88242LS

Help me out here guys, I have a 1994 Formula with twin 502 mag EFI's Out of no where yesterday it started giving me trouble, (Port Motor) I had Idled a considerable amount of time, and it stalled, never acted up or anything poof it was gone, after a check for obvious stuff, kill switches etc, 15 mins or so it fired right up, shut it down a few times fired right up each time, no hesitation or anything, then it quit again, same thing over again, then i ran out for about a hour again no hiccups, pulled into beach and had a few pops and enjoyed the scenery, on the way back we stopped for dinn, up in a marina after running hard back across the lake, no issues, when we left the marina after about a hour or more I didn't make it out of the marina and lost it again, after about 15 mins again fired up ran home no issue,

Now after reading here on OSO I think, key word think I am experiencing "VAPOR LOCK" and probably a issue with the VST, First let me say it was not overly hot yesterday, 80ish, Ive definitely run it harder and longer then idled longer with no issues, (Poker Run) And on hotter days,

I've owned this boat for 3 yrs now and not batted a eye, so I am not really interested in converting the system, its worked fine, sure maybe I need a new part or sensor?

What would be the most common issue here? Ive read a ton of threads, will go and reread them also, But my thought is there is a reason for this to happen now? is there a common fail part? My plan is to go pop the cover off and search for any debris, or anything odd, but the O ring is a over a week away, so i'm kinda stuck there, so I'm gonna go change the separator, probably due anyway, and check the the fuel lines as Ive read there is a clear fuel line that can kink or clog, One question I have is should there be a tube on the black vent on top? neither motor has one but i just thought I'd ask,

Cole2534

iTrader: (1)

Having been through this whole ordeal-

1) Check your mechanical pump for output pressure. Its port are 1/4" NPT so round up a 0-15psi gauge and see what it produces, it should be around 7psi IIRC.
If it does not have adequate flow or pressure it won't be able to keep the electric pump's sump full. http://www.northerntool.com/shop/too...FaY-Mgodzl0AJg

2) Next time it stalls remove the brass plug and see what happens. If it's vents a lot of pressure the mechanical pump may not be able to push fuel into the system. If it's empty I'd suspect the mechanical pump's foot was wearing to nothing, you'll know it when you see it. Carter/Airtex #60932 is a good replacement pump. http://www.offshoreonly.com/forums/d...fuel-pump.html

3) Check the fuel pressure at speed from the electric pump. Your local auto parts store should have everything you need for rent/free. You need 36-38 psi with the engine off idle. If your pump does not produce that, I'd look to replacing the regulator. http://www.cpperformance.com/p-13316...regulator.aspx

4) Look into the VST diaphragm issue, but I don't have any experience with that.

Eddie Young has a pretty good thread on here about helping to cure the vaporlock. In short, plug the VST return port and route the hose back to the fuel tank. You'll need some hose and fittings. The VST sump uses 5/8-18 inverted flare, and from there I'd use -6 push-on fittings back to the tank.

airjunky

iTrader: (2)

The vst blues . Should be a flimsy clear hose to that nipple from mechanical fuel pump .sometimes see rusty crud build up in the little screen on the elec pump inlet don't know how that crap gets there .good luck man let us know what ya found

88242LS

Thanks I will try a cpl of those out tomorrow, after I change the separator and check hoses, will need to track down a fuel press gauge, so ill crack that nut first if she shuts down, I hate this even if its beyond me i just wish the problem was cut n dry,

88242LS

Dobu mean the black thing on top? I assumed it was just a vent? Neither side has a hose on it, this is why I like the boat at home and not at marina on lift lol

silent lucidity

iTrader: (1)

I have written a long blog on this VST .. BS.. I tried new mechanical pumps, checked diaphragms on VST's, even did the return to the tank which helped a little but still would vapor lock on hot days,, I added more ventilation too. Got tired of it and it's a safety hazard if your on a river.. I worked with Eddie Young, who's an awesome help and easy to talk with. I **** canned the entire mechanical pumps and VSTs.. bought aeromotive pumps and fuel regulators, Eddie reworked my rails so they feed fuel from both ends and added a return fitting so I could return fuel through the regulator back to the tank...never a problem since. Runs better than ever and even on hot hot days I can shut off engines without running fans and let it heat-sink and it fires right up.. This option will cost you about 1500 - 2000 a motor..a I ran new AN fittings and braided lines so it was on the higher end.. Wasn't real hard just took time second motor was a breeze.. While rails being reworked figured good time to have injectors checked and cleaned.... Nothing ruins a moment like idling out in your baby and everyone watching as you hit the throttles and she chokes and dies.... Even my wife said fix this would ya.... Yes ma'am DONE. Oh and by the way if you do research on ethanol in fuel you will find that the boiling point is vey low now, merc says they don't want your engine compartment to exceed 160-170 deg.. HA fat chance when your running. 160 thermostats... Shut your engine off I would bet your in the 200- 240 range...good luck with that.

Trash

You should have a tube running from that vent port to the throttle body or plenum area. Fuel can come out of that vent and you don't want that just dumping in the engine compartment.

There is a diaphragm inside the top assembly of the VST. With age (like your 1994) that diaphragm will begin to deteriorate and fuel will bleed through causing issues similar to what you are experiencing. It will seem cause similar symptoms as vapor lock. I just had this happen on a 1995 motor. Diaphragm was beginning to disintegrate. Replaced it and runs like a champ again.

Diaphragm kit is about $60 or so. O-ring kit nearly the same. Lot of money for some rubber.

88242LS

no updates yet, changes separators today, did it once after, we cracked that brass nut but it turns and stops like it hitting something, is this normal? not even a half turn, at the same time i popped the hose off the fuel pump, boat fired right up not sure which caused this, anyways tightened it up, put the hose back on, never a problem again, ran it through some heat cycles, probably a quiescence, waiting on O rings then I'll pop the top and look further, in the meantime I guess I'll have to milk it, Trash i like the diaphragm idea, at least it makes since because nothing else does, only change Ive had is getting fuel somewhere else, and its sposed to be the good stuff, 91 non E, usually I get 89/93 E gas thats the closest place on trailer, this time I filled up on water,

fireguy

Had a similar problem on my '96 502.

I was convinced it was vapor locking. Researched all the VST BS and was convinced I was gonna have significant issues. At the recommendation of a friend we started where we should have air, fuel, spark.

We had no spark. I got in a hurry and did no further checking. Replaced the coil and ignition module and it has performed flawlessly ever since.

Make sure it is actually a fuel problem.

88242LS

parts will be here this week, one odd thing it has only happened to me once since, I pulled the vacume hose or return hose off the lower fuel pump, started right up, no problems since, gonna replace that line as it appears cruddy, and run the line off the separator that apparently I am missing (pic)