bouncing idle so you will likely have to observe the Idle DC gauge to determine exactly what the ECU is trying to do and apply the appropriate changes.
If your idle is always hunting, check your air/fuel ratios. You will probably find a lean spot in the map directly above the idle bins. Richen it up and the idle will probably stabilize.
"Closure Speed" determines how quickly the Megasquirt should close the valve. By decreasing this setting, you cause the Megasquirt to act more quickly on its changes. Increase the number and the changes are made more gradually. "Startup Delay" is the number of milliseconds between when the engine has started and when the Megasquirt starts correcting the idle.
Back in the "Idle Control" window, the "Dashpot Settings" are for the software dashpot which is designed to slow down the drop in engine speed when the engine is returning to an idle after the throttle snaps closed. If you have removed the mechanical dashpot during the throttle body mod, these settings can help prevent the engine from stalling on quick throttle closure. "TPS threshold" tells the Megasquirt when the throttle is closed enough to activate the dashpot function. "Idle Activation Adder" tells the Megasquirt how many RPM above the idle RPM the dashpot should be triggered at. For example, the idle speed in this writeup is set at 1000 RPM, so with an idle activation of 250RPM the dashpot function will be enabled at 1250 RPM. The "Dashpot Settle Time" is how long the Megasquirt will wait for the idle to settle down after the dashpot has been activate. Finally, the "Dashpot Adder" tells the Megasquirt how much to open the BAC to activate the dashpot. With a setting of zero, the dashpot function is disabled. To enable it, put in a low value of under 10. Rev the engine and allow the RPMs to settle. At 1200RPM the dashpot will be activated. What you are looking for is an almost unnoticeable pause as the tach falls. If the RPMs shoot up, you need less Dashpot Adder. If there is absolutely no change, you need more.
Idle PWM Warmup Settings For MS2 Users
Closed loop idle setup for the MS2 is not covered in this writeup at the moment. Here we are using the BAC to create a high idle during warmup only. To adjust these settings, use the "Idle PWM duty Table" dialog. It is a straight curve of BAC valve duty vs. temperature. More duty cycle increases the engine speed while less duty cycle decreases the engine speed. From a cold start, 2000 RPM is a good place to start with a nice taper down to a 1000 RPM idle when the engine is warm. Once you have your cold start enrichments set up, you can go into this dialog on a cold start and adjust your BAC valve to maintain the idle speed you want. Note that this is a duty cycle adjustment, so you won't be able to achieve an exact idle speed as conditions vary. This is basically a rough "idle up" during warmup.