Ok, here is how this idea came to me in the first place.
On my 325, it started to feel very lazy about revving freely and I took it to the agents and my favourite indie. No-one could come up with a definitive answer but the indie suggested taking out the cats and he would then reset the ECU. So, thats what I did. He then reset the ECU, whatever that does, and checked fuel/air mixtures and since then, the engine seems to rev up and down very freely and easily and according to the OBC and my spreadshheet my fuel consumption has improved as well.
On my X5 the OBC tells me that my consumption is averaging around 14,7 L/100Km but my spreadsheet tells me that I'm getting around 25,3 ltrs/100kms.
According to the internet forums the average should be around the 15 l/100 km mark. So, back to the agents and my indie and again no-one can find anything wrong. However, opinions from various quarters reckon that the answer is to decat and remap or chip.
The theory is that the catylitic convertors do restrict the gas flow from day one. It's part and parcel of the way they work. After 100,000 K's though, there is a number of people that argue that the cats then become more restrictive and produce a negative affect on the engine performance. So, back to the theories. If you can improve the volumetric efficiency by getting the airflow through the exhaust to flow more freely, then you can adjust the fuel/air mixture going into the combustion chamber as well, (as the air flow will also improve on the inlet side when the exhaust side is improved) and the overall effect should then be an improvement in engine efficiency compared to what was. And naturally, that would mean an improvement in fuel consumption as well.
With regards to my comment about no-one here having done a chip on their vehicle. That is purely the impression I get from the all the responses over here. So I'm not stating it as a fact that no-one has chipped there car, it is just the impression that I have received.
On the 4x4 forum there are a fair number of people who say they have chipped their vehicles and are very happy with the results to date. Again, if memory serves me correctly, most of those people chipped their turbo charged diesel. I also get the impression that normally aspirated engines do not gain that much with a chip. So the guys that are suggesting remapping seem to have a valid argument. From what I can gather, that is.
So, my prime objective is to improve engine efficiency and thus fuel consumption and hopefully get the figure back to around 15 or even 17 Ltr/100 Km.
And yes, I have heard the argument that if you want fuel economy get a small engined petrol or diesel powered car. I'm just greedy. I want my V8 and a bit better consumption than 25 ltr/100 Km as well.
And yes I know that it's tough at the top but, eish, it's so crowded at the bottom.
