Hi all, 

Long winded explanation but want to give whole picture as not sure what is/isnt relevant to my issue. I have a 1.5TDCI Duratorq MK3.5 Focus with 135k miles and am having consistent problems with the turbo cutting out on longer journeys. Bought the car at 50k miles in 2019 and had it remapped ("roadside", not dyno) for economy and issues began at about 125k miles or 15 months ago.

On longer journeys when the car gets fully up to temp and when travelling on motorways, usually when cruising at 60-70mph, i will go to accelerate and the turbo will not do anything, leaving the car horrifically slow and the turbo will not re-engage until I clear fault codes on my basis reader. This started last summer, was on the first motorway journey I'd done in a few months and I dropped to 4th gear at 60mph to overtake and there was an abrupt stop to the turbo and the car was very slow followed by EML. Code reader showed P0299 (Underboost pressure). I cleared the code but turbo wouldnt work. I replaced the turbo and the problem seemed to go away but the issue would come back periodically. It got worse and worse, i did more research and realised could be the DPF so put DPF cleaner in which again was slightly helpful but problem kept reoccuring. Had static regen done Jan 2024 by family friend mechanic who said it took 90 mins for the regen to finish (apparently long time?) and the reading went from "43 to 0", whether thats 43grams or 43% im not sure. Problem seemed to be sorted but now 2 months later, problem has returned and worse than ever to the point where if i clear the code on the move, the turbo works for 5 seconds but as soon as i come off boost, the turbo wont work again. 

This all seemingly points towards DPF issue but i have tried the old "70mph in 4th for 30 mins" but it somehow makes the situation worse and strangely the hotter the car gets the more the turbo will refuse to work. How can this be so if its a DPF issue? 

Suspect the remap is partly or wholly to blame for the issue but i would love advice from anyone who might have an idea on what the issue is likely to be and how to proceed.

Spoke to Ford and they said they wont touch it until i removed the map, and have asked a couple of mechanics who are stumped. Family friend mechanic who did static regen said exhaust readings, diff pressure sensor readings looked normal. 

Any advice greatly appreciated as all paths forward involve a large expense and I'd rather avoid things that are probably unnecessary.

Thanks in advance!

Has the boost pressure been logged by live data when running?  It could be as simple as a split boost hose or a faulty MAP sensor.

I can't see anything there that would suggest it being a DPF fault.

You can have the boost system smoke tested (literally fill it with smoke to see if any leaks into the engine bay).  And for the cost of a MAP sensor I'd probably just replace that.

4 hours ago, TomsFocus said:

Has the boost pressure been logged by live data when running?  It could be as simple as a split boost hose or a faulty MAP sensor.

I can't see anything there that would suggest it being a DPF fault.

You can have the boost system smoke tested (literally fill it with smoke to see if any leaks into the engine bay).  And for the cost of a MAP sensor I'd probably just replace that.

Okay will try the MAP sensor and look into the smoke test, thanks for the response!

Any luck resolving this issue? 

Not yet. Haven’t tried the MAP sensor yet but will this week. Still open to suggestions!

Did you have any luck fixing the issue yet?

I have replaced the MAP sensor for £33 (its called an Air Charge Temp Sensor according to Ford…) but have not had a proper chance to test the issue yet. It usually only occurs on long 30min + motorway runs. I had a 45 minute journey recently with a short 10 minute motorway run and the issue didn’t appear so potentially the MAP sensor has sorted it. Will confirm back when I test properly. 

So I recently had a good motorway run and the problem has returned but is less prominent. Again, the code that shows is P0299 Underboost pressure. When I clear the code the car’s power comes back and the issue stays fixed for the rest of the journey. I have changed the MAP sensor but not tried the smoke test, so will try to sort that out sometime soon. Any other ideas as to what this could be? Again, this is only when the car is up to temp.

The only thing I can think of from past experience with an old VW Golf GT TDI that used to go into limp mode when st higher speeds and when fully hot was the vanes in the Turbo sticking due to it being coked up and it would cause an over boost and would put it into limp mode. I used to switch the engine off, wait a minute or two then it’d be fine. 
Maybe this could be your problem? 
Do you do mainly short journeys? 
What fuel do you use?

And have you tried any sort of Diesel additives to help the situation? 
 

👍🏻

That’s an interesting thought. I had it remapped at 49k and we’re now at 135k but the problems started at 120k ish. I use supermarket fuel and put fuel additives in every few tanks. I replaced the turbo 6 months ago thinking it was a wastegate issue and before I replaced it Ford said there was no play and it was spinning freely. Having replaced it so recently I would be surprised if the turbo is coked up that much already. I could easily be wrong though. 
 

the code I get is definitely always underboost, I have never had an overboost code. 

i do mainly short journeys yes and a motorway run probably once every 1-2 weeks over an hour. 

I have read of other owners having mapped these engines and afterwards had issues. Was it mapped using a Dyno or just a generic plug and play map? 

I’d personally get it smoke tested as it could be a boost leak somewhere. 

Plug and play map. I will look into a smoke test

Been to an independent today who had a good look over the car, and found the following:

no leaks from 2 smoke tests. Checked the solenoid and mass air flow meter and both were fine. They suspect the map is wreaking havoc somewhere and causing the ECU to think something is wrong with the turbo where perhaps nothing is. They have suggested having the map removed and go back to stock as they are totally unable to reset and values on the ECU at present. Will look into doing that next and take it back to them to calibrate the ECU and see if anything is actually wrong other than gremlins

Sounds like you’ve found the issue then with the map then. You could take it elsewhere and have a custom map added and a dyno run. This should be way more useful and cause less issues. 
Hope you get it sorted and no damage has been caused.