phatboy1969

I have a 1996 Wellcraft Scarab with 454 Mag MPI serial #0F802426. I am having an intermittent problem with the motor shutting down after extended periods of time when its in gear at idle; it never does it at cruising speed or at WOT. The only way I can get the engine to restart is to crack the line going into the VST from the mecanical pump, I always get a lot of air out of the line and as soon as I see fuel drip, I close it off and the engine will start back up and run fine. Sometimes it will do it only once, but sometimes it will happen 2 or 3 times a day. I know it sounds like vapor lock, but it will do it even when the engine is cool. I have replaced the mechanical pump head; not the body; with an upgraded KE pump. It still did not fix the problem. I have checked all the clamps and fuel lines and fittings and all seem to be fine. Could the stock pump body be the problem?

Orestes

I have a '96 502Mag EFI. I've dealt with this issue too. Are you 100% sure that none of the tubing fittings are clogged? I chased this issue on mine too and found the fitting on the air intake horn was clogged.

phatboy1969

Pretty sure it's vapor lock after getting several replies on a couple other forums. Found out it was a design flaw by Mercury in the mid 90's that caused a lot of boats to have the same problem. Mercury even put out a service bulletin about it. Looks like the fix is replace the mechanical pump with an in-line low pressure electric pump to help overcome the vapor lock issue. Never did like the low pressure pump located on the sea pump anyway.

boss252

Do you know the number of the service bulletin? The same thing is happening with my 97 7.4 lx

phatboy1969

Here's the link. http://www.boatfix.com/merc/Bullet/99/99_07.pdf
Found out the pump kit in the bulletin doesn't exist anymore. Here's something I did this weekend seemed to fix my problem though. I ran the boat as hard as I ever do with the normal shutdowns for beer breaks and to people watch, and with an entire day of riding and shutting down,the boat didn't experience vapor lock at all. On Friday, after some brain storming and some more internet searching, I decided I would take a closer look look at my fuel/water separator filter location. The filter on my engine was mounted about an 1/2in from the starboard exhaust manifold, and didn't have any heat sheild!! I think the fuel was boiling off inside the filter, Why the hell I hadn't noticed it before is beyond me. I had enough extra fuel line between the filter and the mechanical pump, that I was able to relocate it on the bulkhead forward of the engine, and for a little extra security I wrapped the filter and the fuel line in ThermoTape that I purchased for the local parts store. After running the lake for a while I would turn off the engine and let it sit for an hour or so; when I would grab the filter it was still really cool. It was such a enjoyable day for us to be able to go out and not have the engine inadvertently shut off. Hope this helps!

boss252

Thanks Phatboy. Good info. I will try and move my filter too.

Orestes

Glad you found a solution.

By the way, which '96 model do you have? I have the 26.

I'm going to add some detail on what was going on with mine in case it might help someone else down the line.

No doubt that vapor lock is the root issue. In my case, (early on) I found that the tubing from the VST was filled with grime from the fuel pump. That same grime had collected at each of the fittings the tubing tied into, and was totally clogged. I cleaned the fittings when I cleaned the tubing, but since the fittings are in places where you can't look into them, I didn't see the clogging that was going on.

I was initially started chasing this issue because I had a "squeal" coming from the engine, with no stalling, ever. I climbed all over that damn thing and finally tracked it down to the top of the VST. But there isn't anything to "squeal" there?!?!? I next thought that the brand new fuel pump in the VST was making noise.

This was all during last season. After having the boat in storage for a few months, I fired it up to prep for a shakedown run early this season. I found a surprise at the VST. The little plastic sleeves on the electric fittings for the pump were busted and spewing fuel. ...but there was no squeal.

Apparently, the squeal was from pressure escaping through some very fine cracks that were in those little plastic sleeves. As it sat over winter, the cracks grew large enough to spew fuel. So I ordered the kit and replaced the sleeves and o-rings. Took the boat out and no squeal. Excellent! ...not really, once it warmed up, the engine started dying everytime that I'd idle along in gear.

I continued researching the VST issue... then while getting ready for another run, I decided to have another look at the tubing between the VST and pump. The tubing was fine so I decided for sh*ts and giggles to make sure all the fittings were open. I pushed a wire into each and found two were completely clogged (at the pump and at the Air Horn). Cleared them out and splashed the boat. Fired it up and didn't have a single stall all day. Apparently, the clogged fittings were preventing any pressure from being relieved. That also seems to explain why the sleeves were cracked in the first place (overpressure).

Even though mine isn't stalling anymore, I'm still going to work toward solutions that will keep my fuel temp down at the VST and try to minimize the need for pressure relief.