om642 p0234 too much boost?
04-20-2013, 06:29 PM
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GL 320 CDI
om642 p0234 too much boost?
2007 GL320, about 150k miles, recently started setting p0234 code. Testing so far seems like it is hitting an upper boost limit and cutting out.
Under full boost, as in accelerating uphill, OBD info shows boost going to about 22psi or a bit above, sometimes when it hits this level it starts cutting out as if fuel is being cut off. This does not happen all of the time, is intermittant. I'm assuming the computer is cutting fuel because it sees an overboost condition, that appears to be what the p0234 code is for.
A few times it has gone into what seems to be a type of limp mode where it will not produce any boost, even under full throttle. OBD info shows no boost even under full throttle and power is way off, not able to maintin speed going uphill. This condition clears after a restart.
Intake pressure/temp, ambient pressure/temp, MAF, and coolant temp sensors seem ok, values all make sense watching OBD data while driving.
I pulled and checked all of the intake plumbing from the turbo through the intercooler and up to the manifold inlet, found no cracks or apparent leaks.
I pulled the controller off of the turbo and the lever that controls the internal vanes move easily, not stuck or gritty at all. Tested the motor inside the controller and it has good power and can cycle from limit to limit just fine.
Turbo spins easily by hand, no indication of any issue with the bearings.
Any ideas on what to look for? Could it be a sticking/clogged EGR? From searching here I see a lot of folks have had EGR trouble before 150k miles, ours has never been replaced. I've had the turbo and EGR off a couple of years ago and remember it was not an easy job, but checking the EGR seems to be the next logical step.
I'd also appreciate any help understanding how the boost level is controlled on this engine as there appears to be no wastegate or bypass. Are the adjustable vanes within the turbo used to limit boost? I was under the impression thosed were used to help it work better at low speeds.
Under full boost, as in accelerating uphill, OBD info shows boost going to about 22psi or a bit above, sometimes when it hits this level it starts cutting out as if fuel is being cut off. This does not happen all of the time, is intermittant. I'm assuming the computer is cutting fuel because it sees an overboost condition, that appears to be what the p0234 code is for.
A few times it has gone into what seems to be a type of limp mode where it will not produce any boost, even under full throttle. OBD info shows no boost even under full throttle and power is way off, not able to maintin speed going uphill. This condition clears after a restart.
Intake pressure/temp, ambient pressure/temp, MAF, and coolant temp sensors seem ok, values all make sense watching OBD data while driving.
I pulled and checked all of the intake plumbing from the turbo through the intercooler and up to the manifold inlet, found no cracks or apparent leaks.
I pulled the controller off of the turbo and the lever that controls the internal vanes move easily, not stuck or gritty at all. Tested the motor inside the controller and it has good power and can cycle from limit to limit just fine.
Turbo spins easily by hand, no indication of any issue with the bearings.
Any ideas on what to look for? Could it be a sticking/clogged EGR? From searching here I see a lot of folks have had EGR trouble before 150k miles, ours has never been replaced. I've had the turbo and EGR off a couple of years ago and remember it was not an easy job, but checking the EGR seems to be the next logical step.
I'd also appreciate any help understanding how the boost level is controlled on this engine as there appears to be no wastegate or bypass. Are the adjustable vanes within the turbo used to limit boost? I was under the impression thosed were used to help it work better at low speeds.
04-21-2013, 05:27 PM
#2
Out Of Control!!
Sounds like there is a issue with the boost positioner sensor/motor. If you or your indy has access to DAS Xentry there is a set of tests to correctly confirm P0234 boost system fault cause!!
04-22-2013, 01:54 PM
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Anyone have a link to recent advice on the best adapter? My searches are turning up a lot of old info so far.
05-14-2013, 02:44 PM
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I finally solved this after buying a star multiplexer and installing xentry and DAS, a bit of a PITA but DAS gives much more detailed diagnostic data than you can glean from OBD codes.
Plutoe you were right, the issue was with the boost positioner sensor/motor. DAS has a specific test that actuates that positioner, and mine would not move when commanded to. Tested wiring back to CDI control unit and it was fine. I saw some possible options for getting the boost positioner rebuilt but ended up just getting a whole new turbo assembly, hopefully I'll get another 150k miles out of that one. Not a fun job to replace the turbo on the GL, it is really crammed up against the firewall.
Plutoe you were right, the issue was with the boost positioner sensor/motor. DAS has a specific test that actuates that positioner, and mine would not move when commanded to. Tested wiring back to CDI control unit and it was fine. I saw some possible options for getting the boost positioner rebuilt but ended up just getting a whole new turbo assembly, hopefully I'll get another 150k miles out of that one. Not a fun job to replace the turbo on the GL, it is really crammed up against the firewall.
