HE351 code for me78569

[hakcenter]

What sensors are you guys using, and do you account for the dead zone variations ?

Without accurately measuring the true scale of the sensor, you won't have a true representation of the pressure. Most sensors that are absolute throw away the first bar of pressure considered to us vacuum, then when you're at the first bar you'll be at 0psi ie unity with the atmosphere.

http://www.nxp.com/files/sensors/doc/data_sheet/MPX4250A.pdf

I've done a lot of extensive programming for map sensors into a car software and it is not a lot of fun.

However check out the pdf, the dead zone on the sensor is 0v to 0.2v then it should be on scale up to 4.9v so anything over 4.9 is a throw away. Of course assuming you use the manufacturer specs for setting up the schematic, decoupling capacitors etc.. you can see the scale sweep on page 4.

If the sensors you use are vented / relative, you shouldn't have to account for atmosphere vs absolute sensors, but the scale really won't change just the output of your setup based on altitude.

[Rx7man]

I have been considering the deadzone.. my sensors are .5V-4.5V for 0-100 psi respectively.. so that works out to a raw ADC value of 103 to 920 for 0-100 psi... the way I do it is I have a 'map' function that uses floating point math..
so my code looks a little like this

float Pressure = mapf(analogread(MAPpin), 103,920,0,100);

Speaking of sensors.. my honeywell EGP sensor packed it in already.. I have no idea why... it couldn't get hot or get hot gases the way it was mounted (3 ft of coiled brake tubing to the manifold)... I'm going to have to talk to them about it.
My sensor is a 'sealed gauge' type, all stainless.. which is why I'm baffled as to why it failed... If it really comes down to it, I'm going to see if I can't use an oil pressure sender for it if I keep having problems.

[hakcenter]

too hot ?

[Rx7man]

was mounted on the firewall by the stock ECU.. it's bloody winter dammit... it couldn't get that hot under any circumstance

[me78569]

My sensor are working great.

I used the ones the guy on cf speed way back when for his code.  Think they are $46 each. .5-4.5v for 0-100 psi.  I am reading pressure in the same way.

I need to finish my work with the obd stuff so I can just read baromelet values from the ecm.

[Bdubb'z]

No problems with my sensors either.  I use this http://jgsturbo.com/dppt.html after my stainless coil of brake line then the exh pressure sensor threads into this.  I also have the mechanical gauge off of this unit as well. Easily drained and cleaned and keeps the sensor safe.  I use this sensor and map it just like Rx7man. It's psig as well.  http://www.auberins.com/index.php?main_page=product_info&cPath=5_23&products_id=271

[me78569]

Yep that's the sensor I am using.

[Bdubb'z]

Oh yeah, if anyone is looking for a psia boost reference, I use this.  I also live at 7000' and travel all over the west and don't seem to have an elevation adjustment issue, or sensor reading issue.  http://www.auberins.com/index.php?main_page=product_info&products_id=150 

Also, WAY back to numbers for the turbo, I seem to run 30-35 psi boost at ~119-123k rpm and around 1250* egt with ~ 40-45 psi bp.  That's about 600 on the actuator position, if it opens more I drop boost and egts skyrocket.  Can't seem to get over that for whatever reason.  I've changed all my boost boots and clamps too, probably need to do a boost leak test next summer.

I like where you're going with the OBDII, I bought this https://www.sparkfun.com/products/9555 a while ago to also tap in for engine RPM, just haven't had the time to implement or play with it.  I need to quit my job so I can get all my projects done!!

[hakcenter]

I would totally boost leak that, seems really odd. What's your altitude though ?

[me78569]

I would totally boost leak that, seems really odd. What's your altitude though ?

I also live at 7000' and travel all over the west

I notice the same thing at altitude, sea level not so much.  Much open beyond 16-18cm makes boost fall off the face of the earth, unless I say into the pedal then it will climb again. 

I can make 35psi all day long but not 40.  did boost leak test and found none.  However if you take the 40psi people see at seal level and minus the 3-4 psi lost due to being at 7000'  it is pretty close.

[Rx7man]

Remember too that turbo compressors don't care about the actual boost, but the pressure RATIO!

so 30 PSI at sea level is roughly 3:1 pressure ratio (30+14.7)/14.7)
30 PSI at 7000 feet (lets say 11 PSI atmospheric) is (30+11)/11 = 3.72... a TOTALLY different pressure ratio for the same boost.

So what does a pressure ratio of 3.72 work out to at sea level?  (3.72*14.7)-14.7 = 40 PSI
So (if 7000 ft = 11 psi) you can see the turbo has to work a whole lot harder to get the same boost pressure.. and that's still not producing the air density it would at sea level (you'd need another 3.7 psi for that (14.7-11).

Clogged air filters are in effect the same as high altitude by reducing the pressure on the intake side of the turbo

[Rx7man]

Wow.. I'm surprised at how good my guess was

   Altitude above Sea Level and Air Pressure


7000 feet is 11.3 PSI... so my calculations should give you a pretty good idea.

As for your truck smoking like heck at that elevation, it makes sense... To get the same density of air into the engine at 7000 feet compared to 30 PSI boost at sea level you'd need to run 43 PSI!.. just about a whole point of pressure ratio more!
Thankfully the likely colder temps will mitigate that at least a bit

[me78569]

Exactly.

Thanks for doing the math I was lazy and just guessing haha.

[Bdubb'z]

Yup!  Thanks, guess I wont worry about why I'm not getting 40+ boost out of this sucker!  It must be working pretty good because I've held about 38-39 psi with a gvw of about 24000 over a 10000' pass.  At that weight I'm way out of the throttle to keep egts under 1500*.....but still passing cars.  6inarow make 'em go!

[me78569]

Understand your pain man.   Biggest PITA for me is emissions.   Even in California they don't do rolling loaded snap tests 

I could honestly Pass emissions the tuner turned up if I was at sea level.  Keep in mind I have ~450 hp worth of fuel

Here in CO Springs we are allowed %30 opacity in 3 test.

1. snap test idle
2. 45 mph snap
3. 55 mph snap.

That was a 0 - %40 throttle take off and a %20 - WOT roll at ~2000' altitude

Dfi 7 x .009 injectors he351ve 2nd gen cummins - YouTube


Here is a my house

~%20 - WOT

He 351 100% - YouTube


Even with the tuner turned off, Just my 100 hp injectors, I won't pass emissions unless I borrow a smarty tuner and enable the 1/2 power mode.    Even then I still have %5 Opacity in the above tests.   I struggle to understand why CO Springs has more harsh emissions standards than California even though we are subject to much much thinner air.