502 mpi problem!!! HELP!!!!!
 

So I just installed a rebuild gen 5 502 mpi mag in my baja, and I am having some issues with it not reving over 3000 rpm.. When you take off its fine, it will run just fine till it hits 3000 and its like it cuts the ignition off, like its not advancing the timing. I have removed the vst tank, and am running just a electic fuel pump. The boat runs awsome in the idle too 2900 rpm, but as soon as it hits 3000 it cuts it off, and just like bogs till it hits about 1700 rpm then it come right back to life..and runs fine...PLEASE ANYONE HELP!!!!

fixx
 

did you check fuel pressure? sounds like not enough pump to keep up,also where is the fuel pump?

I have a factory merc pump for a 280 outboard, its mounted on the transom right back by the fuel rail..I used the factory fuel rails...why would it have enough presure when its has a lot of load on the motor when coming on plain but when im on plane and try to go past 3 grand it cuts out?? What kinda pressure do I need???

If your drive lube is low the engine will not run over 3000 rpms, check it.

how will the engine know if the drive lube is low or not?? Will it cut out at 3000???

If you have a drive lube reservoir there is a sensor in it. It will cut out at almost exactly 3000 rpm.

I dont have a drive lube rez tank, the boat is a 88 and the motor is a 96, so I would asume that in 96 the bravo had a rez tank for the outdrive, but mine doesnt..how can I fit it, and what wire on the wiring harness should go to the tank...

If it doesn't see the sensor I don't think it should kill the engine at 3000. I'll see if I can look it up in the manual and let you know.

ya I wonder if since its not conected it thinks its low, or bad..so its cutting the ignition out...cause when the motor is in nutral, you can rev it way past 3000 with no problem..


another thing, does anyone think that I might have the pump mounted to high? Its mounted right behind where the vst tank was mounted on the motor, just screwed to the transom, and Im useing the factory leads that were on the vst tank, to power the new pump...think maybe that has something to do with it??

You have a pump made to supply fuel for a 280hp outboard and you have a 415hp I/O. Probably can't push enough volume of fuel.

its the same pump as the pump thats in the vst pump, just doesnt have to be submerged like the vst...

Those pumps are not designed to suction that well, that is likely your issue. I have a spare VST complete if you need it, or you should add a boost pump to the set up you have, maybe the mechanical that supplied the VST? That is how the 500 EFI works.

This engine has a host of sensors that control virtually ever aspect of it's operation. I have the manual for mine and in the trouble shooting section first thing it always says "Did you run a diagnostic scan for codes" I am in the process of finding a dealer qualified to work on mine. I 'm begining to except the fact that I can't fix this one myself.

Guys Please Help!!!!

Here is the non-scan diagnosis for the sensor system. Let me know what else you need.

Fixx
 

electric fuel pumps are designed to push fuel not suck! with it being mounted @ the transom that's a long distance for it to suck fuel then pressurize it for the 50psi fuel pressure that the engine probably needs. it could run @ 45 psi, like griff said get the rite fuel pump and mount it as close to the tank as possible and as low as possible so the pump don't have to work as hard to maintain the fuel pressure needed..i would go with a aeromotive,make sure you put a filter in front of the fuel pump,you don't want to jam it up if theirs crud in the fuel tank..

I have the mechanical pump hooked up to push the fuel to the fuel pump itself.

That sounds weird... What size line are running from the mech pump to the elec. pump? It sounds like you might be starving the electric pump for VOLUME of fuel. That big line going into the elec. pump is needed to supply the pump with enough fuel.

Aeromotive recommends putting the pump as close to the gas tank as possible. Do you have access to the gas thank? If you're hell-bent on running the elec. pump you might want to move it to the forward most position in the engine compartment, as low as possible, and mount it before the mech. pump.

That's how Merc does the HP500 EFI, mechanical pump pulls from the tank and feeds the pressure pump in the cool fuel box. If you read that manual page I posted it says the warning system will cut 4 cylinders at 2800 and then restart them at 1200.

Do you know what size line they use though? I can see it working if its a really big line... And, doesn't Merc use the fuel pump mounted on the raw water pump to do this, or is that just in the Gen V mech pump negation GM blocks that they use this in? If they always use that pump it seems like its a much heavier duty pump than the block mounted pump, but I could be wrong...

Maybe its just my experience with Aeromotive pumps and the volume of gas that they need (and big pick up tubes) that skew my thought process on this...

On the 502 MPI it is plumbed to the seawater mounted mechanical pump with 3/8 line and It may even be 5/16 once it is pressurized. Remember that a mechanical pump does a much better job sucking than an electric because it is a diaphragm as opposed to a vane style pump.

Ok, so I bought a bravo res tank tonight, and hooked it up, and its still doing the same exact thing. Im begging to think maybe it doesnt have the exact 46 psi of fuel pressure that it needs. I dont have a guage on it, so I dont know the exact pressure. But I cant believe that its acting like its the "guardian mode" What I heard today was that you shouldnt be able to rev the motor in nutural over 3000 rpm, but I have no problem reving in nutural over 3000, but once in gear I cant get past 3000, its like the wires are hooked up wrong or something...

Did you do the diagnosis on the right side page? It will check all the discrete warning sensors.

heres what i did, remove vst and mech pump. get electric low pressure pump(i use mallory) and put it as close and low to your gas tank as you can. get a cool fuel system and your good. run the out line from the fuel rail back to the gas tank.
will not get guardian mode from sensor not being hook up...