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F4I Engine Trouble when Warm

Old 09-19-2016, 09:33 PM
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Default F4I Engine Trouble when Warm

Hey everyone,

I am a member of an FSAE team that builds an open wheel formula race car for a collegiate competition.

Last year we built a car using a CBR600 F4i engine. We are still trying to get it to run right. We are running out of ideas so we wanted to see if any knowledgeable people here have any ideas on what our issue is.

The engine runs really well, hits redline, sounds right, when the car is first started under cold start conditions. Once it is allowed to warm up (5 minutes and 180F) the engine will not rev past 8000 RPM and is EXTREMELY SLOW.

What we tried:
We initially though that we were over heating the fuel but we dumped a gallon and a half of cold fuel in the tank when the engine was hot and experienced no change. It still preformed poorly

We also assumed there might be a compression issue when hot, but it reads approximately 12:1 on all 4 cylinders cold and hot. The engine build was questionable seeing as we received the completely disassembled. So it is still not out of the question that it could have an internal type issue.

We are looking to see if anyone else has any ideas before we swap out the engine.

Also we received another CBR600 F4I to swap in. It has not ran for a while, is there anything I should do to make sure it is ready to swap in other than put oil in it?

Absolutely any suggestions are welcome! Also I understand this is a completely custom build so it will be near impossible to diagnosis without seeing it, we are pretty much out of ideas. We are open to taking shots in the dark.

If you guys need me to explain things further or get pictures let me know

Thanks in advance,
Old 09-20-2016, 05:48 PM
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Location: Mesa AZ
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Is the engine staying at the correct temp once warmed up and not overheating? Is the O2 sensor hooked up and working [if you have a cali model ECU or any 06 model ECU]?
Is the exhaust stock, and if not have you adjusted the a/f ratio? FYI 12:1 is a full one point lower compression then stock, thats a big drop. Also stock airbox is a big deal I believe.
Old 09-20-2016, 07:46 PM
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Location: Prince George's County, MD
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What are you using for fuel delivery? It sounds like it's not getting enough fuel. If you're using the F4i fuel tank, the fuel pressure regulators are known to give trouble from time to time. Ensure the filter is clear (they are replaceable item), IIRC it's attached to the fuel pump.
Old 09-21-2016, 12:34 PM
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We are running a Performance Electronics PE3 computer with a custom tune. We also have a full custom exhaust but do have a O2 sensor. We tend to run a little rich on the low end of the low end of the RPM scale and lean at the top. But I still don't see how it can the tune could have an effect on run good for the beginning of the run and then very poorly at the end.

Looking at all the engine websites, I see people saying F4I is supposed to have a 12.0:1 compression ratio.

For fuel delivery we custom fabricated a tank. We are running an internal pump 165 LPH fuel pump which pumps into an inline fuel filter. From there we have an adjustable fuel pressure regulator set to 60 PSI. The system is retunless so it puts the extra fuel back to the tank and the 60 PSI worth in the fuel rail We are using a stock (welded over the stock regulator hole) and stock F4i fuel injectors.
Old 09-21-2016, 04:29 PM
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Location: Mesa AZ
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You are correct the compression is not 13:1 until the RR, my mistake.
Have you verified fuel pressure when hot? Is 60psi what the engine see's in the motorcycle? At this point I'd start putting stock stuff on to eliminate variables. Stock ECU, pressure regulator, and pump. Might need to PC3 the ecu to adjust for the full exhaust but sounds like it might be worth it.
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