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I have a 1995 Mercruiser 5.7 throttle body EFI. We have

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Hi, I have a...
Hi, I have a 1995 Mercruiser 5.7 throttle body EFI. We have an ongoing problem with the gas/fuel. Here's what it does. Boat can idle in driveway for hours on end just fine, when we put the boat in the water it runs like a brand new boat unless we turn it off for awhile then it doesn't want to start back up until it sits floating in the water for about an hour or more. Sometimes it will never start back up and it has been known to just die and leave us floating while running down the lake. Now, we have replaced the valve at the fuel tank, replaced the coil, spark plugs, plug wires. Boat is nearly empty now as we tried to get any old gas out. Water bubbles/condensation around throttle body. We have also the water separator about 4 or five times. Disconnected fuel line yesterday and it appears to be wide open from tank to fuel pump. Like I said this boat runs like a brand new one and then just doesn't! I'm ready to let it go at the top of the boat launch and let it sink-can't go through another summer floating and being towed! Thanks in Advance for your help!
Submitted: 2 years ago.Category: Boat
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Answered in 4 minutes by:
5/31/2015
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 17,051
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hello my name is ***** ***** am I speaking with?
The engine is loosing either fuel pressure or loosing spark. What needs to happen is the boat has to go out on to the water, the problem needs to be duplicated. And then spark and fuel pressure needs to be checked to see which one the engine is loosing. Once you figure out which it is loosing, then you can work on a why. Is that something you are able to do?
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Customer reply replied 2 years ago
It must be fuel as when we are in the water we can spray ether into the throttle body and it hits
Customer reply replied 2 years ago
this is Karen by the way, but my husband is here too in case I describe something wrong! it has the two fuel pumps and neither have been replaced but the electric pump is pumping and the manual pump does pump when it gets gas
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Hi Karen. The engine is more than likely vapor locking. Have you ever hear that term before?
Also, have you tried to restart it with the throttle handle in neutral, and in the full forward position?
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Customer reply replied 2 years ago
yes, I have heard of vapor locking. There is air when we crack the lines at the vapor separator tank.yes, we have tried to restart it with the throttle handle in neutral and in full forward.
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Do you have the serial number handy on the engine?
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Customer reply replied 2 years ago
just a second
Customer reply replied 2 years ago
motor number? #428374
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Unfortunatly that is not it. The serial number will be on a metal tag mounted to the block just above the starter motor. The format of it is 1 number, 1 letter, 6 more numbers. For example, 0A123456, 1B654321 ect.
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Customer reply replied 2 years ago
be right back
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Okay.
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Customer reply replied 2 years ago
try 0F428374
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Got it, that is the number. You wrote "There is air when we crack the lines at the vapor separator tank". Are you cracking the high pressure fuel line? Do you hear a hiss when you did that?
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Customer reply replied 2 years ago
yes the high pressue fuel line, both in and out. yes we are hearing a hiss and when we turn it over it is shooting fuel out
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Got it If that is the case you are definitely vapor locking. Are you running ethanol gas, same stuff as the car, or are you running a non ethanol fuel?
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Customer reply replied 2 years ago
running ethanol gas....tried a non ethanol fuel at a marina and I believe got lots of water that day....that's the day we rode it for 4 hours and stopped to swim a minute and it never started again.
do we need to try all non ethanol fuel and fill it up with that? (from somewhere besides the local marina)
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
You are getting vapor lock, that is happening. Vapor lock is boiling gasoline. Part of the deal here is ethanol fuel has a lower boiling point, and ethanol free fuel has a higher boiling point. So if you run ethanol free fuel you have a less likely chance of vapor lock happening. Does that make sense? Also, when was the last time the vapor separator was removed from the engine and cleaned, and the filters inside of it changed?
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Customer reply replied 2 years ago
we have always hear that an EFI can't vapor lock. anyway, the vapor separator was removed and cleaned, torn completely apart and filters were perfectly clean just mid last summer. I will try the non ethanol fuel and get back with you
Customer reply replied 2 years ago
someone even had us put clothes pins on fuel lines to vent the heat out....it worked fine on a cool day but when it was hot we continued to have same issue
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
we have always hear that an EFI can't vapor lock
EFI with the fuel pump in the tank, and the tank located far away from the engine where there is no heat (IE just like a car is built) can still vapor lock. However, it clears a lot faster because the gas in the tank is cool, an any vapors in the lines get purged by the incoming fuel when the fuel pump kicks on and pushes that cool fuel towards the engine. So even brand new fuel injected cars still vapor lock. But you never really notice it because it clears so quickly. But on this engine here you have a vapor tank, which is full of fuel, which sits right next to a hot engine. So that fuel is not cool like it is in a car, it is hot. And it boils. If the fuel in the vapor tank is boiling, there is no fuel for the fuel pump to push towards the throttle body. Those vapors need to cool and condense back into liquid fuel first. There is more to this, but before I go further does that part make sense?
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Customer reply replied 2 years ago
yes perfect sense..go ahead
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
Couple of things you want to do.
1. If it's been a while, you do want to remove and open up the vapor tank, clean it out, and change the filter inside of it.
2. Make sure the impeller and thermostat are in good shape, and that the engine is not running any hotter than it needs to be.
3. When you shut it off, run your bilge blowers in order to circulate cool air into the engine compartment. Ideally the boat should have 2 blowers. 1 should be orientated with a hose that goes down to the deepest part of the bilge, and the blower fan should be positioned to suck vapors out. The other blower should be the opposite, and should be set up to blow fresh air in. The ducting on this hose can point anywhere, but if you are still having problems have it aim toward the vapor tank. When you shut off run the blowers for a good 10 minutes.
4. Run non ethanol fuel.
5. Lastly if you do all of the above and it still gives you problems. Cycle the key from off to run and back a few times. Waiting about 5 seconds with the key in the on position. What you are doing here is cycling the pump and trying to get it to build up peak pressure before you turn the key.
I do want to make sure you are happy with the service I am providing to you before you go. Did you have any other questions on the issue or do you think that covers it? --Jason
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Customer reply replied 2 years ago
I am going to try these things and get back with you if we continue to have issues if that's ok. Thanks for your help as
my frustration level is off the charts and I dread every trip out on the water!
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
You are most welcome and I was glad I could help.
Just incase you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. Please let me know if you run into any problems or errors when trying to do it. If you can not see the ratings box, please reply back "I rate Jasons service as _______" and fill the blank with whatever you deem most appropriate. Questions do not lose out, so if you have to come back tomorrow or next with follow up questions to this you still can even after doing a rating. Tips are always greatly appreciated.
If I do not hear back from you I thank you in advance and good luck!
Jason
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Customer reply replied 2 years ago
I rated your help and will get back after I try your suggestions. thanks very much
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
You are very welcome but it doesn't look like a rating went through. Can you try it again, or just reply back in words how you would like to do a rating.
Thanks,
Jason
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Customer reply replied 2 years ago
looked at the blowers..it has 4 hoses and only 1 appears to be blowing lightly and the other 3 are just vent hoses? they are doing NOTHING I guess.....didn't you say 2 should blow and 2 should suck hot air out? do we need another blower motor? or do like some have suggested and just get a 12 volt fan and hook to battery and let it blow on fuel lines?
Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
You should have 2 blower motors. Each motor has 1 hose on it for a total of 2 hoses per blower.
Click this link to pull up a picture.
http://i.imgur.com/3sHoXio.jpg
The exhaust "blower" is really a "sucker", and that should be installed so that it sucks fumes out from underneath the engine. (Gas fumes sink)
The intake blower is designed to blow fresh cooler air in.
On sterndrives when you shut the engine off all of that heat just stays in the engine compartment. So you want to use the blowers to ventilate the inside of the engine compartment and cool it down. It is the heat that makes the fuel boil, an cause the vapor lock.
After looking at the picture does that make sense as to how it should be set up?
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Marine Mechanic: Jason, Marine Mechanic replied 2 years ago
It looks like you read my reply and logged off. Just a quick question for you. You said that you rated my help but no rating came through on my end. Did you select the start and then confirm it, or just select the star?
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Experience: Degree in Marine Technology. Gas and diesel marine mechanic.

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