View Full Version : Low Turbo Boost at Idle

03-05-2013, 04:04 AM
I'm working on a 2006 Sprinter that I just bought. I recently cleaned up "black death" on the #1 injector and replaced bolt/seal. I installed an UltraGauge. Today I started it and at idle the gauge read -.15 Boost @700 RPM's. Off idle it goes up to .20 @1200 RPM's. There are no CEL's. Should I have some concern? I haven't driven it because I want to make sure it's okay to drive. Any help or suggestions would be appreciated.

03-05-2013, 11:45 AM
No boost at idle is normal and you cant hurt it if you drive it. If there is a turbo issue it will become apparent quickly. Mine actually shows very small negative boost at times. Normal

03-05-2013, 12:19 PM
How do your have your UltraGauge EM set up?
Are you reading boost in PSIG (I think the PID is "Bst").This means your manifold pressure is being read in PSI GAUGE which is OK, but we most often use MAP which is PSI Absolute (PSIA) and takes the current ambient atmospheric pressure into account.

MIght be more meaning full to set it to read the PID "MAP" . The your manifold pressure (with the engine off or just before you start it) will read ~ 14.6 PSIA (at sea level)).
As suggested, when the engine is idling at the normal (for all Sprinters) 680 RPM and you have no additional loads (lights, fans, chargers, etc.) the MAP will be ~14.6 (depends on current barometric pressure and your altitude).
Under the same conditions, the Boost pressure (Bst) will be ~ 0 PSIG (zero) (not affected by altitude or barometric pressure).
So, yes your Sprinter is running normally.
What is more important, when you get out and drive it, is that when you set your UltraGauge EM to also give you the most important PID (parameter identification) which is % LOD when you see the load up in the> thatn 75%
range your boost pressure (BST) needs to go to > 21 PSIG (MAP > 35 PSIA.
That's the max manifold pressure your turbocharger should be making.
At somewhere around 36.5-37.5 PSIA MAP (22.6-23-5 PSIG BST) your Sprinter will be getting into overboost and you could get a code indicating that the turbo is not being controlled well enough
by your electronic turbo actuator.
Rarely you will get an overoost condition that sets the CEL (Check Engine Light) off and puts you into LHM (Limp Home Mode). If this occurs, check all your turbo hoses for cracks and leaks and also
check the top seam on your turbo resonator to make sure the overboost hasn't blown a hose or the TR.
Actually what often happens is you get an overboost that blows something off or up in the turbo plumbing, then an underboost as all your manifold/boost pressure is escaping.
Hope this helps,

03-05-2013, 12:49 PM
This is my UltraGuage EM at idle (I live at around 7000 feet above sea level).

My MAP PSI never gets above 26 in Colorado. When I was in Memphis last year it got up to 32.

Bst PSI jumps around a lot when I drive.

03-05-2013, 01:08 PM
Interesting that you have both BST and MAP PID's running at the same time. It does illustrate the affect of altitude extremely well.
Your boost jumps around alot in the same manner that your % LOD jumps around alot.
They are tied together in the ECM.
% LOD increases, ECM increases the amount of fuel to balance that increase in %LOD and then the turbo vane controller increases
the amount of boost/MAP to balance that level of fueling to keep your engine burning nice and clean.
If you had a perfectly level road, with no wind gusts, curves, dips.....perfectly flat and straight with no atmospheric influences,
and you don't add any additional little electrical loads, your %LOD/MAP-Bst/fueling rate would stabilize.
In the real world we never see conditions that perfect, and the Sprinter is aways responding to little changes in the %LOD.

03-05-2013, 01:39 PM
This is my UltraGuage EM at idle (I live at around 7000 feet above sea level).

My MAP PSI never gets above 26 in Colorado. When I was in Memphis last year it got up to 32.

Bst PSI jumps around a lot when I drive.

My '04 has been known to hit 36 at times:idunno:

03-05-2013, 02:06 PM
36 PSIA MAP at 99% LOD is pretty common for T1N OM-647's.
For short term bursts of acceleration this is near perfect MAP.
Getting near the high boost threshold (I do not have that number) but indicates the
MAP is well controlled.
My 2012 NCV3 OM-642 V6 gets to 36.9 @ 99% and > 3200 RPMs, but this number also indicates the
turbo boost control system is working well as it has never gone to overboost and set a code or CEL.
It spikes @ ~=< 37.0 PSIA for a few seconds and then the %LOD and MAP drop pretty quickly back
to ~ 32 PSIA @ =< 90% LOD @ >3000 RPMs.

03-05-2013, 02:18 PM
Thanks, that is good to know:thumbup:

03-05-2013, 03:09 PM
WOW! Thanks for all of the responses. I learned more about the UltraGauge from these responses, then I did from UltraGauge itself. I really appreciate all of the input. Now, I have some peace of mind on my purchase. This forum is great!