Motor shuts off at WOT and smokes excessively while revving at idle

[btanner1962]

I have a 2000 Mercury 150XL EFI SN OT156629. I bought the boat a few months ago and ran fine, other than some vibration at lower RPM, in a test tank on the trailer, max RPM's while testing ~4500. Took to the lake went to WOT(5500-5700 RPM) ran great for about 30 minutes. Then it stalled. Started right back up. Did this the rest of the outing. The longer I was out the worse it got. Started happening at all RPMs. Compression check: 1- 115, 2- 107, 3- 115, 4-110, 5- 110, and 6- 110. Changed plugs, rebuilt fuel pump, replace full line (except primer bulb), replaced water separator filter, removed and cleaned the Vapor Separator, and cleaned electric fuel pump filter. Started with muffs and as I revved it up it smoked excessively and started running rough. Took back to the lake, ran great for ~ 30minutes, then the same old thing. stalled again as before. Noticed just before it stalled the engine revved slightly. Back to the dock, as I revved dockside, smoke excessively, then became hard to start, plugs were oil soaked. I have talked to a few people and no one seems to come up with anything to help. Any ideas would be greatly appreciated.

 

[marinepartsgrl]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

Were all of the plugs oil soaked?

 

[btanner1962]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

Yes, all plugs had oil on them, but were not soaked to a point they were fouled. It seems like at normal idle it runs for several minutes, then slowly starts running rough. When you rev up, it smokes excessively.

 

[Texasmark]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

I had a 115 tower once and had fuel delivery problems at WOT after running that way for a few minutes.....I was just using fuel faster than it could be resupplied. The fuel line was 3/8 which should have been adequate for that size engine. In the process of seeking a solution I installed an electric fuel pump between the tank and the engine. Even at the low settings (variable pressure dial on pump) like 3 psi, the engine would flood. The combination of internal fuel pump and external just didn't work.

My solution was to remove the pump and improve the routing of the fuel line which solved the problem, rather than going into the engine and bypassing that pump and all that.

HTH,
Mark

 

[gm280]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

I have a 2000 Mercury 150XL EFI SN OT156629. I bought the boat a few months ago and ran fine, other than some vibration at lower RPM, in a test tank on the trailer, max RPM's while testing ~4500. Took to the lake went to WOT(5500-5700 RPM) ran great for about 30 minutes. Then it stalled. Started right back up. Did this the rest of the outing. The longer I was out the worse it got. Started happening at all RPMs. Compression check: 1- 115, 2- 107, 3- 115, 4-110, 5- 110, and 6- 110. Changed plugs, rebuilt fuel pump, replace full line (except primer bulb), replaced water separator filter, removed and cleaned the Vapor Separator, and cleaned electric fuel pump filter. Started with muffs and as I revved it up it smoked excessively and started running rough. Took back to the lake, ran great for ~ 30minutes, then the same old thing. stalled again as before. Noticed just before it stalled the engine revved slightly. Back to the dock, as I revved dockside, smoke excessively, then became hard to start, plugs were oil soaked. I have talked to a few people and no one seems to come up with anything to help. Any ideas would be greatly appreciated.

I'm obviously not an Einstein on these engines, but it surely sounds like a fuel issue. And that fuel issue seems to be too much fuel then the engine can use at any RPM. So I'd check the injectors to see if one or more are stuck in the open position. That would account for the excessive smoking and then shutting off AND the hard restart too. I don't know how your engine is built or the injectors are installed but I do think those are your problem... And engine that smokes excessively is a too much fuel problem. But that is just my opinion...

 

[CharlieB]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

EFI is a whole different creature. Something simple like a temp sensor failing can make the computer 'think' the engine is cold and add fuel.

You need the correct factory service manual. Don't bother with any of the aftermarket manuals, they leave out way too much detail, and it those details that make all the difference in troubleshooting and testing to determine the problem correctly.

One of the other guys has quick reference to which manual you need and hopefully will post that soon.

Do NOT assume anything and buy any electrical parts as there is NO RETURN on electrical parts. Which is another reason for the correct factory manual, how to test to prove a part good/bad before spending the money for something that may not help you.

 

[btanner1962]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

The smoke is black, so appears to be oil, my thought was too much oil. I agree, it does appear to be a fuel related problem. I will pull the injectors and get them cleaned.

I have a manual, but not sure if it a good shop manual or not, some help on a good manual would be appreciated.

 

[CharlieB]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

Does your manual have the test for the engine test sensor. Remove it, test Ohms at room temp, then heat in a pot of water to @ 150 F and test again. If the value does not fall within the range specified in the service manual then the ECU 'think' the motor is 'cold' and adds fuel as it a choke is on.

Again, never assume any part is defective without testing and proving the values are not as stated in the service manual.

 

[btanner1962]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

CharlieB,

I assume you are talking about the temperature sensor. Yes it does have the test for that along with a few others than I also plan on doing. I was hoping this would be a quick easy inexpensive problem and fix, but I am finding out it is worse than expected. Hopefully something will show up so I can get this resolved. I have seen similar post but none with the solution. If I find the problem I will definitely post what I have found. Thanks

 

[btanner1962]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

Update...While performing the fuel pressure test on the electric fuel pump, I noticed that the trigger wires at the connector were brittle and falling apart. Along with the outer covering of the wires, the wire itself was corroded and barely together. I knew at a minimum I needed to replace the trigger. I got the part in and replaced the trigger and thought this was the problem. I started the engine and it ran great, no smoke, seemed to idle fine. The longer I ran it the worse it got though. It would idle great but if accelerated it would run rough and start smoking again. I disconnected spark plug wires and it actually ran with 2 wires connected (3 and 4). Took it to the lake and for the 1st hour it ran great, then it started dying again. So from seeing what it is doing it seems like I may have stuck open fuel injectors. Any help would on this would be great. Thanks

 

[Texasmark]

Re: Motor shuts off at WOT and smokes excessively while revving at idle

Geez, I should pay more attention. Here is another EFI problem I missed noting the EFI. Sorry.

I joined this forum back in '04 as I recall. I learned of a "Snake Oil" (sarcastic term from a farm site) here by the name of Sea Foam. The archives of this site contain instructions of a process ID'd as "Decarb" which can help those with severe problems using Sea Foam.

I have since experimented with it and today I use it in all my equipment be it 2 or 4 stroke, gas, or diesel, marine, farm, or road. I have 3 diesel tractors and they obviously have injectors. I keep a fuel cleaner in the fuel to keep them clean. I also have Multi Port Injection in my gas truck where I also have a fuel cleaner. I use Sea Foam in all and in the diesels I add some diesel specific cleaner.

Food for thought.

HTH,
Mark