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I own a 2014 Ford Ranger 2,2-litre XLS double-cab bakkie with 35 000 km on the odo. I’ve owned it since new, but for about the last year, I’ve been experiencing a flat spot at about 1 500 r/min (most noticeable in the first three gears). There is also a strange noise coming from the engine, which sounds almost as if the turbo takes a double-breath when the flat spot occurs. I experience this during slow to gradual acceleration. I’ve taken the vehicle to two different Ford agents, who unfortunately failed to diagnose the problem.
At 1 500 r/min, the turbo starts to produce meaningful levels of boost because the exhaust energy is enough to power the turbine (the torque peak of 375 N.m is delivered between 1 500 and 2 500 r/min at full throttle). Because 1 500 r/min is a critical point, any deviation in airflow or exhaust flow impacts this region first. We’d suggest you do the following:
• Check for air leaks on the intake piping all the way from the airbox past the turbo
• Look for exhaust leaks on the exhaust manifold running to the turbo.
• Inspect the operation of the VNT actuator. It has a variable-nozzle turbo and, if the mechanism is sticky, can give problems. It operates on a percentage basis as controlled by the engine-control unit (ECU). The dealer should be able to command a percentage with the service tool to see if the output is the same.
• Check boost-pressure build-up. Again, the ECU demands a certain boost pressure at each speed and load condition. The dealer should be able to monitor this command versus the actual boost value, as well as record the fluctuation during the stumble.
• Do a diagnostic check to make sure all sensors and actuators are fine.
• Check the exhaust gas-recirculation valve (EGR). A sticky valve also impacts the part-load region of the engine. You can do a quick check by blanking off the valve completely.