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.

Quotes are screwed up for me at this point ergh.

I contacted them long ago and got a response along the lines of "will calibrate in over several tanks"

The Thread at TDI Club was forwarded to them and Last I heard they were looking it to it.
I think it is likely time for another contact attempt.

dremd -

I would ask them if their driving context/commute is consistent. Ask them to gun it for one tank and be gentle for the next tank and see what happens. But that would cost them $, so maybe that isn't fair.

CarloSW2

There is definitely several loop holes in the way the scan guage measures the TDI. The vag-com system can data log and program with a lap top I believe.
The only person I know that had a vag-com sent it back because he tried to go cheap with third party software and it wasn't warrantied/supported by vag-com.
How the scan measures the load is one big question. The fuel usage has to be measured directly on a diesel because it just goes as fast as it can on whatever fuel it can get. (including it's own crankcase oil).
Other variable is how much fuel is being returned to the tank. It takes two flow meters to measure both supply and return. If they accurately record the amount and duration the injector needle lifts and the pop off pressure on that injector is set properly then I would say they can calculate fuel for that injector. But if they are only checking one injector, then that's another issue. Most cities have diesel injection shops that can test injector and pumps individually. If you replace the nozzles, the pop-off pressures need to be reset, of course. If you change the filter check restriction on the old one before you toss it.

Some thoughts.

I did quite a few Demo rides in the TDI this weekend, same route, similar temps, similar loads. The fuel economy in the same spots at the same speeds varies significantly. I wonder if this is a potential cause of the SGII issue?

2) EGR: my intake hasn't been cleaned in 50,000 miles which means it probably is 30% plugged, which may affect EGR flow, which may affect engine "load" which would throw it off as well . . . .

the surge on coast means its is getting fuel from somewhere. could be engine oil building up in a PVC system, or whatever is restricting the fuel is letting loose for instant, example collasping hose somewhere or fuel sloshing and cleaning the screen off in the tank. my old VW has a very fine screen in the tank which can get plugged a cause a vacuum in the supply line, but if you have a pump in tank then it could be plugged and not even show a vacuum. check fuel delivery pressure under load.

I definitely need to check fuel supply vacuum, I tried last week, but my vac gauge wouldn't fit over the T that I had on hand, I'll pick one up soon.

I probably should pull the pickup out of the tank equal parts to check the screen, and also to check for cracks/ air leaks.

ALH's (pre 2004) do not come equipped with a lift pump, but they are a common "upgrade" for performance reasons

A group of us from Cleanmpg drove a euro-spec Honda i-CDTi across the country last month. It does have an obd-ii port, so we hooked up the scangauge. We also found it hard to calibrate. We never did get it to read anything accurate. I think the SG is not calculating right for diesels. Best hope may be for a software update or maybe a new version.

Just to chime in here, I have a similar problem with my Wrangler. No, it's not a diesel, but experienced a similar problem. I calibrated it for my daily drive and it seemed pretty good; hit the road for a Jamboree and it was off - whole gallons off! Wheeled all day (low speed, low gear) and the refill was wrong the other way. I think it's using some form of averaging on my vehicle, like your TDI, and is only as accurate as the pattern against which it is calibrated.

I have discovered that different vehicles report different #'s to OBD, Fuel economy is calculated from those values . . . .

I'm assuming that the more Data is given the better the accuracy.

What I wish was that you could tweak the calculated Curve . . .

Edit: If mine was always within 1 gallon I'd be happy, My last fill was 3.7 gallons off . .

So this doesn't really help as I'm not a diesel, but it does add a twist....

When calibrated, my SG has been very close to accurate - the reason it'd be off (in my opinion) is that the fill up doesn't go into as fine a resolution as the fuel pump (so round off error). A few months ago, I was really stressed out - and went through about 4 or 5 tanks driving pretty terribly as far as ecomodder driving goes - but the SG was still dead to nuts precise as before (which was near to accurate). I always used the same gas station, same pump, faced the car in the same direction, filled up the same way every time...

But I'm a gasser... and here's the twist! I have NO CLUE how load is calculated... It's a MKIV Jetta 2.0 - but load isn't what I expect. If I keep constant throttle while accelerating, load goes up. If I floor it at low speeds, load doesn't change much, and goes up with speed.... Just goofy... Not exactly related, but just throwing it out there that calculations seem to vary from car computer to car computer....

The estimations aren't quite right on my Honda Civic, upon installation of the device they were far too generous, then it sensed a disconnection so I had an asterisk next all stats for the remainder of the tank. Upon refill it just underestimated everything for the next two tanks. I just reset it on my most recent fill up and it is back to grossly overestimating, but I hope upon refill it will attempt to recalibrate and become more accurate.

In regards to figures, over estimation: I hit 80 mpg current today.
Under estimation: I was lucky to hit 30mpg.
For actual fill numbers I average around 55 mpg, check profile for tank specifics.

If it freezes up, do a reset, refuel, do not adjust fill.

your issue is likely due to SGII not registering a significant portion of the tank.

trebuchet03 -

IMO this makes sense because OBDII is a specification that VW implemented. Each manufacturer has to meet the specification, but their implementation could lead to variations in output. In a VW service department, the custom VW software that interacts with their implementation could account for the variation, so probably no biggee. When the SG interacts with it, it may be "exposing" the variation.

If I was a manufacturer, I would emphasize the accuracy of sensor output that effects emissions requirements. Other than MPH and maybe throttle position, I don't know what that is because I'm not in the smog test business.

CarloSW2

dremd
I noticed on the scanguage.com site that now the TDI's are not all covered by scanguage. I wonder of VW figured out a way to fullfill the OBDII obligation, while at the same time forcing people to go to their dealers. The whole reason for OBDII in the first place.

Hmmmm Very Interesting. I actually purchased one through a group buy on TDI club direct from Liner Logic. I wonder if they are working on the issue/ are concerned about the devices performance on the TDI . . . ..

I drove the 2000 TDI NB with SGII yesterday, it appears as though the SGII is accurate(based on fillups on a regular commute) and some quick quasi experimentation makes it appear as though it is off in the opposite direction than mine (that is lower indicated consumption on high flow rates and higher indicated consumption at low flow rates). Economy stays rather near 30mpg from 55mph to 82mph, we all know that is incorrect.


Differances in her car from mine.

1) Auto
2) 11 mm pump head (autos have 11mm 5 speeds had 10 mm)
3) lower mileage she is around 120,000 miles I'm around 175,000
4) More worn engine, hers had the wrong oil for the majority of its life, cam is worn down, and I suspect the rest of the engine is the same
5) I THINK more Aero drag (bug Vs Golf), (also missing suspension dams, under tray,an added spoiler, and wind deflectors on windows)
6) Larger, non Low Rolling resistance tires
7) Timing belt done by stab and pray (unknown pump timing)


Any thoughts?
Encourages me that some cars read one way and others read the other . . . . .


This makes me finally realize why she keeps telling me that she might as well drive 80; because her milage is basically the same, her scangauge has been giving her false information!!

Excuse me for jumping in here.

Scangauge is great, but it has some inherent limitations. SG is obviously relying on the OBD2 protocol. As far as I can tell, OBD2 simply does not report injector behavior (pulse width/duty cycle). Why not? Who knows. I guess the folks who designed OBD2 in the early 90s were not thinking about what a bunch of people are thinking about now: accurate, realtime reporting of fuel consumption. I think monitoring injector activity is probably the best way to do that, but OBD2 doesn't get us there.

Since the injector information is not available, SG calculates fuel flow indirectly, by relying on something else that OBD2 does report: air flow. I guess that method works well enough on most vehicles, but it seems to have problems (at least for some people) on two types of vehicles: diesels, and vehicles with lean burn (Honda VX, HX and Insight).

Lean burn is a challenge for SG because it's relying on the assumption that mixture is usually close to stoich. OBD2 does provide O2 sensor data, so I think theoretically SG could make corrections, using this data, but I think it doesn't do that. Anyway, that's still indirect and prone to error, compared with watching the injectors directly. Trouble is, OBD2 doesn't allow that.

I think something similar might be happening with diesels. I have a feeling that SG will have an accuracy problem with any vehicle that is not running mostly at stoich, for whatever reason.

A digital DMM with a dwell feature ($33) can monitor the injectors directly. That might be a good way to go if you want to watch instantaneous fuel consumption in a more direct manner.

Anyway, maybe this answers some of the questions that were raised. Someone please speak up and correct me if I'm missing something.

Another problem with assuming stoich is that even 'normal' cars don't run stoich when cold. My hunch is that this is another factor that introduces errors, for all cars, into the data SG displays.

Another problem with calculating consumption indirectly (instead of looking directly at the injectors) has to do with DFCO (deceleration fuel cutoff). I think SG only knows about this indirectly, because the user enters a constant representing the known DFCO threshold in rpm. This probably works well in most cases, but there are things that can go wrong, so it's not as good as watching the injectors directly.

A good discussion about mixture issues on diesels is here:

http://www.eng-tips.com/viewthread.c...=130502&page=1

monroe74 -

Thanks for this analysis. I have had similar misgivings, but you describe it a *lot* better than me.

This is one reason why I am skeptical of what the SG reports when someone applies the "IAT Resistor Mod" to fake HAI temperatures to the ECU/PCM. I think the SG relies on the IAT temp, but the ECU/PCM mostly ignores the HAI during closed-loop operation. Garbage in, garbage out.

CarloSW2

cfg: "you describe it a *lot* better than me"

Thanks for the kind words.

"IAT Resistor Mod"

Interesting, I hadn't heard about that before. Yes, another good example of how the SG can get fooled because it's not watching the injectors directly.

It's probably worth mentioning that the SuperMID and the Opengauge take the approach of watching the injectors directly. In other words, they don't rely on OBD2 the way SG does.

I don't intend to be slamming SG, because it's a great tool, and very popular. It's just a good idea to understand its strengths and limitations.

Monroe: See Post #1 I still like it, I'd still buy it, I still recommend it, but I wish it were at least close.


Does anybody know what Load is calculated by?

As far as I can tell the 3 primary inputs the SGII is Load, RPM, MAP.

That said the Bug seams to always have much higher indicated Load, due to vehicle differences, or . .. . .

dremd -

I think that LOD is a PID that is derived from the ECU/PCM in your car. The SG works with what it is given :

Project obdii Summary
http://prj.perquin.com/obdii/
EDIT: I got the above from dcb :

ElmScan + Customized Scantool Software = data logging!
http://forum.ecomodder.com/showpost....65&postcount=2

CarloSW2

Agreed, it is a reported value from ECM; but from what data/ how . . . .
Any Ideas?

Well My SGII instant mpg now appears to be reasonable.

What did I change you say?

Injector Nozzles, 2 of them were in fact fairly sticky (definite "pop" when sliding pin by hand.

I also had the injectors Balanced.

Will it calibrate close?

Who wants to guess?

But my highway mpg, and city mpg are in the "reasonable" range now so I'm bound to be closer than before.

Did you went with stock size? I got a set of .216 waiting, which I will probably sell. I bought those b4 I started being FE minded. I'm a little over 200k on stock nozzles, maybe I should have a look at them.

Running Power Plus 520's http://www.kermatdi.com/servlet/-str...LUS-520/Detail
on advice from TDI club. Apparently they have the best spray pattern. It has also been theorized that larger nozzles inject more fuel closer to the optimal timing point, and therefore have better economy. Regardless the car is quitter at speed, pulls smoother, and lets face it Torque is fun from time to time.

Most see some fe gain from the pp520's some see no change, some see losses.

An other report of TDI related SGII inaccuracy. ANYONE getting accurate ScanGauge readings on their VWs? - CleanMPG Forums

If the MPGuino can work on the TDI and prove accurate, I'm pretty sure there will be good money to be made over at tdiclub.com for finished units or even just kits.

YES Setup is required . . ..

What bladder are you talking about?

However after making this thread, I had a thought, what if I mis-informed the SGII of engine displacement? It could alter the equation in such a way that it would be correct . . . . .