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Matt, Mechanical Engineer
Category: Ford
Satisfied Customers: 23081
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2 litre 51 plate Mondeo TDDI. Car continues at same

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I have a 2 litre 51 plate Mondeo TDDI. Car continues at same speed when foot lifted off accelerator. Also when accelerating hard through the gears there is a regular slight hiccup. I thought it might be the potentiometer, but no fault code showed. I urgently need an answer as this fault has just developed as I am about to sell the car! Any suggestions, please?

I'd suspect that it may be running off its own engine oil

as this is easily burnt as fuel on a hot engine

The first thing I'd check is the crankcase pressure relief valve (PCV) these are sprung loaded and are only meant to 'burp' excess pressure every now and then. The exiting gas is piped back to the inlet , however should the valve stick open then the engine tends to suck the air out of the crankcase all the time and this carrys oil over with it.

If you remove the air intake pipe and look inside where the crankcase breather is plumbed in you may find evidence of oil.

If you do find oil replace the valve.
Customer: replied 3 years ago.

Hi, Matt. Thanks for reply. Have tried to find out where the PCV valve is located on TDDI engine and not even Ford Jennings, a Ford main dealer can tell me! Have you any knowledge of this engine?

Hello John

on any engine the PCV must be connected to the engine intake thats pre throttle on normally aspirated engines and pre turbo on turbo chanrged engines

as you need a vacuum on the drawing / feed side for it to work

so look on the intake for a 1/2" pipe that will be tee'd into the main intake pipe and then it will run back to the main engine and either go onto the side of the block or the cam cover
Customer: replied 3 years ago.

Thanks Matt. I will look at the Haynes manual to try to identify what you've mentioned. Will let you know early next week if I am successful. Thanks. John

Customer: replied 3 years ago.

Hi Matt. Have looked at Haynes and there is no mention of a PCV for the diesel - plenty for the 4 & 6 cyl petrol engines.Could a sticking EGR valve have the same effect? Will continue to look for the valve. Thanks, John

Hello John

Ok in that case check inside the intake just after the turbo for any signs of oil as this would be an indication that the turbo oil seal is starting to fail and a replacement / rebuilt turbo may well be required. Have a feel of the turbine wheel - there should be no play radially at all - but a little bit of axial / end to end float is normal
Customer: replied 3 years ago.

Hi, Matt. Haven't had a chance to dismantle anything yet. How come the engine revs freely when not under load? The problem only occurs when in gear travelling at an even speed, when it fails to slow down. I've discovered there's a fault on the alternator, and it's been suggested that this could have an effect. Would you agree? I'm hoping to get a replacement tomorrow. Thanks,John


just revving up when not under load isn't putting any work or fuel flow of any consequence into the system

only when you're driving along is everything being used as it should

now if the alternator isn't charging then yes this also needs looking at as low battery voltage will give all sorts of odd faults , and while its unlikely to cause your fualt I wouldn't rule it out either

bear in mind that often an alternator can be repaired instead of just fitting a new part
Customer: replied 3 years ago.

Thanks for reply. The alternator was producing an erratic charge. Have since had it checked by an autoelectrician and it's not repairable. Have just purchased a secondhand unit from a Ford specialist dismantler as I've spent enough on this motor-next car, a 3.0 ltr Tdi '55 plate Audi A4 Avant is waiting on the drive under cover but I must sell this one first! Will tell you if this repair works. Thanks,John

Hello John

best of luck

just get back to me on this post
Customer: replied 3 years ago.

Tried to change alternator but couldn't slacken belt enough! - 5 frustrating hours! However, just travelled 15 miles and the problem didn't reoccur! I obviously removed the 3-pin connector and sprayed it with electrical-cleaner before reconnecting, so possibly could have been the cause of the erratic voltage readings? Will be travelling further tomorrow so will give you an update later. Thanks, John.

Hello John

a dirty connector could be the issue as its this connection point that switches it over to charge

as for replacing / loosening the belt, the bottom bolts of the alternator have to be undone and you also have to remove the tensioner

see here for good how to

Customer: replied 3 years ago.

Hi Matt. The tensioner on the Mondeo is accessed via a 13mm square recessed hole-only problem is that there is only 1" clearance between it and the inner wing! You either need the special tool from Ford or make one as a bloke on e-bay has. Anyway, the problem seems to have disappeared for the moment so possibly the contact had simply deteriorated with age. Many thanks for your suggestions. Next questions will probably be about the Audi! John

Understood John

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