Just one question for wise ones to answer, what effect would you expect to see in the CO level at natural idle if fuelling a car, fitted with a knock sensor, with an octane rating above what it is quoted by VAG to use.

I'm currently using Shell V-Power - which someone has said is 97/98 RON, with a BBY engine which is quoted to be able to run somewhere over the range 92-95 RON (I think).

Thanks in anticipation, I know that there are only three choices, ie LOWER, SAME or HIGHER.

The object of me using V-Power is to try to clean up the inlet tract/combustion area and reduce pinking, but I do intend to revert to ordinary Shell soon after the summer is over and I've completed 3000 miles using this fuel.

Edited 30 September, 201213 yr by rum4mo

The more fuel you burn the higher the co2 level.

They in theory burn cleaner thus could be reduce co2 levels but there are so many factors its unlikely to make a massive difference.

The ECU has to be able to take advantage of this fuel if not it cannot take advantage namely in the form of advancing ignition timing, most people use higher octane fuel for performance more det resistant.

I'd say same CO level.

I know it's recommended that the AUB engine runs on 98RON Shell V Power which is what I'm running mine on, as the lower octane and some granny style driving can lead to a build up of carbon, stuffed o ring seals and the engine ingesting it's own oil. Is this something that VAG sorted out with the BBZ engine? Personally I'd stick with V Power, you can't be doing it any harm, and I've noticed the oil and petrol consumption get better, so although it's a few extra quid a tank, on the other end it probably evens out

Thanks for your answers so far, the reason that I am using V-Power is for its extra cleaning properties and to get rid of pinking. I have already cleaned up the EGR pipe port etc and the throttle body, replaced the EGR valve - though the old one seemed okay, replaced the servo pipe as the one-way valve was passing, though probably not leaking to atmosphere.

At all previous MOTs, all the emissions figures have been very very low - ie well within spec, at this MOT, while the car was running V-Power and has been for over 2,000 miles, the CO level at natural idle was 0.25 - limit is 0.30, normally it was well below 0.1, so, I was just wondering if the higher octane and probably higher calorific value of this fuel was influencing the CO level at natural idle. The control Lambda probe should be able to intervene and limit the fuelling if it was getting too rich, but as I said originally, this engine's ECU might not have the freedom to advance the timing to optimise this fuel's octane rating - so something will probably happen other than just wasting money at the pump.

While using this fuel, the engine feels for flexible, ie more torque though there is no improvement in MPG in fact it has stayed lower than normal, but consistantly lower - maybe a 10% reduction in MPG, but I am not using V-Power to try to improve MPG - just to try to clean it up a bit and get rid of pinking during normal running.

My B5 Passat 2.8 V6, though can make use of higher octane fuel and as I have run it over the past 2,000 miles using ESSO's higher octane option fuel, it does feel livelier, though its never been short of low end torque while using the lower octane ESSO, but using the higher octane fuel has resulted in improved MPG - this time by 10+% on all sorts of running - which is to be expected.

Edited 30 September, 201213 yr by rum4mo

... so, I was just wondering if the higher octane and probably higher calorific value of this fuel...

The bolded bit had me scratching my head, so I checked with Wiki, and came away with this quote from their 'octane rating' page:

"Octane ratings are not indicators of the energy content of fuels. (See section 4 of this page and heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced"

I suspect you have developed a problem with air metering, lambda sensor or cat since the last MOT and CO measurement.

Easy way to check whether the change of fuel is relevant: chuck in a tank of normal petrol, drive around 'til most of it has gone through and the ECU has done any adjusting it may do, then take it back to the same place that MOT'd it and see what their gas analyser machine says. They'll probably do it for a fiver?

CO, carbon monoxide, relates to incomplete combustion. What's the mileage? Another angle to those already mentioned by Wino: dribble from an injector(s). Might tie in with pinking: carbon deposits. I'd try a FI specialist if V-Power doesn't work over time.

Edited 30 September, 201213 yr by Nortones2

CO, carbon monoxide, relates to incomplete combustion. What's the mileage? Another angle to those already mentioned by Wino: dribble from an injector(s). Might tie in with pinking: carbon deposits. I'd try a FI specialist if V-Power doesn't work over time.

Injector(s) dribbling, well I think that I've read that that is what usually happens to these injectors as a failure mode.

Mileage is 85,000 and all the running is on 10+mile runs and from new its only ever been fuelled with ESSO/BP/SHELL "unleaded" - that is until I started using V-Power about 3 or 4 months ago - I just checked the manual and it should be fuelled with 95 octane fuel, fuelling with anything higher "will have no consequences or advantage", fuelling with 91 octane can cause pinking until the knock sensing system gets control. That last bit is a laugh as these engines seem to knock very quickly when fuelled on "unleaded" and normally never stop until you have backed off.

Carbon deposits, yes both my VWs have very "dirty" engine internals and both have only ever been fuelled with ESSO/BP/SHELL "unleaded" - well until 3 or 4 months ago. My VX CAV GSI and wife's Fiesta 1.6SI always had clean internal when used as these cars have been.

On the car with the BBY 1.4 engine, this MOT and all the previous ones showed very very low CO levels at the higher engine speed, as did this car at the natural idle until this MOT - that could tie in with dribbling injectors.

I do intend to revert back to "unleaded" soon, so might look out my good old exhaust analyser that has not been used for many years - and compare what my Passat is spitting out WRT what the Polo is spitting out now - then see what happens when I revert back to lower octane fuel after giving the ECU a few tank fills to learn new values/settings.

Edited 30 September, 201213 yr by rum4mo

The bolded bit had me scratching my head, so I checked with Wiki, and came away with this quote from their 'octane rating' page:

"Octane ratings are not indicators of the energy content of fuels. (See section 4 of this page and heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced"

I suspect you have developed a problem with air metering, lambda sensor or cat since the last MOT and CO measurement.

Easy way to check whether the change of fuel is relevant: chuck in a tank of normal petrol, drive around 'til most of it has gone through and the ECU has done any adjusting it may do, then take it back to the same place that MOT'd it and see what their gas analyser machine says. They'll probably do it for a fiver?

"Where the octane number is raised by blending in ethanol, energy content per volume is reduced" that is not what I had hoped to find out - at one time UK refineries were said to refine the oil "higher up the stack" to increase the octane rating - but EU refineries were known just to dump in ethanol - maybe UK refineries also now just dump in ethanol!

Edited 30 September, 201213 yr by rum4mo