Any mechanical geniuses willing to throw some light on this?

[wobblybox]

I have a Ford s max 2.0 tdci zetec with 107k well maintained and generally well looked after. I have recently noticed a surging sensation when sitting at 70 mph plus. Although the speedo doesn't move it feels fairly significant (so much so my girlfriend has noticed it which in itself is incredible!). It accelerates well in 1st, 2nd, 3rd and starts to hesitate in 4th, it stutters and struggle but does continue to accelerate it then pulls fairly well in 5th and on into 6th.

The surging sensation is very annoying as it's at motorway speeds that it's evident.

I have had it checked at the garage and no faults are stored, no split pipes and nothing evident.

I bought the car with 85k on it and from the day I've owned it it makes a paaa chooo noise (awesome description) when you change gear. Sounds similar to the 190k boras with daft exhausts that infest my home town every sunday night.

Add to this the Abs/traction light is coming on periodically and the mpg has dropped from 42 to 33 and I'm starting to think it's all connected.

My garage think it could be a clogged turbo and I'd like a 2nd opinion before I invest my hunnerds of pounds in replacing the turbo.

Many thanks for reading and if you need any further information I'm more than happy to provide you with whatever I can.

[MC Bodge]

Sticking variable turbo vanes?

I'd probably give it a good, solid "Italian tune-up" before I did anything else.

My mk4 Mondeo 2.0 tdci used to occasionally hesitate (boost dropping/surging?) under acceleration at Motorway speeds when I first got it, but it very rarely does it 6 years later. Not sure what changed, but I do, on special occasions , floor it and rev it out. I suspect that many drivers never do


Ps. When it began hesitating/hiccupping at low speed a while ago I changed the fuel filter and it has been great since.

[LanceRS]

Try something called Cataclean. It’s a bottle of fuel additive that seems to work quite well when I use it.

[wobblybox]

I have done the Italian tune up quite a bit to be honest and drove home at 80 odd in 4th with the revs quite high. It would be a bit smokey but I have the very basic dpf apparently. A fault came up on the wee plug in computer thing which indicated a fuel pressure sensor problem. It was cleared and drove on for a while (the mechanic tightened up the female side of the plug which were apparently loose) now it did again there recently so I'll see if the fault is present.

Coincidentally, my girlfriend left it very low on fuel (shocker I know) and I drove it about 5 miles and it started to really surge and hesitate so I think it was running out of fuel, I filled it up about 300 metres after it started really surging and it ran normally. I'm thinking it's a fueling issue

[Rat_Fink_67]

When was the fuel last changed? These engines are very filter sensitive and are due every 3 years. When they start to block it restricts the flow and usually causes low rail pressure fault codes. Symptoms are usually ok for around town driving, but under higher engine speeds and loads the fuel delivery can't keep up with demand due to the restriction. That would be where I'd be checking initially.

[wobblybox]

Yeah it was changed when the diagnostic threw up the fault code. It's still happening after filter replaced. The garage had a mondeo in with the same issue but much more noticeable and it was the fuel pressure sensor. The push in connection in mine was quite loose and he tightened it up a but, it did go better for a while but it's as bad as ever again. I'll get back on the diagnostic and am pretty sure it'll throw up the fuel pressure sensor fault. Replace sensor and hopefully job done!