SGII Not quite right

[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....