Before the details... Here's a short drivetrain history of Pepper.

- JB+ left at stock settings
- AEM 21-721C CAI
- ALTA BOV Spring
- 2nd cat & res delete
- ALWAYS fill up with either BP or Shell Premium
- 49,000 miles


So here's the problem. In the last week or so, she's been stuttering under heavy acceleration (3/4 to WOT). It happens in any gear, with the SPORT on and off, DST on or off, and usually starts around 3000-3500 RPM and up.

When I say it stutters, it's not one hiccup and then back to normal. It's like a rapid fire stutter. Imagine the pop and burble when you let off the gas, but during acceleration and each time it pops you lose a bit of power like the clutch is slipping momentarily or the traction control is limiting you. When SPORT is turned on, there is a pop for each stutter. When it's off there is no pop but the stutters are still there, albeit less frequent.

I've only noticed it after the last fill up. There haven't been any codes. Could this be a bad batch of gas, or is there someone out there that has seen or experienced this before.

I have a few ideas on what it might be, but I'd like to pick your brains first. Thanks guys!

 

Have you ever put a can of BGK44 in your gas tank or walnut blasted the intake valves?

 

Nope. Can't say that I've done either of those... I also have no idea if the previous owner had done it. I bought the car @ 30,000 miles from a reputable MINI dealer.

 

Since you say it's only been a problem since your last fill-up then I'd like to think it's bad gas. BGK44 is only $20 and it's highly regarded. However you may have to call around to some local shops before you find it in stock.

 

I think for the rest of this tank of gas I'll disconnect my JB+ just to be safe. I found a local store that carries BGK44. I'll check it out. Thanks.

 

Two suggestions:
1). You have a few mods, a number of which can impact fuel/air mixture and induce some form of a misfire or shuttering that you are describing. Removing them and re-testing is the only way to rule this out;
2). I had a similar experience with my modified N14 with Alta Stage 2 tune. At WOT, the car used to sometimes stumble around 3-5 RPM range, but pulled strong below or above. Not always, but often enough to really bug me and send me into a long and fruitless troubleshooting mode. Fast forward to this winter when I finally collected a check engine light that was traced back to dying High Pressure Fule Pump (HPFP) - a common problem on N14 engines that was covered by MINI USA warranty. Intuitively, it made sense that HPFP was intermittently failing to provide enough fuel flow at WOT, and intermittently starving the engine, which was stuttering from running too lean.

I have read conflicting reports on whether N18 engines (2011 was N18 cut over, right?) are similarly impacted by unreliable HPFP's, but to my knowledge MINI USA has not offered prolonged HPFP warranty for N18s.

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Sorry about the typo, but it's BG 44K

 

Chrome apparently knew what I meant... It took me to their site. I didn't even notice til you just pointed it out. XD

 

I'll be doing a few different sets of troubleshooting to see if any mods are causing the issue... It just seems really odd that this kind of issue would have no CEL to go with it!

 

But it drives fine other than that? No rough idle or feeling of power loss?

I'd probably pull the JB first only because it's the easiest and most immediate change you can make.

 

I have had ZERO issues with the JB+ in the 6+ months that it's been on the car... But yes, it is the easiest thing to check. Unfortunately, I can't 100% determine if it is the JB+ until I get a good tank of gas in the car. It may just be that it was a bad batch and the added boost from the JB+ is only causing the issue due to poor fuel quality.

Other than the stutter, I haven't had any issues. Over the winter when I would have to cold start in temps from -10F to 30F I would have the random RPM drops during idle while it was warming up, but as far as I can tell, that's normal. These were drop from 800ish to 300ish for a second or two and return to normal idle.

The rpm drop during a cold start idle hasn't happened since the weather has gotten warmer.

 

I had the same exact issue as OP. Mine sounded like the car was hitting the rev limiter but RPM's are nowhere near redline...

Pull and check gap on your plugs. I had #3 plug burnt and plug gaps were inconsistent. Replaced spark plugs and gapped to 0.22 (N18) and stuttering went away... good luck!

 

Good to know. I'll ad that to my list.

 

I'll jump in with a recent experience and say that it could also be a coil going bad on whatever spark plug is having issue (if any plugs come out burnt, fouled, etc.). My coil on cylinder #3 went bad and the spark plug on the cylinder looked far worse than the others.

 

This has happened to me before and thought it was bad fuel or oxidation in the tank... so action taken were:

1. cleaned MAF sensor with can of CRC & Seafoam treatment, same results;
2. replaced the plugs, same results;
3. replaced HPFP under warranty... ran very smooth.

Mine never threw a CEL until about 3K miles from the day I noticed that there was something wrong.

So it's gotta be in the fuel delivery as if there's not enough continuous fuel being supplied, IMO.

 

Update: I drove the 25 mile trip home from work with the JB+ removed. Nothing has changed...

Next on the list is to check the plugs and the plug gap, and then let the last 1/2 tank of gas run out and put in a fresh tank. Thanks for all the great info guys. I really hope I don't have to deal with a bad HPFP. :P

 

Let us know what the verdict is and good luck!

 

Sorry about the delayed update... I just started my new job this week and things have been hectic. XD

So I ran the tank nearly dry and got a half tank of known good gas. No change. Still stuttering under load from 1/2 to WOT.

I dug out my ELM327 OBDII device and read the codes. Here's what it came up with:

P306C - Fuel system: Pressure briefly too high, RPM and load factor limited
P0300 - Cylinder Misfire, Several Cylinders
P0301 - Cylinder 1 Misfire Detected
P0304 - Cylinder 4 Misfire Detected

I have found that driving like a granny keeps the misfires at bay. I'll have to drive like that till I get some time to check the plugs. I'll also be running some BG 44K once I get a full tank.

 

It might be worth swapping the coils around and seeing if the misfires follow before buying new plugs.

 

Based on those codes and random multiple misfires, you have a bad HPFP. Dealer will replace it for free for 10 years 120,000 miles. They'll want to walnut blast your intake valves as part of diagnosis. My experience is it will not solve the misfires but it does improve power and throttle response. I've heard dealer wants as much as $1600 for walnut blast. Independent mechanic as low as $400 or you can buy a blasting kit and do it yourself. I think ECS Tuning and Way Motor Works sell the kits. Don't bother messing with the coils in my opinion. You don't need spark plugs until 60,000 miles on an R56S. When I changed plugs on my R55S they still looked great at 60,000 miles.

 

Plus one on the spark being the issue. This happened to me and it was a coil down.

 

I'll add another to spark plugs.

 

FWIW that warranty is only for the 07-10. I recently spoke to the dealer about the HPFP recall and they said it did not apply to '11+ models.

Edit: I didn't see the year in the OP's post or I missed it completely so forgive me if I'm off base here.

 

Put me down for vanos solenoid. What prize does the winner get?

 

Check all of those listed above, check the easy ones first like the plugs and coils. You are low miles but I have seen some carbon build up but it was the N14 engines that seem to have it more. You have an N18. But its good to check.

Then the HPFP , which is 13517592429 for the N18 engine up to 3/2012 when the changed the design gain.

Good luck and let us know what you find on the ignition.