Help! Thirsty SDI - any idea what I should say to the dealers?

[patrickd]

In an earlier post I asked if anyone could explain wny my fabia SDI had grown thirsty. I've changed the air filter, tried fuel additive, waited for warmer weather, all to no avail. The increased fuel consumption seem to start after the cambelt was changed with its 60,000 mile service.

Various people have suggested that the timing may have been altered because of the work on the cambelt, causing the car to use more diesel. When I've mentioned this to the dealer they dismiss the idea and say if that was the case it would be difficult to start which it is not. It just uses more fuel and seems to run a bit rough, particularly at speed when it seems to whine a bit.

I know nothing about mechanics and the car is going back to the dealers in a few days for further investigation. Can anyone tell me how I can persuade them it was the work that they carried out on the cambelt that caused the problem? I really don't want to pay out for more work to be done but don't feel confident enough in my understanding of diesel mechanics to argue my corner.

Any explanations of exactly why the faulty installation of the cambelt could cause the problem would be gratefully received.

many thanks.

[Tom_vRS]

The cambelt keeps the top half of the engine and the bottom half of the engine in sync with each other. Should the belt be fitted incorrectly, the timing will be out. If it was out by a long way it wouldn't start, but just one tooth out will mean it runs just fine, but with possible loss in power, smoothness and economy.

[P-A]

I would agree with the above. I think you need to stress that it was ok before the cambelt change. You've given it a fair amount of time to see if the problem goes away, but it hasn't. It looks like you will have to be quite firm with the garage.

The only other common cause of problems like this is a faulty MAF (air flow). This device measures air-flow and when faulty will give incorrect readings back to the engine computer. This in turn causes running problems - usually a loss in power and using more fuel.

[patrickd]

Many thanks for the advice, I really appreciate it.

I'm off to the dealers tomorrow morning so I'm hoping I can hold my nerve and sound convinving

[patrickd]

I don't know if anyone is still reading this, but after further checks on the SDI today, the dealer still can't find anything wrong with it to explain higher fuel consumption.

I'm getting a bit fed up with the situation. The car is definitely getting around 10mpg less than it used to AND has developed a distinctive whine at speed but after three visits to 2 seperate dealers no one can find a problem. I've also changed the tyres, fitted a new airfilter, used numerous fuel additives, all to no avail.

I've told both dealers that I think it relates to the changed cambelt but both of them (one of whom actually changed the belt) deny there is any problem.

What else can I do but roll over and take it????

[Chrispy]

Poor fuel economy on a weasel is normally associated with excessive smoke. Have you simply had someone stood behind the car when you rev it hard? There should be a little but nothing excessive. If the MAF was gone then it would be overfuelling and sooty as hell. If the valve timing was slightly out it could result in a rough running engine or a lack of power which may give you poor economy too.

The other side of it maye be the engine coolant temp sensor. If it thinks the engine is cold then it will be overfuelling slightly to compensate for what it thinks are low temperatures and poorer combustion. The sensor is based upon electrical resistance. The higher the resistance, the lower the temp. Infinite resistance (the sensor being duff or disconnected) means the engine is read as mega cold to the ECU and as such it would deffo overfuel. Worth a check.

[ExAudiSi]

Could the fuel pump timing be out after the belt change or are modern electronically controlled diesels different to the previous generations?

...think I may have just answered my own question, I'll get me coat....

[Tom_vRS]

Errr, you mention a whining at high speed. A worn wheel bearing would be noisy and could reduce economy. Are your brakes binding at all? Are your tyre pressures as they should be?

[patrickd]

Thanks again for all the responses.

The car isn't excessively sooty/smokey so I sort of ruled that out.

As for it being due to the MAF - I'm not entirely sure what that is but it sounds a wee bit expensive. As it's been to 2 seperate dealers and had a number of diagnostics carried out on it I assumed they would have picked up on something like that. Am I being niaive???

Likewise the engine coolant sensor - wouldn't they have checked that??? Carrying out any checks myself is way beyond my limited mechanical know how.

As for the whinning, I thought it might be due to worn wheel bearings but it seems to be related to the engine, the whole thing sort of settles down into a reverberation at certain cruising speeds like the old aircraft propeller engines. I also had the wheel bearing replaced at the back recently. They had been playing up for a while and the wheels were difficult to turn by hand when jacked up, but this never seemed to effect the economy.

[anton]

went on my first trip down to Cornwall over easter in my sdi estate with loads of luggage got stuck in some terrible jams so it was a 10 hour job with speeds of 75 when i did get out of the crawl , anyway with the driving i did down there i got 510 miles before the beaper went off so im ok with this.

I was getting alot less in the weeks before with the cold weather and the hilly yorkshire terrain sometimes having to try to get 50mpg