RomRaider

Hi

Does the MS45 DME use the Barometric pressure signal from the PC board mounted sensor in the fuel trim control loop?

Background
I spent a lot of time in the E46Fantatic forum, helping people solve their engine problems. This uses OBD2 PID data logs to identify the problems.

There are 4 unexplained "Rich fuel trims on both banks" cases on my desk. 3 with MS45 and 1 with MS43 DMEs. The usual cause of a rich on both banks case with a stock DME flash is a faulty sensor.

All have new pre-cat O2's and new VDO MAF's. Still have rich (more than -10% total fuel trims) conditions.

Looking at Calculated Load (SAE PID 04), there is some weird results. The PID 04 formula, its primarily driven off the MAF values, with correction for standard temp and pressure. So, looking as the DME PC board mounted Baro sensor.

Sensor has a 0 to 5V output with range of 15 to 115 kPa. Sea level Baro is 103 kPa at 4.2V, so a low reading Baro sensor will give readings for denser air. If the DME is using the Baro in the fuel trim control loop, then that would give you rich fuel trims.

Using a 2 pronged approach:
1) Confirm if the Baro is being used by the DME for the fuel trim control loop. The reason for this post.
2) Read/test the Baro sensor and see if the pressure reading is off. Most scanners do not provide the Baro sensor as an output. While I have a written procedure to test the sensor with the DME lid off and the DME running, I'm reluctant to send it out to people of unknown capability. The risk of shorting something out and killing the DMe is all too real. So, back to point 1, is the sensor used? If not, then no need to test it.