Hello!

Been fighting a battle with my 2010 Ford Focus 1.6 TDCi (110) for a few months now. I'm hoping I can get some advice here as the local Ford garage refused to work on it due to the turbo not being the OEM Garrett one and another garage I took it to had no idea.

The symptoms

A little while ago, I had issues with low power and a rough bottom end. At the time, I had EML for EGR stuck closed (P042F) and low turbo boost (P0299). It seemed the EGR code was causing the variable turbo to open the vanes all the way, I guess causing it to act more like a conventional turbo than a variable one. The Ford garage wanted £300 for a new EGR and £750 + labour for a new turbo if the EGR didn't sort the boost issue. Instead, I bought a blanking plate for £8 and blanked the EGR in a weekend.

I no longer get the EGR issues or codes and the VGTDC readout acts as normal, however the underboost code persists. Boost builds slowly compared to how a VGT should and it struggles to break around 12psi a lot of the time and often will struggle to get past 3k revs, even with foot to the floor. Coming off the accelerator for a second at high revs, then flooring it again, is the most reliable way to force it to make full boost pressure (over 21psi), but this is uncommon and never when I actually need it. I have attached a crudely annotated demonstration of this.

The high boost pressure, when it does appear, brings me to my next issue: turbo overboost. I also have a EML code for Turbo Boost Limit Exceeded/Engine Overboost Condition (P0234). With all this, my economy has tanked to low 30's with my normal urban commute and car is flat. Power is never there when I need it and at the worst times, it decides to boost fully and scares me with the unexpected power. Once the turbo has built full boost, it seems to more readily build boost on subsequent accelerations if revs are kept high and a medium amount of boost is sustained.

What I've tried

It's had a new air filter and the oil was changed only around 300 miles ago. I've run several bottles of diesel cleaner through it (Wynn's and STP) to no avail (not that I expected anything to change with the turbo, but worth a shot for a tenner).

I've visually inspected the turbo intake and found oil around and inside the turbo, but there is little to no play in the compressor. From what I can tell, the compressor wheel looks to be good shape. The job of replacing or rebuilding the turbo is outside my limited mechanical knowledge so I'm afraid of fiddling with it any more than that. 

There is no smoke at all from the exhaust at idle or revving in neutral, I haven't seen any while driving. It makes a noise similar to this when it's making under 2psi at low load, but the noise seems to disappear once it's making more than that. Unfortunately, I don't have my own footage on hand to demonstrate this, I will try to get some tomorrow.

The garage I took it to said their diagnostic reads the DPF as clear and unclogged and I do a fair amount of country driving, it's not all urban. The garage also found no vacuum leaks or intercooler leaks. 

The problem has completely stumped me, with my very limited knowledge, and everyone else who's looked at it, and a lot of the common causes for turbo underboost online don't seem to be the cause in this case either (such as vacuum leaks, bad air filter, etc). The only suspect parts I haven't inspected or replaced are the boost regulator and the turbo itself.

I'm holding out hope that someone will come to my rescue. The car needs some other work doing and it's due a cambelt change, but I'm wary of paying or doing anything until I know the engine will at least work properly once those expensive jobs have been done.

If you read this far, thank you for your time and patience.

Cheers

Interesting (I think) development today. Coming home from work, the engine went into limp mode due to turbo underboost. I pulled over and decided to simply unplug the vacuum line to the VGT turbo actuator, remembering how the EGR error code threw the vanes all the way open, making it act like a conventional turbo.

The first thing I noticed, once I restarted the engine to remove the rev limiter set by limp mode, was how responsive the engine was in the low end, despite making literally no boost at all until about 2k revs. It had no problem reaching and exceeding 3k revs and easily ran all the way to redline, where it made a max of about 12-14 psi. Not great for top end power as it still needs a lot more air, but it's more power than I was getting before. I have attached a graph to show how that looks when the turbo isn't changing its geometry.

So, this leads me to deduce that the issue with the turbo is that the vanes aren't opening enough to allow all the exhaust gas out on the exhaust stroke, preventing the engine from making power and building boost, and explains why it was having so much trouble passing 3k revs, it literally can't because there's too much exhaust still in the chamber.

I ran it for maybe 8 miles in this state, thinking maybe I could burn some crap off the vanes while there is less restriction for exhaust gas. I'm really glad I found this, because it means the obstruction/issue is not in the DPF or in any sort of intake, and it can still build boost which suggests to me than the compressor wheel itself is not damaged.

However, despite this, it doesn't tell me whether the fault is in the turbo controller or the turbo itself. It's a difference of a £60 part or a £1000 part, so let's hope it's the former. I believe the turbo controller (I think Ford officially call it a Turbo Boost Regulator?) isn't a difficult job for the novice DIY mechanic. I understand it's just some vacuum lines and a wiring loom. I want to try replacing this part first and see if there is any improvement. Maybe it's just clogged or something.

The turbo was replaced before I got the car (aftermarket though, not the OEM Garrett one) but I don't think the turbo controller was. The previous owner said the new turbo hadn't fixed the underboost issue, so I can probably assume it's something else.

Failing that, I'm going to assume it's sticky vanes, and I suppose I had better find somewhere that can clean the exhaust side of the turbo professionally as I don't really feel competent enough to do it myself. 

If anyone has any input or can provide any assistance, I would love to hear it. Maybe this thread will help someone with a similar situation in the future. Thanks for reading :)