502 Mpi, Stutters At 3800rpm
 

I Have A 272 Baja With A 502 Mpi And It Stutters Under Load At 3800 Rpm, If I Throttle Back Under 3800 Rpm It Runs Fine, Some Things I've Already Tried Are Changed Plugs, Plug Wires, Distributor Cap And Rotor,ignition Coil, Fuel Seperator, I Have Also Tried Disconnecting My Tach To See If It Was Grounding Out And By Passed The Limit Switch In My Shifter Assembly, Still Does The Same Thing Looking For Advice, Thanks

I this a VST 502? If so, there is a screen in the VST on the suction side of the electric fuel pump that plugs and limits fuel flow to the fuel pump in the VST that supplies fuel to the rail.

what does vst stand for ?

I dont know what it stands for but I would start by checking fuel pressure ,you can pick up a cheap gauge that will screw onto the schrader valve somewhere on the top of the fuel system and see what it reads when its missing

what should the fuel pressure be?

Not sure about the fuel pressure. If you have a repair manual it should say. Check the computer for codes before you go too crazy. Could be an easy fix.

If a code doesn't come up. This is a similar problem I went through with a 525 EFI. I went through the entire electrical, then fuel system, then wiring harness. Found a loose wire in the harness. The one that connects to the remote solenoid.

How many hours do you have on the motor? If its a decent amount I would agree with Thundersrtuck. If its newer, less than 100 hours you might want to check for loose wiring. I could have fixed mine in about 5 minutes had I just took a pair of needle nose and shock EVERY wire.

Good luck. EFIs are great set ups but can be a nightmare when these things happen. Either way keep us posted on your progress.

Rob....

Thought this thread may help you narrow it down.

http://www.offshoreonly.com/forums/s...d.php?t=160428

vapor seperator tank

thanks for the advice guys, will check things out and get back to...Ron

Most probably it is your fuel pump. Same problem on my '99 502 MAG/MPI . I have a fuel pressure gauge and if I went over 3900-4000 RPM it would die out if I throtted back it would regain power. This was 8 years ago, this spring I fired the boat up and it ran for about 15 seconds and died. You could hear the pump run but it would only have about 15 psi, its supposed to be around 36-38.