SGII Not quite right

[dremd]

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

[tasdrouille]

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.

[dremd]

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.. . .

[tasdrouille]

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

[diesel_john]

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.

[cfg83]

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?

Originally Posted by tasdrouille

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.

...

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

[dremd]

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?

[tasdrouille]

Originally Posted by diesel_john

Does the TDI recirculate fuel back to the tank like my rabbit does.

Yes it does.

Did you buy it new or used (could the injectors have been changed.

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.

Does it otherwise run good ( start good in the winter, good mpg).

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.

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.

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.

[dremd]

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?

Quote:
Originally Posted by tasdrouille
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.

...
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'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 . . . ..

[Lazarus]

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.

[dremd]

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.

[cfg83]

dremd -

Originally Posted by dremd

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 . . . ..

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

[diesel_john]

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.

[dremd]

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 . . . .

[diesel_john]

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.

[dremd]

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

[PaleMelanesian]

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.

[awillard69]

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.

[dremd]

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 . .

[trebuchet03]

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....