Please Help - Bad 502
 

My 1995 Baja 272 has a 502 Mag in it. It runs great for the first hour then it starts going down hill. At full throttle 4900 RPM's. It will miss like it looses fire or fuel for a split second. Then if the water is rough it will start doing it when you hit a decent wave. After a while it get so bad that the boat will hardly get on plane. If you are ideling in a six knot zone it will sound fine. If you put it in neutral and rev it up sometimes it will rev fine and sometime it will just die and not rev up at all and sometimes it will pop out the intake a little. The boat always makes it in under its own power and always starts fine. Im stumped. Obviously it is a fuel for ignition problem. I have inspected the Distributer, plugs, wires, all the grounds on the motor, all the plugs in the wiring harness for tightness corosion and dryness and everything checks a ok. Also I have replced the fuel water seperation filter twice along with dry gas in the tank. The boat ran fine the first few trips out this year so the problem has developed since the winter sit. My latest thought is that the vapor seperation tank has a problem in it. Maybe a faulty float or valve. If anyone has heard of something like this and can give a suggestion, I would be very happy. If I dont get it fixed soon, I will be looking at a pretty big bill from the local dealer when i take it in.

I am no expert but it sounds like the floats. If they are too high a good jarring will flood the motor. If may be time to rebuild the carb or a simple adjustment may do the trick. Good luck

Its EFI...

You need to check the fuel pressure. Low fuel pressure will cause the symptoms you describe.

Adjusting the floats on an EFI won't help.:D

Could be fuel pressure or clogged injectors.

Did you check the anti syphon valve? If you are getting crud in your tank this can become dirty and cause intermittant fuel loss problems.

The other thought I have was vapor lock. Make sure all your fuel lines are not in contact with something getting hot.

If you shut it down and let sit until cool, does it miracculously run well again?

BT :cool:

I just got back from the water with the boat. I had tried a few things to no availe. I dont think its vapor lock becasue It started doing it right away and its only 60 degrees here. I am going to order a code scanner from Rinda tech tomorrow. Hopefully that will tell me something.

Where should I check the fuel pressure at. The injector rails after the high pressure pump or inbetween the two pumps. What should they be??
John

Check for a good hot spark at the plug wires with a spark tester the pop in the intake sounds like it is too lean.

Probably a bad set of wires and a bad coil. plug wires only last about 5 years. also check for water under the dist cap.