ScanGaugeII surprise

syrjohn · May 2nd, 2012, 14:10

I recently had my clutch and turbocharger replaced on my 2002 Golf TDI with 235,000 miles on it. I disconnected the SG before the work and reconnected after. Then soon after I noticed something strange about its operation.

I was driving along and noticed my Today MPG was just above 50 as I approached a 1/2-3/4 mi downhill so I did my usual downshift to avoid using the brake and let it coast in gear. When I got to the end I noticed I had lost about 1 1/2 mpg. This has never happened before. I decided to do a test on another long downhill by getting up to speed and putting it in 5th. I then switched to Gauge setting so I could get an instantaneous mpg reading. Then as I coasted down the hill I switched back and forth between in gear and out of gear. The mpg reading was roughly twice as high out of gear than in. This makes absolutely no sense. The reading should be much higher in gear since the rolling of the car is turning the engine over with no fuel. In fact, my older SG used to read 9999.9 when I coasted in gear.

Could they have set something wrong on my engine when they did the work?

jettawreck · May 4th, 2012, 12:58

My older SG installed in the '01 reads 9999 when coasting in gear, the slightly "newer" version SG in the '03 reads a variable number in the hundreds when coasting in gear. Never figured out why, but both are quite accurate.

Honeydew · May 4th, 2012, 15:42

Quote:

Originally Posted by jettawreck

My older SG installed in the '01 reads 9999 when coasting in gear, the slightly "newer" version SG in the '03 reads a variable number in the hundreds when coasting in gear. Never figured out why, but both are quite accurate.

Firmware change, I think. Our older one used to read 9999 then I sent it in for a firmware update to get the x-gauge functionality. After the update it reads like yours does.

jettawreck · May 4th, 2012, 18:08

Quote:

Originally Posted by Honeydew

Firmware change, I think. Our older one used to read 9999 then I sent it in for a firmware update to get the x-gauge functionality. After the update it reads like yours does.

That's what I suspect(ed).
Kind of odd that the older version is closer to correct since no fuel is being used when coasting in gear. I bought the "newer version" one used and the previous owner has already added some xgauge features, although I really don't have a use for them.

Cogen Man · May 4th, 2012, 20:13

My SGII, bought in 2008 shows 0.00 LPH(liters per hundred kilometers) when coasting in gear. When I come to a stop, foot on the break and in gear it shows 0.07 LPH the same as the cluster readout. When I had it on my previous rig a gasser it always went to 9999.9 when at a stop in gear foot on brake.

syrjohn · May 5th, 2012, 09:48

Thank you all for your comments but I'm sorry I included the distraction about 9999.9.

The real issue I have is with the mpg being less while coasting in gear than it is out of gear. Years ago on this site I got the impression there was a fuel cut off if you put it in gear while coasting. Can anyone tell me if this is true or that I'm mistaken? The theory was that you should stay in gear going down a hill to save fuel.

jettawreck · May 5th, 2012, 10:39

Quote:

Originally Posted by syrjohn

Thank you all for your comments but I'm sorry I included the distraction about 9999.9.

The real issue I have is with the mpg being less while coasting in gear than it is out of gear. Years ago on this site I got the impression there was a fuel cut off if you put it in gear while coasting. Can anyone tell me if this is true or that I'm mistaken? The theory was that you should stay in gear going down a hill to save fuel.

I do know for a fact they (maual tranny at least) shut the fuel OFF when coasting in gear. That's why the 9999 mpg is displayed. Its as close to infinite it can display.
I have no idea why your SG reads higher in gear than when in nuetral coast, but it may be a software "estimate". I do know there is a difference between my two SG in the way they report/display this info.

syrjohn · May 5th, 2012, 14:02

Quote:

Originally Posted by jettawreck

I do know for a fact they (manual tranny at least) shut the fuel OFF when coasting in gear. That's why the 9999 mpg is displayed. Its as close to infinite it can display.

Thanks for validating that point about "cut off".

Now since my SG was performing normally before the turbo replacement (in that it would indicate a few hundred mpg on an in gear coast but much fewer on a neutral coast), but now behaves just the opposite I am left to wonder if something was done during the repair to alter the automatic "cut off" feature. If any of you are experienced mechanics and know of something like that happening I'd appreciate knowing about it.

jettawreck · May 5th, 2012, 18:15

Quote:

Originally Posted by syrjohn

Thanks for validating that point about "cut off".

Now since my SG was performing normally before the turbo replacement (in that it would indicate a few hundred mpg on an in gear coast but much fewer on a neutral coast), but now behaves just the opposite I am left to wonder if something was done during the repair to alter the automatic "cut off" feature. If any of you are experienced mechanics and know of something like that happening I'd appreciate knowing about it.

The fuel shut off soleniod is on the top of the IP (single wire attatches to it). If I recall, power to the switch/soleniod opens it. So I don't think they could have damaged it or the engine wouldn't start/run.
Know anybody that you could swap SG with for a test?

syrjohn · May 6th, 2012, 05:39

Quote:

Originally Posted by jettawreck

The fuel shut off soleniod is on the top of the IP (single wire attatches to it). If I recall, power to the switch/soleniod opens it. So I don't think they could have damaged it or the engine wouldn't start/run.
Know anybody that you could swap SG with for a test?

Thanks for the feedback. I'll give it a try.

40X40 · May 6th, 2012, 06:47

Reset the SGII and start over. Diesel A? and 1.9 engine size.

Bill

syrjohn · May 7th, 2012, 14:36

Quote:

Originally Posted by 40X40

Reset the SGII and start over. Diesel A? and 1.9 engine size.

Bill

I've tried the last 2 suggestions and think the resetting made the most sense. After the reset I tried it down the hill and actually got a 9999 in gear. Later on it settled down to hundreds or low thousands but reading much better than when out of gear. Now I'll have to go thru the fill up recalibration. So, thanks to you all I guess my cut off must still be working.

steffen707 · May 15th, 2012, 16:57

Quote:

Originally Posted by syrjohn

I've tried the last 2 suggestions and think the resetting made the most sense. After the reset I tried it down the hill and actually got a 9999 in gear. Later on it settled down to hundreds or low thousands but reading much better than when out of gear. Now I'll have to go thru the fill up recalibration. So, thanks to you all I guess my cut off must still be working.

What fuel cut off value are you using? The manual says 24 is the default. I've read some use 6. What have you guys been using?

syrjohn · May 17th, 2012, 09:06

Quote:

Originally Posted by steffen707

What fuel cut off value are you using? The manual says 24 is the default. I've read some use 6. What have you guys been using?

I don't know much about this so can't answer for some of my repliers. Perhaps you could try a private message to some of the more experienced.