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      02-02-2019, 03:48 PM   #1
Eddien123
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BimmerLink and obd2 reader giving weird boost indications

I just recently purchased a Bluetooth obd2 device and the bimmerlink app. It gives me all kinds of info such a temps, pressures, etc. however the boost pressure at idle or throttle lift off is 1050 hPa which is like 15 psi and at WOT it's at around 1500hPa (around 21psi). My question is why is it saying I'm making 15 psi at idle?

My car has a Dinan tune and therefore should be above the stock psi of 6 or 7. Even if I subtract the difference it gives me 500hPa or around 6-7 psi.

Anyone using this app with similar issues? I'm wondering if the tune is throwing off the boost pressure levels. All other info the app provides seems to be accurate.
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      02-02-2019, 07:49 PM   #2
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That is probably reading absolute.
1 atmosphere is ~15psi (14.7) at sea level.

Stock boost varies, as the DME targets load and not boost, but should be around 7psi without tune.
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      02-02-2019, 11:55 PM   #3
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Quote:
Originally Posted by Tchao View Post
That is probably reading absolute.
1 atmosphere is ~15psi (14.7) at sea level.

Stock boost varies, as the DME targets load and not boost, but should be around 7psi without tune.
That makes sense. Problem is if I'm pushing 7psi then that means either the tune isn't doing anything or it's corrupting the boost pressure gauge. I'll figure it out eventually I guess lol
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      02-03-2019, 09:06 AM   #4
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Quote:
Originally Posted by Eddien123 View Post
That makes sense. Problem is if I'm pushing 7psi then that means either the tune isn't doing anything or it's corrupting the boost pressure gauge. I'll figure it out eventually I guess lol
If it's a piggy back "tune", then the boost sensor reading has been fudged, so it depends on where your gauge is getting its data.
If it reads off the OBDII then the data is post fudging.

So you will see what the computer see's...which is a modified data. How Piggy backs work is to trick the computer to see different parameters so it can up the boost without the computer knowing.
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      04-23-2020, 11:42 PM   #5
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sorry to bump an old thread, but I am discovering this issue right now. Using bimmerlink I'm 14.7 PSI at idle and get to about 20 on WOT. Running a JB Stage 1. Are you saying 20 PSI is the normal boost pressure but it's secretly hitting the 23-24? thx
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      04-24-2020, 10:34 AM   #6
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Quote:
Originally Posted by Sylverlee View Post
sorry to bump an old thread, but I am discovering this issue right now. Using bimmerlink I'm 14.7 PSI at idle and get to about 20 on WOT. Running a JB Stage 1. Are you saying 20 PSI is the normal boost pressure but it's secretly hitting the 23-24? thx
No, not at all. Reread the thread as it was pretty much discussed already. Why would you be making 14.7 psi of boost at idle lol?

1. Whatever you are pulling from the app is not actual boost. 14.7 psi is roughly atmospheric pressure. So, that's basically barometric pressure not boost. Boost is typically "gauge" pressure - e.g., the increase over atmospheric pressure.

2. The DME targets load, not boost, so the actual boost your car will run varies with atmospheric conditions and other variables.

3. The JB is a piggyback that intercepts boost signal and tricks the DME, so the DME does not know it is running higher boost. Therefore, if you are reading boost directly from the DME, you are not going to see the increase from the JB, just what it thinks its running.

4. Roughly speaking, a stock N55 will run 6-10psi.

5. Sell the JB+, get a flash tune, do some datalogs, and start learning more about the car.
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      04-24-2020, 10:38 AM   #7
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Quote:
Originally Posted by thejeremyman9 View Post
No, not at all. Reread the thread as it was pretty much discussed already. Why would you be making 14.7 psi of boost at idle lol?

1. Whatever you are pulling from the app is not actual boost. 14.7 psi is roughly atmospheric pressure. So, that's basically barometric pressure not boost. Boost is typically "gauge" pressure - e.g., the increase over atmospheric pressure.

2. The DME targets load, not boost, so the actual boost your car will run varies with atmospheric conditions and other variables.

3. The JB is a piggyback that intercepts boost signal and tricks the DME, so the DME does not know it is running higher boost. Therefore, if you are reading boost directly from the DME, you are not going to see the increase from the JB, just what it thinks its running.

4. Roughly speaking, a stock N55 will run 6-10psi.

5. Sell the JB+, get a flash tune, do some datalogs, and start learning more about the car.
Thx for the explanation. JB is fine for me. Have a fast second car already
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      04-24-2020, 12:25 PM   #8
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Quote:
Originally Posted by Sylverlee View Post
I'm 14.7 PSI at idle and get to about 20 on WOT. Running a JB Stage 1. Are you saying 20 PSI is the normal boost pressure but it's secretly hitting the 23-24? thx
Bimmerlink data is reading absolute. 14.7psi = 1 atmosphere aka standard sea level Earth pressure.

So your boost the DME is seeing is 20-15 = 5psi

That is exactly what JB-1 does, under report boost a bit so the computer compensates with more boost. In reality you are running a few PSI higher.

Like the guy above me has said, its best to go flash tune, as you are not tricking anything, and the computer can control the engine as it should. Car not only runs much faster, but it also runs much smoother. Worth the extra few dollars. Plus all the programed safety features in the DME still operate as it should because the data coming in is true.
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