I started a thread a few weeks ago inquiring whether or not it would be feasible to install an MPGuino fuel efficiency gauge in a TDI. The consensus was that it couldn't be done (easily, at least). But I've pressed on with this project and so far I'm quite pleased with the results.
What is an MPGuino? It's an Arduino based open source fuel economy computer based on a ATmega168 microcontroller. The assembled product looks like this:
It is designed to calculate fuel economy by tapping into a vehicle speed sensor and a switched 12V supply to a gasoline engine's fuel injector. Two questions needed to be answered in applying this gauge to a TDI. In the absence of a 12V signal to a fuel injector, is there a workable equivalent signal on the TDI electronics? And, will I fry my ECU or other components in doing so?
In reference to the fuel injector signal, after completing Chris Bell's MFA cluster conversion in my 96 Passat, I became interested in tapping into the fuel consumption signal generated by the ECU which feeds the MFA. I had no idea what this signal looked like, but ecomodder.com user rmccomiskie was kind enough to post an oscilloscope graph of the fuel consumption signal on his Audi A6. I assumed (correctly, as it turns out) that the signal on the VW would be similar. Here it is:
Second question: will I fry my ECU by tapping into this signal. Looking into the Arduino website, it states the following:
Next step was to tap into the VSS and fuel consumption signals from the ECU. Since I had just completed a cluster conversion, I had easy access to the plug on the back of the cluster containing the two necessary signals. Pin 26 on the cluster provided fuel consumption and pin 27 provided VSS.
I decided to install it in the ashtray recess. I scavenged an ashtray from a salvage yard Passat and gutted it so I was left with only the faceplate, then carefully cut out the openings for the LCD display and three pushbuttons. Since an unswitched 12V supply is also needed, I tapped into the cigarette lighter power which was conveniently located nearby.
With all four wires attached, it was time for a test drive. Based on research I had done on the ecomodder.com forum, rmccomiskie had tried adapting this signal from his Audi, but he found that a change in the code was necessary to prevent GPH readings from reading backwards (i.e. GPH rising while coasting/falling while accelerating). After making necessary changes to the code, the GPH and MPG readings started responding as expected. I've spent the past few days calibrating it and it's looking like it's providing pretty accurate readings. Prior to buying the Passat in '07, I had a '98 Jetta equipped with Scangauge and the MPG numbers generated by the MPGuino look very much in line with those generated by the Scangauge (different vehicles, mind you).
The finished product: ( this pic was taken very early on in the calibration process, so it's reading a tad optimistic
)
I realize that Scangauge is WAY easier than going this route. I have a 96 Passat with the OBD-D BK ECU, so that wasn't an option for me. Also, this can be done for around $50-60 installed, which may be attractive to some. It's available in kit form here or a complete pre-assembled unit here. AFAIK, the pre-assembled kit isn't equipped with a USB port which may make changing the code a bit of a challenge, but I've contacted the seller about selling the units with the code changes pre-installed.
Lots more reading can be found here and here.
What is an MPGuino? It's an Arduino based open source fuel economy computer based on a ATmega168 microcontroller. The assembled product looks like this:
It is designed to calculate fuel economy by tapping into a vehicle speed sensor and a switched 12V supply to a gasoline engine's fuel injector. Two questions needed to be answered in applying this gauge to a TDI. In the absence of a 12V signal to a fuel injector, is there a workable equivalent signal on the TDI electronics? And, will I fry my ECU or other components in doing so?
In reference to the fuel injector signal, after completing Chris Bell's MFA cluster conversion in my 96 Passat, I became interested in tapping into the fuel consumption signal generated by the ECU which feeds the MFA. I had no idea what this signal looked like, but ecomodder.com user rmccomiskie was kind enough to post an oscilloscope graph of the fuel consumption signal on his Audi A6. I assumed (correctly, as it turns out) that the signal on the VW would be similar. Here it is:
Second question: will I fry my ECU by tapping into this signal. Looking into the Arduino website, it states the following:
I recall reading elsewhere that they draw 0.7 mA. With that information on hand, I ordered and assembled the kit. Despite my lack of board-soldering experience, I soldered the thing together, plugged it into a USB port, and Voila! it came to life.
Next step was to tap into the VSS and fuel consumption signals from the ECU. Since I had just completed a cluster conversion, I had easy access to the plug on the back of the cluster containing the two necessary signals. Pin 26 on the cluster provided fuel consumption and pin 27 provided VSS.
I decided to install it in the ashtray recess. I scavenged an ashtray from a salvage yard Passat and gutted it so I was left with only the faceplate, then carefully cut out the openings for the LCD display and three pushbuttons. Since an unswitched 12V supply is also needed, I tapped into the cigarette lighter power which was conveniently located nearby.
With all four wires attached, it was time for a test drive. Based on research I had done on the ecomodder.com forum, rmccomiskie had tried adapting this signal from his Audi, but he found that a change in the code was necessary to prevent GPH readings from reading backwards (i.e. GPH rising while coasting/falling while accelerating). After making necessary changes to the code, the GPH and MPG readings started responding as expected. I've spent the past few days calibrating it and it's looking like it's providing pretty accurate readings. Prior to buying the Passat in '07, I had a '98 Jetta equipped with Scangauge and the MPG numbers generated by the MPGuino look very much in line with those generated by the Scangauge (different vehicles, mind you).
The finished product: ( this pic was taken very early on in the calibration process, so it's reading a tad optimistic
)
I realize that Scangauge is WAY easier than going this route. I have a 96 Passat with the OBD-D BK ECU, so that wasn't an option for me. Also, this can be done for around $50-60 installed, which may be attractive to some. It's available in kit form here or a complete pre-assembled unit here. AFAIK, the pre-assembled kit isn't equipped with a USB port which may make changing the code a bit of a challenge, but I've contacted the seller about selling the units with the code changes pre-installed.
Lots more reading can be found here and here.
