Hello guys, this is my first post so please excuse me if I do anything wrong . Anyways, I'm having a problem with my F4i where at WOT from idle, it bogs down a ton and almost wants to die at first, and it also does not have a stable idle from what I can tell. I had this issue earlier before I had done anything to the bike (bought it a couple weeks ago) but it was not as bad as it is now. I have replaced the cctl, did the clean air mod and reused the pair valve by taking out the internals and plugging the two vacuum hoses and capping the two vacuum hoses attached to the airbox, replaced the stock filter with a k&n filter, changed the spark plugs to NGK IMR9C-9H, cleaned up some black deposits on the throttle bodies, and messed around with a PC5 that came with the bike (was not plugged in originally). I have done some others things like tires, a chain, overall just cleaned up the bike, etc but nothing that would affect/cause the issue I’m having, as well as it had the same issue, just not as bad when I bought it. Like I mentioned earlier, the issue is only at WOT from idle specifically, and has a rough idle. When blipping the throttle and getting it into the higher revs it does fine and sounds okay, but specifically from idle to WOT it almost feels like it has a two step at 2k rpm for a couple seconds then it revs up like normal. I have two videos that I will upload with this post that show the issue in action and the rough idle I'm having. As far as what the bike has on it, it has a steel dan moto exhaust, and stock headers with a jet hot coating on them. Anyways, the first video is with the oem style filter with the right air intake taped up (I had taken the K&N out because I heard it could have too much airflow, but I initially tried it with the k&n filter with the right side taped and it did worse than with the hi flow oem style filter), with the power commander v on a two brothers slip on tune. The second video is with the oem style filter with the power commander unplugged and the tape taken off. One other issue that I am also having (although I am not sure that they are connected) is that while riding, although more prevalent at higher rpms, if I pull the throttle ever so slightly, there is a point where it sounds like its sort of cutting out, and the engine isn’t running correctly. It is around the point where I would apply the throttle to maintain a certain speed. Currently from all of the searching on the forums I have done, I could not find anyone having the exact same issue that I was having, except one guy that seemed to have almost the same issue, and people attributed it to either a vacuum leak, camshaft position sensor, or the fuel pressure regulator. From what I can tell all of the vacuum lines seem alright and connected, nothing majorly off about them to cause this big of a problem. I went ahead and ordered new air box seals a b and c to be sure its airtight, and ordered a new fuel filter, fuel pump gasket, and fuel pressure regulator. Unfortunately the cam sensor is discontinued so I would have to order a used one off of eBay, so I'm crossing my fingers mine is alright.

- one last thing, when replacing the spark plugs, some of the plugs had a small bit of oil on them, which may be normal, I'm not sure, but it's worth mentioning.

I am sorry for the very long post, but I want to be sure I leave nothing out! Please help, I am at a loss here!

For some reason the videos I uploaded to youtube uploaded as youtube shorts but I am tired of waiting for it to upload so here are the links haha
Video 1: Video 2:

 

Put everything back to stock 1st. Factory filtre, disconnect PC and plug stuff back into factory harness.

Measure MAP sensor according to manual: ref voltage line, ground, shorts to ground.

Then do 3 measurements:

1. MAP sensor output, key ON, kill=RUN engine not running, volts=???

2. MAP sensor output at idle, volts=???

3. MAP sensor output at 3000rpm, volts=???

 

Welcome to the forum, follow danno's advice and I'm sure you will be well on your way to getting it fixed. With so many changes it will be very difficult to narrow down the faulty item. Get it running right as a stock bike then work from there.

 

Okay, thank you for the response! Can you give me more specific instructions on how to measure the MAP sensor? I looked in the manual but all I could find about measuring the MAP sensor told me to have a test harness and measure it that way, which I would like to do without if possible. I thought about just piercing the hot wire coming out from the plug but because its so brittle I don't want to cause a spilt. How would you recommend doing it?

 

Well, I ended up figuring it out, and got the voltages.

1. Kill switch on: 2.86 volts

2. idle (~130 deg. F): 2.21 volts

3. 3k rpm (~135 deg. F): 2.06 - 2.08 volts

From what I can tell and from what I have read in the manual this means that the MAP sensor is not faulty and is working correctly, so... now what?

 

Alright, a quick update, I just replaced the fuel pressure regulator on the F4i, and unfortunately that did not solve my issue . I honestly havr no clue what it could be at this point, If anyone has any knowledge on what it may be please let me know!

 

Did you replace with brand-new genuine factory OEM FPR from authorised Honda dealer? If not, put original back on as it’s obviously not problem. And you may have introduced additional errors into system.

Without actual pressure and flow numbers, you have no idea what’s wrong with fuel system. Could be clogged filtre, failing pump, clogged injectors. Even bad vacuum line to FPR may be only problem.

Measure fuel-flow from pump according to manual. 10-sec flow = ??? cc
Measure fuel-pressure according to manual, psi = ???


Also measure injectors actual flow-rate. They may be clogged or stuck open. No idea which until you measure them. cc/min of each injector = ???



Somewhere, some place, you will measure a number that doesn’t match what manual says it should be. The more numbers you measure, the more likely you’ll find problem.