Boost limited to 0.6bar even with Performance FC

My car is currently limited to 0.5bar boost (2nd) and 0.6bar (other gears)....

Now this would be the correct boost pressures for a standard car BUT I've a got a Performance FC receipt in the service history confirming stage 1 mapping to 0.8-1.2 sustained boost and 2bar overboot; receipt details mapping, cpu & boost control valve all fitted.

So i'm confused why the after market boost gauge fitted is only showing a max boost of 0.6bar....



I've a couple ideas as to the problem but thought I'd sanity check my thinking with you sage people first...

1. Is the after market boost gauge incorrectly fitted?

If I compare the fitting of the aftermarket boost gauge in my car .vs the forum guide on how to fit, there is a difference. In the forum guide the pressure feed it taken from the intake plenum (pic1, blue Samco hosing) but on mine it looks like its being taken from the rear of the engine block (see pic 3,4,& 2).

Did the previous owner connect the gauge in the correct location?
Should I re-engineer the feed to use the intake plenum?


2. The Boost Control Value is set to low/standard boost pressure....

So I'd check this myself but only 1 problem....I've yet to find the boost control value! So I've an external (expel to atmosphere) dump value and typically I'd expect a boost control valve to be connected between the turbo and wastegate but I'm really struggling to find a candidate for a boost control valve in that location.

Someone help point me in the right direction of where you''d connect a boost control valve? I'm expecting it to be in the front of the engine, to the right of the turbo, behind the radiator, around or below the intake plenum and possibly under the battery shelf...I'm expecting it to be easy to access for adjustment purposes.

Where else would you connect a boost control valve?


3. Aftermarket Boost Gauge is Defective

It could be the aftermarket gauge is knackered and cant measure over 0.6bar..... will look into this when I remove the centre console but I think this is less likely...


4. No obvious ECU errors

Check with my diagnostic software and cant see any obvious ECU error codes. There was only one (0A – Lambda Sensor Integrator) error code but cant see how its linked to the boost limiting issue...

1. Is the after market boost gauge incorrectly fitted?

Source for boost gauge reading is typically taken from any vacuum source at the intake. In your case (Pic 4), it is taken from the back of the plenum. This is fine.


2. The Boost Control Value is set to low/standard boost pressure....

What boost controller is fitted in the car? Trace the hose lines the come from the wastegate actuator and turbo compressor housing...and you will find the boost controller at the end of it.

3. Aftermarket Boost Gauge is Defective

Possibly...but i would check that there are no kinks on the vacuum line to the boost gauge first. Check that there are no obstructions / debris within the line too.


P.S. In your second picture, the short blue section of the vac tube should be connected to the fuel vapor solenoid to the right of it. The nozzle from it appears to have broken and someone has blocked off the ends.

Thanks Kelv27

1. Thanks for confirming, I'll rule that off the list
2. Receipt doesn't say and managed to pop out between shower to check and the vacuum pipe between the turbo and wastegate has a pipe join connector - so something was connected in previously but since gone....
3. Will need to get at the back of the centre console for that, weekend job...

The short blue section of the vac tube - traced that pipe back and its a vacuum pipe connected to the same T-piece as the pipe that leads back to the intake plenum.. is the fuel vapor solenoid connected to the same vacuum line?

Thanks in advance!

DS

https://images.app.goo.gl/xYUTGyMTCGVc2ot66

Is no.11, 'Pierburg solenoid' in the above picture the standard boost control solenoid on the 20VT? If so, the bottom two pipes have been capped off in mine, leaving only the feed from the top...which feels pointless IMHO.

DS

Just answered my own question, yes it does. The pipe should go between the plenum and the 'fuel vapour recirculation pneumatic valve'. Try saying that after a few beers! Great spot Kelv27!

Page 43. http://storage.fiatforum.bg/Books/C...gine%20Fuel%20System%2020vlv%20turbo.htm

DS

Yes, the Pierburg solenoid is the EBV (Electronic Bleed Valve) that the ECU uses to control boost as standard.

The bottom 2 hoses are from the high pressure side of the turbo and to the wastegate :
The middle hose on lower side of ebv (next to electrical connector) should be marked red and connects to the high pressure side of turbo.
The outside hose on lower side of ebv (furthest from electrical connector) should be marked blue and connects to the wastegate on the turbo.
The top hose is the bleed off and connects back to the turbo intake.

If there's a separate PRV or boost controller fitted then sometimes that would just use the 2 bottom hoses and the top hose would be left connected to the original EBV, so sounds like you probably have some custom boost control method fitted. Or if those 2 bottom hoses are just connected straight together then you'll get base boost in all gears.

Trace the small bore hoses from the turbo high pressure outlet and the wastegate and see if they're connected together or connected to some other boost controller. Sounds like you're getting base boost (about 0.6 to 0.7 bar) in all gears so maybe the 2 hoses have just been connected together with a hose joiner.

Thanks, literally just printed the diag of the air intake system from the manual to troubleshoot where those pipes go (and I think you’re right and I’ll find a hose joiner linking them.....)

Update to follow,

Just stripped the inlet...

So I think this will not be helping with my boost issue....

Oh and...no boost controller but turbo is connected directly waste, by passing the solenoid all together....

DS

So as suspected direct connection there is causing base boost. Possibly done to hide the misfire/lean running under boost that would be caused by the split intake hose.

Agreed just don’t understand why you’d go to all the trouble to short the turbo vac pipe when its the same amount of work as changing the pipe!?!

Replacement pipe order anyway....

Will let you know the outcome

DS

**Just to close out the thread**

Kelv, Graham - Massive thank you both!

Put the fiat back together and it now boosts to near 1.5bar and oh my god is it quick!

Top job gents....

DS

Isn’t great when you press the shouty pedal and all of a sudden things happen

Nice one.