Lately when driving my 2007 MCS and it's not fully warmed up I sometimes notice LOUD multiple pre-ignition knocks when I step on the throttle say 75%, I'll say about three of them! It's like high intensity lightening in a bottle, when you hear it, it scares the crap out of you!

Now I know I should wait until it's fully warmed up to be going anywhere near WOT, but none the less it's something I have noticed and perhaps it could bite me later, a sign of things to come. These high pitched sounds get your attention if you're near the car when it happens.

I have had all the timing chain components replaced by my Mini Dealer ($1627), dealer mechanic explained when asked, that he adjusted the timing mechanically on the cams, then checked it when plugged into the computer for programming the timing via the ECU.

My only guess with my limited knowledge is carbon build-up on the intake valves, I recently had my valve cover replaced (also PCV since it's integrated) and no longer need to add any oil between 5000 mile oil changes when before I needed a quart every 800 miles.

Your help is appreciated!

Regards,
Systemlord.

 

cold start warming sequence involves the wastegate arm and plate being near fully closed which can cause a rather loud tinny sound when revving a little. you sure its not this? it sounds retched for the first minute or two of driving, and you can clearly hear it with the windows down....

 

You could call it a loud high pitch tinny or pinging sound, but only occurs for a second. It never lasts more than that, happens mostly in "Sport Mode" under high boost.

 

Well I'll be taking my 2007 MCS in tomorrow for the pre-detonation, but would like to know before hand what the Diagnosis is most likely to be. It happened again when I let my brother drive it, he was attempting to pass another car on the freeway and we hear what sounded like the gas igniting in three of the cylinders in succession with a sudden loss of power.

That to me means that when the pistons were at the bottom of the cylinders the gas ignited when the piston is on its way upward, therefore the pre-ignition doesn't make it any easier to travel upwards which in turn accounts for the power loss. How can the gas ignite before the spark occurs?

 

Lean air fuel mixture, spark plugs gapped too wide(from age and wear), or incorrect plugs, poor octane rating, excess heat in combustion chamber.

I's be damned if you could hear three knocks at the same time but I guess weirder things have happened. The loss of power sounds consistent, misfiring as well can cause this which means a lean mixture or fuel delivery issue could be the culprit. Did you try running 93oct and see if it subsides at all? If it does then it's certainly knocking.

 

"The definition of pre-ignition is the ignition of the fuel/air charge prior to the spark plug firing. Pre-ignition caused by some other ignition source such as an overheated spark plug tip, carbon deposits in the combustion chamber and, rarely, a burned exhaust valve; all act as a glow plug to ignite the charge."

Taken from here: http://www.contactmagazine.com/Issue...ineBasics.html

 

All very good guesses, how about the HPFP? That would account for the lean fuel mixture. Been using Shell V-Power 91 octane, no access to 93 octane.

 

yeah, hpfp failure can cause lean mixture of course but you'll most certainly get a CEL or at least 1/2 power warning light....the car knows

 

It turns out that I have a ridiculous amount of carbon on my intake valves! He told me that the carbon coated valves were restricting the intake air and that was messing with my air/fuel ratio. It's going to cost $800 to clean the valves!

 

Once the valves are cleaned from the dealer, I would suggest changing the oil as well, get new spark plugs, and throw some fuel injector cleaner into your gas tank. Then about every 7-10K miles Seafoam the valves to keep them clean. I Seafoam around that mileage and I started because at 15K miles I was having the same issue (granted not as loud or as significant). Seafoam works great in cleaning the valves when there is minor build up. I would not recommend doing it if carbon buildup gets that bad again.

I also live in a state where 91 octane is the highest rating. I think a less pure burn as a result will cause carbon to build up faster on the valves.

 

There is nothing "unpure" about 91 octane. Octane is the rating of the burn rate if the gas, the higher the rating the slower the burn. Also putting injector cleaner in a direct injected engine that operates at 2000 plus PSI and does not shower the vales is just wasting money. Your carbon build up is mostly attributed to a faulty pcv system in the valve cover

 

Here's an update, I had the intake valves walnut blasted on Monday at the Irvine Mini dealer and boy was it bad! Even after replacing all of the timing chain components, new valve cover and a carbon cleaning of the intake valves I still have what I know are intense pre-ignition and today I heard what sounded like my first backfire in the intake track! It wasn't through the exhaust because I know what that sounds like and this was different.

This is the very first time that I have actually heard it since March when purchased the Mini. This means that the fuel is being ignited before the valves close, am I correct? If so do you believe that since the intake runners and valves were blackened with massive carbon deposits that my spark plugs may also be causing the pre-ignition?

The dealer had my Mini hooked up to the computer and there are no faults of any kind! The dealer did re-program the car after the carbon cleaning.

Thanks for all your help!

Thank you, Systemlord.

 

I would get new spark plugs. Get some from Way of Way Motor Works:

http://www.waymotorworks.com/cold-he...-cooper-s.html