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Old 08-29-2008, 08:39 AM   #21 (permalink)
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Hardware idiot check - there is 1.3 volts on pin2 at idle. I am using Analog In pin 2.

Software:
I have added "int press = 0" here:
--------------------
byte screen=0;
byte holdDisplay = 0;
int press = 0; //declare press

#define looptime 1000000ul/loopsPerSecond //1/2 second

void loop (void){
--------------------


Removed the "int" from this line:
-----------------------------------------------------------------------
press = analogRead(2) + 1; //press is common rail pressure approx in bars
-----------------------------------------------------------------------

And modded the display as you suggest.

Press is displaying 0.1 at 1.3 volts, rising to 0.9 max when driving. Maybe a display issue?

InstMPG is zero for any value of "us per gallon" and currentMPG is 999. It looks like it thinks no fuel is being used. Instant raw data shows a "random" value for injus. Could it be that the value is out of range for calcs and for displaying a sensible number?

On the plus side, CPU is now down to 52% from 500%...


Last edited by ecoxantia; 08-29-2008 at 01:53 PM..
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Old 08-29-2008, 08:43 AM   #22 (permalink)
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Quote:
Originally Posted by wagonman76 View Post
Did you possibly get the VSS and INJ wires switched around? I did even after checking quite a few times. Others have too, seems like a common mistake.
Well the displayed mpg has been making some sense, so I think I escaped this particular mistake! It did take me many attempts to get the right wire for Vss: as they say, measure twice, cut once. Not so easy to measure something that needs the wheel to turn though.

My only complication is an injection system that varies in pressure by 10x...

Last edited by ecoxantia; 08-29-2008 at 01:05 PM..
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Old 09-09-2008, 08:47 AM   #23 (permalink)
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Quote:
Originally Posted by ecoxantia View Post
Press is displaying 0.1 at 1.3 volts, rising to 0.9 max when driving. Maybe a display issue?
That looks pretty good actually We avoid floating point math on these little chips so instead the display routine assumes every number you pass it is 1000 times larger than it is.

So multiply the pressure number by 1000 before displaying it if you want to see it as a whole number.

So it would be something like 100 to 900, which is like perfect
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Old 09-09-2008, 10:37 AM   #24 (permalink)
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Oh I see! Why didn't I think of that Good news.

My breadboard is looking dangerous so I'm taking time out for an enclosure, decent connections and tidying up. This is my daily driver so I can't afford any mistakes. Besides my partner thinks I've lost the plot, what with filling the car with bare wires!!

I got as far as multiplying pressure by a thousand for the mpg calc, and at that stage mpg was kind of making sense. I get the impression that pressure has a far bigger effect on fuel burnt than injector duration.

I have read that 1350 bar is unlikely to be seen- since there is only a small window at 4000 rpm where it's called for. And in any case my pump is 120 000 miles old!!
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Old 09-09-2008, 11:05 PM   #25 (permalink)
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Cool, some more unsolicited thoughts:

Note the analogRead*1000 reading and the pressure gauge reading at minimum pressure.

Note the analogRead*1000 reading and the pressure gauge reading at maximum pressure.

Note the analogRead*1000 reading and 25% pressure. At 50% and 75%

Graph and determine linearity or if curve function needed to predict pressure from analogRead.


the injectorDelay is probably a lot less than the typical 500. That initial pulse probably isn't 500us long. Might just be 100 us. How long is the pre-pulse?

The flow is a function of time and differential pressure. You have the input pressure, might need to guess at the BMEP (150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci) ). Given that your injectors are at like 3000 psi at idle, and bmep is maybe 300 psi at full throttle? It won't represent more than a %10 error, should be much less. But worth thinking about.

What is redline on that anyway?
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Old 09-10-2008, 05:33 AM   #26 (permalink)
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Thanks. The analogread is all I have for pressure, I was going to assume linearity. Non-linearity is not a problem I had anticipated!

I also agree that the cylinder pressure should not significantly affect injection, I'm not going to worry about 10% effects.

My enclosure should arrive today
I have read that the "pilot injection" is a few us long, I could not separate it from the main injection last time I scoped it. So for my purposes I hope I can treat the injection as a single event. I'm thinking that running a scope whilst driving would be illuminating at this stage.

Redline is about 4500rpm; but I rarely exceed 2200 as peak torque is 184ft-lb at 1750rpm. Nice and relaxed!

Last edited by ecoxantia; 09-10-2008 at 05:49 AM..
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Old 09-10-2008, 08:21 AM   #27 (permalink)
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I would check linearity with the system pressure gauge and the analogread just to be sure, simple enough test.

Sounds like at 72 volts and tons of pressure you can just about turn injectordelayUS to 0.
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Old 09-14-2008, 10:17 AM   #28 (permalink)
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Hi ecoxantia

I'm looking at building an MPGuino to put into my 2001 A2 1.4TDi - am I looking at similar challenges in getting things to work as you are with your HDi? Or can I use the standard code with the VSS & injector control signals?

I'm in the UK too - can I ask where you bought your bits from?

Eamonn
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Old 09-14-2008, 12:13 PM   #29 (permalink)
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Hi eamon, I would direct you to the TDI guino thread, it looks like a different animal but I'm no expert on diesels. dremd has been preoccupied with hurricanes, but he has a TDI and is looking to figure it out also, as is wyatt and tas and I'm sure more than few others for whom a scangauge won't work.

http://ecomodder.com/forum/showthrea...lity-3978.html
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Old 09-14-2008, 01:18 PM   #30 (permalink)
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Thanks dcb

Eamonn

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