Turbo Overboost

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Bosley99

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Having problem with turbo overboost. Replaced turbo pressure sensor and solenoid and thought all was good when driving around ... normal max around 18psi.
This morning drove for around 40 mins all good. Reached Mt Ousley (long & steep) all OK in the first half of the climb then changed down to 4th and the boost pressure increased ... up to the 35 psi max on my auto meter gauge. I backed off as much as I could but the pressure was still well above 20 psi until I reached the top of the mountain.
Turned around and drove down the hill and stopped for over an hour just in case it was heat related (I'm running out of possibilities). No code thrown (I have a scan gauge).
Continued home (about 30kms) keeping boost as low as I could get. Took it out for a drive around the block after a few hours and same behaviour i.e. I can get boost to 35psi without too much effort on the flat.
No performance issues i.e. if I didn't have the gauge I wouldn't know there was a problem. The gauge moves normally i.e. nothing jerky, smooth as you would expect. It's like there's no pressure limit.
The only other out there possibility I can think of is that under load and heat the turbo vanes stick. Don't think it's the gauge because it behaved normally to the overboost trigger point.
Would appreciate any educated advice. I haven't been able to find any other situation like this having spent quite a lot of time researching.
 
Could be sticky vanes. What does it drive like down low? It is really sluggish taking off from a stop or does it feel normal?
 
Not sluggish. Drives really well, just like before I had the problem.
Disconnected the vacuum tube from the actuator to see if the vanes were stuck in the open position. No boost at all so I guess the actuator is doing what it is supposed to do. By the way it’s a 2007 stx.
 
I take it the gauge reads zero when the motor is turned off? Is it a mechanical or electronic gauge?
 
Yes at zero with the engine turned off. Does the full range i.e. 0 through to 35 whilst driving.
It’s mechanical.
 
maybe get an obdii bluetooth plug and use an android phone with the torque app. to compare boost readings.
would think if your boost is near doubling, the car would have some different performance characteristics!
 
^^that would be my next move. Autometer are good quality, I have them in mine and have never had a problem. That isn't to say something internal hasn't failed in the gauge and giving an incorrect reading.
 
Scangauge ought to show boost pressure too, shouldn't it? If not, the OBD adapter + Torque app is the way to go.

Turbocharger overpressure will do several things:

1) Make your vehicle performance change. Usually feels a little more powerful, and no sign of black smoke

2) Throw a "turbocharger overpressure" engine code. Mine's done it when the hose popped off my Tillix valve and the turbo was given full "go". Engine light came on with that exact error.

3) Pop the hose off the intake manifold. This happened to me moments after the hose popped off the Tillix valve. I saw my boost pressure skyrocket then heard a 'pop' from under the bonnet, checked the mirror and sure enough the caravan had disappeared in a cloud of black smoke. Quickly pulled over (don't want to run unfiltered air for too long) and put it all back together.

So, I would suspect a faulty gauge too, like the others.
 
Errm i got a 2007 stx too theres no variable vane turbo on that rig mate
Shes an old school garrett setup
variable vane electronic turbo started in 09 i think?
Correct me if im wrong

Also if you're boosting at 35 psi you'd friggin know about it
Thats a lotta boost
Gotta be a faulty gauge surely...
 
Errm i got a 2007 stx too theres no variable vane turbo on that rig mate
Shes an old school garrett setup
variable vane electronic turbo started in 09 i think?
Correct me if im wrong

Also if you're boosting at 35 psi you'd friggin know about it
Thats a lotta boost
Gotta be a faulty gauge surely...

i was under the impression all d40's had variable vane turbo's, pre 09's are vacuum, post are electronic. D22's are fixed vane.i had vacuum leaks, resulting in the actuator not closing the vanes, so they were open all the time. this slowed the boosting and made the car much louder
 
i was under the impression all d40's had variable vane turbo's, pre 09's are vacuum, post are electronic. D22's are fixed vane.i had vacuum leaks, resulting in the actuator not closing the vanes, so they were open all the time. this slowed the boosting and made the car much louder
I have a feeling the single cab dx had a wastegate turbo. Can't remember the power output, 104kw maybe?
 
Yep for sure. All the others definitely have a variable vane turbo. Earlier ones were vacuum controlled and later ones electronic control.
 
Thank you all for your responses.

ericcs ... you're correct. I have a Garrett M24 EC2 turbo ... see link, it's a VNT
https://garrett.honeywell.com/product-search/?lang=en&/#/detail-result/?q=105083&p=UNLINKED

Old.Tony ... my old Autel scan gauge doesn't have anything I can use to monitor turbo boost. I'll check out more modern gauges.
Can't notice any performance improvement, no smoke and no codes. If I didn't have the gauge I wouldn't know there was a potential problem.

Initially I thought because the gauge is mechanical there would be a low probability of a problem. Having thought about it, pressure coming into the gauge must come up against some form of resistance that moves the dial. If that resistance is lower than it should be then I would get an incorrect reading. Not sure how they work but have emailed Auto Meter in the US. I'll see if I can confirm the gauge is showing the correct pressure during the week.

Thank you again for sharing your knowledge and experience ... it's good to know you're out there and willing to help.
 
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Problem solved. Hose to Boost Sensor was disconnected. Obviously not properly pushed on when the boost sensor was replaced, so when driving for about 40 mins then proceeding up a few kms of steep highway, changing down a gear and giving it a bit of throttle, it finally came off.

Also, I found the MAP reading on my scan gauge that showed 100kPa (complete vacuum) even when I drove it around. After reconnection, it sits around the 14kPa level at idle.

So as far as I understand it, the ECU doesn't get a reading and continues to tell the solenoid to apply vacuum via the actuator, thereby keeping the vanes closed and ramping up boost as engine revs and therefore exhaust gasses increase.

What I don't understand it why I wan't getting more power as the PSI climbed to 35psi+. EGTs remained low, so I guessing there wasn't more fuel being added.

Anyway, for me, an education in VNT turbochargers and an opportunity to interact with people who are prepared to help.
 
Good stuff, glad it was an easy fix. Interesting too that it was boosting, I didn't think they worked without vacuum, but obviously they do.

As for the power, you are correct. The ecu would have a set fuel map for throttle position and load. Even if the boost is higher than what it should be, it won't increase fuel. Boost without fuel just lowers egts. I'm surprised the ecu didn't go into limp mode with an overboost, I guess since the ecu wasn't seeing boost it didn't realise...

I guess it also shows the advantage of having a mechanical boost gauge. As you said, it drove normally. 35psi long term wouldn't do the intake system or engine a lot of good and without a boost gauge you would never have known.
 
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