502 problems! please help!!
 

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

Re: 502 problems! please help!!
 

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.

Re: 502 problems! please help!!
 

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

Re: 502 problems! please help!!
 

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

Re: 502 problems! please help!!
 

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.

Re: 502 problems! please help!!
 

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.

Re: 502 problems! please help!!
 

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)

Re: 502 problems! please help!!
 

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

Re: 502 problems! please help!!
 

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!!

Re: 502 problems! please help!!
 

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*?

Re: 502 problems! please help!!
 

If you just did a service and changed your fuel filter they can be hard to start the first time after the filter change. It takes the system a while to prime back up. That wouldn't concern me unless its still hard to start next time you take it out.

Re: 502 problems! please help!!
 

You either have a bad Exhaust Coolant Temp (ECT) sensor or they forgot to hook it back up when changing the thermostat.

The rough running when warmed up and RPM (rev limit)reduction are both symptoms of a bad ECT sensor and subsequent active trouble code 14 on a MEFI 3 system (like yours). A code or scan tool could be used to confirm this. I can tell you how to make your own code tool for less than $1.00 if you are interested.

With a code tool and (factory) service manual this would be a simple diagnosis.

As far as the long crank time on initial start - new (empty) fuel/water seperator will cause this.

Dave

Re: 502 problems! please help!!
 

i had a very reputable dealer change the cap,rotor raw water pump and thermostat. after i changed the fuel filter it did take several tries to get the motor started but after that it was fine. i pulled a few plugs and they look good as new. light brown color. i bought a fuel pressure guage to hook to the shrader valve to check that. what should the pressure be at idle/WOT? if thats ok i'll replace the sensor dave spoke of. it's funny. the ticking, actually clanking in the exhaust right buy the solonide started when the motor died. i'll see if i can pull it apart enough to see if there's a restriction. that would choke the motor out if restricted. thanks for all the advice guy's! i really appricatet it. this is my first big boat and this motor is a littel overwhelming!...james :D

Re: 502 problems! please help!!
 

James,
Before you do anything else, at least check the connection at the ECT sensor.

Dave

Re: 502 problems! please help!!
 

where is this sensor? i just checked my fuel presssure(not running) and it looks like about 10-11 lbs. i'm going tofire it up tnd check the pressure then...james

Re: 502 problems! please help!!
 

32 psi at idle and 30 psi at 3000rpm on the hose. i'm going to hange the fuel filter and check again. these numbers are low from what i've read. could this be my problem?

Re: 502 problems! please help!!
 

Should look like this

Re: 502 problems! please help!!
 

thanks dave. it's plugged in. i changed the filter and pressure remained the same. no water in fuel. how can i test that sensor? thanks....james

Re: 502 problems! please help!!
 

Dave N
I'm interested!
How do you make a code tool for less than $1.00?
Thanks
Greg

Re: 502 problems! please help!!
 

found out what the ticking noise was in my exhaust. the quick and quiet valve screws came out and the valve was rattling around in the exhaust. could i ditch the quick and quite and put in a straight piece of pipe? would water come in from the outdrive? thanks...james :D

Re: 502 problems! please help!!
 

You need to cap the y-pipe ears if you remove the divertor valves. Otherwise that's a big hole for water to come in. A PVC pipe cap works perfect for that.