1995 50 efi loses power and hole shot

"I have a 1995 5.0 efi. The bo

"I have a 1995 5.0 efi. The boat starts and runs fine until it warms up (approx 10 min). After it gets warm, I lose the hole shot and top end. On the top end I lose 500 rpm and 7 mph. In reading other posts, someone mentioned that engine box temperature may effect the fuel pumps. Does this sound like the issue? What can I check myself without taking it into the shop?"

"Check your fuel pressure and

"Check your fuel pressure and clean your flame arrestor. If these don't help, you'll at least know if they're OK since these are the most common reasons for power loss I see. While you check the fuel pressure, take a fuel sample and see if you have water in the gas.

If you can prop the motor box open a bit and turn the bilge blower on, it's going to be a lot cooler and if this matters, you'll know pretty fast. How old is your impeller? Do you have an oil cooler on the boat? I would check it for weeds- small pieces can become lodged and block off the raw water flow. If you killed an impeller in the past, you may have pieces of that somewhere it shouldn't be, too.

What does the temperature gauge indicate? If it looks lower than normal, I would suspect an overheat since hot air won't read as high as hot water and the water jacket where the temperature sender is located may be dry. It's not the one wire sender, look on the head for a two wire sender."

"I did go through an impeller

"I did go through an impeller 2 years ago when this problem started and has gotten worse. When the boat is allowed to cool, it will go back to normal performance. Where do I check for parts of impeller that would make this happen? I was reading a tech manual that said the fuel gets cooled before going to the injector. Could the fuel be vaporizing at this point?
I had it in the shop last fall and they could not get it to fail. I would guess they were running it with the box open and it din't get too hot in there(it was also October and cool outside). They did pressure checks on the fuel system and said everything was fine. They also checked the fuel and it was clean.

The temp guage runs normal. Is it possible when the enging box heats up, a vacuum line or vent compresses or fails? (I'm not sure if there are vacuum lines anymore. I haven't worked on an engine since my 67 Camaro in high school). I will try running it with the box open this weekend and see if that helps. Thanks!"

"If your impeller is still the

"If your impeller is still there after two years, you need to change it. Running it once with no water getting in can ruin the impeller and after overheating the motor repeatedly, there's no telling how much has been damaged. IIRC, the V-P impeller is mounted like an OMC and is easily accessible (on the back of the outdrive). If it is in this position, there's absolutely no reason to ever have an old impeller.

If you have no cooling water getting in, yes, the fuel could be boiling. Do you have closed cooling on your boat? If not, you're cooking the motor every time you run it.

When it does this again, touch the exhaust manifold (briefly) and if it's too hot to touch, you probably have a blockage. You should be able to backflush the cooling system (after it cools) and see if any impeller parts come out. remove the thermostat and see if anything collected in that area, too."

"I ran the boat on a cool morn

"I ran the boat on a cool morning with the Engine box open and blower on. It did seem to help. Also, when it did fail, the manifolds were cool enough to touch and the impeller is pumping well. Is there a specific sensor I should be looking at? As I mentioned before, when it fails it is like flipping a switch. You can hear the engine bog and the RPMs go down by 400."

"If the ECM sees an overheat,

"If the ECM sees an overheat, it goes into RPM reduction and won't generally go over 2000 RPM. It does this by switching the injectors off, alternating between the two (on TBI) and between banks (on MFI). If you have TBI, look at the injectors when it starts running funky to see if they're alternating. If they are, look for the two wire engine coolant temperature sensor (ECT) and make sure it's plugged in completely. BTW, the gauge sensor has one wire and the sensor sending to the ECM has two (yellow/black)."

"I have MFI and it will go wel

"I have MFI and it will go well over 2000 rpm. Am I leaving anything else out of my descrition? You have been a great help! Someone is actually listening. "

"You said they checked the fue

"You said they checked the fuel pressure- at what speed or RPM? When I went to Mastercraft tech classes, they said we needed to check it at key ON, idle, 2000 RPM and WOT for it to be a valid test and I agree. They may have only checked it at idle and this could be part of the reason it takes a while to show up. Also, fuel pumps HATE to be run dry. If yours was and you don't know about it, the impeller in the fuel pump could be bad.

Did they scan for codes? If not, there could be some stored that should be erased. If you look for the ALDL plug on the motor (that'e where the diagnostic computer is connected), you can check the codes with a paperclip, as long as you have a check engine light on the dash. If you don't, you can use an LED test light. Let me know if you want to do this and I'll tell you how.

I wouldn't rule out loose wires, either, specifically ground wires. "