Will leaky exhaust effect fuel economy?

[Marcus G]

Hi All,
I have a stock standard VL and fuel economy is poor (around 14l/100k).
I have checked the AFM and adjusted to 382ohms, as per other posts.
Idle rpm was high (around 950rpm). Adjusted back to 750rpm as per Ellery manual.
I have noticed that the rear muffler has broken away from the pipe, would this effect the fuel economy?
Thanks in advance,
Marcus

[Tree cutter]

If the muffler has rusted away from the pipe it is possible that the baffles inside the muffler have collapsed, which will cause a restriction and upset fuel economy. Check the LEDs on your computer, the red and green should flash together if everything is OK. A crook oxygen sensor can cause bad fuel economy.

[Marcus G]

Thank you tree cutter,

I am able to get stable red & green LEDs flashing at about 1 flash every 1.5 secs. It seems best with the AFM set to about 170ohms, but I have set it to 382ohms as per posts in this forum. Do you think I should set it back to that giving the best result?

Could a faulty oxygen sensor still give a good indication on the ECU?

[Tree cutter]

If you can get the red and green LEDs flashing at about 1 flash every 1.5 secs then the oxygen sensor must be working. I would set the AFM so the fuel mixture is correct by the LEDs. Check your coolant temp sensor also, there are two on your engine, one for the temp guage and one for the ECCS. If the one for the ECCS is faulty it can make your engine run rich. Also check the vaccum hose that goes to the fuel pressure regulator, if this falls off or has a hole in it then the fuel pressure goes higher.

[Marcus G]

Thanks Tree cutter,
I think the temp. sensor is OK because when I disconnec tit the engine revs increase (with the engine at operating temperature).
I'll check the fuel preasure regulator on the weekend.

[ucwepn]

Air leaks can cause bad fuel economy also (intake pipe and TB area), as mentioned above replace coolant temp sensor and O2 sensor to be sure they are fine (they cost bugger all). The exhaust leak could cause bad fuel economy but being back toward the rear of the car its doubtful, if the leak was at the manifold or the flange it definately would.

I just fixed a nasty airleak on mine at the afm->intake pipe and fuel economy has improved dramatically, from 300km's a tank to over 500 now. Am happy as to say the least.