Yap session incoming. Hello everyone I have a 2003 F4i that’s been giving me COPIOUS issues. First, the idle was rough, with it fluctuating around 1500 rpms. When starting, it has no “bite”, and idles at 500 rpms before speeding up. When warm, it would sometimes jump up to 2500 rpms. Next it struggles to rev past 3k and 5k rpms, but if I upshift, rev back up to 3/5k and then downshift, it’s able to rev up. Furthermore, it won’t rev past 11k at all in first gear, and 9k in any gear beyond that. As I upshift to 5th and 6th gear it actually becomes slower somehow. When the throttle is fully open, it makes a buzzing sounds from the exhaust and the revs drop slowly. I’ve replaced the FPR, the fuel pump, and the spark plugs. After replacing the spark plugs, the idle is steady, and it has a slightly easier time getting past 3/5k rpm’s. The high rpm issues, and buzzing still persist. I can take videos if that would help. My best guess is the valves, but I’m poor and I’d like y’all’s opinions before I take it to a shop for a diagnosis. Thanks for reading

 

How many miles has it done? Have you checked to make sure it is firing on all 4?

 

Just over 11k. I’ve had it since 7k, and it was fine for a while. At some point it wouldn’t rev over 10.5k. I’m pretty sure it’s firing on all 4. All the injectors are working and the old spar plugs look equally worn

 

Shouldn't need the vales doing at that mileage, those symptoms would generally point to the FPR, have you test the flow from the FPR as per the manual?
Did you have it any crap in the tank when you changed the pump that might be in the fuel line?
Have you checked all of the vacuum hoses and made sure the airbox is clean and no debris in there? If it is sparking correctly (ECM issue if not) then can only be air / fuel that is causing the issues.

 

I’ll check out the FPR. That was the first thing I swapped out, and it still wouldn’t rev above 10.5. There was some rust in the tank and in old the pump, so I’ll swap to the spare pump I have and update. Air box and air filter are clean though.

 

Minor Update: The bike is off, and upon disconnecting the hoses, I noticed that there is fuel flowing out from the return line that connects the pump to the FPR. Is that normal, considering fuel is supposed to flow from the FPR back to the tank? Could that be causing my issue?

 

Dont think so, I believe that the fuel return is to the FPR and the tank so probably not. Couldn't find a definitive fuel flow diagramme in the manual.

 

Sorry for the long wait. I switched out the FPR, and that solved the jumpy idle issue. I also replaced the fuel filter, and that solved the low RPMs on startup issue. The bike still struggles at 3K and 5k and still has the issue where it won’t rev above ~11k. I’m thinking the injectors are clogged? I tried two different fuel pumps and they both had the same issue. Any suggestions?

 

You said in March that the injectors were working - so why would you now say they are clogged?

 

I already replaced most of the parts in the fuel system. I figured it’s more likely that the injectors are partially clogged than both fuel pumps having the same issue. Any other suggestions?