I have a 2002 F4i that has developed a sputter at part throttle. However it’s not a consistent sputter. When the bike is started and left to idle, I can hear constant miss on one of the cylinders. Once I get the bike going and hold a consistent part throttle, say at about 1/8 open. The engine runs fine without a miss, but as the RPMs build up the engine develops a misfire. This causes the engine to drop in RPMs, once the RPMs drop the engine clears up and runs fine. The cycle will keep repeating itself as long as I hold part throttle. If I open it up to ¾ or full, the engine runs fine.

I replaced the vacuum lines about two months ago and the problem cropped up then. I replaced the old lines with silicone vacuum lines. I dumped the FI code and it indicated a possible vacuum leak or a MAP sensor problem. I checked all the vacuum lines and they were all connected fine. I buttoned everything back up and the problem persisted. I decided to replace the soft silicone lines I used with neoprene thinking that the silicone lines were collapsing on themselves since they were pretty soft. The neoprene lines I replaced them with have much harder walls than the silicone and not as likely to collapse on themselves. I also replaced the spark plugs since they were due to get changed out.

When I buttoned it all up, the engine continued to exhibit the same symptoms. I took temperature readings at the exhaust headers and the number 4 cylinder was running about 155-200 degrees cooler than the other three cylinders at idle. The FI indicator no longer shows any trouble codes. When the system initially gave error codes, the other possible problem area was the MAP sensor. However, from what I’ve read in the shop manual, it will require a special harness to check the voltage output from the MAP to the ECU. I guess I could switch the coil pack from cylinder #4 to another cylinder and see if that cylinder drops temperature. I’m not sure what else it could be going on. Any suggestions would be helpful.

 

i had a similar symptoms on my bike a while back. When putting the throttle body together, i mix up the vacuum hoses. i think i hooked up the hose that goes to the MAP with the hose that went to the Fuel Pressure Regulator. You might want to double check of the hoses are hooked up correctly.

 

I have a California bike, so there are a whole lot of vacuum lines. I pulled them one for one when I replaced the original lines. But I might do another check to see if anything is crossed up.