Bogs down at High Speeds

[bigbaulla 0]

Hi all,

 

I have a 2007 Cyclone with the 5.7 L Black Scorpion. I'm experiencing a loss of power at speeds above 30 mph. The engine will backfire / misfire and slow way down but doesn't die. I put in neutral and can accelerate again but will repeat at anything above 30 mph. It starts and idles fine and will run great at speeds below 25. I have replaced the distributor cap, rotor, plugs, water / fuel separator. Connected a fuel pressure gauge at the valve on top of the engine and it read 20 psi at turn key. Started the engine and it read about 30 psi. I know there are 2 fuel pumps but I can't determine if this is the issue and if so which one might be bad. Any ideas of what might be going on?

 

Thank you for any help!

[daz28iroc 73]

Fuel filter would be the first thing to check on my list.

 

Then fuel pump.

[Jake707 171]

Agree, check/change fuel filter first. Should be cheap enough. Is it speed related or RPM? I don't think there is any form of speed governor so the MPH should affect anything. It sounds like it is being choked out at high RPMs after extended amounts of time, which would lead me to check fuel system first, then ignition ie check spark plugs any fouling etc

[bigbaulla 0]

It only occurs at higher speeds / rpm's. When it gets around 30 mph it acts like I've put the throttle in neutral. It sputters, backfires/misfires and tries to recover but never can. Runs fine at idle and up to that point. I've replaced all the spark plugs as well.

[NW Boat Sports 232]

Put a fuel pressure tester on it. I bet it's dropping in pressure..

[bigbaulla 0]

Does anyone know what the PSI for the fuel system should be reading under normal conditions?

Edited October 5, 2016 by bigbaulla

[bigbaulla 0]

I changed the inline fuel filter and the issue has been resolved. Thank you all for your suggestions!

[Jake707 171]

Glad to hear it.

[Mitch925 0]

What is the correct fuel rail pressure?

[InfinitySurf 302]

Good call. Dirty filter must have decreased flow enough at high rpm to starve it for fuel.