MariahMadness

ok, motor ran great in florida. brought it home and had it servised. they changed the raw water pump,thermostat, cap and rotor. i changed the fuel filter and oil and filter. today is the first day i have run the boat since february. the motor is a 1999 mpi 502 that is stock. when i went to launch it i had to crank it over several times before it would start. it usally starts right up. we launched and idled for several minutes till we got out of the no wake zone. i then took it up on plane and it ran good. i ran it at 3500 rpm's for a few minutes. when i brought it up to wot, it stalled. it would not start right up, just cranked. after a few minutes it would fire up but die when i hit 4000rpm. there is also a ticking noise near the silent choice solonide. any ideas? when i rev the motor up in netural in the water it cut's out at 4000 rpm. please give me some ideas to check out. this is my first I/O. ineed some pointers. i dont want to take it back to the shop! $90 an hour is scary! thanks .....james

Dave1972

Could be a number of different things. I have an older 502EFI and the VST tank gave me issues but I don't think you have that. My problem was the filter/screen in front of the high pressure electric fuel pump was clogged and didn't have enough flow to keep up....keep the RPMs down and it would run....then stall after a little while. Easy fix is a fuel pressure guage while running.

Since you changed your dist. cap and rotor perhaps it was put together with a couple wires switched?

Let us know what you find out.

MariahMadness

what kind of fuel pressure guage should i get? where do i install it? and should it be installed perminatly? my knock sensor wire isnt plugged int anything. where should the wire plug into? also, do you think that the fuel filter may havea restriction in it? it isnt the kind that has a clear bowl on the bottom to collect the fuel. i think i'll change that. thanks...james

MariahMadness

here's another piece of info to help you guy's reconize my my problem. when we bought the boat the thermostat was installe wrong. it never came up to temp. now it comes up to temp but runs crappy. any ideas? thanks

Dave1972

Wow...sounds like the motor may not be stock or perhaps it's been "tinkered with"? At any rate, the knock sensor is connected to the side of the block...if you are looking toward the back of the boat, it should be on the left side of the block just in front of the block drain plug on that side.

As for fuel pressure gauge, you can buy a cheap one at just about any parts supply store. You would only use it temporarily unless of course you want a full-time guage in the dash. I believe there is a schrader valve at the front of the fuel rail (on the top of the motor at the end of the rows of fuel injectors). You just hook up the fuel pressure guage to that fitting and away you go. You would want to take readings at idle and while running at WOT. I believe you want to be right around 38PSI at idle and at least that same amount at WOT.

You can do a search on here for "502 fuel pressure" and find the specs that you would need for sure.

I'm not sure why your boat would run worse with the thermostat in it other than perhaps since the knock detector is not connected the timing is retarded so much that when the motor gets hot it doesn't make any more power....could bet that your ECM has put the motor into limp mode....it sounds like you might be better served hooking up the Merc/Rinda Scan Tool while you are running the boat on the hose and check all of the settings and see if there are codes stored in the ECM that would indicate a problem. Your local MERC dealer should have the scan tool or you can buy one for a few hundred dollars.

Let us know if you need anything else.

MariahMadness

thanks! ill hook up the knock sensor and get a fuel guage. i'm wondering if i could be sucking air at the screw on fuel filter.

Dave1972

I can't imagine being able to suck air at the screw on filter as you would end up having gas all over from that type of leak....I guess it's possible. Sounds like an all-around tune up is necessary to begin with. You might want to check plugs, wires, and distributor cap and rotor while you are at it. You could be a having some issues related to ignition if the cap/rotor are shot/moisture. I would say take your time and do the total tune up as far as you can first. Check and re-check everything. Once you've gone through that process, perhaps you can re-assess and see if the problem remains. If so, then use the scan tool to help read inside the ECM.

For reference:
Spark Plugs should be MR43T gapped at .045
I use Accel distr. cap & rotor part number 8132 (around $30 total)

robyw1

I didn't know that the ECM would allow it to hit 4000 in neutral. Anyway it sounds like an ignition problem somewhere. That cap & rotor would be the first place I look. If you have enough fuel pressure to run it at 3500 with no problems then the fuel pressure shouldn't have anything to do with why it won't start right up. I think from what I have learned on the board that the ticking noise you hear is just the silent choice itself and not related to your problem. Some audio of your engine cranking and running will help me figure out what is going on if possible.

Roby

Dave1972

I agree with Robyw1 on this one. I would lean toward ignition rather than fuel. Although my motor will run as high as I want it to in neutral all the way to the rev limiter. One thing I'm not familiar with is the "cool fuel" setup on this motor. I have VST and that is where my issue was. The VST pickup has a screen/filter before it and it was probably 95% clogged...needless to say it would get enough fuel to the engine at idle and very low RPM but would just run lean and dry out and die...had a heck of a time. I also took the time to take each injector off of the rail as there was a small screen/filter at each injector and each of those were pretty dirty as well....sounds like the engine is in dire need of a tune-up anyway!!

mjb

Just a thought...but you said the motor dies at higher rpm and you hear a clicking at the silent choice solenoid. Maybe the silent choice is stuck in the closed ,"idle only" possition. That may cause excessive back pressure at higher rpm's and cause the solenoid to click as it tries to open the butterfly???

Also, if you changed t.stats, make sure you used a stat with the same rating as the original. The ecm is programed for this stat. I think it's 160 or 165*?