26 Sept

With the exhaust leak fixed, we need a new problem, and alas, one turned up. The AiM MXS digital dash has been working fine, except for a strange error reading MAP. The MAP value is sent over to the dash via the CAN bus, along with engine speed and several other parameters. They all work fine, but the dash claims that MAP isn’t the usual 22-24 kpa at idle, but instead, something lower. After maybe 30 minutes of run time, it’ll even display 0 kpa, which is a perfect vacuum… not likely. Meanwhile, the ECU sees a correct value for MAP, which is the exact same value being sent to the dash. That’s the old problem…

The new problem started several days ago, when oil temperature started to lie. Unlike MAP, oil pressure is a voltage, read by both the ECU and the dash. As soon as ignition is turned on (like first thing in the morning), oil temperature should be about room temperature, and it is – so says the ECU. However, the dash claims that it’s 51-52 degrees C, which is nonsense. However, as oil temperature rises, it seems like the dash starts reading the actual value once it’s above its false 51 degrees C floor.

Neither problem can be explained by a wire being loose. In the first case, since MAP is in the CAN packet, all other values should be messed up as well, but they’re fine. In the case of the oil temperature, if the wire was broken, the reading should go to max, and if the voltage is shorted, it should read zero. It does neither, and if it was shorted, it would affect the ECU’s reading as well, but it’s fine.

As a hail mary, I updated the firmware in both the dash and ECU – no change. To add insult to injury, the engine now gets limited at a lower rpm than before; I hope it’s my test tune and not some mystery feature of the new ECU firmware. It’s always something.