2.0JTDm Strange Boost When Idling - Alfa Romeo Forum
You are currently unregistered, register for more features.    
 
Thread Tools
(Post Link) post #1 of 9 Old 19-07-15 Thread Starter
Status: -
AO Member
 
Join Date: Oct 2010
Location: I would rather not say
County: -
Posts: 10
2.0JTDm Strange Boost When Idling

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.
Attached Files
File Type: xls 2.0JTDm Boost Log Idle.xls (34.0 KB, 12 views)
janyboy is offline  
Sponsored Links
Advertisement
 
Status: zzzzzzzz
AO Platinum Member
 
symon's Avatar
 
Join Date: Dec 2005
Location: United Kingdom
County: Oxfordshire
Posts: 36,928
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.
symon is online now  
Status: -
AO Member
 
Join Date: Jan 2014
Location: United Kingdom
County: Essex
Posts: 743
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.
R.T. is offline  
(Post Link) post #4 of 9 Old 21-07-15 Thread Starter
Status: -
AO Member
 
Join Date: Oct 2010
Location: I would rather not say
County: -
Posts: 10
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.
janyboy is offline  
Status: -
AO Member
 
Join Date: Jan 2014
Location: United Kingdom
County: Essex
Posts: 743
Ah! Sorry janyboy, I was thinking pre-throttle diesels. It looks like your sensor is working, 943/950 is a small error. I agree with your logic but don't know why the pressure is lower than 'desired boost'.

Last edited by R.T.; 21-07-15 at 18:10. Reason: Typo
R.T. is offline  
(Post Link) post #6 of 9 Old 22-07-15 Thread Starter
Status: -
AO Member
 
Join Date: Oct 2010
Location: I would rather not say
County: -
Posts: 10
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
janyboy is offline  
Status: 159 Cruiser and Guilietta pocket rocket
AO Silver Member
 
giblets46's Avatar
 
Join Date: Jul 2012
Location: United Kingdom
County: Warwickshire
Posts: 4,729
Garage
Is it anything to do with fuel savings when idling?


[color=gray]Sent from AutoGuide.com Free App[/color]
giblets46 is offline  
Status: [URL
AO Silver Member
 
Join Date: Oct 2007
Location: United Kingdom
County: Wrexham
Posts: 1,758
Maybe function of egr also, im sure i heard some cars use inlet butterfly flap to reduce manifold pressure to aid pulling in egr gas as they also close vnt vanes to create more back pressure for same thing.
sussexa is offline  
(Post Link) post #9 of 9 Old 08-08-15 Thread Starter
Status: -
AO Member
 
Join Date: Oct 2010
Location: I would rather not say
County: -
Posts: 10
Quote:
Originally Posted by sussexa View Post
Maybe function of egr also, im sure i heard some cars use inlet butterfly flap to reduce manifold pressure to aid pulling in egr gas as they also close vnt vanes to create more back pressure for same thing.
Yeh, could be. I just thought i had a problem with the car when noticed the big diffrence between atmospheric pressure and boost pressure while idling. Now knowing this is normal (not being a fault) i am not worried. I made another data log and things with boost (actual vs desired) look OK (3-rd gear 2000-4500 WOT).
janyboy is offline  
Reply

Go Back   Alfa Romeo Forum > Supported Alfa Romeo Models > Technical & Vehicle Assistance > Engines (TS, JTS, JTD & V6)

Tags
20jtdm , boost , idling , strange

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome