[MkIVTDI]

Good afternoon all,

Been having an issue with my PD130 Bora for a while now where the fuel economy has been absolutely dire. Strangely, this came out of nowhere. The has been mapped and had an EGR delete since I bought it, and used to average 50mpg mixed driving, and 64mpg on a good motorway run at 70mph. All of a sudden, this dropped out of nowhere to around 35mpg average, with me struggling to see much more than 50mpg on a run at 70mph now (so basically about a 10-15mpg drop both average and on a run).

I have checked multiple things, obvious stuff such as the tyres are all at the correct pressure, tracking is fine, no brakes dragging. Lately it's been a little smoky on startup so have been doing logs in VCDS. Torsion value was absolutely fine, sitting between +1.5 and -1.7, MAF is working as it should, injection quantities both via rpm and MAF are as they should be as well. The deviation on one injector is slightly out at around -0.8 mg/str, which again is still well within spec. Only values that are off is the N75 duty cycle being a little low at 25-65%, with the actual boost lagging slightly behind the desired/specified boost. Coolant temperature sits around 80-84 degrees C, and I have changed the thermostat for good measure.

I have also tried different fuels - supermarket, standard Shell, and VPower, with little difference.

Is the turbo spool being too late likely to be cause of this poor MPG, or am I missing something? It's always spooled slightly late but the N75 duty cycle has never been low until now. Personally I'd have thought the late spool wouldn't affect it as the ECU is compensating by injecting much less fuel until it spools anyway, though I may be wrong?

All thoughts, suggestions and advice welcome!

Thanks in advance.

 

[ChippyTDI]

When was your fuel filter last changed? In the past mine has dropped economy when a change has been due.
Also check over the fuel temperature sensor readings for a hot & cold engine as this affects fuel injection duration and timing.
Might be worth a good old Italian tune up and blow the carbon off the injector tips and free up the turbo VNT mechanism.
You are correct about the spool as the smoke limiter will just hold back fuel until sufficient boost is reached - unless adjusted by a remap

 

[MkIVTDI]

I'd say roughly 6 months ago when I did a full service (oil & filter, fuel filter, air filter). What am I looking out for/what's normal and what isn't when checking for fuel temperature readings?

Injector tips definitely worth a look, hadn't thought about that one. I wonder if it's worth trying some injector cleaner or something through it (doubtful they actually do much really but worth a go)? To be fair, the turbo is starting to pass oil anyway so I may change it at some point over the summer anyway and throw a 1756 and supporting mods on.

 

[ChippyTDI]

For the fuel temperature:
Cold engine - about ambient
Hot engine - up to around 80/90°c anything into the mid 100s is suspect unless your on a track day in the peak of summer haha.

I've used diesel purge in the past, combined with a good hard run. Seemed to help loosen things up but could just have been a placebo, approaching 180K so something much be working.

Might be worth checking over and renewing your vacuum lines, a hairline crack is all it takes!

Yeah if you feel like giving the car a little refresh, at the moment there is so much choice of turbos for the 1.9 it's unbelievable!