E67/E38 Map Sensor Limit

I have been working recently on the 255kpa limit on the E67 ECMs. This limit is regardless of what linear and offset is entered in.

The Reason this limit exists is due to the way that the source gathers the voltage from the sensor and converts it to the kpa value. The Raw Sensor data is stored in a short integer value. From this, the Source puts it on a linear scale using the linear and offset values. The way this is done (poorly) goes over the limitation of the Short value. Before the value can be saved back into the Short Integer space it must be truncated. This truncation is what causes the limitation of the MAP sensor.

I am assuming this was done without thought that no one in their right mind would put over 20psi of boost on these engines. Well, Here we are…

I was asked by multiple parties to look into this, and have found a solution. Initially I thought this was an impossible task. Since the way it was written left little room for a easy and quick fix. After a very peaceful vacation I stumbled upon a invasive but simple fix.

Intentionally leaving out the details of how I fixed it. But you can see it working in the log below. I have not yet figured out a solution to logging. The VCM scanner still reports a value with a maximum of 255kpa. However what i did was to set the VVE table to be 1:1 with the map sensor. This allowed me to log the value of the map sensor without VCM scanner getting the value wrong.

This test was done on a test bench where i could exactly control the map sensor via a potentiometer. RPM for this test was kept consistent ~1500rpm.

You can see in the log that the new MAP value (VE) traces exactly with the Map sensor until the 255 mark where it continues on up to ~415kpa.

Also shown in the g/s (which is not valid for any engine) the fueling calculation is being updated correctly and does not top out with the original Map sensor.

Overall I am happy with this project. If you are interested in Testing this out please reach out to me.