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Matt
Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 20611
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have Ford Focus late 2008 (MK2.5). Recently I noticed

Customer Question

Hi Brian,
I have Ford Focus late 2008 (MK2.5). Recently I noticed strange pulsing in the boost when accelerating between 2000-3200 rpm. The turbo boost to 1.5 bars and then it looks like the ECU is limiting the boost to 1.25-1.3 bars and after that again to 1.5. No DTC error codes or check engine light is present. So far one of the electro magnetic sensors for VNT management of the turbo was changed but this doesn't solve the problem. I suspect either a turbo actuator sensor problem or dirty and not moving VNT vanes of the turbo.
Please advise if you have experience with similar problem.
Best regards,
Veselin
Submitted: 3 months ago.
Category: UK Car
Expert:  Matt replied 3 months ago.

hello Veselin

I'd agree that this sounds like an issue with the boost control side but the 1st thing to check for is a boost leak as this can result in a cyclic behaviour in boost pressure as you describe

I'd first check all the high pressure hoses post turbo/s for any split hoses or cracked metal pipes, also check the ends of the intercooler as its not unheard of to pop the end caps off under high boost.

If this is OK then check the small vacuum lines to the turbo and its connected control solenoid onthe bulkhead, any cracks or leaks can give turbo issues

Also have a feel around with your bare hands with the engine running to see if you can feel any escaping gas under your touch. Another method is to use a soap and water solution sprayed onto any suspect areas - if there's a leak it'll bubble upwith the engine running

If this is OK then check for air leaks after the mass airflow meter - The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.