2003 MCS, ~74k miles

A few days ago I had 1/4 tank of 93 octane gas left. For whatever reason, I decided for the first time ever hmm maybe I should try to mix in 1/4 tank of 89 octane gas from Hess and see how the engine runs.

Driving on the 93/89 mix, a couple of times (maybe 3-4 times) my engine would stutter when I stomp hard on the gas pedal. Almost the same sensation when driving on snow/ice with traction control on but felt worst. The exhaust made lots of marshmallow puffing noises during the stutter. No warning lights came on when this happens.

Yesterday I emptied the tank till my est. range was about 2 miles. Put in 6 gallons of Mobile 93 octane as usual and went for a "test run" thinking that the bad gas was the cause of the stutters.

The engine was running great for about 4 miles until I saw a bumpy train track, heal toe downshifted from 5th gear to 4th to 3th to 2nd.... and rolled over the tracks, fun.. except that the engine started stuttering immediately, CEL and DSC lights came on! I pulled to the side and turned off the engine, waiting a couple mins, started the engine and it sounded like it was choking. So I held the gas pedal @ about 2k rpm for a while and the choking stopped.

DSC light went off a few mins afterwards. CEL stay on. The stuttering happened twice since I rolled over tracks. Just a few hours ago I decided to blast down the highway in 3rd gear and 5krpm, maybe that should clear the mini's throat. Well after the blast the CEL turned off !

I'm not home and don't have any tools with me to diagnose the problem.


So the question is.. what the hell do you think happened?
Bad pump? Dirty gas on the bottom of the tank? Lets brainstorm so I can prepare to fix it when I get home.

 

You're #1 problem here is Hess gas. Per prior personal experience, and that of other local club members where I am at, DON'T BUY HESS GAS. My issue was with sputtering at cold start. Turn engine off, re-crank, started up with no problem. Traced my driving habits to that station. I stopped using Hess, and the problem went away. You can read my post in our local forum here: http://www.hrmini.com/component/opti.../topic,2573.0/.

Go ahead and do a full fillup with a known-good company, such as your Mobil, BP, Shell, Exxon, etc. Go the extra step and get a bottle of STP Fuel Injection Cleaner (the black bottle, #3 on the 4-option scale STP offers). Or you can opt for a can of SeaFoam, whichever you prefer.

I've read numerous posts previously about using 89 octane gas to help clean out the system. I think that's bogus. I know our MINIs have computers, and they are supposed to be sensitive to the knock sensor and properly retard the timing to compensate and prevent detonation, which is the bane of a boost-fed engine. I don't care how many people would make that recommendation, I would NEVER take that chance.

MINIs have two separate fuel programs, one that is maintained by the computer and one that is wide-open-throttle (WOT) mode. The computer attempts to maintain a proper A/F ratio up to 80% throttle. Then it flips to WOT mode. Are you really willing to chance a lower octane gas when you're tacking 6K RPMs with the hammer down? I'm not.

Here's one thread on bad gas topic: https://www.northamericanmotoring.co...-tier-gas.html. You can find many more by seaching for "89 octane" or "bad gas."

 

It could also be coincidental and not have anything to do with the gas.
Something else just broke, right after you got gas.

Dave

 

Not sure if you have done the "emptied the tank till my est. range was about 2 miles" procedure before the stuttering problem, but as far as I know is not advisable to do because of impurities on the bottom of the tank get sucked in easily, clogging the injectors and such.

Could it be it?

Maybe it's time for a SeaFoam treatment!

Best regards,
RayanMX

 

You're right, when I got home, busted out my mini diagnostics tool, misfire on cyl #3. Checked the terminal, holy **** it was rustyyy and it had a drop of water on it!


note: all the other terminals were rust free!

 

I inspected the spark plugs and the 3rd one was caked in carbon. I guess the real problem was a combination of too much carbon build up (probably from the bad gas) and the lead 3 corrosion.

3rd cyl stopped misfiring after I replaced the spark plugs with the original 4prong ngk's that had 55k miles on them.. lol

 

Glad you fixed it.

If you're gonna go with Brisk plugs again, Try the DOR15LGS'. They are the equivalent to the stock NGK BKR6s. If you have done a pulley and/or CAI and tune, get the DOR14LGS' (equivalent to the BKR7s); that's what I have now.