Peter Florance's postings about grounding convinced me that there must be something up with mine. This was pretty much confirmed when I had a look at a log file he sent me. His CLT and MAT in particular were much smoother than mine. Hard to be sure with TPS because the default log file formatting is just an integer and my TPS didn't jiggle by as much as 1%, but I bet it was smoother too. I also noticed that his Batt.V was smoother, which I put down to his BMW not having ancient French electrics...
Because my MS is buried behind the dash, it took me nearly a day to get the work done, but it is definitely pleasing to see much less jitter in the analog sensors. I was a bit surprised that the Batt.V smoothed out too, but perhaps I have the wrong impression of what this is measuring. Anyhow, a quick synopsis of what I did and I'll also have a go at explaining why this is important in layman's terms -- since those are the only terms I have.
I started with Peter's "quick" check: unplug the MS and check that the ground terminals of each of the engine room sensors -- TPS, MAT, CLT -- have no path to the battery -ve. The only path to ground should be via the MS -- in at the sensor ground pin (pin 19 in my case) and out by the other connected ground pins. So the sensors should be completely isolated if the MS is unplugged. If there is a path to ground, something's wrong.
Sure enough, when I did this test, something was wrong. Nuts.
I knew I had followed the diagram in making the connections from my existing harness. Turns out that what I hadn't done was make the
disconnections. It turned out that there was another path to ground through the idle air valve. I just needed to separate the sensor wire grounds from this and all was well. Kind of frustrating that it took a whole day to find the one cut and two solder joints that were needed, but difficult diagnosis and easy fix is nothing new to a programmer.
Moral of the tale:
- I think the installation manual could be improved by including Peter's simple check when the harness is about to be plugged in.
- An explanation of exactly why this is important would also be nice. Here is what I think it's all about:
The MS board maintains a 5V reference voltage which is passed to the sensors. It regulates this voltage continuously so that there is always 5V higher than the MS ground. Perhaps surprisingly, the MS ground can vary appreciably relative to the car's battery -ve. This is not a problem because every jiggle on the ground is matched by a corresponding jiggle on the 5V wire. But by connecting the 5V wire to the sensor and grounding it somewhere else, the jiggles no longer correspond and you get a noisy result.
- Having someone's known good log file is a worthwhile thing. I've only ever installed this one ECU, so it's a bit hard to know when something isn't right. Perhaps making a "standard" ideal log file available wouldn't be a bad idea.
Does my new noise-free TPS signal negate all the umpteen pages of to and fro in this topic? I don't think so. It is probably true that I wouldn't have posted in the first place if my TPS had looked as good as it now does, but having a minimum significant movement before tpsDOT is calculated gives great sensitivity and I'm very happy with how responsive the car is. AFAICT, the smoother A2D readings haven't made a tangible improvement, but I'm very pleased just to know they're so much better.
Finally, many thanks Peter for the suggestion.
Have fun,
Rob.