Cruise Control Oscillation: Causes & Fixes

Hello everyone!

My T4 tends to start rocking back and forth when I reach the limits of the power and drag range while using cruise control. Sometimes, on a flat road, it almost seems like the engine control unit doesn't know whether to accelerate or decelerate. I didn't observe this phenomenon with my previous vehicle, a Ford Galaxy 1.9 TDI. Is there any explanation for this?

Thank you in advance.

Peter.

Hello Peter,

I would most likely attribute the error to excessive play in the drive shafts or the wheel suspensions.
If there's a faulty speed signal at the engine control unit, which disables the EDC's anti-kickback function, the cruise control should also stop working. Simply disconnect the speed sensor at the transmission and check if the cruise control still functions.
What do the speed values in the measurement blocks of the EDC indicate when speed sensors are connected?

Best regards, Rainer.

Hello Rainer!

Since my T4 only has 50,000 km on it, I hope that a major issue in the drivetrain can be ruled out. Also, wouldn't such a large amount of play be noticeable audibly? As you said, the cruise control no longer works after disconnecting the speed sensor.
I haven't gotten around to reading the data blocks yet, but recently, during a test drive, all the speed readings were perfectly reasonable. When I move the vehicle back and forth while it's stationary with the gear engaged, the amount of play seems to be within the normal range.

Regards, Peter.

My machine can do that easily too.

'Especially when I'm in the range where the turbocharger starts to build boost (around 1500-1700 RPM, approximately 70 km/h), the whole thing starts to oscillate. It seems that the turbocharger boost control and the cruise control are interfering with each other in a way that causes this oscillation. You can't feel it by pressing the accelerator.'

Since I never use the automatic mode at that speed, it doesn't bother me. Trucks drive at 80 km/h, and after that, the problem is over.

I think this is a software problem in the control loop.

CU Gremlin.

Hi!

War am Montag mal für einen Sprung in Venedig und habe auf der Fahrt dort hin wieder etwas genauer nach gefühlt. Es ist egal welches Tempo man fährt, 50, 100 oder 170, es ist egal, diese Symptome treten immer wieder auf. EcThat's strange...

Regards, Peter.