Very poor fuel economy Peugeot 406 1.9 HDI Diesel.

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jonnya
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Very poor fuel economy Peugeot 406 1.9 HDI Diesel.

Post by jonnya »

Hi, I have just bought an 2003 1.9 406 S Estate 90bhp 105000 miles. It is only returning 41 mpg on average. A friends X reg diesel 406 (similar miles) is constantly returning 49+ mpg in similar driving conditions. I am puzzled by the low return of fuel economy. Several people have looked at car (with fairly reasonanble experience with diesels) but no one can pinpoint reason. The car has a fresh relatively unworn engine....no smoke at all (unless the car is revved while stationary and the smoke is still only slight) Someone suggested that is a blocked air filter and is burning excess fuel. Would an air filter make that much of a difference? Oil has not been changed in the 2000 miles I've had the car.

Will be changing the filters and oil very soon but dont think that will make all that difference. Brakes arnt binding and tyres are good.

Your help and ideas would be very much appreciated. Thanks. Jon
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Post by CitroJim »

Prima-facie, I don't think the engine is the problem here although a good service would not go amiss, especially an oil change. The oil that is in there now may be a bit too thick and causing excessive friction. A change to a good quality oil of the right grade is advised.

My gut feeling is that you need to look to the drive-train to find the lost MPG. Check the obvious things like tyre pressures first and then check each wheel for even just a little brake binding and then have the tracking checked.

It's amazing how just a bit of brake binding or a small tracking error can up the rolling resistance quite considerably.

Finally, what tyres are fitted. If you have a set of £10 fitted and balanced made in Chavakstan specials than these can have frightening rolling resistance. So too can odd tyres on an axle.

Good quality tyres, although dearer initially, can pay for themselves in fuel savings...

If all of that is not the answer, suspect a partially blocked exhaust.

Have you given the car a really good "Italian Tuneup"? That can make quite a difference.
Jim

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jonnya
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Post by jonnya »

Thanks for that....all really good info...yes oil mite be an issue... tyres might also (they are cheap ones).
Tyres are wearing evenly but will have a second look. Do have a hunch it could be rear wheel bearing (i have replacement) it making noise.
All really helpful info....was wondering what the Italian tune-up was...but am guessing is a good old blast with the right foot!
Thanks. Jon.
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Post by CitroJim »

jonnya wrote:was wondering what the Italian tune-up was...but am guessing is a good old blast with the right foot!
That's it Jon, a perfect description. Generally up to high speed in a lower gear with the engine running reasonably fast and maintained for long enough to get the exhaust really hot. You'd be amazed at just how much carbon can build up in a diesel exhaust if the car has enjoyed an easy, gentle time. Do it at night on a well choked up system and you may even see lumps of glowing carbon in your rear-view mirror....

Great fun for any poor soul who happens to be following....
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Post by Citroenmad »

Am i correct in thinking this is a 2.0HDi 90bhp and not a 1.9TD?

If your it will be most likely your MAF sensor. Ive just replaced one on one of the C5s and economy has improved to what it was and performance is also up.

Also, is your 41MPG from the cars trip computer (if it has one?) or is that your calculations. If its from your trip computer then they are rarely accurate.

You could get it on a lexia system and have the fault codes read. Mine was showing the MAF sensor fault code. £100 for a genuine unit, and i wouldnt recommend aftermarket sensors, they dont work as well.

Not sayins its 100% the problem, but it might be something you want to look into. Even try giving it a good clean with some contact cleaner or injector spray, but be careful, its fragile.

I also use a good dose of injector cleaner on every service and when i buy a car. On my 90 2.0HDi 206 it made a world of difference to performance. Followed by a good thrashing ('italian tune-up')
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Post by jonnya »

Yes its the 03 model 2.0 HDI

Is the MAF sensor on the air filter box?

The 41 mpg is taken from the computer....my friends shows an average of 49 for all his driving...and is far better fuel econ...mine always is around 41mpg. If anything im lighter footed.

Will try cleaning it and see what happens.

Have put cleaner through...just need to thrash it a bit ...will try all mentioned ...have a hunch it could be that bearing and the low quality tyres.

Had 406 saloon petrol before....the 406 S has slightly firmer suspension and is a dream to drive.

thanks for your ideas...will try

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Post by Citroenmad »

Yes, thats it on the top of the pipe leading from the air filter housing.

I usually get 40-42MPG average on the trip computer from the two 2.0HDi 8v C5s we have, both are 110bhps. However, when i check this againts the MPG i calculate of my fuel refills, the actual MPG is always 4-5MPG BETTER than my trip computer was telling me. So my car does 45-47MPG actual, but my car tells me its doing 40-42.

Thats with my normal, spirited driving, i can easily see 50MPG on the trip if i take it easy, which is actually 54-55MPG.

Might be worth trying it and seeing how far out your trip is.

I find our facelift C5 16v always reads over by 3MPG. They are rarely right.
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Post by dieselnutjob »

CitroJim wrote:If all of that is not the answer, suspect a partially blocked exhaust.
I have experience of this. From about 120,000 my Passat TDI had steadily increasing fuel consumption. It dropped from 47mpg to 40mpg.

I cut the cat off and replaced it with a straight piece of pipe and the economy went straight back up to 47mpg.

My Peugeot 806 HDI still gives good economy with over 200,000 on the clock (well I think 38mpg isn't bad for a hard driven 8 seater), but it has fully synthetic engine oil and transmission oil, though the tyres are fairly cheap. It also has no cat.
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Post by a4gom »

Do diesels not require a CAT then for the MOT?
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Post by CitroJim »

a4gom wrote:Do diesels not require a CAT then for the MOT?
Nope, not yet :D :D :D :D

Bin it with impunity. Diesel cats are there to mop up NOX emissions and there's no easy way for legislation to measure this in an MOT test environment.

Petrol cats are there to reduce CO emissions and CO is dead easy to measure with very basic kit and unskilled operators. Diesels don't produce significant CO so there's nothing to measure with ease.

No doubt in the future a "visual" will be made to check the cat is present.
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Post by a4gom »

Good news, my 406 1.9td estate has just started blowing from the weld before the cat and although I don't think there is anything wrong with the cat a straight bit of pipe would be better.

What affect will this have on fuel consumption / power?
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Post by CitroJim »

a4gom wrote: What affect will this have on fuel consumption / power?
There's a good chance that after a hundred thousand miles or so the cat will be a bit blocked so expect to see a difference in both :D
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Post by a4gom »

diang dang doo, first couple of hours I have spare i'll bring out the angry grinder and get shut!
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