Open loop tuning guide:

This is the open loop version of this guide, this is how engines has traditionally been tuned for the last 30 years or so. It was good back then and it's good now. It's also the 'one person tune' that most of you will have to use.

First of all, most people use far too many load bins. It will make the tuning time consuming. I suggest that you put load bins at: 20, 30,50, 70, 90, 102, 120, 140, 160, 180, 200 and 250 kPa. Note that this applies to boosted AND normally aspirated engines. Using all 12 load sites in the normally aspirated range will only increase your workload.

Secondly as this is the open loop guid you need to disable closed loop lambda control: Settings->EGO(Lambda) control. Set Lean limit(%) and Rich Limit(%) to 0.

We assume that the injector opening modeling parameters are ok, with small injectors it's easy to get it close enough but with large injectors it's fairly hard. With some luck you have injectors that we have documented the opening characteristics for. (As of December 2005 there are no properly verified entries.)

It's very important to understand that any WBo2 readings taken when the engine has missfires, bogs or just acting strangely is unlikely to be correct. For example a missfire reads lean! because the sensor only measures burned petrol, liquid petrol is ignored and only the air will be measured. Under conditions like this you need to read the plugs to get it right.

We start with the extremely low load sites.

Start off by letting the car idle, now tune the VE at the loadsite the engine use until the actual Lambda is the same as the target lambda (the value in the Lambda table under Settings-> Lambda table). No need to be anal about this, within 0.02-0.03 is good for now. You will probably need to blipp the trottle a few times to clear up the engine when doing this, expecially when going from a pig rich base tune.

Now increase the rpm somewhat, 2k or so is fine. Do the same here, tune VE until the actual lambda is the same as the target. The same 0.02-0.03 applies here.

Continue doing 3k in the same way.

You can now copy the value you have at 3k to 4k and so on all the way up to your higest rpm site. Now copy the low load sites upward toward 70kPa load or so. Normally I would go to 100kPa but as this is time consuming in megatune it's enough with 70kPa. You will do the 'copy upward' routine several times and doing it all the way to 100kPa every time will get on your nerves.

It's now time to take the car for a spin, mentally prepare yourself to hold a few load sites and start the logger.

50kPa: 1100rpm, 1600rpm, 2200rpm, 2800rpm.

Now check the log and compare the actual lambda and the target lambda for each of the tested sites, actual lambda/target lambda will give you a multiplier that you need to apply on the load site. After making the corrections on the above sites you copy upward and to the right. Now repeat the above 50kPa loadsite to check if the change was enough or if the sensor was bottomed out.

When the 50kPa sites above is tuned fairly well you can go to the next three rpm sites, still at 50kPa: 3400, 4000, 4600.

Again copy upward and to the right after going through the 'test, adjust, test' cycle.

You are now ready to go to the next load level (70kPa) You need to be more careful now as problems can start causing engine damage now. Just let it run steady state for 2-3 seconds or so on each site the first time until you know that you are starting to home in on the settings. You also need to listen for detonation now and read the plugs for signs of detonation between the runs.

Again copy upward and to the right after going through the 'test, adjust, test' cycle.

Continue repeating the above procedure for all the load sites until the car is tuned at all loads and rpms.

As are likely to have the wide band lambda option you will probably want to run the car in closed loop from now on. It will eliminate most of the very time consuming cold and warmup tuning as the car will run in closed loop mode and compensate for things like bad intake air temp sensor tuning and such things.

If you are going to run closed loop you can be a bit more lax about the end result of the above tuning procedure as you will want to go through the closed loop tuning procedure as a final step on those cases.

The reason I use the open loop procedure first is that it's faster and that it's harder for most people (and engines!) to screw up. Some people like to run the closed loop tuning procedure from scratch, some others want to start with closed loop and then switch to open loop for fine tuning and then enable closed loop again. All of this is highly dependent on tuner preference.

Jörgen Karlsson