Pontoon Boat & Deck Boat Forum

The Mercury 90hp 4 cycle EFI motor starts great cold and runs strong without issue. However, once its turned off for an extended period of time, say 30 minutes, it starts fine but runs like crap. It lacks power and just falls all over itself and cant get over 3K RPM. Eventually after a few minutes of feathering the throttle, it will perk up and run fine.

I am not currently running the gas from my marina so the first step will be to burn the old gas out and try a different gas. I am also running Stabil if it matters. Remember its a EFI motor, no carbs.

Any thoughts on what is causing this?

I was having similar issues with my E-Tec. I could tell it was struggling and found my bulb was soft. I pumped it up and smooth till I idled down then rough again. Replaced the bulb with a good one ( been buying cheap) from Evinrude. 2 trips and a week between runs and I have to pump maybe once or twice to get it firm. So look at your fuel lines for bad bulb or kinked line

After you do the basic fuel supply elimination things...

High pressure fuel pump.

The way to prove it is to connect a gauge on the test port on the vapor separator (looks like a tire valve). It should be steady at 42-44 PSI wherever the motor is running. This is about $150 (discount price, more like $300 at the dealer) so you want to be sure before you start throwing parts at it.

You might as well replace the fuel line from tank to motor too. I replaced mine last spring. Even though I use straight gas (no ethenal), the liner inside the gas line was all deteriated. It's cheap maintenance to change line and bulb.

I went to the lake today but did not do any in depth troubleshooting on it yet other than to say the gas supply lines from the tank into the outboard looks "visually" fine.

The "no power at hot startup" condition occurred again and it could not rev over 3K RPM. Just to try something different and for troubleshooting purposes only, I raised the motor out of the water, started it and smoothed out perfectly. I quickly dropped it into the water and then the thing ran like a champ all the way up to 5.8K RPM. Wierd???

I have determined that it does have an electric fuel pump mounted on the outboard. I can hear it running when the key is turned to on. It definitely does not appear to have a squeeze bulb so that can be ruled out. I intend to check the fuel pressure as soon as I can find time to actually troubleshoot rather than go boating plus I am going to replace the gas line too.

With all that said, anyone have anything else to add as the solution to the problem.

I've never seen a boat without a primer bulb. Is this boat new to you?? If so, is the problem new or has it always done that.

I would continue looking and make 100% for sure that there is no primer bulb. I've have numerous outboards including Mercury EFI's and they all had bulbs.

He is probably talking about an inline fuel pump in the line from the tank. That would eliminate the need for a primer bulb but it is also something else to fail. I have only seen them on big offshore boats where the tank was in the bilge and pretty far away from the motor(s).

Tmore wrote:I've never seen a boat without a primer bulb. Is this boat new to you?? If so, is the problem new or has it always done that.

I would continue looking and make 100% for sure that there is no primer bulb. I've have numerous outboards including Mercury EFI's and they all had bulbs.

For full disclosure, this is the first boat I have owned so I am a rookie. Also I am extremely mechanically inclined, just not on boat outboards. I also want to say I appreciate everyones input.

There is a plastic cover about 12" in diameter on the middle of the rear swim platform. If I remove the cover, I see the fuel cap, the rubber fuel line to the outboard and the fuel level guage. I can trace the fuel line from the tank all the way to the outer case of the outboard and there is no squeeze bulb. Unless there is one under the outboard cover, I dont think there is one. Again it definitely what sounds to be an electric fuel pump under the covers of the outboard.

Maybe the original owner removed the bulb. Should there be a squeeze bulb?

The boat did it at the dealer and they worked on it and it did not repeat the problem upon the second test drive. The dealer is much too far away to simply return the boat and have them look at it so thats out. I might be able to work something out with them if I can determine the problem. Knowing what I know about motors, I completely agree that it looks like a fuel delivery related issue. When I go to the dock today, I am going to take an automotive fuel pressure test guage to try to get a reading assuming my guage fits the fuel rail assuming it has a fuel rail.

You should have a bulb in that line. It also functions as a check valve.

Older models;
There is a mechanical fuel pump under the cover, a round doodad bolted to the back with 3 screws in it according to the parts catalog. (my 60 has a square pump).
They have a semi clear fuel filter before you get to the pump.

A little farther along you have the vapor separator (the cast aluminum thing) and the electric high pressure pump is inside that.

Newer motors (1B366823 & Up) have a fuel supply module that uses 2 electric pumps in a self contained unit. That is oval shaped with cooling fins around the side. You can replace the parts inside but they may try to sell you the whole thing $$$$$ YIKES. ($800)

The pumps are about $200 each so try to figure out which one is really the bad one.

http://www.boats.net/parts/search/Merc2 ... parts.html

My boat also came with no primer bulb from dealer. I was told by service manager that this motor didn't need one. I added one a short time after buying boat and motor ran like crap. It cost me about 400 rpm. Took bulb back off and motor has run fine ever since. Don't ask me, I don't understand it either...

I visually checked all the fuel lines and saw no issue. I did find the fuel pressure test valve but my guage wont fit it so I still dont have a valid pressure reading to work with.

Motor is now doing something else bad now. It starts up and idles fine to the no wake buoys just fine but after a minute or two running like a champ at wide open throttle, it just bogs down and becomes unresponsive and wont rev over 3K RPM. I can also hear it spitting and sputtering a bit. Its the same bog down condition like what I get after restarting it after a 30 minutes or so once its parked in the lake.

So to summarize, the motor is bogging down horribly after a minute or so at WOT after leaving the dock and it bogs down when trying to retart it after being parked in the lake. It starts great and idles fine. Also it definitely does not have a primer bulb and the dealer says it did not come with one.

I am in the process of running the tank out and getting new gas in it from my local dock. I have no idea what condition the gas in there now is since we just took ownership of it last week. Still feels like a fuel delivery problem to me so i will continue to try to find a pressure guage that fits.

Sure sounds like the fuel pump to me. I had a bad one and so did my neighbor. What I ended up doing was taking out the valve stem on that test port and hose clamping a pressure gauge in there on a short piece of 5/16 fuel line.
I tucked it under another hose so the cover would go on and it is still there.

This nailed the problem. Working, it was over 38PSI, failing it was 5 or less.
The new pump was rock steady at 44

Is the fuel pump a pretty intuitive install and can it be done in the water? Is it simply a small pumping motor being replaced or a larger assembly? Again I am very good with the tools but I need to learn outboards.

I just talked to my dealer and they are thinking it is a issue with the VST tank. I am not real sure exactly how the thing works but it sounds like I might need to learn. Anyone have any first hand experience with the VST issue?

I also learned that my motor has warranty till June 2013 but I need to have the warranty transferred over from the old owner. Thats terrific news and I will plan on taking them the boat after the seaon winds down.

My boat was rigged out with a fuel line with primer bulb. I had some hot start problems. Took it to a different shop for some warranty work and they removed the fuel line/ bulb and replaced it with a one piece line. Starting problems solved. They indicated that it was not supposed to have a primer bulb.

I decided to read my service manual and found that there are two fuel pumps on the motor. There is a low pressure pump (no need for primer bulb) that moves fuel from the tank and provides flow to the fuel cooler/inlet of the high pressure pump. The high pressure pump provides correct pressure/flow to the injectors. This is similar to a modern automotive fuel system. When the key is turned to on the low pressure pump will run until the fuel system has pressure and it will cut off. It will turn back on a run as the high pressure pump draws on the fuel system. I usually turn the key to run for about ten seconds before starting the motor. Works every time.

Not sure about the other problem as the bulb in my system did not cost any HP that I was aware of. I would suggest that you order a service manual from Mercury if you are going to even think about working on this motor.

Hope you get the warranty and most of all hope you get it fixed.