go propless

Does anyone know anything about a vapor locking problem. on 97 502MPi engines?
My problem occurs after short idle time 3 to 5 mins coming out of no-wake zone. Then trying to come up on plane one of my motors will shut off. Then after a short time it will start and be fine???

LordStanley74

Does your 502 have the Cool Fuel system installed?

GO4BROKE

If your motor doesn't have a mechanical pump feeding the electric pump, there is a kit to install it. Merc tried to do without the mechanical pump around that year, it caused vapor lock issues. Although I don't think your problem is vapor lock. That generally causes the engine to not start. Stalling while running is probably something else. Possible pinched/chaffed wire, or water in the fuel tank that rolls back when you come up on plane. Switch them both to feeding off the tank the motor that stays running is on and see if it stays running. Take a fuel sample when it won't start.

hp500efi

had trouble with my 99 502EFI only it would be a problem after a long run and then beaching it for awhile. The sun beating down on the hatch with the heat trying to dissipate from the motor created a vapor lock. If I raised the hatch a nd let it sit for awhile, all was fine.

go propless

MY motors do have mech fuel pumps before the SVT. Thanks GO4BROKE we tried all of those things last year with no resolve. I think it is vapor locking because I talked to a guy in ohio with a 97 302 boss same motors and same problem. He talked to someone from Mercury at the Miami show they told him that it was vapor locking that's why they put the fuel coolers on them in 98?? someone in Q&A told me about a vapor lock kit part# 862264A4? I called my tech he is was out so I not sure if this is a merc part or not. Raising the engine cover is ok if it will work every time but I want to fix the problem the correct way. thanks for the help guys I hope I get this figured out soon.

GO4BROKE

There was a bulletin back in the day about it, I don't remember what it entailed. If there is a fuel pressure test port (I can't remember), try opening it when it stalls to check for air. I have also heard of tiny cracks at the tank fittings or connections from there to the motors allowing air to get sucked in. You have decent access to the fuel tank sending units, shouldn't be hard to check. I also once had a fuel line collapsing just ahead of the filter that only caused trouble at WOT. You might want to peek inside the lines at the barb fittings just to cover that base too. Let us know what you find.

GO4BROKE

That part number you listed is to add the mechanical pump:

862264A4 PUMP KIT-FUEL 862264A4 $371.73 $335.00 $0.00 $0.00 5.51 Lbs No Picture

go propless

Just got a 4 page fax on the service bulletin from mercury.

I going to read over it and go from there. thanks for the help guys if you think of any thing else let me know.

45sonic

Quick fix!! Get rid of the fuel injection and go with carbs. When I repowered my '95 42 I did away with the fuel injection and put new carbs, electric fuel pumps, and distributors. Ran great no more problems after that.

Before doing that the engines never did run right, always put black soot on the transom, dumping too much fuel through the exhaust, sensors always going bad, no start, vapor lock, etc. What a pain in the a$$.

jiram

Assuming that version has one Check first for a cracked coil on that engine. I had identical problem-runs fine until temp goes up-then crack opens and shorts to ground. Cools back down and everything fine until warm again. Crack can be almost invisible.