Hi

CAR: 2008 Mk2 Ford Focus 1.6tdci Zetec, 94k, FSH. 

ISSUE: Went into limp mode, diagnosed as DPF codes. 

PRIOR TO ISSUE: very good running order with full service from Ford and some reputable garages. Returned average 55mpg. 

DURING ISSUE: Ran car approx 800 miles in limp more without any problems other than the usual lack of power. Returned average 35mpg. 

ACTION: Finally got round to major service including (new) timing belt, water pump, full service, glow plugs, DPF, EGR and ECU & manual regen. Injector cleaner/fuel additive may have been added by the garage but not too sure. 

(BTW - the initial problem stemmed from failing glow plugs that got masked by the DPF codes. The DPF was absolutely fine but because the glow plugs weren't picked up in the codes the DPF got clogged and then ironically failed too). 

RESULT: after the works the car drives like new car with max power. However the fuel consumption/mpg is still averaging the 35 mpg mark. 

THE QUESTION: WHY???

Any help, advice or guidance would help me stop me the scratching of my head especially having forked out £800 on parts and labour :/

Q

Have you had the injectors tested? They can cause all sorts of wacky issues.

I'm not sure if the Injectors have been tested. I'll ask the mechanical but (because I don't know) how do they get tested? And what issues can they cause?

800 miles in safe mode!  The mode is designed to allow you to get off the carriageway to a safe spot while minimising the potential for engine damage (or minimising any damage already caused) not to plough on regardless.  Although commonly called such by the internet, its not a limp mode and you're not supposed to limp about the place on it.

Injectors is a could be.  Take it to a diesel specialist, not a regular garage, no matter how reputable they may be - there's likely a Bosch/Siemens/Denso/Marelli etc authorised service centre somewhere not too for from you.  The pressures in the fuel system are vast, hundreds of bar, and they can punch holes in piston crowns if faulty (another good reason not to drive about in safe mode).