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Doughnut Van Man
04-17-2012, 10:07 PM
I have an 06 Dodge that goes into Limp Mode in about a minute after start up. Had my mechanic hook up his snap on mobus and boost pressure reads 14 psi at idle and doesn't change when revving. Changed the boost pressure sensor (I Think) with a known working one and had no change. Code reads turbo overboost which makes sense with the boost the ECU is logging.
I will go ahead and make the assumption that no turbo should be able to produce 14 pounds of boost at idle. So, could anyone tell me what sensors the ecu uses to calculate boost and locations of the sensors. I have another van I can steal parts from to diagnose the problem. If there is a thread on this somewhere I am sorry, I couldn't find it.

sailquik
04-18-2012, 12:22 AM
Hi Doughnut Van Man,
Did your mechanic read the boost pressure in Absolute (PSIA) or Gauge (PSIG)?
If in Absolute, the outside ambient atmospheric pressure @ sea level is 14.6-14.8
PSIA.
So, yes, the turbo can easily be showing 14 PSIA at idle.
It's barely turning and the boost level is actually the ambient atmospheric pressure.
Suggesy you try to move the turbo actuator linkage (on the front of the hot side
of the turbo. The linkage needs to be lubricated and/or freed up from time to time, and
a frozen turbo actuator linkage will prevent the boost level from increasing as the RPMs
and demand increase.
The lack of boost (underboost) will very quickly trip the sensors....they signal the ECM to
put everything into LHM.
Hope this helps!
Roger
OBTW.... If the boost is measured in Gauge units (PSIG) it will go from zero (0) at idle to
approx. 20 PSIG at full demand and > 2500 RPMs.

skippytdi
04-18-2012, 01:11 AM
Hi Doughnut Van Man,
If your mechanic reading the boost pressure in Absolute (PSIA) or Gauge (PSIG).
If in Absolute, the outside ambient atmospheric pressure @ sealevel is 14.6-14.8
PSIA.
So, yes, the turbo can easily be showing 14 PSIA at idle.
It's barely turning and the boost level is actually the ambient atmospheric pressure.
Suggesy you try to move the turbo actuator linkage (on the front of the hot side
of the turbo. The linkage needs to be lubricated and/or freed up from time to time, and
a frozen turbo actuator linkage will prevent the boost level from increasing as the RPMs
and demand increase.
Hope this helps!
Roger
OBTW.... If the boost is measured in Gauge units (PSIG) it will go from zero (0) at idle to
approx. 20 PSIG at full demand and > 2500 RPMs.



I agree with Sailquik.
Underboost bad. Its a turbo rpm issue. Assuming its monitored like a veedub.

Doughnut Van Man
04-18-2012, 03:09 AM
Thanks for the quick replies. Should I be able to move the actuator linkage with my hand? When I start the engine the actuator works for a bit and then snaps back when it decides to go into limp mode. Would that suggest it is working? The turbo seems to spool and produce close to normal power before it goes into limp mode although that van seemed a little sluggish when not in lhm compared to the other vans in my fleet.

GREYGHOST
04-18-2012, 05:51 AM
I have some isuues with turbo limp home mode (partial LHM). what you should do is not what I did and start replacing parts. I have a MAF issue as it turns out, but haven't figured it out completely or fixed it yet. I dont know for sure if I have a bad MAF or a short /bad wire to the ecu or ground. my symptoms are startup boost pressure good( 3.5ish BOOST at idle) thats on a scanguage II. Placed in drive, boost good until deceleration.Then scanguage will read Negative at idle. Turn off engine, unplug maf connector. restart . boost returns, smoke dissapears, mileage back up to 23 (was 24-25) I have been driving with MAF unplugged for three months. I would do this test first and then go to the IAT sensor next. when you start the vehicle, you may notice the linkage arm move down, thats bad. i have posts with discussions on this, with good advice from others. i think you can search posts by username as well as subject. Good Luck.

jmoller99
04-18-2012, 01:39 PM
At the altitude I live at (around 7000 feet above sea level), I see -3.5 psi (or about 10.5 psi) on my UltraGauge EM all the time at idle, but it goes up by 12 to 14 psi if I step on the acellerator and am climbing a hill.

if you are going into limp mode, it will most be throwing some sort of errors (you will need a Sprinter capable ODBII reader to see what those errors are).

The Turbo will be disabled if ECU detects any data missing or improbable - like an air leak in the hoses or turbo resonator and if the temperature sensor (its in the plastic tube that goes between the intercooler and intake manafold) is reading open or its way off (I also monitor this temp on my UltraGauge to make sure its functioning). These things are usually thrown as errors, but some can't be read with a generic ODBII reader.

I would suspect the Turbo hoses or Turbo resonator, the after Intercooler temp sensor, or maybe even the vacuum hose that goes to the Turbo. LHM can be caused by a lot of things, that yours shuts down quickly makes me think its something like a sensor that has failed, or a major air leak in the Turbo hoses (into it or out of it). Of course, your EGR may also have failed (that would also cause immediate LHM).

talkinghorse43
04-18-2012, 02:33 PM
...maybe even the vacuum hose that goes to the Turbo.

The OP has an '06, so the turbo's vanes are not driven by vacuum, but are driven by an electric positioner.

Doughnut Van Man
04-18-2012, 10:05 PM
Well I'm starting to think it is the turbo. Hooked up my Boost leak tester and found no leaks in the intake system. I also swapped the sensors (i think) the ecu uses to calculate boost. Before limp mode sets in I get a lot of dark smoke and somewhat reduced performance. The actuator arms moves down on startup and snaps back up when lhm sets in. Also, when the arm snaps back up it makes a kind of quick scraping sound which doesn't seem normal like the veins are damaged or in need of lubin. I'm kind of hazy on the method someone would use to lube the actuator arm and/or veins so I will try to swap the turbo from another van. I guess with 420,000 miles on this thing I shouldn't be too suprised, I just can't stand paying 3k to have it fixed at the dealer.