Citroen XM Forum

Aerodynamica wrote:I know Russ but I want it fixed!!!

Quite.... I don't blame you one bit. Bit like mine at the moment. Cold start is still a bit ropey. And I want it fixed.

Hi Chris, might just do that as it seems the best option - I'll search for something local.

Ran beautifully today! And what's the only recent change? I filled up with high octane petrol instead of the usual unleaded cheap stuff. I'm wondering now if this car maybe doesn't like the cheaper UL stuff from supermarkets etc.

That might be a feature caused by the non standard performance chip in the ECU.

Most cheap ones alter the base ignition timing and do state high octane fuel must be used, either that or its running higher compression or boost, trouble is this wouldn't affect idle or any throttle position unless under high boost/load situations where octane rating would be crucial.

D

You really do need to swap out that chip (or the whole ECU) to know what's going on.

Personally, I avoid supermarket fuel like the plague. Today's performance fuels are all about relatively expensive additives (particularly in the case of diesel), and supermarket fuels just don't major on these.

Haven't run a petrol car for years, but if diesel is anything to go by, I'd not be buying their petrol if I had the choice, especially for a performance-tuned car like the XM.

I'm keen on swapping the chip/ECU in for a short test to see what's what. I've always avoided the 'ultimate' type of petrol due to the higher cost and that I always have old cars it always seemed a bit anachronous to run them on a fuel they were not designed for. But the XM is semi-modern with its multipoint injection so perhaps it is suited to the good stuff after all. I am told the supposed increase in mpg offsets the higher cost per litre. This might work in the XM but not certain it'll work in the likes of my 1983 CX that uses a carburetor.

You really do need a stock ECU to play with................ I'm on it, honest!
Any vehicle with a knock sensor should (in theory) be able to take advantage of higher octane fuel, I say in theory because I don't think the tct runs either high enough Cr or boost, stock boost is only in the region of 7psi, its hardly worth the effort, you could point it at a stiff breeze and get 7psi of air pressure at the nose

Were you aware there was a download for your ECU type MP3.2 to correct stalling when cold on a trailing throttle? I wonder if the replacement chip has negated this somehow?

D

White Exec wrote:You really do need to swap out that chip (or the whole ECU) to know what's going on.

Personally, I avoid supermarket fuel like the plague. Today's performance fuels are all about relatively expensive additives (particularly in the case of diesel), and supermarket fuels just don't major on these.

Haven't run a petrol car for years, but if diesel is anything to go by, I'd not be buying their petrol if I had the choice, especially for a performance-tuned car like the XM.

Over the last 200,000 miles, I can't find any difference in the way a diesel runs on "better" fuel, other than V-power definitely giving LESS mpg.

The big difference in diesel fuel quality I was referring to is not the the difference between main brand standard and super (diesel and diesel plus), but between main brand standard and supermarket/budget standard.

I agree it's difficult to see much advantage in running main brand posh/expensive diesel, and the price difference is considerable.

What should be avoided though is prolonged use of budget or supermarket standard diesel. It just doesn't contain the cleaning agents and cetane improvers that main brand fuel does, which goes some way to explaining the price difference.

The worst you can do is run on cheap diesel, and potter about on shopping and local runs - and then wonder why there's a smoke problem at Testing time! Diesels need regular open road runs to keep themselves in good condition.

When our 2.5 (and ZX and BX before) were in the UK, up until 2004, the difference in running on Esso's then Diesel 2000 was quite noticeable: more torque, a quieter engine, and better consumption by about 2mpg. Here in Spain now, a similar performance advantage is to be had with Repsol standard e+ diesel. The way our Toyota D4D runs is the same - we can pull strongly up certain steep hills in 2nd with no problem on Repsol, but struggle to do this on cheap fuel.

Budget diesel can be improved by adding something like Wynn's Diesel Fuel Additive, or Miller's Diesel Fuel Plus - both of which contain a similar naphthalene cetane improver, plus lubricants and cleaning agents - but this just brings the price per litre to roughly that of decent standard fuel.