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Low boost in high gear

4K views 12 replies 5 participants last post by  Massivesiege 
#1 ·
Hello y'all.

Im having this problem.

Let me first say that i use the app torque and i know it isnt very accurate. But it giving me very consistent reading so im guessing its okay

In 1st en 2nd gear the boost can go up to 9 psi. but in higher gear like 5th and 6th gear, the boost will not go higher than a max of 6, with sometimes a peak to 6.5 psi. Max PSI should be around 8.5-9(0.6 bar) PSI right?


My Fuel pressure sensor is having some problems sometimes and i have a new one already.



Disconnected the battery multiple times and drove it the first time like i should for adaptation


With DSTC off and on same results. And also with the yaw sensor disconnected same result.

mods are

HD TCV
Bigger intercooler
3" exhaust from the cat, the rest still in the making

V50 T5 AWD

I have a dice, and i have good knowledge of the tuning aspect of a car. But i dont know where to look at in this modern car. Like maybe there is some safety function that holds the boost down or something
 
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#2 ·
Ive droven again, and its more like max 5-5.5 psi. And its not very constant.


But it goes quickly to around 5-5.5 psi and then goes up and down .5 psi.

Possible TCV failure? Can i check the duty cycle inside vida? like 0% or 100%
 
#3 ·
You say you have VIDA use that. Torque is guessing; turbo Volvos do not provide manifold pressure/boost in an OBD-II pid.
 
#5 · (Edited)
OBDII does not provide a boost PID so you will never get that info. You can read MAP data through VIDA, that is it.
Look into that HD TCV. Is it stock or Pierburg? If not swap in a stock one. Many aftermarket TCV are not good and do not play nice with Volvo.
Having a fuel pressure issue will definitely hurt performance. Find out if sensor, pump or pump module. VIDA can help point to whats wrong through test plans and additional info in fault tracing. System may be limiting torque due to fuel pressure loss.

I would also look for a intake/boost leak where your Bigger Intercooler is as well as rear hose from turbo that is under turbo, seen those leak.
 
#6 · (Edited)
+1 on the TCV - it's a cheap repair and a problem at the higher mileages. The only other thing I would question is maybe your exhaust bypass not staying closed at the longer runs at higher boost. I mean the amount of time one spends in 1st/2nd is much less than 3/4/5. But of course, start small.

When mine went bad I went with the HD unit from iPD/Elevate, but they don't play nice with tunes, the stock pierburg or the hd pierburg work much better with tunes.
 
#7 ·
I forget to mention yesterday that i already swapped the FPS in the 2nd post. And in torque app the fuel pressure seems to me much better. 43.5 psi, with the old it could go up to 50 or higher. It was out of range in my graphic But it didnt help my boost problems




Today i tested with vida and it shows the same results as the torque app. Only about 5-5.5 psi. Readings between vida and torque are almost the same.

I ordered a pierburg porsche TCV today and tommorow it will be deliverd. That will replace the current mac valve. Worked in my miata great for years
 
#8 · (Edited)
So replaced FPS and TCV. I bought the Porsche TCV, wich is a direct replacement and for what i see know the TCV works perfect. But only till around 5-6 psi.

WOT duty cycle is around 100% like it should, but close to 5-6 psi it cuts to around 50% and it holds pressure till redline. Its like the ECU cuts the boost. It should reach around 8-9 psi for what i could find on the interwebz

The TCV works good and reacts good, but cuts in at to low boost.

Now its the same in all gears

First time driving with this new TCV it looked good from time to time. It did reach 8 psi in 4th gear yesterday.

 
#9 ·
Time to replace the MAP/IAT sensor on the output side of the intercooler.
 
#10 ·
Hmm, after some reading it seems to be that the map sensor on the intercooler in these cars only function as a fault detection or something. Not the main function in measuring boost pressure for the ecu. Is that correct?
 
#11 ·
The sensor measures both pressure and temperature. And the ECM pays attention to its values and can and does pull boost if they go out of expectations.

These sensors do go bad, and this type of symptom can result. Not the only cause, but not unlikely. I've replaced mine, once, for similar behavior.

Your choice, let us know what you find otherwise.
 
#13 ·
Ill replace that one. I do find it strange because all the readings looks oke.

But lets see if that works

Thx for anwsering. Lets find out tommorow if it works. Found one near me
You should be looking at other parameters that can cause the ecu to pull tcv dutycyle , notably knocking which can been seen as the "ignition retard due to knock" parameter which is an indication of how ignition timing in degress is being retarded along with tcv dutycyle to reduce boost pressure

here is my thread https://forums.swedespeed.com/showt...quot-Ignition-retardation-knocking-(CA)-quot)

where my brothers s40 t5 faces the same issue as you describe with only boost hitting around 4 to 5 psi and nothing more , he has replaced a ton of parts and the only thing now yet to be done is a piston soak to decarbon the piston crown to rule out that as a possible pinging source

hope this helps in finding out the low boost issue
 
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