OBD MPGuino gauge

[Froggy]

I think the init routine could be more informative on the failure, and I'll look into that... feedback would be highly informative to working out the kinks.

On thing to check is to verify that the device is talking to the car. Use a volt meter and check that the K line pulses (at the OBD plug). If it remains a constant (or no) power, then the device is not communicating. Check your wiring for a bad connection (a bridged or bad solder joint.)

From here, it may be that your device is not listening to the car (a bad connection), or that the car is expecting slightly different timing than what the OBDuino works on. Right now the timing is hardcoded, and will not change. You could recompile with slightly different values and see what happens. (The official 9141 timing has a wide range of acceptable timing values, and OBDuino focuses on just one set within the ranges... )

[Demonhawk]

I went and double checked all my connections and made sure there were not any bridged ones. I seem to be fine in that area. Quick question for checking the K-line that would be pin 4 on the freescale chip correct? And would I just need to put one probe from the voltmeter on that and the other on the chasis gnd?

*Edit- Also one more quick question, what are the range of the acceptable values for iso? Is there a list of them somewhere, and around what line in the code is that located on? Thanks

*Edit - update: I just went outside and checked the k-line, as the arduino boots and tries to run the init sequence the voltage on that line jumps all over the place. When i unplug the power to the arduino, the voltage on that line is a steady 13v. Should that line have voltage constantly? I know that the connection is bridged with the resistor.

[Froggy]

Check the K line from the device at the OBD plug. This ensures that the cable is correct (if it's a home made job), and it's easy access the pins. Just connect to the ground (PIN 5) and the K line (PIN 7). You'll see the device maintain a high of 12 volts (or 5 or so if running from USB connector), then fall down to zero three time (or so) as it tries to connect. The auto MUST see this to react.

For the timing variances see prj.perquin.com where it lists the 14230 timings. The 9141 should be the same, but I can't verify.

It states:

0-20 Inter byte timing in ECU response
25-50 Time between end of tester request and start of ECU response or between ECU responses
25-5000 Extended mode for "rspPending"
55-5000 Time between end of ECU response and start of new tester request, or time between end of tester
request and start of new request if ECU doesn't respond */
5-20 Inter byte time in tester request


We currently wait 3000 ms between attempts (maybe your car needs a longer wait period?)

We currently wait 60ms before listening for ECU response, maybe your car responds at earlier and we miss part of it's response?

Can you test your gauge on another car?

Yes, the K line on the car side is held high, and falls to zero for communication.

[Demonhawk]

I purchased my obd2 cable, and when i check the voltages it is in fact connected. I'm unable to test it on another car because both of my parents cars are 2008+ models so they are CAN protocol. I'm going to look over the code when I get a chance to see if i can toy with the timings.

[Demonhawk]

I have an update. I've been slightly successful at getting the obduino to connect to my car. I discovered that if I have it unplugged from the obd port until the actual Iso9141 init message comes up it will usually connect about 90% of the time. I don't know if this is due to an issue with my car requiring different init timings or not.

I still have an issue though. RPM, Temperature, MPH are all displayed properly and all seem to be around the correct values, but my fuel consumption does not change. It just sits at 0 gallons per/hour which leads to no mpg being calculated. Any advice on where i should go from here?

Thanks

[Froggy]

I've hit a similar snag with the OBDuino, where it will continue with FAILED until I unplug it and plug it back in (with the car still ON.) No idea why... Certainly an issue though! For me the problem is very rare...

It might be a change in the pause at the start will work for you. (Not sure WHAT change...)

What about turning the car off once OBDuino has connected, will it reconnect ok once the car starts up again?


As for the fuel consumption, this is during a drive? When you shut off the engine, does the shut down sequence show 0.0 gallons wasted too (assuming you idled at red lights for a while)? Did you try other fuel consumption settings? (Trip, outing, tank...)

Glad to hear you have it at least chatting with the car. Not perfect yet, but, getting there...

[Demonhawk]

For me the problem isn't rare. It does it all the time, lol.

As for turning the car off after the obduino has connected it will usually successfully reconnect after i turn the car back on. Unless of course I remove power to the obduino then it struggles to reconnect again upon booting. I'm currently using a usb boarduino which i'm powering from my laptop during testing so it has constant power.

In regards to fuel consumption, correct during a drive it does not increase the fuel consumed. When i shut off the engine it says "Trip saved 0.0 gallons wasted". I also ran through all the different settings and none of them that were related to mpg, or fuel consumption were working.

I don't quite understand why all the other readings work correct though (RPM, MPH, Temp, etc), and the fuel related ones do not.

[dcb]

Can you see individual pids while running?

Do you have a MAF pid?

If not,

Did you set an engine displacement? Do get a reading on the MaP (Manifold absolute pressure) Pid? How about RPM and Intake Air temp Pids?

(And someone remember to add short term fuel trim into the equation some day)

[Magister]

Originally Posted by dcb

(And someone remember to add short term fuel trim into the equation some day)

I tried, it changes only +/- 2 or 3% of the fuel consumption, so I didn't care... I also tried to add the lambda given by my wide band O2 sensor but it's the same, it changes +/- 2 or 3%.

The OBDuino is not an absolute scientific gizmo, and here with fuel variation because of temperature, those with 5% or 10% ethanol, etc, it introduces other percentage of "error" anyway.

[Froggy]

Hi DemonHawk,

You're dealing with two issues. The first is non-connection at startup. This will take some trial and error to suss out, but you CAN work around it, so let's back burner it for now.

The second more important issue is no fuel consumption recorded...

The fuel calculation relies on several other PID's from the vehicle before it bothers to calculate how much fuel is used since last calculation.

To check that we have valid PID info, using two screens of PIDS, display:

RPM, SPEED, THROTTLE, FUEL SS, (MAF RATE) or (MAP and INTAKE T)
(if MAF RATE is selectable, we use that, if not we use the other two (and RPM))

If any of the PIDs used show ERROR (or zero RPM), then no fuel use can be calculated.

If all are valid, then fuel use should be calculated from the data available... Fuel use is calculated in the accu_trip() function.