Issues with Starting my 7.4L MPI

Pellwm

Cadet
Joined
Sep 25, 2011
Messages
11
I have a 7.4L MPI Mercruiser Bravo 3, Runs great when its running. I bought the boat off of a friend after it had been sitting around for almost 2 years, out of water and not getting any use. Properly winterized and everything as the family was trying to sell.

A little background with the engine while in my possession:
Put two new batteries in it and after the two years I was surprised to find it run perfect. Filled it up with gas and ran fuel treatment through it, changed the oil and put a new oil filter on it. Didn't have any problems for about 5 runs on it and then it died. Came to a slow stop and then died. Found out the problem was it wasn't getting gas to the engine due to a clog.

At this point I changed the fuel/water separator filter and removed the fuel pump/cool fuel system where we found the real problem. While removing the hoses to the cool fuel there were rubber chunks piling up inside, AKA the impeller. Just to be safe we tested the fuel pump and it worked, thank god. After getting the pieces out and rehooking up the entire fuel pump system I could again hear the fuel pump working which was a relief. From here I changed the impeller, put a new housing on it and a new serpentine belt as the one prior was tearing. Even had a mechanic come and look it over because I was taking it out for the WEBN Fireworks and I just wanted to make sure I wouldn't die in the middle of the river again, and he stated "it sounds excellent and ill get good service out of it", and i was a believer. The boat was running better, sounded smoother, and I felt great.

Took it out to the Fireworks for the weekend, everything was going great ran through about a tank and a half before the weekend/fireworks were over between playing around and restarting to charge the batteries during the day. Get on the path of heading back to the dock and half way back it dies out the same way as before. And just to clarify on it, the boat slowly dies off, as in the gas is being bled dry in the lines... which in reality is what the problem is. So the boat will start and Last about 15 seconds before dying and then start again for about half and then just wont turn over as the fuel line has now completely bled out. I get towed back and unfortunately have to head home and leave for vacation the next morning so I cant work on it for the next two weeks.

My buddies look at it, finally get it to run but again it dies. Try again a couple days later and the same thing. I am now home and yesterday I popped off the water hoses to the cool fuel system and wouldn't you know it starts right up and runs without problem, maybe took it 10 miles, stopped to eat, got back in and started right up and I thought maybe there was something in it again and it fell out or cleared out. Tried starting it this morning and it wouldn't turn over. I popped the hoses off again and it turned over for a second but then shut off and wouldn't turn over after that. I check the fuel pressure regulator located on the top, kinda looks like the piece you pump air into on a bike/car tire, and its funny because it won't bleed out any gas for a bit which is how i know its not getting any gas and the main reason behind the starting failures plus the fuel pump doesn't come on (which I believe is the ECM detecting an issue and shutting it off) but each time I pop off the hoses, drain the water and put them back on the fuel pump can be heard and the fuel pressure regulator spits out gas when I press on it.

Now I know gas is getting back into the lines, turn the key and it starts right up. Ran it for about 20 miles, stopped to eat and when i came back it started up initially but then died. I repeated all the steps of removing the hoses from the thermostat and the pump, basically anywhere water was running, draining the water, and it started up after a bit of tinkering around with it and ran well all the way back to the dock. Cleaned it off and went to start, wasn't surprised to find it wouldn't turn over again. Runs perfect while running, no RPM shifts, no lack of power, I just don't understand why I have to continue the removal of hoses in order for it start. Maybe there were pieces of the impeller that went further into the engine than the clog I found first time around and they are creating a problem. The obvious thing would seem that it has something to do with the hoses/something with the water flow since time and time again it has done the job but short term, I need a long term solution. Anyone have any advice or ideas before I just have a mechanic look it over.

Thank you very much for reading and I appreciate any advice in advance.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,241
Re: Issues with Starting my 7.4L MPI

Ayuh,... Welcome Aboard,...

Ever heard of a Paragraph,..??
I can't even read yer word soup....
 

Pellwm

Cadet
Joined
Sep 25, 2011
Messages
11
Re: Issues with Starting my 7.4L MPI

Well on account that it was 2 in the morning the last thing I was worried about was grammar, but it wont let me tab off paragraphs so ill just split it up for ya. Even though grammar wasn't exactly the answer to my boat problems lol but maybe it will be more legible now and someone can give me boat related advice, sorry about that
 

Pete104

Lieutenant
Joined
Apr 30, 2011
Messages
1,439
Re: Issues with Starting my 7.4L MPI

I'm surprised Bond-O didn't bust you for "no serial number"!
 

mpdive

Chief Petty Officer
Joined
Apr 23, 2011
Messages
567
Re: Issues with Starting my 7.4L MPI

When you are draining the hoses, what temp is the water when your draining it out? Cold, warm, hot? Is there a fault light on your dash lit up? I'm just going on a hunch that your coolant sensor may have went bad or is failing. If it has failed voltage wise reading hot engine, fuel supply would be minimal on startup. Draining the water and exposing the sensor to ambient air may be sending the signal to the ecm of cold engine and thus a cold start enrichment would be enacted. Don has some manuals in the sticky to check the sensor for proper voltage signals.
 

Pellwm

Cadet
Joined
Sep 25, 2011
Messages
11
Re: Issues with Starting my 7.4L MPI

When I would come back from eating and try to start the water was def hot, steam could visibly be seen. But at the initial start ups for the day the water is cool. There is no fault light that i can see, I always get the two warning beeps when I turn the key to middle position, let those stop and then start, but that's how its always been since I knew and rode around with the prior owner. I spoke with a mechanic and he thinks I may have a bad valve/my engine model may not have one at all, somewhere that allows the hot water to drain back into my cool fuel, which as your saying could lead to the faulty readings or even a faulty sensor. Ill check into this more, thank you.
 

mpdive

Chief Petty Officer
Joined
Apr 23, 2011
Messages
567
Re: Issues with Starting my 7.4L MPI

When I would come back from eating and try to start the water was def hot, steam could visibly be seen. But at the initial start ups for the day the water is cool. There is no fault light that i can see, I always get the two warning beeps when I turn the key to middle position, let those stop and then start, but that's how its always been since I knew and rode around with the prior owner. I spoke with a mechanic and he thinks I may have a bad valve/my engine model may not have one at all, somewhere that allows the hot water to drain back into my cool fuel, which as your saying could lead to the faulty readings or even a faulty sensor. Ill check into this more, thank you.

You can follow the flow chart for testing the CTS. Very straightforward.
 
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