AR159 2.4 210HP P0237 overboos issue, yet boost gauge shows normal pressure - Alfa Romeo Forum
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(Post Link) post #1 of 18 Old 10-08-16 Thread Starter
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AR159 2.4 210HP P0237 overboos issue, yet boost gauge shows normal pressure

Hi. I have 2 quick questions (these might be very obvious / noob questions).
So last time on the highway the "check engine light" came on when I accelerated hard from the intersection. More specifically, I floored the car in 3rd gear and at the exact moment when I switched to 4th gear the engine light came on and car lost a lot of power (limb mode?).
I restarted the car and the power was back.

I took the car to a mechanic who hooked it up to a computer. The following error popped out: P0237.
We took the car for a spin and it really showed some crazy numbers. Past 3000 rpm the turbo was supposedly providing 3000mbar of pressure, although the signal from the engine was to decrease the pressure.
We changed the overboost valve, but the problem is still here. Now the mechanic will run some more tests on it and will check the turbo bypass and other stuff. I will leave the professional to do the magic.

But. I would have 2 obvious questions.

1) Since turbo is providing 3000mbar (or more, this is where the sensor is at max reading) why the car doesn't go faster? I mean (by my simple logic) - the more (pressurized) air the engine can get, the more output power it provides (the richer the explosion). Yet, the performance is as it was before this error started.
Am I right to assume -> more air, more power? So at 3000mbar the car should be flying.

2) if the computer is reading 3000mbar then why is the boost gauge on the dashboard only showing about 1400mbar at full throttle? Who is wrong here? And why the different readings? At 3000mbar this gauge should do the 2 spins around the clock and not stop at ~1400mbar (1600mbar is max reading)?

Again, these might be silly questions, but still.

Thank you in advance for your insights.

Last edited by tej147; 10-08-16 at 22:31.
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Hi. I have 2 quick questions (these might be very obvious / noob questions).
So last time on the highway the "check engine light" came on when I accelerated hard from the intersection. More specifically, I floored the car in 3rd gear and at the exact moment when I switched to 4th gear the engine light came on and car lost a lot of power (limb mode?).
I restarted the car and the power was back.

I took the car to a mechanic who hooked it up to a computer. The following error popped out: P0237.
We took the car for a spin and it really showed some crazy numbers. Past 3000 rpm the turbo was supposedly providing 3000mbar of pressure, although the signal from the engine was to decrease the pressure.
We changed the overboost valve, but the problem is still here. Now the mechanic will run some more tests on it and will check the turbo bypass and other stuff. I will leave the professional to do the magic.

But. I would have 2 obvious questions.

1) Since turbo is providing 3000mbar (or more, this is where the sensor is at max reading) why the car doesn't go faster? I mean (by my simple logic) - the more (pressurized) air the engine can get, the more output power it provides (the richer the explosion). Yet, the performance is as it was before this error started.
Am I right to assume -> more air, more power? So at 3000mbar the car should be flying.

2) if the computer is reading 3000mbar then why is the boost gauge on the dashboard only showing about 1400mbar at full throttle? Who is wrong here? And why the different readings? At 3000mbar this gauge should do the 2 spins around the clock and not stop at ~1400mbar (1600mbar is max reading)?

Again, these might be silly questions, but still.

Thank you in advance for your insights.
Not sure how it works on your car but the ECU normally reads absolute pressure. If it is absolut pressure 3000 mb is 2000mb boost pressure or relative pressure. Does not explain you problem but.

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(Post Link) post #3 of 18 Old 11-08-16 Thread Starter
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Tnx for replying.
Can anyone else shed some light on this as well?
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Tnx for replying.
Can anyone else shed some light on this as well?
Hi

http://www.alfaowner.com/Forum/alfa-...0237-code.html (159 1.9 Diesel - P0237 code)

? :-)
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P0237 means faulty MAP sensor electrickery. why not check that?
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(Post Link) post #6 of 18 Old 15-08-16 Thread Starter
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I did see that thread and the issue the OP had looks very much the same. But before I disassemble the turbo I would like to be sure that that's the issue. BTW - how much work is involved in removing the turbo and cleaning it?


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P0237 means faulty MAP sensor electrickery. why not check that?
Thank you for the tip.
If I remember correctly this was checked and the reported pressure at idle was OK - was around 1000mbar which says that the sensor is working.




Still, can someone answer my question as to why the boost gauge shows values around 1400mbar at full throttle, but computer reports pressure over 3000mbar?
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(Post Link) post #7 of 18 Old 19-08-16 Thread Starter
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Bump for the question.


Today we will be changing something like "boost sensor", but not the overboost valve (this has already changed - no difference). So if this test today shows that it's not the sensor's fault we will be disassembling the turbo and cleaning some mechanism.
Will post the solution in the end.

Please excuse my layman english but I'm not exactly a mechanical engineer.

Still, if anyone has the answer to my questions above I'd be very happy to read them.
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Take off pipe on exhaust side of turbo, fill that side of turbo with ovencleaner, wait 1 hour then go for an italian tune-up..

Sounds like your turbo got stuck in low-rpm position & then cant regulate back (VNT stuck)

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Bump for the question.


Today we will be changing something like "boost sensor", but not the overboost valve (this has already changed - no difference). So if this test today shows that it's not the sensor's fault we will be disassembling the turbo and cleaning some mechanism.
Will post the solution in the end.

Please excuse my layman english but I'm not exactly a mechanical engineer.

Still, if anyone has the answer to my questions above I'd be very happy to read them.
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(Post Link) post #9 of 18 Old 24-08-16 Thread Starter
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Take off pipe on exhaust side of turbo, fill that side of turbo with ovencleaner, wait 1 hour then go for an italian tune-up..

Sounds like your turbo got stuck in low-rpm position & then cant regulate back (VNT stuck)
Hi, you are correct. We have narrowed down the cause to VNT being stuck and delaying/being stuck at high rpm which causes the engine to go to limb mode due to higher than expected boost pressure.
My mechanic told me that this is probably due to car not being used for longer periods (weeks or more). This is indeed quite true, sometimes I don't use my car for a week or more (my work is in walking distance of my home and I usually use the car only for the weekend trips or sometimes business trips).
Now I was told that this part will be screwed off and first manually cleaned, if this will not help this part will be sent to a professional service which specialize in turbos.
Will report back if successful.
Thanks for the inputs so far!
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P.S. Would really like to know what "overboost valve" is...Never heard about that on a VGT-equipped engine ;-)
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(Post Link) post #11 of 18 Old 29-08-16 Thread Starter
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P.S. Would really like to know what "overboost valve" is...Never heard about that on a VGT-equipped engine ;-)

it's the item on the picture below:
https://www.shop4parts.co.uk/?name=s...4807&sku=54384

actually it's boost regulator valve, not overboost valve. Sorry for my layman english.
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Hey, im danish, so no native english here to..Prob a few that had a laugh of me, so thought i could take a bit revenge ;-) sorry :-) No, actually thought you meant wastegate :-)

Theyll be cleaning the small "spunge" thats hidden behind the small cover on the regulator valve? Tell them to be very VERY careful when removing cover..The cover really wanna jump off to never to be found again land..I would recommend taking the entire thing of the car & open it in a place where the cover cant get lost :-) Heard about a few where it was totally filled with crap & only needed a good clean of the "spunge-thing" to get it working again :-) Good luck :-)
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(Post Link) post #13 of 18 Old 06-10-16 Thread Starter
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Hi all. So here's the update.
We took the turbo off to check it. It was indeed a problem in variable module (VNT?) - it was stuck hard.

But. There was also another problem which was not noticeable until we took the turbo apart (did not affect engine performance).

Upon checking the turbo we also noticed that the turbo is damaged on that side where gas runs thru. The "fan" was damaged because something flew thru it. Apparently it was a piece of hardened soot+oil, glued together. This is again due to not using the car for longer periods and driving it for short trips. Also the entry to EGR was really dirty.

See the image of turbo below:

https://s21.postimg.org/ppawffkbr/496846788.jpg


So now we need to rebuild the whole turbine. It's costly. I am not ready to buy a new one as I am in process of selling the car (either this autumn or next spring) and buying either giulia 2.0T or bmw335. I am avoiding diesels from now on.

So, do you know for a good specialist that can repair / replace my turbo? It is a garrett turbo, 210HP (i believe its GTB2056V).

Thanks.
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Depends on where you are.
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(Post Link) post #15 of 18 Old 19-10-16 Thread Starter
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I got it repaired locally. It should be ready tomorrow. 550€. Will post how the car behaves once we glue it back together again.

Apparently the intake manifold (if i got this correctly) was so dirty that they had to clean it 3 times and so was the EGR. Will post pictures of it.
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(Post Link) post #16 of 18 Old 4 Weeks Ago Thread Starter
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Just to update the thread. The cost was actually 1100€, as they had to fix the turbo and do some other minor repairs.
The car is now totally reborn as it was also cleaned throughout and now pulls off like new. The bad thing is that it costed lot of money and that I'll be selling the car in spring. The new owner will be a lucky person.

Thank you for all your help here! Cheers!
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(Post Link) post #17 of 18 Old 4 Weeks Ago
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Same happenned to me in the 156. Actually wasn't anything that went into it and destroyed the turbine, was caused by long time driving with a defective vnt, exhaust gasses did too much pressure over that part, high temperature, you can see it like melted, not broken!
Also your vnt flaps are slightly bent, which confirm the excess of pressure and heat.
Do the color on the turbo shaft reveals overspeed/lack of oiling?
Try to get a used turbo from a scrapyard, will be way cheaper
Don't forget to check the DPF, these things kill engines when they clog up
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(Post Link) post #18 of 18 Old 4 Weeks Ago
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Good you got it fixed.

Diesels arn't that bad. It is the EGR that makes it bad.
But if you don't do long trips. Stick to petrol
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