502 MPI/EFI wont reach rated RPM and now has a surge at idle and slow throttle

[Working OT]

i got this boat at the end of last season and the engine a 502 mag would only get to 1400 rpm and has slow throttle. Over the winter I changed the cap and rotor,plugs,filters, and cleaned out the fuel vapour tank, I also bench tested the pump and it had 35 psi. I put the boat out yesterday and it is getting to 2000 RPM but when i returned to the dock it has a bad surge at idle. I noticed the engine has a new style thermostat housing and the valve cover vent hose dont go to the intake, so im not sue if this is adding to the problem?

 

[Bt Doctur]

sounds about right if its hooked to the Exxon Vadez

 

[Glastron_V210]

First, the basics to find out what you are starting with:

1) Check compression
2) Check spark plug condition, triple check firing order and make sure the plug is ACTUALLY FIRING
3) Check timing, both base and advance
3) Check the injectors are firing...You can use a screwdriver to the ear...should make an audible click which changes with engine rpm

If it's a sensor problem, the most likely culprit would be the MAP sensor. I'd grab a new one and try it.

Chay

 

[skippy2235]

I think 35 PSI of fuel sounds low.
I know 5.7 trucks chevy need 56 psi, and my ford needs over 50 psi.
I would do some reading and verify 35 will work.

 

[skippy2235]

This is a copy paste from a service bulletin.

EFI / MPI Fuel Pumps With Low Pressure
Models
Alpha Sterndrive Engines.
MCM 4.3L EFI: S/N 0L360469-0L360789.
MCM 5.0L EFI: S/N 0L359672-0L376549.
MCM 5.7L EFI: S/N 0L359121-0L375658.
MCM 350 Mag MPI: S/N 0L372105-0L376283.
Bravo Sterndrive Engines.
MCM 4.3L EFI: S/N 0L360474-0L360638.
MCM 5.0L EFI: S/N 0L359653-0L372286.
MCM 5.7L EFI: S/N 0L346472-0L375995.
MCM 350 Mag MPI: S/N 0L359066-0L376282.
MCM 7.4L MPI: S/N 0L362686-0L373270.
MCM 454 Mag MPI: S/N 0L352940-0L370234.
MCM 502 Mag MPI: S/N 0L352957-0L370246.
Ski Engines.
MIE 350 Mag MPI: S/N 0L305670-0L305774.
MIE Black Scorpion: S/N 0L305536-0L305577.
Inboard Engines.
MIE 350 Mag MPI: S/N 0L303829-0L303890.
MIE 350 Mag MPI Horizon: S/N 0L305377-0L305813.
MIE 7.4L MPI: S/N 0L303950-0L304264.
MIE 454 Mag MPI Horizon: S/N 0L303787-0L304120.
MIE 8.2L MPI: S/N 0L303516-0L303517.
Situation
Engines within the serial number ranges listed may be equipped with an electric fuel pump
that is painted black with a brass outlet. Under certain conditions, the check valve in the
brass outlet of this pump may ?****?. This will cause low pump pressure above 4000 rpm
and a loss of engine performance.
NOTE: Painted pumps with an aluminum outlet or unpainted pumps with the brass outlet
have a different style check valve and spring that will not ?****?. Refer to the drawing.
Page 2 of 2 JUNE 1999 99-8
Inspection
If one of the engines listed has a loss of power above 4000 rpm, use a fuel pressure gauge
to measure the fuel pump pressure. Any reading below 22 psi (152 kPa) at 4000 rpm and
above would indicate this check valve problem. Also, a 0 reading on the pressure gauge
shortly after shutting the engine off is another indication.
Remove cover from the cool fuel assembly to see if the fuel pump is one that may have the
check valve problem.
76328
a
c
b b
d
c
Good Good Suspect
a - Aluminum Outlet
b - Brass Outlet
c - Area of Pump Painted Black
d - Unpainted Pump With Brass Outlet
Correction
Replace fuel pump with new one and retest pump pressure.
Part Required
(1) 861156A 1 Fuel Pump Assembly.
Warranty
Fill out warranty claim and send it to your normal warranty processing center.
NOTE: The replacement of part (s) and labor under warranty, to the products outlined in this
service bulletin, will expire December 31, 2000.
Warranty Code and Labor: MJ32 2.0 Hours
Diagnosis/Test: MJ40 1.0 Hours
Old Part: USA and Canada: Return with warranty claim.
All Others: Retain for disposition by a Marine Power representative.