I have a 2005 MCS that I have owned for a few months. It sat for upwards of a year before I bought it. It pinged quite badly when I got it, but refilling with good gas helped considerably. I replaced the coil pack and leads (corrosion on terminals present). After a few tanks of gas, it was running fine.

I put on a 17% pulley, new JCW injectors, new JCW-spec plugs, and JCW CAI. The engine is otherwise stock, and I don't believe it has ever been tuned. I get pinging again, starting at around 3000 RPM and up to redline.

In trying to fix the pinging, I have done/observed the following:
-fuel pressure normal at idle (not tested under load)
-cleaned inside of intercooler
-IAT is less than 100*F on hard acceleration in ambient temp of ~40*F
-advance is at 19 degrees at higher RPM (say 4000+) at WOT, not sure what normal would be.
-cleaned MAP and TMAP
-compression test showed around 150psi on all 4
-replaced fuel filter
-ST fuel trims between +10 and +20, increasing with higher unloaded RPMs, it comes down to around 7 at WOT
-LT fuel trim at +7 (+10 at idle, are there supposed to be 2 LT fuel trims?)
-fuel is Chevron 94 octane ethanol free

The fuel trims surprised me, I thought it would be rich with the JCW injectors, especially when out of boost.

I have ordered a O2 sensor for upstream, and a new fuel pump. I'm thinking fuel delivery volume may be a problem, simply because I seem to have run out of other alternatives, but wouldn't the fuel trims be higher if there was insufficient delivery under load?

Any ideas, other things to check? I don't have any way to check AFR.

Thanks,
Eric

 

Exactly what plugs are the JCW spec plugs? You should really be one step colder than JCW because of the 17% pulley.

 

Stock plug for JCW: NGK BKR7EQUP, which is what I am currently using. It is one step colder than the stock plug for a standard Cooper S (BKR6EQUP). You think going one more step cooler would help?

 

I didn't remember what the JCW was, it won't hurt trying the 8, and could at least give you more insight into what might be going on, for the price of a set of plugs. (The BKR8EQUP is what is recommended for the Sprintex because of the higher boost levels)

 

I tried the colder plugs, they made no difference. I have also done the following, with no improvement on the pinging:

-checked fuel pressure under load (around 59-60 psi)
-replaced O2 sensor
-replaced MAP and TMAP sensor.

I don't know what else to do! Fuel trims are still positive (up to around 10 short term, 7 long term), suggesting the mixture is not too lean. Intake air temperature is well under 100.

Intake leaks somewhere? If this was the case, wouldn't it show up in fuel trims? Carbon buildup on head?

I've run out of ideas...

 

If you haven't thrown a code, an intake leak is doubtful but check your SC boots, etc. (A stethoscope or length of hose will help find a tell-tale hissing noise.) I'm tending to agree with the carbon build-up scenario. Any info. on previous maintenance history, quality of gas used, etc.?

 

I have some maintenance history, it looked pretty normal. No idea of gas used...

 

The only code I occasionally get is "over pressure" (I forget the code), as I'm hitting ~17 psi boost at redline. I assume this means the boots are good!

 

Yep, 17 psi with a 17% pulley is healthy but you could use a smoke tester to be sure. Continual pinging is not good. Are you showing any signs of plug fouling? Short of pulling the head, you might try using a borescope to check for carbon build-up.

 

You haven't said you mapped it for the changes, and 94 octane is low, another thing to check for is any engine rattle that could be from the rockers, as if there is any lifter play on the exhaust side in particular, it will be pinking as you describe.


Just my2p

 

No sign of plug fouling. I guess I'll have to think about looking inside with a bore scope.

Engine has not been remapped.

ExclusiveWorkshops, where are you located? I'm in Canada, where 94 octane is about as high as you can get, short of racing gas. I think it corresponds to 98-100 octane in Europe and other areas. I'll take a look at the rockers when I get a chance.

 

I did a Seafoam treatment today - lots and lots of smoke after sitting 10 minutes. Smoke continued for 5-10 minutes driving. I had done it previously without much smoke, today was quite different. Pinging was unchanged...