Mercury outboard help?

[A&M]

I have a '96 Mercury 150EFI that cold starts perfect and runs like new until it is warmed up and I shut it off, then it is a 50-50 shot as to whether it will start again. The longer it sits and cools down, the more likely it will restart, but generally speaking, the only way to get it to fire is to advance to half throttle in neutral and crank it like crazy until it finally sputters to a start. Once it does start it won't idle, so I have to try and fast idle it in neutral and then try to quickly slam it in gear and throttle up before it dies. After getting it going and putting it on plane for a few minutes it runs perfect and idles like new again. I've changes filters, plugs, and wires with no effect. If anyone has had a similar issue and knows how to fix it, I'd greatly appreciate that information.

 

[Mr Bya Lungshot]

Sounds fuel related to me. Fuel lines or carb issue or fuel pump.

 

[Cmp1]

I'm certainly no expert, but you could have a bad coil that is breaking down when it warms up, easy to ohm out the windings,,,,I would check that first,you changed the wires,right?

 

[Cmp1]

Other than that, probably fuel issue,,,,

I had a coil that ohmed out good cold,,,,warmed up and the windings expanded, and opened,,,,

 

[SwampMoss]

I had a coil that went bad.

 

[A&M]

It does sound fuel related, but everything between the tank and the fuel pump checks out, and the fuel pump is coming up to pressure like it should. The coil issue sounds like a possibility. Yes Cmp1, I did change the wires. I'll check to see if I have something to test the coils with.

 

[divinginn]

If it idles good and runs good at times I doubt it is the carb,sounds like electrical related.
It could be coils or other ignition parts heating up intermittently.

 

[Taco4x4]

I had the same issue with my 96 150 xr6 a few years ago. It was a switch box going bad. It would run great on your first run but you might as well fish that spot a while because it was not going anywhere till it was cooled off and ready to go. What was happening was when it got hot one of my switch boxes would stop working and that means you drop three cylinders when that happens. The switch boxes are kind of like the distributor on a older car and they control the spark. There are two of them and one controls 1,3,5 cylinders and the other controls 2,4,6 cylinders. We used a spark checker and hooked it up cold and all six were good. I run the boat and then put it on the trailer with motor still in the water and checked it again and sure enough now only three were firing. I replaced both switch boxes and problem solved. Its not hard to do. Just take a few pics before you remove any wires. Let us know if that does it or not.

 

[A&M]

Taco 4X4, thanks so much for your reply. Sounds like the exact problem I'm having. Switch boxes are not a difficult fix, I'll post back to let you know how it works out.

 

[A&M]

Update: I unhooked the battery and installed 2 new switch boxes, and the motor is worse now than it was before. So I either got a bad switch box or the underlying problem ie. stator or voltage regulator are showing up now?? After several attempts to start the motor on the hose with no luck, I advanced to half throttle in neutral and it sputtered to a surging fast idle and then quit. Tried several more times and every time it started it would require at least half throttle and it would surge, sputter, and then quit. It would not idle at neutral throttle for more than a few seconds, then quit. I've got a hunch that my voltage regulator is bad since my RPM gauge quit working a while back. I replaced the gauge and the new one didn't work either. Looking at my stator, I can see what looks like tan colored glue running down aroung the coils toward the block, and the copper coils are black in color, so maybe it got too hot and needs a replacement as well. Very frustrating.

 

[Whitefeather]

It sounds like it’s a fuel issue to me. Gummed up injectors with deteriorating fuel lines will cause you fits. I have an older one that is not EFI and it would idle but not run at WOT. The next week it would run WOT and not idle. I wound up replacing every single piece of rubber hose and pulling the tank out to clean it.
If you could run it on a gallon of fresh premixed gas with a different hose then you could eliminate the fuel issue.

 

[NE GA Pappy]

advancing the throttle doesn't change the spark, except to advance the timing a little. Sounding more and more like fuel issue

 

[A&M]

Not saying it is not fuel related since I've been down that road before, but I replaced all my fuel lines including the pickup about 2 years ago and run only ethanol free 87 octane fuel with stabile marine 360. EF 87 is recommended by Mercury as the fuel for this engine. I replaced my supply from the pickup to the fuel pump with a new pump ball about 8 months ago. If this were a fuel issue like I've had in the past, it would act up all the time not just once it is warmed up. I'm gonna put the old switch boxes back on, drop the vst tank and check for debris, then see if it will run again.

 

[A&M]

Put the old switch boxes back in and drained the vst tank to check for debris. Nothing but good clean EF87. Turned the key and it cranked right up with the old switch boxes, checked some of the voltages coming out of the rectifier and everything looked good, except my tach still doesn't work. Bigger concern is that I felt the cylinder temps with my hands by the plugs and number 6 was cool to the touch compared to the rest. Pulled the plug wire off and the engine didn't miss a beat. Checked continuity and resistance on all the wires and coils and they all checked out the same. Time to buy a compression gauge and start there. If compression is good, I may get lucky with just a bad coil. If not, crap!!!

 

[Taco4x4]

Were they new switch box's. I have always used CDI electronics on my Mercury. Ok you mentioned your Tach not working. What about your volt meter. If your voltage regulators are bad it effects the Tach by the needle jumping around or like yours not working at all. What was your volt meter putting out when it was running. Have you tried switching the signal wires on the VR's. Each VR has a grey wire but only one is used. Maybe try switching to the other grey wire and see if the Tach works.

Loose ground wire on my cranking battery cost me big a few years ago. It caused my VR's to burn up and it took the Stator with it. Look for the signs. Jumping Tach or not working at all. Volt meter not putting out what it should. The stator has a low side and a high side and it sounds like you lost the low side. Start with the battery connections then look at your VR's for sign's of overheating. Where they plug to the stator will melt when this happens. The wires burnt into on mine. Good luck with it man.

 

[Lukikus2]

The tach is the first place I would start. Had that happen on a Merc before, replaced it and it ran fine after.

 

[Taco4x4]

The tach is the first place I would start. Had that happen on a Merc before, replaced it and it ran fine after.

A&M said he replaced the Tach and still didn't work. It's either a loose ground wire or bad VR not giving a signal through the grey wire.

 

[A&M]

Thanks for the replies Taco 4X4 and Lukikus2. The switch boxes were brand new. I couldn't find any CDI's so I went with another aftermarket. The old switch boxes seem to be working fine now. Checked compression on all the cylinders and they all pumped up to 120, but while running, #6 cylinder still felt cool compared to the rest so I checked for spark and no problem there. It was running good on the hose so I took it yesterday and ran it on the lake. Overall it ran great even though I had to advance the throttle in neutral just a touch to get it to fire up any time I wanted to crank up and move. I still think that I may have a voltage regulator issue. I do have one wire coming out of the stator going to the VR that looks like it got really hot at one point, plus my tach doesn't work so I may just need to replace the VR and see what that does. If I did lose the low side of the stator, would the boat still run good?

 

[Taco4x4]

The Stator is fine. It would not run good if either side has failed. You have two VR's. You can only see half of one of them sticking up from behind the coil plate. You have to remove the plate to get to the bottom VR. The bottom one will have a grey wire that's caped off and the top one will have the grey wire plugged into the stator. Switch these two wires and I bet your Tach will work. The way your boat is running now seems like the timing just might be off a bit.

 

[A&M]

Thanks Taco4X4, I'll give that a shot. So if I switch those two grey wires and the tach works, does that mean that one of the VR's is bad?