scangauge questions

[spdracr0]

Ok I have a couple of questions about my scangauge....

1.What kind of boost do you guys see with the scangauge? I get 35 then settles down to mid 20s when at full throttle. Also what kind of MAP reading do you get at like 70. I get 17-18.

2. Why does it never get less than 14.6? I know that is atmospheric pressure but doesnt a turbo cause vacuum at no throttle or am I wrong about that??

3. I hear guys get like 40 to 50mpg on teh hwy. Mine typically give a reading of approx 2.3 GPH and in teh 30s on mpg.

I am sure I will have more later but just got the thing teh other day..Thanks for any input..

 

[Ben1000]

For #2... Since there is no throttle plate on a diesel vacuum does not occur readily.

For #3... Have you setup the engine size & fuel type yet?

 

[Vhunter]

#3, if you haven't calibrated the gauge for MPG by running a good part of a tank and then entering the gallons used into the unit, it will be off a bit.
I found that you have to run a good percentage out of the tank and then fill up or it will be hard to get it really close on, as small errors when working
with a small sample will show up as larger errors.. It took me a while to figure
out that 300 or so miles was not enough to get good results quickly.
I have a correction setting of exactly 50% this last time I checked and it was within 1 MPG of what I calculated by hand. But like they say, your mileage may vary! I suspect that there are several things that come into play when the unit calculates MPG. The MAF is one, and the software and injector nozzle size you have in the car comes to mind. I know that
with VAG-com you can adjust the reading of the injection quantity, and I suspect but have not verified that this might have an effect on the reading.
From what I read in some other thread, it does not actually use the injection quantiy data block from the ECU, but I think that this would indirectly affect the block that shows the % engine load reading.. which MIGHT be used in the calculation of the MPG and GPH... MIGHT... I am just guessing on that.
#1, With the ECU software I have the guage will go to 37.4 and drop to about 35 or so and stay there as long as I am brave enough to hold the "go" button.
Thats a little high for the stock turbo so I try not to do that very often!
#2, like the previous poster said, there is no 'throttle plate' like in a gasser. The only restriction is your air filter and the compressor wheel in the turbo.
Once its started and warmed up, the turbo should not cause much restriction at all while at idle.
Laters!

 

[spdracr0]

Thanks, I did not think about no throttle plate in the diesel...guess it shows I am used to gassers....

 

[McBrew]

You can make an xGauge for boost... basically it subtracts atmospheric pressure from the MAP reading. I did this and called it "TRB". Check the ScanGauge thread in the OBD section for instructions on setting that one up.

 

[02 jetta]

The turbo does draw a vacum if you create the x gauge like McBrew said mine read somthing like -.8 Psi at idle

 

[McBrew]

Keep in mind that you are assigning a single value for the atmospheric pressure correction... so the "non boost" level may be in the + or - based on the barometric pressure for the day.