502 MPI problems
 

Hi

I have just installed a 1999 502 MPI in a 1988 Baja 235 Force.It idles OK but when advancing the throttle it starts surgeing , in neutral up and down 1000 rpm and when in gear up and down maybe 200 rpm. Could it be that it does not get enough fuel or that the fuel is contaminated with water?

Mats

I would put the ECM in service mode, check timing, then read codes, the ECM controls the idle by advancing and retarding the timing [to a point] also check your idle air control valve, might as well get a fuel sample and check pressure also[ did I forget anything!!!!]

Does it clear up at higher RPMs? If not check that the map sensor is plugged in, also check the throttle postion indicator

Checked spark and base timing. seems OK
Tested to run it with new fuel from a separate tank with a new fuel filter and new spark plugs. Same thing, the engine surges over 1000 rpm. tried to advance the throttle further and not much happened. It does not deliver enough power to get the boat on plane and it idles rough as soon as the engine warms up.
Plugged in a scantool. All sensors deliver normal values, ignition advance seems reasonable.
The only thing left is to check fuel pressure. Anyone experienced something similar?

Sounds like too much timing. Did you use the plug in tool to set the timing? Its a requirement, can't set it without it. The scan tool will not tell you, its programmed to provide "X" amount of timing, period and when it reaches that point or senses detonation, it kicks it back.

Rod

Dear OSO members. Now it is getting complicated. The problem is the fuel pressure, it is only 20 psi. Further ,i have narrowed it down to the fuel pressure regulator. Now to the problem; The engine is a 1999 model,which should have a "new style" ECM. However, it has been modified at some point and has an old style ECM and an electronics box on the engine. The ECM part number is 860253R1. Since the nominal pressure on the regulator and the ECM program must match,does this mean I should use a fuel pressure regulator with part no 860349A1 instead of 861126A1 that you would normally find on a 1999 502 MPI? Do they give
different pressure? Is there any way to identify what program is in the computer? On the ECM there is some white plastic where it says "8E58" on it. Does that ring a bell?

THE 8E58 IS THE CALIBRATION CHECK SUM NUMBER. CALL MARK BOOS AT PRECISION MARINE IN KENNER LA. HE CAN TELL YOU IF THE ECU IS CORRECT, AND ALSO MAKE ANY MODIFICATIONS YOU MIGHT NEED, IF ANY. HE IS THE MAN . HE HAS BEEN ABSOLUTELY VALUABLE IN SEVERAL PROJECTS I HAVE DONE. THE NUMBER IS 1-504-469-7463.
HOPE THIS HELPS
STEVE;)

You could modify the older one by using a Vortec adjustable regulator. Then you could set the fuel pressure to where you want it. Now the big question, what should the fuel preesure be?
I don't know, but I bet someone here does.

43 psi is stock for your motor.

Hi
I have now modified the fuelpressure regulator with a Vortech kit. The old spring was all corroded and broken close to one of the ends. That is why it still worked but with a lower pressure. I will do a testrun with 43 psi to be on the safe side since the faulty regulator was a 43 psi.Further , I will try to get hold of a scantool to figure out the SW version in the ECM. Assuming that the ones who modified the engine knew what they where doing, they probably crammed in 1999 SW in the 1998 ECM HW.

Thanks for the help!

Mats