SGII Not quite right
 

I've owned a SGII for about 9 months now. I have yet to get the calibration correct.

The best I can describe it is that on Low Fuel Flow rates it reports Low, and on High Fuel flow rates it reports High.

So if I drive it on the highway with my "in town" calibration my SGII indicates very high consumption (around 30mpg). If I drive all Highway with the cruise (75~77 mph) my fillups are in the very low 50's. (non Hypermiling driving)

If I Drive in the City with my "Highway" calibration I can get my indicated adverage mileage to go very high. Normal (non Hypermiling) in the mid 80's (mid 40's based on fillups) and Hypermiling in the 300 MPG indicated range (actual based on fillups Low 70's)


What I've Done

Tried 3 different SGII units

Replaced Thermostat (appears to have improved situation, but still unsure)

Tried Driving "normal" God I hate doing that now.

Tried filling up around half tank to increase the number of Data points.

Trying the 1/2 correction now, but I think all I'm getting is a better average, still off in same direction for highway/ City driving.

I'd like to say that I still love the SGII, and I do not believe the issue to be with the unit, but with my Golf in some way. All of the other ones I'm around work GREAT.

Theories

1)Partially Plugged Injectors flow well at low pressure, and poorly at high pressure (incomparisn to new)

2) Injector "lift" sensor faulty/ in accurate

3) ECU issue

4) Something I can't think of.




Here's a thread I posted in on TDI Club. http://forums.tdiclub.com/showthread.php?t=203066
As a side note I have been PM'd by 4 other cars with the same issue who were afraid of posting because I was ostracized for posting in another thread which has since been deleted.

Also I always fill my car to the Brim (normal practice on a Diesel) so it is safe to say that my fillups are with in 1/4 Gallon and should be much closer than that.



Any and All Ideas Welcomed

You are not alone my friend. I too have this exact same problem with the TDI. I think the way the SG computes consumption for the TDI is flawed and is only accurate if you always drive in the exact same manner you did when you calibrated it.

BTW, do you have vag-com? My unofficial cable unfortunately stopped working, but it would be interesting to compare the fuel consumption reported by vag-com vs the SG.

Did you PM me on TDI Club?
(I'm keeping a tally)

The Other TDI in the Family has a 120 mile a day round trip commute (at 80+ ERGH), so I can't say for certain that it suffers from the same illness or not.. . .

I was not of those who pmed you. I have the same forum handle over at TDIclub.

Does the TDI recirculate fuel back to the tank like my rabbit does.
Does the Scanguage use pulse width to calculate fuel flow. Injector lift sensor is that in #3 injector the one that cost $300. Look at that wave form on a scope and the VSS.
The fuel delivery pressue would need to be correct (filter restriction) tank vent, collapsing line. Are any fuel lines kinked or soft.
Did you buy it new or used (could the injectors have been changed.
Does it otherwise run good ( start good in the winter, good mpg).
This is a very interesting issue. I would like to learn more about it.
If the car is running good with no codes then I would lean more to OBD interface related. Is the computer stock? Is there anything fuel related that has been worked on?
If the engine is starved for fuel then the ECU will increase pulse width to compensate.

oh, hearing about more than one with the same issues, now.
Is it possible to record all the parameters off the scan for both scenarios and then compare and look for unreasonable inputs.

dremd -

This consistent with my impression, Jack of all trades and master of none. The SGII is dependent on the *implementation* of the OBDII standard by the auto manufacturer. I think that because there are fewer diesels on the road, they may have more "esoteric" implementations. Do you know what I mean?

This also makes sense because from my POV, the calibration value is a "constant" based on how you drove your previous tank. Change the way you drive, and the constant loses validity. If you have a "reliable" commute that is consistent over time, the SG calibration is fine.

PS - I am not complaining about the SG. It is a fantastic relative barometer of fuel consumption. But I think we need to understand it's limitations.

CarloSW2

I don't Understand the Multiquote just yet, so the BOLD is Diesel John and the Italics is me


Does the TDI recirculate fuel back to the tank like my rabbit does.
It does. Route is basically Tank-> pickup (which can crack)-> Soft Line-> Hard Line-> Soft line-> Fuel filter -> Soft Line -> Injection Pump -> Soft Line -> Hard line Then I don't know exactly how fuel makes it's way back to the tank

Does the Scanguage use pulse width to calculate fuel flow.
According to a member on TDICLUB
Scangauge is reading:
0C - RPM
04 - Load
05 - Engine coolant temp
0B - MAP
0F - Intake air temp

Then using the engine displacement, the "Diesel A" formula, and the correction factor, SG calculates fuel consumption.

There are no other codes being read, so (after this and other testing) I'm forced to come to the conclusion that there is no way to read any directly related fuel info (like inector pulse width, or VAG monitor group 15, zone 3) through the OBDII protocol on Diesel VWs.


The fuel delivery pressue would need to be correct (filter restriction) tank vent, collapsing line.
Getting up on 20,000 miles on Fuel filter at this point have not checked anything else at this point

Did you buy it new or used (could the injectors have been changed.
Bought it used I do not believe that the injectors were chnaged, I have an extensive service history + fuel logs for the car from the previous owner, and injectors are not on there . ..

Does it otherwise run good ( start good in the winter, good mpg).
Runs Great 97% of the time It has 2 issues 1) occasionally idles TERRIABLE but that clear up if you blip the throttle, or turn on the A/C and 2) Occasionally when Decellerating in gear (0 load) it feal like the car has been rear ended (lightly) Have no Clue on either count.

This is a very interesting issue. I would like to learn more about it.
If the car is running good with no codes then I would lean more to OBD interface related. Is the computer stock? Is there anything fuel related that has been worked on?
ECU is Stock (as far as I know) but most with chips report that their SGII's still work correctly

If the engine is starved for fuel then the ECU will increase pulse width to compensate.
Definitely a possibility How about if I plumb a VAC gauge to the Injection Pump input?

Yes it does.

The car has been in the familly since new and has 200000 miles on stock injectors. I'm installing new nozzles this summer so that should help.

It runs pretty good. Never had starting issues and I got it to 45 mpg driving like I stole it last summer when I was really not into FE.

The ECU is stock, but I installed a pot in line with the piston movement sensor of the fuel pump so I can dump more fuel in, and a turbo bleed so I can get more air in. I haven't touched those since I started driving for FE though.

I'd be OK with the SGII as is if need be, but I know I can get MUCH MORE out of this car if it was correct. I have an issue with highway driving it now (psychological) Basically if I'm going to get poor mileage I might as well go fast, it snow balls, and I end up like the average jack ass in about an hour.


I THINK that it works properly on MOST TDI's, BUT I could be dead wrong. This is primarily attributed to the fact that most people posting on TDI club are insistent that theirs is DEAD ON, they could be lying, or maybe only a few are dead on and they are the ones who post . . . . .. . .

And if it works on most cars I wish it would work on my car . . . ..

Have you email the folk at Scan gauge and see if they have anyone else with TDI with the same issues? I think they are very good at replying to concerns.