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wayneskid
03-27-2013, 09:24 AM
At idle it shows -1.X or so. This is happening along with a CEL that started a week ago. Just noticed the neg boost yesterday. Anyone seen the neg BST? BTW, engine performance is normal.

I'm scheduled at MB Salem (Oregon) later today to look at CEL issue. Anyone heard anything about this dealer?

2008 NCV3 w OM642

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sailquik
03-27-2013, 12:26 PM
wayneskid,
Not sure how a ScanGauge II could read negative boost.
What is your altitude?
Have you tried changing the PID (Parameter Identification) to MAP to see if there's also an issue with that?
MAP should be 14.7 @ sea level to =<37 PSIA at max boost.
That would be a good question to ask the engineering folks @ Linear Logic.
Roger

wayneskid
03-27-2013, 01:08 PM
Altitude when I first noticed it was 2700 ft. MAP seems normal. Right now I'm in the van ready fo drive to Salem. At idle, temp coming up, BST is 0.2. Will watch it on the way over.

Thanks,
Wayne


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autostaretx
03-27-2013, 02:31 PM
The ScanGauge measures "Boost" by subtracting the ambient air pressure... if it knows it.
To avoid having negative boost, the two pressure sensors have to be accurately calibrated in relationship to each other, with matching response curves.
I sincerely doubt they are. (we're talking accurate-to-sub-millivolts per PSI here, on two $5 parts)

What the Sprinter actually *sees* is MAP: Manifold Absolute Pressure... that's the air going into the cylinders.
It don't care diddly about "boost", it only cares about MAP. That's what's available to burn the fuel.

Why folks are so hung up about "boost" kind'a escapes me...

--dick (MAP all the way...)

Aqua Puttana
03-27-2013, 02:37 PM
...
Why folks are so hung up about "boost" kind'a escapes me...

--dick (MAP all the way...)
Because "boost" is what my mechanical gauge reads. :lol: It works just fine for me. :cheers: vic

P.S. - My next gauge will likely be the fuel pump output pressure after the filter. I haven't decided on a direct read or electronic sender type yet. The hose should be easy to Tee off.

wayneskid
03-27-2013, 05:02 PM
The ScanGauge measures "Boost" by subtracting the ambient air pressure... if it knows it.
To avoid having negative boost, the two pressure sensors have to be accurately calibrated in relationship to each other, with matching response curves.
I sincerely doubt they are. (we're talking accurate-to-sub-millivolts per PSI here, on two $5 parts)

What the Sprinter actually *sees* is MAP: Manifold Absolute Pressure... that's the air going into the cylinders.
It don't care diddly about "boost", it only cares about MAP. That's what's available to burn the fuel.

Why folks are so hung up about "boost" kind'a escapes me...

--dick (MAP all the way...)

I don't think the SG measures anything, it just displays the data that's available on the OBDII. So the pressure sensors are in the Sprinter and I'm guessing that being MB parts they are more than $5.

kmessinger
03-27-2013, 05:11 PM
I have seen - boost but don't remember the exact circumstances. I think I was at a stop sign first thing in the morning having come down the hill coasting.

Keith

autostaretx
03-28-2013, 04:33 AM
I'm guessing that being MB parts they are more than $5.
For you to buy the assembly from MB, yes, far more than $5.
But i was referring to the actual electronic pressure sensor, such as a Silicon Microstructures SM5420C, a piezoelectric-based sensor capable of zero to 100 psi Absolute... $2.46 each, if bought 100 at a time.
Mouser's catalog: 987-SM5420C100AHS
data sheet: http://www.mouser.com/ds/2/589/-219546.pdf

--dick

mofo989
04-02-2013, 12:42 AM
Mine also reads a little negative at times.

Aqua Puttana
04-02-2013, 12:56 AM
My direct tapped mechanical pressure gauge on my T1N shows negative pressure at different times. Surprisingly it isn't always when the engine is holding back the Sprinter like going down hills with the cruise control set. For future reference I'll try to pay more attention to when it does go negative.

Anyone using MAP wouldn't notice at all because it should never even approach a negative number. FWIW. vic

autostaretx
04-02-2013, 10:07 PM
My direct tapped mechanical pressure gauge on my T1N shows negative pressure at different times.
..which brings us back around to the "does the turbo block enough to provide engine braking" discussion of another thread.

And i appreciate (and believe) Vic's tapped-mechanical boost reading. (it always helps to describe what you're measuring with)
My comments on "not trusting negative" were on the assumption that it was a calculated Boost from a ScanGauge or the like.

--dick

sailquik
04-03-2013, 12:21 AM
Dick,
Care to explain "calculated Boost" vs MAP on a Scan-Gauge II.
AFAIK everything I've heard from Linear Logic Engineering is that the signal for MAP to the ECM is precisely what the
Scan-Gauge II reports.
Where does the calculation come in?
Roger

autostaretx
04-03-2013, 02:11 AM
Care to explain "calculated Boost" vs MAP on a Scan-Gauge II.
Brain fart on my part :idunno: ... i thought they offered BST as one of the X-gauge commands
(i have a pre-X-gauge ScanGauge 1)
Can i excuse myself by noting that i said "and the like"? UltraGauges (and probably DashDaqs) have BST.
There are Xgauge commands for "barometric pressure", so it's kick-Linear-to-allow-two-parameter (MAP minus Baro) X-gaugery.

--dick

sailquik
04-03-2013, 02:31 AM
Dick,
Also AFAIK the latest firmware upgrade (Version 4.2) offers a choice between MAP Manifold Absolute Pressure in PSIA (same as the previous firmware) and BST (Boost in PSI) without
resorting to programming an X-Gauge.
I still have the HPR (horsepower X-Gauge) programmed in my Scan Gauge II.
I had the firmware upgrade about 6 months ago.
It was a very straight forward process....fill out the form....enclose a check for $25 USD....mail the unit (less cables) to Linear Logic LLC in Mesa, AZ.
It was mailed back, all upgraded and with a new manual and Quick Start Guide in < a week.
Great customer service!
For anyone thinking of purchasing a Scan Gauge II for their Sprinter, the direct price, from Linear Logic LLC is currently $169.00.
I agree, there would only need to be a simple mathematical correction applied to the MAP data (Like X-14.7 PSIA) to equal Boost.
At times, I think I would like to invest in some sort of logic analyzer; a flow meter; and a couple of other gauges and double check what the Scan-Gauge II displays,
but not sure I want to tap into the Sprinters systems that deeply.
Might learn something, and completely goof up the Sprinter's engine management systems in the process.
Roger

autostaretx
04-03-2013, 11:40 PM
This thread: http://sprinter-source.com/forum/showthread.php?t=25945
is what led me to believe that newer scangauges could casually flip between MAP and BST.

--dick (i knew i'd seen it somewhere....)

4wheels
04-04-2013, 01:01 AM
At idle it shows -1.X or so. This is happening along with a CEL that started a week ago. Just noticed the neg boost yesterday. Anyone seen the neg BST? BTW, engine performance is normal.

I'm scheduled at MB Salem (Oregon) later today to look at CEL issue. Anyone heard anything about this dealer?

2008 NCV3 w OM642

Sent from my iPhone using Tapatalk

Mine SG did the same . The fix is/was simple - inlet pipe from air filter to turbo was loose and almost off. No negative boost after fix.:bounce: