Hello, fellows. I saw a strange in my opinion thing when checking my car yesterday on my laptop. My boost pressure is some 170-190mbar lower than the atmospheric pressure. How's that possible? Usually it should be equal or a bit higher than the atm pressure. That's not my case. With atm pressure of 955mbar i get 760-780mbar of boost pressure when idling. Any ideas why? Is there anything i should be worried about? No DTCs, no loss of power, just normal engine work. I am attaching a data log i've made.
janyboy
At idle speeds the boost will be lower than atmosphere.
The reason being that the car is sucking in air and causing a vacuum in the inlet manifold. Once above idle the turbo will spool up and instead of a vacuum you will get positive pressure.
The reason being that the car is sucking in air and causing a vacuum in the inlet manifold. Once above idle the turbo will spool up and instead of a vacuum you will get positive pressure.
That does not look good to me. It's lower than the desired boost pressure by a significant amount. Either the sensor is reading low, or you have something restricting the inlet. What does it read with the engine off? If still low the sensor, wiring or ecu are faulty; probably the sensor. If it reads atmospheric pressure you have something blocking the inlet, which is potentially dangerous for the engine.
On key on i got boost pressure of 943 mbar with 950 mbar atmospheric pressure but when i start the engine boost pressure drops to 800 even 750 mbar. I saw a parameter called throttle angle [%] which i believe is the throttle body valve duty cycle and when key on i got 5% and when idling (820 rpm) i got 78.75%. So if the throttle body is closed with duty 78.75 % when idling it seems logic to me to have boost pressure lower than atmospheric. When i hit the throttle up to 4000-4500 rpm (car still stationary) the valve duty goes to 5%, not less.
I do not know if my thinking is at the right direction. I have a 1.9 8V JTD 105 Euro2 car (no throttle body) and there everything is normal - atmospheric pressure 950 mbar, boost pressure 953 mbar.
I do not know if my thinking is at the right direction. I have a 1.9 8V JTD 105 Euro2 car (no throttle body) and there everything is normal - atmospheric pressure 950 mbar, boost pressure 953 mbar.
Because i am a very curious person i looked at my boost pressure maps (in the car software 2.0MB, EDC16C39) and things seem to be clear now. According to my boost/turbo maps at idle engine speed (820 rpm) and respectively IQ=5-8 mm^3 (IQ is injected fuel quantity) we should have boost pressure of 780 mbar. That's what i have logged the other day. What still bedazzles me is why desired boost pressure in my data log is 955 mbar knowing what my boost/turbo map say (780 mbar). Maybe this is some kind of software bug. I am using Multiecuscan to make the data log. Think case is closed for now.Best regards
JB
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