Hi all,

I had lots done to my car recently as I love it and cannot part with it. Latest was fitting a new (used) a/c pump and re-gassing. Now the air con is ice cold. The car runs beautifully however I noticed my MPG has suddenly dropped massively. Unbelievably I would get around 800 miles on a tank, when going to manchester 230 miles, it would use 1/4 tank and the return trip another 1/4 , so half a tank there and back in total....amazing! Even in town I would fill up every three weeks or so.

Now suddenly I have used 1/2 tank on just 160 miles in town and on a run. Something is way off even if it runs lovely with no power loss, or rough idling ...nothing!

I read that the oxygen sensor could be over compensating and becasue of this, gives bad mpg....also a change of fuel filter could help... I bought both and went to my mechanic yesterday, he fitted the fuel filter but said..."your can doesn't have and oxygen sensor" I have looked around but can't see any Octavia that doesn't have one, infact there should be 2, one after and one before the CAT. So my question is:

Is my mechanic mistaken or do you guys know of any other octavia's that don't have one? also, if that's the case, any other suggestions as to what could be causing the sudden drop in mpg?

I have had it on the computer and there are no fault codes, nothing misbehaving, no problems whatsoever. I expect the aircon to waste a few miles extra, but not half! The aircon is also functiong properly, switching on and off according to settings in the car, so i am baffled by this scenario, and the fact that I have no oxygen (Lamda) sensor.

Any ideas would be welcomed.

Thanks in advance.

 

Diesels of that era didn't use oxygen sensors, because they always ran with excess air. You may be thinking of petrol engines when you refer to oxygen sensors before and after cats.

Latest diesels do have 1 oxygen sensor, but I think only the Common Rail (CR) generation of engines. 1.9 TDIs aren't in that category.

Thank you for you comment and info. Nice to know! 

From reading different posts the only other thing suggested that could cause my sudden MPG drop could be the MAS. Is it worth changing that Do you think? 

Other than that, any other suggestions you may have?

I mean the car is running beautifully with no other problems or faults, But now getting such poor MPG is both expensive frustrating and worrying me. 

On 27/06/2024 at 07:12, Breezy_Pete said:

Diesels of that era didn't use oxygen sensors, because they always ran with excess air. You may be thinking of petrol engines when you refer to oxygen sensors before and after cats.

Latest diesels do have 1 oxygen sensor, but I think only the Common Rail (CR) generation of engines. 1.9 TDIs aren't in that category.

 

I'd be tempted to look for fuel leaks, for such a dramatic change, but you'd probably see that on the ground, or smell.

I'm not really very clued up on diesels/turbo diesels I'm afraid.

 

On 27/06/2024 at 06:30, ha33y said:

. Latest was fitting a new (used) a/c pump and re-gassing. Now the air con is ice cold. The car runs beautifully however I noticed my MPG has suddenly dropped massively.

Have you tried running with the A/C off and rechecking the fuel consumption?