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Old 03-26-2011, 12:36 PM   #641 (permalink)
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2001 VW Jetta TDI Diesel ???

Hello - have been following this thread for some time and finally broke down and bought a few boarduinos to test with. After a bit of experimentation (see previous post) I managed to get the voltage comparator circuit initially submitted by schlorkist functional. A huge thanks to everyone who's contributed to the project, very cool stuff!

Wondering if anyone has any knowledge to share relevant to using OBDuino for diesel application. At first blush it appears I'm only getting data back for PIDs 04, 05 and 0C (load, temp and rpm) on my VW Mk4 TDI. If not, I'm hoping someone might steer me in the right direction as to where to start. I'm going to assume I need to assemble a list of supported PIDs but not really sure where to start there. I would love to make this work over OBD, but I fear a completely different method of estimating injected fuel quantity may be necessary due to the diesel engine's lack of a throttle blade.

And while I'm thinking about it, regarding the issue njakts was working on, you might also try commenting out:

Code:
#define do_ISO_Reinit
#define skip_ISO_Init
#define carAlarmScreen
as there appears to be an issue with ecu polling and / or the security screen. Mine will init successfully (only on the second attempt) when these are commented out, but never when using the default config (security screen enabled). Wondering if anyone with an ISO vehicle could try r187 and confirm?

Lastly, does anyone know the source of the "clunkiness" in the menu mode? It's almost as if the code is only seeing the rising or falling edges of the button transitions. Weird stuff. I would be willing to attempt to fix this but I've got a large laundry list ahead of me with the other issues mentioned, so any thoughts on this would be greatly appreciated.

UPDATE: it also appears I'm getting VSS. I think my problem may be timing b/c I'm getting no more than 2 pids / sec.

UPDATE #2: After configuring ISORequestDelay down to 10 ms I'm seeing everything I think I need. Now to hack something up for consumption - from what I've been able to gather the way others have done it uses PID 04 (Calculated Engine Load). This looks to be interesting b/c I noticed this number drops to 0 instantaneously during DFCO. Didn't I see mention somewhere about detecting DFCO in code? Wouldn't monitoring this PID work for that more simplistically?


Last edited by spfautsch; 03-27-2011 at 10:15 AM..
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Old 03-27-2011, 11:25 AM   #642 (permalink)
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thanks for your help spfautsch, but now after a million zillion sucesfully uploaded shetches my arduino board wont work anymore
its the avrdude sync bla bla bla error. tried everything and nothing works... atmega 168 uploads like a charm, but 328 doesnt. daaaammmmmnnnn!!
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Old 03-27-2011, 02:37 PM   #643 (permalink)
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Just a guess, but if you have it in-circuit while trying to flash you'll need to disconnect rx/tx lines from the voltage comparator so it doesn't interfere with serial comm (speaking from experience).
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Old 03-27-2011, 05:01 PM   #644 (permalink)
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yeah, I discovered that a while ago, and this time I was also like ''oh yeah, rx and tx... ill disconnect them and it will work''
nothing
nothing is connected to the board.
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Old 03-28-2011, 11:39 AM   #645 (permalink)
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Consumption calculated from PID 04 / LOAD_VALUE ???

Curious if anyone's ever attempted to use this PID along with a flow constant to calculate rate for gas or LPG vehicles. I cobbled together some quick + dirty changes yesterday to see what would happen for my diesel, using a wild guess for injector flow rate. After a little testing and a ballpark tweak of the flow rate, my first session looks very promising. The trip / average numbers from my first commute test were very close to what I've been logging at fill-ups before any calibration. My calculations are way off for instantaneous, but it got me thinking of the possibility of a universal replacement for the maf / 14.7 method. Obviously it has the downside of requiring some trial and error for calibration, but it appears (at least on my ECU) to compensate for ECT based mixture changes, and DFCO as I mentioned previously.

Having dabbled with lean burn on another vehicle I own, I can tell you that especially for cold-start idling, part-throttle cruising and wide-open foolishness, 14.7:1 goes way out the window. I don't know for sure that this is plausible for all applications, but if it is it would greatly simplify rate calculations. If it would happen to work for speed-density applications it would also free up some processor bandwidth and / or memory for other cool stuff.
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Old 03-29-2011, 09:47 AM   #646 (permalink)
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to: spfautsch

according to
Interpreting OBDII Data
or
http://obdcon.sourceforge.net/2010/0...ed-load-value/

PID04 is MAF/maxMAF
for diesel engines it is something else, but essense should be same.
and probably you will be back to 14.7 at some point.

DFCO detection is done using PID 0x11 (THROTTLE_POS) and PID 0x03 (FUEL_STATUS). For now it looks like PID 0x04 could be used too.
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Old 03-29-2011, 09:58 AM   #647 (permalink)
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Quote:
Originally Posted by Bix View Post
Also my K line just gives a constant 11.1 volts to my multimeter, other people said it was supposed to fluctuate, is there something wrong or is my multimeter too crap?
It does not have to fluctuate in multimeter - multimeter is to slow and does not show comunication in K line. It shows only average. For disconected K line it is normal to see somthing bellow 12V.
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Old 03-29-2011, 10:42 AM   #648 (permalink)
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Thanks for the reference. According to this info for diesel it's supposed to correlate directly to output torque so that should be close enough. Perhaps adjusting for RPM would give output power, which would (or should) be a more direct correlation to fuel consumption.

If it's directly related to air flow for gasoline engines it shouldn't drop to zero during DFCO, and my idea would be invalid. I'm just curious if anyone has noticed what this value does during DFCO for gas / LPG as I don't have the equipment to look at this at the moment (laptop battery is toast).

Quote:
Originally Posted by eimix View Post
PID04 is MAF/maxMAF
for diesel engines it is something else, but essense should be same.
and probably you will be back to 14.7 at some point.
The power output of a compression ignition engines is not governed by a throttle blade. The quantity of fuel injected in the combustion chamber is the only means of controlling engine output, and they do not operate in a closed loop stoichiometric burn mode, at least not in the same sense as a gasoline engine. Some newer "clean" diesels do have something that looks like a throttle, but is in essence part of an egr system to deal with soot.

Most diesels from 1999 and up that utilize oxygen sensors do so only to reduce smoke. But they don't operate at a fixed mixture - at part throttle cruising speeds diesels can run as lean as 22:1. That's the primary reason why the ALH TDI and some of it's successors can achieve >52MPG without hypermiling techniques in a 2800lb car.

Quote:
Originally Posted by eimix View Post
DFCO detection is done using PID 0x11 (THROTTLE_POS) and PID 0x03 (FUEL_STATUS). For now it looks like PID 0x04 could be used too.
I just thought it might be an easier way to detect DFCO for gas - reading two PIDs takes twice as long as one...
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Old 03-29-2011, 03:23 PM   #649 (permalink)
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Tested in my car (gas + lpg) but engine load PID04 does not drop to zero.
At low revs 1% engine load, downhill with DFCO it shows 3% engine load.

So PID04 does not look promising for DFCO detection.
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Old 03-29-2011, 04:07 PM   #650 (permalink)
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I tried a lot of things to have a more accurate value, using wideband O2 sensor value, lambda value, etc.

After thousands of logs, I saw that the correction using this PIDs was not really worth it. About all the corrections were between 0.97 and 1.03, so adding time to ask for these PID (some car do not have wideband O2 sensor anyway) was a little bit useless. Especially that at the end, the average was about right.

I found that gas that have 0% ethanol or 10% ethanol, having winter tires, being -30F outside, having tires at 44psi instead of 22 psi, etc, all have greater influence on the fuel consumption, sometimes as more as 10%.

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