Turbo over boosting/wastegate not opening

[charlyW]

Checked all the vacuum hoses they are going where they should according the various diagrams, both the TCV and the other electronic thing on the fresh air hose close to the turbo are plugged in unless the colours have been dotted incorrectly on the TCV. Two intercooler hoses have been replaced with genuine volvo parts all vacuum hoses are brand new silicone PCV done earlier last month full stage 0 completed including cam belt.

What else can cause fuel cut and do you know at what bhp the fuel pump will begin to slow.

[jblackburn]

OK, the other thing could be that your CBV has gotten tired and isn't opening to let out the excess boost pressure, so it spikes and hits the fuel cut. I think your best bet to see what's going on would be to get a boost gauge and attach it to see what's happening before beginning to throw random parts at it.

[boosted5cyl]

Are you sure the fuel is being cut? In terms of the fuel pump, it runs at a constant speed, through a pressure regulator and the fuel amount adminstered into the cylinder(s) is controlled on an active basis by the injector ON time via the ECU (or ECM in Volvospeak).

I think for the money (£0) its worth cleaning out the TCV using the guide I posted earlier. For sure it helped my T6 which was suffering similar symptoms (and uses the EXACT same TCV from pierburg). The valve gets actuated many times a second so although it might work "okayish" it might be crudded and not actuating as quickly as it should, I would say this would have an amplified effect with a chipped motor. Even if the plumbing looks good, for the money it wouldnt harm anything to replace it. I dont think its going to 100% solve the issue, but like I say, it cant hurt and I think given the cost.

After that I think it's time for a boost gauge and or a laptop with some obd software to log some live MAF readings etc. Provided your 850 has OBD II.

Another thing that comes to mind is a stuck\crudded up CBV (Compressor bypass valve), ie the pressure release on the inlet\fresh air side of the turbo system...

/Edit...Ah I think I get what you mean by fuel cut now.... Do you mean at what stage/BHP can the stock fuel setup no longer provide enough fuel?

[charlyW]

I think the term fuel cut is a term when the ECU cuts the fuel pump/injectors to protect the engine from creating too higher boost.

You mention stuck CBV where is that and how do I clean it ? Can you link your post on cleaning TCV please any further suggestions would be appreciated. I'm getting a boost gauge as soon as I can

[jblackburn]

CBV = Compressor bypass valve. Geez, I'm getting as bad with the acronyms as the government

It can't be so much cleaned as the spring just wears out and it stops working properly. IPD sells heavy-duty versions that you may want to look into if you're planning on modifying this car further like you want to. There are 2 versions, so figure out which turbo you're going with and how much boost you're going to run before you order one.

I think the turbo control valve can be taken off and cleaned with carb cleaner shot into the ports with a the little red straw that comes on the things.

You may want to look into a new one of those too for upgrading - the factory ones can spike at high boost; whereas the IPD one like I've got smooths out the turbo response a little more.

[boosted5cyl]

I'm not 100% sure where the CBV lives on the T5, maybe someone can chime in on that..... If it helps its the valve some people (unwittingly) replace to get the "whoosh" sound when you suddenly close the throttle under boost.

Heres the link for checking\servicing the TCV: http://minimopar.knizefamily.net/solenoids.html
Scroll to the bottom section "Diagnosing and Repairing Solenoids"

Hope this helps.

[charlyW]

Tomorrow [saturday] I'm going to see if the wastegate vacuum side is working I have a feeling it's jammed solid: I intend of putting 10psi into it and see if the rod moves correct if I'm going about this wrong : Reasoning behind this is when I removed the split pin I had to back the rod head down 6 times until the pin would drop into the hole at rest with no pressure did the same at 4psi 30kPa way above the B5234T specs as it should only be 12.5kPa or 1.8psi the rod did not move, the wastegate head head [part with the pin which has the split pin pushed through once its located on the arm] is moving freely possibly a little too freely for my liking.

The engine will not be running so there will be no possibility of engine damage if the wastegate vacuum side works then I will move onto the TCV

[charlyW]

Just a thought since getting the remap and white injectors I haven't replaced the spark plugs with better ones could this be causing my issue of hessitation? Currently running NGK FR7DTC installed month before last... Would Bosch 4 electrode be a good upgrade or bosch platinum suggestions please



Don't suggest Volvo OEM Plugs they're made by Beru or Denso in the USA had a set in my N/A caused all kinds of fun issues from codes to hessitation soon as they were replaced with NGK all the problems went had the same with a 740 and 760 so won't entertain Volvo OEM plugs

[jblackburn]

Would Bosch 4 electrode be a good upgrade or bosch platinum suggestions please

That's about the worst thing you can do for it.

I like the NGK plugs (used to own a Honda), and they were what came in mine. Stick with those since they're new anyway.

That sounds like a good plan to me; as rusty as mine is, I wonder if the wastegate rod could work a lot better, and the actuators DO wear out over time.

How do you know you're "overboosting", are you throwing a code for it or just feeling the engine cut out during hard acceleration?

[charlyW]

Might be a good idea to describe the symptom

between 60-80mph on hard acceleration while overtaking or messing around the boost needle rises to above 3/4 rpm needle climbs to 5500 I feel a slight hesitation or the beginning of a hesitation. To confirm what I feel is no where near as severe as the night I first drove the car home without having any pipes on the TCV along with two blown intercooler pipes

I'm trying to get the same symptom lower in the rev range so I can be sure so far it's only at the top. I haven't had a high speed test since I backed the wastegate rod down @12.5kpa or 1.8psi