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Vapor Lock in 1994 PCM 5.8 HO

fishga0130

New member
My 1994 Supra with the PCM 5.8 HO has been plagued by vapor lock. It starts great when cold but after it sits a bit with the cover down when hot (like anchoring for a swim on a hot day), it will refuse to start. I have added Stabil Marine 360 to attempt to sure the problem but it doesn't. The only thing that seems to work is to pour a couple of cups of water onto the low pressure fuel pump. That tends to break the lock and allows it to start right back up.

Does anyone know of a more permanent fix??
 

makomark

Silver Medal Contributor
sounds like the engine compartment is getting too hot....the easy fix is to try opening the cover as well as cooling down the engine temp before shutting it off...specifically (especially after a good long run or pulling a skier) let the engine sit in neutral and raise the idle to 1500 RPM and set the anchor...after a few minutes, shut off the key and open the engine cover...

If that is a big improvement, the more elegant solution is to add additional ventilation to the engine compartment...some may require a separate fan (blower) solely to dissipate the heat...
 

fishga0130

New member
Thanks for the reply. Opening the cover while all of us are swimming might be a bit dangerous. The motor box is right in the middle of the boat and slipping and hitting hot metal would not be such a good thing.

I have been contemplating an additional blower but I have to check out the wiring to see how easy it might be to install. Nothing about this boat is easy. The bilge blower is in a separate compartment next to the stuffing box. To get the cover off of that compartment, the engine cover has to be completely removed.

Sometimes I long for my Mark Twain with the Mercruiser IO. It wasn't easy to work on but at least the front half of the engine and the pump and blower were accessible. Sigh........
 

makomark

Silver Medal Contributor
you want to leave the bilge blower and its plumbing alone....

Most engine installation guides call for the ambient air to not exceed 150 deg F, with the engine running and the boat underway...usually, not a problem until you stop...today's "gasoline" does not like hot engine compartments...
 

hotstang71

New member
My 93 Pro Boss EFI was doing the same thing after it got hot and was shut down for more than 5-10 minutes. The temporary fix was to prop the engine cover open (about 12" with a ski rope handle) I later bought a kit from PCM that deleted the canister style fuel filter on the engine and moved an in line filter to the back of the boat near the fuel tank. This solved the problem.
 

fishga0130

New member
Hotstang,
I have also been thinking that an inline fuel filter closer to the low pressure pump might be a solution. Do you happen to have the part number from PCM??
 
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