Offshoreonly.com - 502 surging and loading up?

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Quote:

Originally Posted by bdbwtie (Post 4791244)

I have a mercruiser 502 serial im guessing is OK173702. It is in a 98 powerquest. Cold it runs like a champ, good oil pressure, no surging. After the engine is up to operating temp, guage shows 160 and I come into a no wake zone the engine will hunt. I usually try to pump it slightly off throttle just for sake of thinking its gonna stall. It isnt enough to make the tach fluctuate, but you can definelty hear the engine varying in rpm. If the no wake zone takes awhile to get through the engine almost seems loaded up, trying to take off it feels flooded, can tell its not responsive and sounds loaded. Usually giving it more throttle or coming off the throttle and then back on will clear it up within 5-10 seconds but doesnt seem right. I have noticed alot of black on the transom and under swim platform after every use. Any ideas what to look at, or being fuel injected am i stuck to having it scanned?

Check the yellow looking lines coming off the mechanical fuel pump and the VST system. They usually 'T' together and are connected to the intake either near the TB or the rear of the intake. They should be dry inside. If not it is likely fuel venting into your intake when causing your issue. Either the mechanical pump diaphragm is bad (one source of the leaking fuel) or the internal VST diaphragm is bad.

AD said serial # is cool fuel

I'm having the exact same issue with the exact same engine I have the mercruiser 502 MPI in my formula boat my problem is very similar in that let's say the boat's been sitting awhile because we've been fishing for a few hours when I try to drive run it or cold started I have to throttle it up literally get it to start it just turns over over and over unless I throttle it up with these solutions help me as well as the original poster

Thanks everyone for the replies. This weekend I will be looking into a vacuum leak, and checking the timing. I am kinda leaning toward IAC/throttle body being dirty because when i snap the throttle and come back to idle it will act like its gonna die and takes 5 seconds or so to recover.

On another note I noticed when running through hull exhaust the starboard exhaust will spray the water out, but on the port side its just running out. Is this an issue or something to look into? Does have a new sea pump, never gets over 160-170 temp wise. It does have alot of volume coming out so I dont think flow is an issue.

Water flows the path of least resistance, so no issue at idle. Higher rpms they should start to even out some more because of more volume

you need a scanner to check the timing, timing must be set in base mode

EDIT, Ive had a few 502 mag mpi like yours and the water flow was always very equal out of both pipes

Quote:

Originally Posted by F-2 Speedy (Post 4792928)

you need a scanner to check the timing, timing must be set in base mode

EDIT, Ive had a few 502 mag mpi like yours and the water flow was always very equal out of both pipes

I was told you could put it in base mode with a paper clip and check it, this not true? I did talk to a marine shop who thinks its due to the fuel system having paint on the inside and clogging injectors. Which may be true, but most everything ive experienced with clogged injectors ran like crap all the time, not just warm and at idle. Of course they cant get it in until after the fourth. As far as the water I understand the path of least resistance, put I never seen a through hull not spraying. Repair shop wondered about silent choice baffles being hung up so I will look into that as well.

Dirty to the point of clogged flame arrestor.

Normal Exhaust pulsing causes the water to spray. So yeh, if the water is just running out, sonething is eliminating or avoiding the pulsing .

Quote:

Originally Posted by bdbwtie (Post 4792932)

I was told you could put it in base mode with a paper clip and check it, this not true? I did talk to a marine shop who thinks its due to the fuel system having paint on the inside and clogging injectors. Which may be true, but most everything ive experienced with clogged injectors ran like crap all the time, not just warm and at idle. Of course they cant get it in until after the fourth. As far as the water I understand the path of least resistance, put I never seen a through hull not spraying. Repair shop wondered about silent choice baffles being hung up so I will look into that as well.

Yes Ive heard of this, I use a scan tool.......not something from the teachers desk.......:riding: