Flat Spot

[xavtia]

been for recall and flat spot, they told me there was no fault showing but i was insistant so they went away again and came back saying there was now a fault that they have reset, been told to use ron 98 petrol as its probably supermarket petrol causing it

 

anyone else been told to use this and does it make a difference?

[Z3M Roadster]

How ridiculous, the type of fuel makes no difference to these engines. They are designed to run on 95RON. 98RON super will have no effect on the way they perform as proven by numerous tests.

 

Only cars with high compression ratios will notice a difference using higher RON fuel, the C4 does not have a high compression ratio.

 

Yet another get out by Citroen.

[bill03]

So what is the compression ratio???

[kfk]

A high performance car running 95 ron will have a tendency to pink and suffer with poor performance.

 

A normal engine designed to run on 95 run will sometimes see benefits from 98 ron fuel particularly if suffering from preignition problems (pinking).

 

This difference in octane quality means that you can expect your engine to work more efficiently to deliver improved performance and better fuel economy while protecting your engine.

 

When the manufacturer states the Ron of the fuel that is the minimum recomended.....anyone remember 2 star 3 star & 4 star?

 

As to whether this is the answer to the original post is another matter.

 

It would be helpful to know what age/engine size were talking about here and where the flat spot occurs, engine rpm, gear,speed etc.

[xavtia]

its only a 1.4 its 17 months old and has 10k on the clock

 

the flat spot occurs at the traffic lights roundabouts and when turning corners it got a bit more frequent recently but didnt have any problems on the way back from the dealers

 

it was suggested it could be supermarket fuel thats causing it but i'm sceptical about that

[wozza]

Might not be the cause of the problem but the TU engines do run fairly high compression. My 1.6 is 10.8:1 i think. Which is quite high..higher than your Z3 M anyway. So maybe it does make a difference and maybe theres a reason it says use 98ron on the cap.

 

Either way the cars have knock sensors dont they? So shouldnt they be able to cope with differening octane fuels. I have ran my 1.6 on 95ron for a while but it is deffinately smoother on 98ron and does feel better to drive.

[Mike5483]

Ive just filled up with V-Power.

 

Obviously I dont really know what difference its going to make, although the engine seems smoother at idle.

 

Ill let you know how it goes.

 

Anyone else use V-Power.

 

I have the 2.0L 138BHP engine.

 

Is the 2.0L petrol common in C4's (other then the VTS)??? The techs at the dealer I use say its a bit of a rarity, most people buy either the diesel or smaller petrol engines.

[wozza]

Isnt the 2.0 138bhp the diesel one im pretty possitive the 143bhp is the petrol one.

 

And there seem to be a fair few people on here with the 2.0 litre engines isnt the highest engine you can get in the exclusive as well i think other than the diesels.

[Mike5483]

Isnt the 2.0 138bhp the diesel one im pretty possitive the 143bhp is the petrol one.

 

And there seem to be a fair few people on here with the 2.0 litre engines isnt the highest engine you can get in the exclusive as well i think other than the diesels.

As far as I know, the C4 was launched with the 2.0L 138BHP petrol engine to Euro 3 emmissions standards.

 

Then in 2005, they brought the engine up to Euro 4, reduced emmissions and upped power to 143BHP.

 

Hence, me car tax cost me £190 last month, where as the newer engine is cheaper because its in Group E where as mine is group F :(

[Z3M Roadster]

..... My 1.6 is 10.8:1 i think. Which is quite high..higher than your Z3 M anyway....

My ///M is 11.3:1, which by my basic grasp of maths is higher?!

 

The proof is in the written tests, 98 RON fuel won't make any difference to small engined cars.

[wozza]

Are after further looking theres 2 compression ratios it seems for the Z3 M came in 11.5:1 and 10.5:1 depending on the year.

 

And it might not make any performance increase but im telling you now it does make a difference to how smooth the car runs and MPG and im not the only person to have noticed this theres enough people over loads of forums to all say the same thing on various cars.

[Z3M Roadster]

The Z3M was built with the S50 E36 M3 EVO engine with 321bhp and then in 2000 they put the new S54 325bhp engine from the E46 M3.

 

I would put money on it that if your car was to be rolling roaded with 95RON and 98RON there would be no difference whatsoever.

 

The feeling with some people is psychological don't forget

[wozza]

Ok its in my head when my mates even comment on the fact it runs rougher when on 95ron... And they dont even drive the sodding thing!

 

At no point did i say it had a performance increase i said

 

And it might not make any performance increase but im telling you now it does make a difference to how smooth the car runs and MPG

 

Seriously it does make a difference the car feels different.

 

Especially while taking off from traffic lights etc

[Z3M Roadster]

Well I wouldn't waste your money. Stick to the cheap stuff.

 

I used to run my Westfield on 95RON and that had a modified Zetec, I also had an Astra coupe turbo which I ran on 95 RON.

 

If I didn't have to run my Z3 on 98 I wouldn't, especially seeing as Optimax/Vpower is £1.04 a litre here.

[wozza]

Much cheaper here sainsburys super is 94 or 93 i think currently normal 95 is 89 and V power is 96.9 i think. Gonna go fill it up in a short while so will know then when i passed the esso staition earlier though 95 was 89p

[Z3M Roadster]

People in the ///M Power forum say they are noticing a difference in the V-power over the old Optimax.

 

Didn't know Sainsburys did a Super. I have tried Tesco 99 and mine certainly doesn't like that stuff or the BP Ultimate Petrol.

[wozza]

Same on clio forum everyone is saying there getting higher MPG and theres a deffinite increase in power. optimax was 98ron v is 99ron not sure if it makes a difference to me not tried it yet.

 

And sainsburys have a 97ron super cheapest around only a couple pence more usually. And BP ultimate is bloody expensive then again all the BP garages are up here everywhere else is 89.9p for 95ron its still 94.9 at BP.