Recently, I drove a Ford Mondeo 2.0 TDCi diesel hire car, June 2017 reg, 8094 miles on the clock.
I was driving in 6th gear at 70 m.p.h. then I braked while approaching a roundabout. At approx. 20 m.p.h. I put the clutch down to 'block change' into 2nd gear but the engine cut out. I kept the clutch down, coasted onto the roundabout (it was clear) and took the first exit. Fortunately this was a farm track with no traffic so I was able to stop safely and restart the engine.
I phoned the car hire company and said that the engine had cut out while the car was moving at about 20 m.p.h. so I thought there was a fault and I didn't consider that the car was safe to drive. They said it could be the auto stop/start. I said that couldn't be the reason as the auto stop/start should only work when the car stops. Then they suggested that I should call the AA.
I asked the AA patrol man to plug in his OBD scanner to check for faults but he found no fault codes stored. He then told me that it is a 'characteristic' of high-geared modern cars with common-rail diesel engines and 6 gears that the engine cuts out below a certain number of r.p.m. He wasn't able to give me a precise figure but I continued my journey making sure that the revs never dropped below 1000 r.p.m. while decelerating and the engine didn't stall again.
I read elsewhere on TalkFord that on the Mondeo Mk3 diesel, the ECU stops firing the injectors below 650 r.p.m. and that 6th gear is 2000 r.p.m. at 76 m.p.h. If it's the same for Mk 4 then 650 r.p.m. would be 24.7 m.p.h. which would explain why the engine cuts out if you decelerate to 20 m.p.h. in 6th before changing down.
Has anyone else had a problem with this 'characteristic'? Does anyone else think it is unsafe? I think that car hire companies should warn their customers about this.