Hi all.

I own a 2005 MCS with low mileage (21500 miles) and have been suffering with detonation problems since I bought it a few months ago.

I am located in South Africa and we use 95 Octane unleaded fuel down here. I bought the car from an older lady who bought it new, only used it in town and drove very carefully, judging from the trip computor that had never been reset since new. (average speed showed 17.8 miles per hour)

I could hear light detonation around the 4000rpm range when accelerating hard, took it to the local dealer who plugged it in and diagnosed nothing. No problem they told me. I have suffered engine failure on a previous vehicle due to detonation and did not want to walk the same road again. I installed a progammable "unichip" to be able to manipulate the timing myself. Got it better but not completely sorted out.

I als added a custom build exhaust system, modified the airbox, fitted a k&n and for good measure got denso irridium low temp plugs from Outmotoring. Managed to get the detonation under control, but not completely gone.

Got a Palo Uber hood scoop to try and get the intercooler temp down. This helped and the detonation only happened when the motor was very hot from towndriving and then planting it. Went away when speeds rose and the intercooler temp dropped. We are in the middle of our winter down here so temperature do not go higher than 21deg C this time of year.

Thinking that the problems are under control I got a Alta 15deg pulley from Outmotoring fitted it and hoped for the best. I must say the little car goes like clappers now, but the detonation returned. Even If we retard the timing by up to 3 deg it still detonates. The fuel mixture is fine and the temperatures are fine as well.

Has anybody got any ideas as to what can cause this problem other than the obvious causes, (timing, fuel octane, high temp, etc)

Below is a link to a run just the other evening. Goes really well, and would hate to break the motor due to some overlooked problem.

http://www.youtube.com/watch?v=Upa0aAuDGTA

 

the mini's have a knock sensor under the intake manifold. i would think that if there as any problem with detonation there would have to be a SES light on. havge ou run the car without the Unichip?

 

Thanx for the reply.

Yes I have run the car again with the standard mapping. Knocking even worse. I had it at the local BMW dealer for an inspection service yesterday. I specifically asked that they check the knock sensor. No problem & the dianostics shows no errors.

Problems started when car was untouched and stock standard. Somebody told me that if the Cat was gone it could cause it? Another guy told me that there is a rubber mount by the supercharger that when perforated or cracked could cause it? Personally I dont see how either of these problems would cause knocking. If the supercharger was losing boost by the rubber it would actually help reduce the problem?

 

It's whatever gas you're using, switch to the best brand you can find (Shell, Exxon, Hess.) The knock sensor/ECU can only patch up timing to a certain extent and will not throw a code. The MINI ECU will also learn it's way around the unichip rendering it completely useless unless you reset the ECU every time you go for a drive.

Everything else you're using will only have very minor effects on knock, if you're positive it's bad (these cars make all kinds of weird noises) install a meth injection system and it'll go away.

 

We only have 95 octane unleaded available here. Have tried all the brands - no differance.

Somebody told me that because the car was driven so slowly before I got it, that carbon could have built up on the piston crowns, and this could be glowing, causing the detonation. The vehicle was owned by an old lady and was only used as an estate agent vehicle in the city.

Also went back to the standard mapping yesterday and added a octane booster to the fuel to try and see what happens. Pinging very badly when in town in slow traffic. Problem gets way better when on the open road and the intercooler does its job. Also physically checked the knock sensor yesterday. Had to remove the intercooler and unbolt the supercharger. What a job. Seems ok and gives a strong signal.

Going to retard the timing again today before it breaks.

 

If you retard the timing with the piggy-back the factory ECU will realize something's not right and adjust its self until it sees that it's back where it wants. The carbon theory could be correct but I dunno. Like I said before, a meth kit will completely eliminate it and can usually be had for $250-$300.