Stalling out

[Rhinohio]

Hello folks, nubee here... I would like to thank everyone for allowing me to participate on this forum.

I finally got to put my 2006 Suntracker 20 with a four stroke 50HP Mercury Bigfoot in the water over the weekend. It's a nice boat but there is a problem with the motor some of you may be able to advise me on. It pulls strong and runs smooth as glass but it unpredictably falls on its' face and stalls like it's running out of fuel. In my haste to get in the water, initially I left the vent on the fuel tank closed and it eventually sucked the hose flat. I vented it and thought all was good. Some 15 minutes later it stalled out again. I pumped the primer bulb but it seemed to be pumped up. Throughout the day it would stall out but I could switch the ignition off, place it in neutral and it would start right back up with out hesitation. Then it might run for miles or stall out again within minutes... there was no pattern to it. At the end of the day I replaced the fuel line and primer bulb assembly thinking that the check valve might not be working but it still run erratically although the it only stalled out twice the second day in the water. Here are my questions:

Do you think I have water in the fuel

Is there a check valve or filter in the pick-up tube in the fuel tank

Is the fuel pump bad

Is the motor junk

We are boating on the Ohio River where there is a lot of barge traffic and the thought of being stranded in the channel is rather unnerving. Have any of you ever had this kind of problem and how did you fix it. My grandkids are driving me crazy about going out on the boat but I can't with good conscience take them until the problem is fixed. Any advice or suggestion for trouble shooting would greatly be appreciated. Thanks to all in advance.

Mike

[mike]

Welcome, a standard troubleshooting tool is to get yourself a portable gas tank with a separate primer bulb and motor connection. Then fill with clean fresh gas and run off the new tank. If your problems go away, it would indicate you have something in your gas/gas line causing the problem. This is probably the cheapest first step and you end up with a spare tank for a reserve!

[GregF]

First be sure this isn't just bad fuel.
No beeps? (computer detected errors)


2006 I am assuming EFI. This could be the high pressure fuel pump. That is exactly what my 60 was doing when it went bad. There is a test port that looks like a regular tire valve, on the vapor separator (port side near the front) If you have a screw on/snap on tire gauge you can hook that up and watch it while you are running. It should always be 42-44 PSI. Mine was dropping to about 10-15 when it failed.
I took the valve stem out and hose clamped a 5/16 hose to a gauge right on the stem body. Be aware this thing will spit a little gas when you depress the valve stem. It is not much (maybe a CC) but you don't want it in your eye. Wrap a rag around the tool you use to press the stem in.

The MAP also calls the fuel pressure regulator but I replaced mine with no joy. The regulator was about $80 and the pump $130 or so as I recall.
They are fairly easy to replace.
If the ball is hard and pumping it doesn't fix anything, the low pressure pump is probably OK.

Do the testing before you buy anything.

[scfishnman]

I would go with the earlier suggestion of hooking up a portable tank with its own fuel line and test it as the first trouble shooting action.

I had an identical symptom with a brand new cabin cruiser V8 engine. After several visits to my marina by the dealer, he finally decided to check the fuel tank/line. That was the problem. There were large pieces of masking tape in the fuel tank that would eventually get pulled into the fuel take up tube and block the fuel flow. When the engine was turned off for a few minutes, the lack of suction on the fuel line would let the tape fall free. There is probably something causing a similar type of temporary restriction in your fuel line somewhere. Since you say the fuel line bulb is firm when the problem is occuring, my guess would be that the restriction is between the fuel bulb and the engine.

[MichaelB]

If when it stalls out you can't do anything but let it die and then restart it you probably aren't looking at bad fuel. Try choking it when it stalls to see if it gets better or worse. I'd check the pressure as well as Greg suggested. That's a lot easier than rigging a temp can.

[Rhinohio]

Thanks to all for the quick response... you guys are awesome.

I can borrow a 6 gallon fuel can from a friend of mine so that will be an easy/inexpensive test. I have a fuel pressure gauge so I can check that as well. A couple of more questions.

First be sure this isn't just bad fuel.
No beeps? (computer detected errors)

There is an alarm that sounds when the ignition key is switched on but thought that was a normal confirmation the system is working. Does it make audible tones that vary with conditions... overheating, low oil pressure, etc.?

Try choking it when it stalls to see if it gets better or worse.

I neglected to mention this is a fuel injected motor... does it require choking? The ignition key does double duty as a choke switch ( push to choke) but didn't think that was necessary with EFI motors. Please clarify.

Again, thanks to all for your time to respond... I can see this message board is going to be a great asset.

Mike

[GregF]

One beep at key on is normal

Here is the MAP from the shop manual

[Rhinohio]

Update:

Installed an auxillary tank per suggestion... it acted the same.

Did find the gas in the tank was sour and siphoned it out (all 30 gallons). Replaced it with fresh fuel, a can of Seafoam, and added a fuel/water separator. Also rerouted the primer bulb fuel line so it was "pointing up", something I discovered while researching the problem... it acted the same.

Replaced the mechanical pump (low pressure) with recommendations at the marina. The guy told me the Merc's had a history of bad fuel pumps and he could get it covered under warranty if he installed it. Well that wasn't happening but it was a pretty good indicator since the symptoms were exactly like my motor had. Add to that they had it in stock which made me think this was a common failure... it acted the same.

Found a fuel filter inline with the high pressure side of the VST but it was clear. This filter was not obvious because it is buried down inside the motor and has a piece of tubing covering it. I discovered it while studying the parts list on Mercury's website. It is not shown on the breakout for the VST, it is a separate parts list for the fuel line and filter. Something to keep in mind if you are having fuel delivery issues.

Checked the high pressure pump and it was within spec. I did not measure it while in the water (as one poster suggested) but it checked good with the muffs on. Now what? I'm ready to scrap the damn thing and by a Honda or Yami. After checking what that would cost, doing so was not an option.

While struggling with purchasing a high pressure pump (roughly $400.00) I noticed a "strainer" on in the VST that the pump pulls fuel thru for delivery to the injectors... talk about an ah-ha moment. Pulled the VST and separated the valve body from the tank but did not see the strainer. That's because it was trapped in the bottom of the tank by the funkiest shit imaginable. The material resembled soft wax and the strainer and its' retainer were completely encapsulated with the crud. I pulled the strainer from the tank and dug out enough gunk to fill the lid off of a can of spray paint. I scrubbed and scraped and brushed and wiped until no more would come loose then hosed it down with two cans of carb cleaner. The strainer cleaned up nicely and all of the other parts were in good condition. Reassembled everything and now all is good.

This motor had to be having problems for a long while. Given the restriction the pump had, I'm surprised it would even start much less run. Obviously, the guy that sold me the boat was trying to screw me. He knew it had problems but didn't tell me about it. Guess that's why I got such a good deal on it. I did not test drive the boat but I'm not sure that would have tipped me off considering the random way it would stall.

Anyway, I thought I would post my findings in hope that my experience and knowledged gained might help a fellow boater in the future. Thanks again to all contributors.

Mike

[fwood]

Sounds like residues loosened by the ethanol gasoline cleaning out the tank and fuel line. Make sure the fuel line is ethanol compatible. The old gray fuel line that Merc used to use is not. Had similar issues with a Merc 15 hp 4 stroke motor and it's fuel system. I got a good deal on that motor too.

[GregF]

Good deal. I guess that means you have to use your boat more, keep that fuel fresh

Ed has lots of stories about ethanol fuel gumming up the works so this is probably one more for the pile.

Maybe you guys should add "draining the VST" to your winterizing routine. There is a drain plug in mine.

[badmoonrising]

Yep. ALWAYS use Startron blue, every fill up. I do all summer and then drain my fuel tank completely in the winter. No fuel in the tanks = no crappy ethanol gas to turn to mush.

[evinrude2stroke]

I wasn't able to contribute to the advice but I'm glad to see that everything worked out. It's good to know that you got a deal on the boat at least for the few weeks of aggravation that you had to deal with. Enjoy.

[Bamaman]

90/10 gasoline separation is why I use two 12 gallon plastic tanks and one 6 gallon steel tank instead of one large built in tank. I wouldn't use a full large tank per year's usage--virtually never running 100% fresh fuel.

Hauling my own 5 gallon gas cans 50 yards down the hill to my boathouse saves $5 per can. That is well worth my effort over buying fuel on the lake 5 miles away.

I prefer to keep the tanks empty over the winter.

[Rhinohio]

Got the boat out over the weekend for the first time since cleaning the VST and high pressure pump filter. The first thing I noticed was it ran much smoother than it did before. Not that it was running rough but a noticeable improvement my wife pointed out. Then we came out of the channel and I got into the throttle and all I can say is "WOW". Prior to cleaning the VST I was able to get ~4500 rpm at WOT but it jumped right up to 5500 rpm and held rock steady... no fluttering or hunting. I put it thru the paces, long runs, short runs, idling, cruising WOT or suffice to say a typical day of boating for us. It never faltered. Started right up and would "jump" out of the hole... it was unbelievable. The screen that the high pressure pump pulls thru is very fine... finer than a women’s stocking and it doesn’t take much to restrict it. Anyone with one of these Merc four strokes that's having performance issue should check here. Anyway, it's all good and now I can put it up for the winter knowing it will run come spring.

One question for the experts. We found a restaurant we liked about thirty miles upstream. Is it acceptable practice to make long runs like that near or at WOT. It doesn’t seem to mind but didn't know if I can cruise that far without a rest. Thanks to all that weigh in.

[GregF]

I seldom run mine at full WOT. I find there is not much extra speed to be gained and fuel consumption is a lot worse. 4500 is a nice cruise speed on my boat but I usually run a little less than that. 4200 gets me up over the bow wave and seems the best compromise between speed and fuel use but YMMV.