I drive not very well but still manage to clock up a fair few miles a week. My problem is the 406 (1.9 td 90 BHP estate) does 35mpg only. The tyres are properly inflated, the handbrake disengaged, the brakes aren’t rubbing.
The car had a computer connected and the guy said its electrics/electronics were fine. Any ideas what and how I should check? The engine is smooth (for a diesel), starts easily whatever the temperature, pulls well for the box this size. The fuel consumption remains the same whatever the area or terrain. Oh, before I start being abused for having a heavy foot, I tried driving below 2000rpm, no change to mpg.
Is there anything I can do?
I fancy a change of car at some point, but we need to recover after 5 months of joblessness first before I buy a 1999 Celica 1.8VVTi 🙂

Are you going by the on board computer? Or filling the tank up, driving a set distance (100 miles) and refilling the tank to see how much fuel has been used?

The later is the only true was of finding out. Other than that, your trip sensor may be faulty.

Full tank – 70l gives me circa 850kms only. It should (judging by other 406s’ results) allow me at least 1100kms.
Sadly the trip sensor works well, I always have a Garmin with me to keep track my mileage.

there is not really much electronic in the 1.9td. Yes the 406 did have some but nothing like the modern engines. It is basically an agricultural unit so should be easy for someone who knows the engines well to find the problem.

Check for black smoke – its a sign there is either not enough air (boost) or the injectors are not atomising properly – ie need a clean/replacement.

But 1st thing is a service – including all filters, especially air and fuel. I use AEP direct for my filters as they are OEM ones. Fuel filter might seem like an odd one but if clogged the engine driven pump will have to work harder and flow will be reduced so you may be putting your foot down harder without realising it as it has been gradual.

Also check for boost leaks in the turbo piping and if you have a ‘cat’ get rid of the inners as it will probably be well clogged by now and they are not a legal requirement.

The EGR system can also lead to your inlet manifold being completely caked up in oil so always worth checking and cleaning if needed. (I disconnected mine on my HDI)

More info required…

Age/milage/condition/service history of the car would help… Any known problems, past or present too…

When was the last time the fuel filter was changed? When was the air filter last cleaned?

The 1.9 TD engine in the old Peugeots isn’t as economical as people would expect anyway, added to that the 406 is a HEAVY car, I don’t think you should expect more than 40mpg roughly unless you drive like your grandmother anyway!

FWIW, my 1999 Passat 1.9 TDi is running a bit inefficiently right now, but I know what’s causing that… Most VW Tdi’s have a Variable Vane Turbocharger, that the vanes get stuck in the open position on, causing the car to overboost under a lot of conditions, which causes poor fuel consumption under constant load situations (ie. motorway cruising). I’m getting 38-40mpg average at the moment, when it should be 48-50! This is relatively easy to fix, as long as I can get to the turbo, all I’ve got to do is clean the exhaust housing out using a turbo clean kit. I’m not sure than any Peugeots of that vintage had VNT turbos though…

Oh, and my Passat is to all intents and purposes, otherwise immaculate and well maintained. I’ve run a couple of bottles of Forte Diesel additive (recommended if you haven’t already) through it to see if it was just the fuel system needed cleaning, but it is definitely the turbo on mine… I know cos it’s gone into limp home mode a few times when I’ve had my foot down past 3500rpm!

When you say a full tank, are you running to nearly empty and working the mileage out based on using 70L? Or keeping a log between fill ups? Because the first method will be quite inaccurate.

35mpg is low for one tbh but it will be getting old now so if all the above checks out then it may just be a combination of worn out bits. If you have a bosch set up you can run it on veg oil to save a bit. Not too much and if the temp drops again and we get back to more snow deffo be careful as it can gel.

Different kettle admitted but I drive an 07 tranny, duratorque diesel etc and that being super modern etc only returns 30 mpg, and to be fair it’s always driven virtually unladen bar building hand tools!! Is that the norm??

178k miles, driven usually empty save for me and my CD’s.
No leaks, it doesn’t even take oil at all. Turbo works, I can feel the kick.
There’s no smoke at all either, unless I fuel up at Tesco.
I know the pump had been fiddled with before I bought it as it was idling at 1100 rpm. It’s now down to 900rpm as suggested by the Peugeot garage in town.

andyI, green diesel is also cheap but I wouldn’t be as it’s a bit naughty here in Eire, would I? 😈
It has the Bosch pump, I know I can fuel up at Lidl…

is green the same as our red? Risks are far too high despite to low chance of detection.

If it’s been fiddled with it may not be set right. If you are using veg then deffo do a fuel filter service as the veg can bring all the crap off the fuel line walls. You need to change the filters a lot more regularly.

@wrightyson – this it not meant to be an negative comment but are you sure you are driving it right? Diesels need to be driven right to get the most out of them and van gearboxes make it worse. Also are you doing lots of runs over 50mph as van aerodynamics are not exactly the best for that.

FWIW, my 1999 Passat 1.9 TDi is running a bit inefficiently right now, but I know what’s causing that… Most VW Tdi’s have a Variable Vane Turbocharger, that the vanes get stuck in the open position on, causing the car to overboost under a lot of conditions, which causes poor fuel consumption under constant load situations (ie. motorway cruising). I’m getting 38-40mpg average at the moment,

I only used to get that out of my ’56 plate 2.0l 140bhp Passat – I did have a heavy right foot though.

I get 30mpg out of my 2.5l 170bhp 2t Ford Ranger.

I tried but it wasn’t worth it (veggie stuff). Green diesel is the same as white but tax-free as it’s for farmers only, ehem.
I change oil and filters every 6000 miles, next change in a week. I also use Diptane to clean the gunk off. More info on it here.

2002

Record, Longest Distance Covered on a Single Standard Tank of Fuel

Peugeot 406 HDi Diesel

2,348.3 km’s covered in 36 hours, on less than a standard tank of fuel from Melbourne to Rockhampton Australia

I know its the HDI and it being Aus, I’ll bet the driver never had to change throttle use.
But it shows what the 406 can do. Theres a good chance that your car does have a fault of some kind, but I have to ask, how do you drive it? Lots of traffic, stop start driving? High speed driving, motorways etc?
Basically, leave off the brakes, coast in gear, try and anticipate further down the road, and don’t change your throttle loading. One of the biggest savings is to be had from keeping a steady throttle. Always used to add a a couple of MPG on the computer of the ex’s Clio when I drove it, mainly because she was incapable of keep her foot steady!
Not suggesting your aren’t already trying this things, but I used to get 50+ out of my old 306 Dturbo quite easily.

Andy don’t worry, I’m not the usual stw’er who flies off the handle at the slightest possible criticism, to be fair it’s all short journeys 7 to 10 miles, I’m usually late, and it’s got s roof rack. However I’ve had diesels for years as well as my petrol head cars but don’t seem even on a run to squeeze more than 35 mpg out of her.

According to the comp my 307SW 1.6 does ave >52mpg, never bothered to get the calculator out but seems about right, goes up and down a a fair whack motorway vs town.

But doesnt have anywhere near the poke my old 405TD had.

Someone was telling me not so long ago how they were filling up their 406 and then they looked down their feet were soaked in diesel. Tank had just cracked open, had to get the fire brigade out and everything, lol.

Maybe worth checking your driveway.

I drive mostly on motorways at the constant 110-120kph (approx. 65-70mph) for some 26 miles, then a few miles of 50mph and then stop. No jams, no hills, no braking as I agree with Clarkson’s saying look ahead and think in advance. I also generally have a pretty friend with me so I’m relaxed rather than stressed out.
What annoys/puzzles me, when I loaded it to the limits with stuff and went on a 826 miles trip across Europe with the accelerator pressed in all the way it gave me 40mpg. And I drove at the limit of its capability for hours on end.

tinribz, there’re no leaks, no obvious faults, only the bloody thirst of the oil burner.

I only used to get that out of my ’56 plate 2.0l 140bhp Passat – I did have a heavy right foot though.

I get 30mpg out of my 2.5l 170bhp 2t Ford Ranger.

The newer 16v 1968cc VAG diesels are notoriously less economical than the old 8v 1896cc units… Mine’s a 110bhp “AFN” coded engine and should return over 50mpg on the combined cycle. And it should be high 40’s to 50mpg on a motorway cruise, not 40mpg at best!

30mpg out of a Ford Ranger isn’t bad though, double cab pickups may have powerful engines these days, but short gearing and piss poor aerodynamics mean they are not machines for cruising economically in…

Could the cam/alternator belt adjustment be slightly off to cause the thirst?

it is possible the timing for the pump is out but this would result in lumpy running.

If the turbo is working right, car is well serviced and the injectors etc are all fine then it could be a pump set up issue if it has been messed with.

It is very common for people to “screw the pumps” which means they mess with the settings on the pump to increase fuelling and also alter the turbo wastegate.

You should see puffs of black smoke when booting it. If there is none then something is wrong. If there is lots then something is wrong. Smoke behaviour is a very good indication of problems on a diesel, especially the older ones.

At 178k then it is going to be getting tired though. Turbos especially.

Oh and remember you need to thrash diesels once in a while to clear out the crap. I really would consider getting rid of the cat inners too.

Wrightyson: Good to hear! 😀 as for the van, what are the official figures? No one ever really gets within 10% of them but that does sound low compared to the Mercedes Sprinters I used to use back in my student days. I guess you fall into the usual “rag it” when late so its not going to choked up! Maybe it’s been a bit previously mistreated if you bought it used?

There are a couple of diesel specialists with web sites that may be worth a look on – dieselbob, dervdoc etc.

I’ll add some Diptane next time I fuel up, that WILL clean the guts. Filters etc next weekend too. Rag it? I’ll do my best to degunk the engine.

When my old 306 started doing that it seemed to be the turbo, it was very noisy and the power dropped right down. Flogged it as didn’t want a huge bill.

The newer 16v 1968cc VAG diesels are notoriously less economical than the old 8v 1896cc units… Mine’s a 110bhp “AFN” coded engine and should return over 50mpg on the combined cycle. And it should be high 40’s to 50mpg on a motorway cruise, not 40mpg at best!

My MkV GolfS returned low to mid 50s and my MkVI does high to low 60s if driving err lively or mid to high 60s if driven sensibly. I do tend to be a ‘smooth’ driver though planning ahead and sensible gear changes.

I’ve given it some having dropped Mrs Hairychested at work. 3.5-4k rpm, went like a stink, no smoke behing. Will clean the engine and get the pump checked I reckon.