I've had my 03' JCW MCS for a few months now, and I've noticed that when ever I run 91 fuel in it.....I will get some slight detonation when I'm on the gas hard under full boost. It's definitely detonation....because if I run 93 or 94 fuel, I don't hear that tell tale pinging sound when I'm wide open on the gas. I can't think of anything else it could be but detonation.

I've replaced the plugs, and that didn't help. The motor runs great, doesn't use any oil, and otherwise seems to really run good. I know that the manual says to run at least 91 premium fuel.....so is it normal to get some detonation or "pinging" with 91? Isn't the knock sensor supposed to take care of an detonation if you get any?

Should I HAVE to run 93+ fuel to keep the detonation away, or is there something else going on?

Thanks!

 

93 helps on a car with a pulley, but it should be fine with 91 i think...
Any chance the car was modded before you got it, then the mods removed before you got it, but not returned to 100% stock (custome tune/pulley left on, but other items removed sold)?
Some folks find they need to run the jcw plugs (1 step cooler then stock s plugs) to get best power with a pulley...not sure what you have from you sig.

 

PS
Mini's like most euro cars in the us are detuned a bit to run ok if lower octane is used/due to the avalibilty of (or lack there of) of 93/94 octane....

 

It's a JCW car.....so it's got the JCW pulley (11% I think), JCW exhaust, JCW intake, JCW head, and JCW plugs. I just replaced the plugs with a fresh set, but that's all I have done to it.

I've heard a lot about carbon in the combustion chambers upping the compression, causing pinging.......maybe I need to run some seafoam through the motor to decarbon it?

I heard somewhere that JCW suggests that you should run a minimum of 95 octane fuel...but I'm not sure if there is any truth to it.

But, like I said.....93 fuel runs fine...91 makes it ping. Not sure if that is common or not......

 

Jcw on a gen1 car can mean lots of differant things...
So you do have the engine kit.
is the pinging just a feel, or do you have codes on a specfic cylindar?
the 95 octane should not ever be needed on a stock car...it is race fuel...higher octane than normaly sold, and remember, the US uses a differeant octane rating system than most of the rest of the world...so numbers that are not for the us is sometimes quoted...they are higher numbers, but essencially the same as us 93.
i would try a diffent gas station....
mid grade fuel is a mix of low test+ premium...only 2 types delivered at most stations..possible you got an iffy mix, or some with lots of ethanol or something the car does not like...
Injector cleaner might help....(most will actually lower the octane when added)
seafoam imo if done right may also help (could hurt if done wrong...)

Most gas stations sell 87, 89, 93 in my area, i just run 93...many folks in parts of the country (like ca) can only get 90 as premium...and do so without issues..
but if 93 fixes it, why not..

 

I'm not getting any codes, I'm just hearing the pinging come from the motor. It only does it when I run 91....but if I run 93 I don't hear it. Maybe I just need to start running 93 all the time. I just thought 91 was what you were supposed to run.....

The part that confuses me is that I thought the knock sensor was supposed to dial back the timing if it sensed and "knock" to keep the engine from pinging......is the sensor not working? It sure doesn't dial back the timing at all....when it starts to ping, it keep doing it as long as I have the pedal down.

 

The knock sensor prevents knock..detonation..ping is differant.
the car is 10 years old...so the need for a couple extra points of octane would not be entirely unexpected...not a great sign, but i think common for many cars as they age.

 

My mechanic swears by BG44K. Might help. Good luck.

 

Besides some carbon buildup in the combustion chambers, what else about an older car would cause the need for higher octane fuel? If anything...I would think worn rings would = less compression, which would require less octane.

Are different brands of 91 fuel better than others? If I run Connoco 91 I get ping, if I run BP 93 on don't. Would trying another brand of 91 even be worth it? Are some brand of 91 not really 91??

 

Additives are generaly the differance....but a differant station might belend it differently...gas stations are usually independantly owned....who knows...fuel in one area usually comes from the same pipeline....
Octane is a measurement of how hard it is to ignite fuel...high compression and high intake temps do need high octane, but hot spots in a cylindar, uneven fuel flow...tons of stuff can cause an issue...ping if i remember right as opposed to detonation(knock) is also refered to pre ignition......

 

Thanks for the info..I may try a few different gas stations and see if I get any different results. If not...I'll just stick with my 93 or 94 that I can get.

As far as pinging vs. DEtonation....I was under the assumption that they are the same thing....pre-ignition. Not really any different....I think if it's "light" people call it pinging, when it gets worse...and louder...people call it detonation or knocking. They are both just pre-ignition...right??

 

No...very different ....

Detonation/knock can destroy a motor in seconds...it is an explosion....hense the knock sensor...ping while related is differant...it is moreof an controled,early burn..less destructive butpower robbing.

 

Do the knock sensor won't pull back timing or make any changes at all until the pinging gets louder...and turns into knocking?? Seems like it should detect the first sign of pinging/knocking/detonation...and make some changes to prevent it.

 

Yep its the gas.
I had pinging in CA and after 2 separate moves to east coast, noticed pinging went away in NY using 94 Sunoco then came back upon return to CA, then pinging went away upon move to PA using Shell and Sunoco 93 octane then the pinging came back after returning to CA. Also noticed on previous MCS that while living in Las Vegas I would put 100 and ping would go away after a tankfull then after a weekend of CA gas it would start to ping slightly then go away after I returned to Vegas and put 100 gas.

 

No mention of ethanol being a problem yet. 91 octane should be sufficient but if it is laced with corn cobs, that could cause problems. Before I was educated, I kept getting knock errors and finally had to have the knock sensor replaced, pretty dang expensive. I've located all the E free stations around my location but use this website to find MINI friendly stations while traveling.

http://pure-gas.org/index.jsp?

 

All the CA ones are near Oregon, that 92 in Fortuna seems nice, too bad its like 350 miles away.