Its been a long wait, but its finally here! OBD read and write is available for the MG1 BMW ECU's as found in the M140i and M240i.
We have now completed Stage 1 ECU tuning and our BETA program will start. More about that at the end of this blog post for those that are interested.
The difficulty when tuning a new version of ECU (in this case known as the MG1) is where to start, thankfully with our knowledge of this engine and previous datalogging that we have carried out with the JB4 system we have a good idea of the B58 engines characteristics, what it likes and doesnt like. Straight away we ran into our first issue.
After taking a backup read of its ECU we got our own test car (BMW 540i B58 Xdrive) onto our 4wd linked dyno and carried out some testing through 4th and 5th gear to get some baseline logs and power curves. This gave us the information we needed to start building a V1 tune.
Straight away we hit an issue, the much talked about 'fuel cap' or limit of fuel available to safetly make the desired amount of boost pressure, ignition advance and power. The images of datalogs below show this issue well, firstly what happens when you hit the maximum fuel limit in the ECU:
As you can see, it was all very promising until around 5600rpm and then power and torque drop significantly. You may also notice a spike in the torque around 2700rpm, so left us plenty to work on for V2. But lets look at why the power and torque dropped so suddenly. Firstly was it a dyno glitch such as loss of grip or a traction control problem? Lets look at requested ECU load, this is a good indication of what the engine is being asked to do.
This was great info, it shows the boost spike in lower rpm as well as the ECU requesting that engine load is reduced. This confirms it is infact a car issue and not caused by a loss of traction or other dyno anomaly. We then looked at how the ECU had reduced power by requesting less load, heres the boost pressure log:
As you can see, the boost spike at 2700rpm is there, and the drop in power matches the engine load reduction, confirming that the ECU isnt happy about something, from experience we know that this is ususlly temperature, fuelling or igntion advance related. So we looked at exhaust gas temps first:
With EGT's being very close to stock and nothing obviously wrong here we looked at IAT (intake air temperature) as we know that these B58 do suffer from heatsoak due to their chargecooled 'intercooler' system:
Again, very close to stock and no obvious problems to cause the drop in ECU load. Next up was to check ignition advance timing, otherwise known as timing or spark advance. Now we are running more boost, we expect to see less ignition advance, but what we did find was at the same point in the RPM range that we had dropped power, we saw a sudden dip in timing:
Last on our list to be checked is fuelling. We know that a weakpoint of the N55 engines was rail pressure, and many piggyback users such as JB4 also hit this issue on the B58, basicly the high pressure fuel pump (HPFP) cannot keep up the demand in fuel rail pressure to satisfy the speed that the injectors are emptying it. This was given the name of 'fuel cap' very early on in the B58 tuning days. As you can see, we are suffering a sudden drop in fuel rail pressure, starting at around 4800 rpm.
We quickly identified the cause of the issue from these datalogs, went back to the map and corrected the 2 obvious causes of the problems we encountered in V1, the boost spike and the rail pressure drop. V2 showed instant improvements but a few more hours of work was required to get to a point that the logs were completely healthy, overnight we worked on V3 and these are the results:
In v3 we have resolved the rail pressure drop and the boost spike, using less boost, and all of the other logged parameters are also extremely healthy, including IAT, Timing, EGT, Engine load and oil temperature. We found that this car made closest to its stock figures of 340bhp and 450nm in 4th gear (actual dyno figures were 345nhp and 475nm), so we chose to use 4th for our final power testing as it gives the most accurate indication of gains over the stock BMW claimed figures. Here are the results:
As you can see, the boost spike and power drop have been completely solved. Power delivery is smooth and peak numbers are great, but dont ignore the Delta gains, these are the gains over the entire RPM range, the volume of power throughout the midrange RPM is huge, at 4800rpm we have a gain of 100bhp and 160nm of torque!
On the road the power increase is significant, the car just pulls and pulls from 1500-6500 rpm the acceleration is relentless. Once we hav carried out some road logging and further testing we will get some GPS based times.
We will be offering some Beta testing for customers with M140i / M240i, these cars will go through the same exact testing on the dyno as our own car. The purpose of Beta testing is to evaluate how different software variants respond to tuning and to get feedback from customers, we may find that we need to flatten out the torque delivery for 2wd cars to increse traction, we need to dial in the throttle response mapping and look at the posibilities of Stage 2 tuning, mapping on Sport button, cold start delete, speed limiter removal etc.. and the more cars we tune, the more info we will have about these extra features and knowledge on how these cars respond on the road with such a big uplift in power.
In return for the feedback Beta testers will get a discount and free software updates (if required), this is not a 5 minute job and we will need your car for 1 complete day. If you are interested just drop us an email on: firstname.lastname@example.org