Hello All,
I have a 2003 R53 Cooper s that I'm looking for some guidance on a Misfire or Hiccup I'm having (leaning towards misfire). Full throttle at low RPM makes it happen. Going above 3500 RPM is smooth with no misfire. It use to happen at high RPM like on the highway when accelerating but the changes below its shifted to low RPM (<2800) when I give it full throttle. If I dn't give full throttle, I can't say I've seen it misfire. I've seen a misfire code only once.

I've done the following to see if it goes away but its still t here. Car runs great besides that with these changes.

• New plugs (NGK BKR7EQUP)
• New Fuel Filter
• New Fuel Injectors (from a JCW)
• Put back my stock coil pack and wires
• Have always run 91 Octane good gas

Modifications:

• K&N airfile
• 15% pulley
• Milltek headers
• Milltek high flow cat
• Milltek full exhaust
• O2 Oxygen Sensor Spacer (
  Amazon
  Amazon
  )

What else could I try to figure this out?

Thanks!

 

Do you have a tune? With those mods, bigger injectors with smaller pulley and full headers back exhaust, you should have a tune.

 

what he said! Especially if you went from 330cc injectors to jcw 380,

 

Thanks Folks. It did start happening all of a sudden rather than after any particular mod. That said, what would a "tune" actually consist of? Are there other things I should try like checking for air leaks or change the PCV, etc?

 

Tune would run around 600 remote tune from Jan at revolution mini. I would suggest doing that even if you end up getting the issue fixed, it can cause more damage to the motor otherwise.

Have you checked your belt? sometimes the belt can slip at low rpm's in full throttle like that. There is a gauge to look at on the belt tensioner to let you know if your belt is stretched too much and needs to be replaced, also check your belt tensioner while your at it.

 

Check the fuel pressure. The R53 has 2 pressure regulators. 1 by the fuel rail, 1 in the filter assembly.

 

Thanks. I'll have to look up how to check that or get it done by a mechanic. Probably need an inline measurement I'm guessing.

 

There's a shrader valve at the LH rail end. You'll have to remove the intercooler to hook up the gauge. Start up pump pressure should read around 52psi, idle at 42psi.