7.4L MPI Engine turns over but immediately stalls

[zavalanche71]

Re: 7.4L MPI Engine turns over but immediately stalls

Waterone1, is there a website that I can find this service bulletin? I cannot find a place on the mercruiser website with any service bulletins. I have a Clymer service manual but if you think I need a mercrusier service manual, I will order one. I do not believe the fuel pump was ever replaced. I bought this boat from a dealer with 18 demo hours on it. I have had it for about 5 years and only have 90 hours now. <br /><br />What is the best way to check the lines from the tank to the fuel pump? In this configuration the line comes from the tank to the fuel filter/water separator (located in a plastic 2piece case) and then goes under the engine from the left side to the lower right side and the fuel pump is in a casing far low on the right hand side. I believe the engine needs to be pulled in order to service the fuel pump. Do you have any suggestions for testing the line?<br /><br />Meanwhile, I ran the boat for about an hour yesterday. It ran fine, temperature never went above 160 +/-5 degrees. Again, this is just like how it performed before when after a few more hours I ran into a problem. <br /><br />Since I do not see any gasoline glaze on the little water by my bilge, so I assume if there is a pinhole it must be before the fuel pump.<br /><br />Could a bad IAC or pressure regulator allow air into the fuel rail?<br /><br />Newport Dave, I am located in Michigan, so it is not extremely hot weather here. I agree somehow the air is getting in the fuel rail. Nothing has been taken off the engine, so I assume the heat shields are there. As I mention above, the fuel filter/water separator is located in a 2 piece plastic casing. Any other ideas on how potential vapor lock can be found in the rail?

 

[newport dave]

Re: 7.4L MPI Engine turns over but immediately stalls

z71,<br />If your 7.4L MPI is betweeen these serial numbers; 0L362686 to 0L373270, then the Merc service bulletin 99-08 would apply.<br /><br />If both heatshields are in place and your weather is not unusually hot, you probably don't have a vapor lock condition. Could the fuel you are using be a winter formula (easier to vapor lock)?<br /><br />The IAC valve and/or fuel pressure regulator are not likely to cause your problem.<br /><br />At this point, you might try monitoring (with voltmeter) the fuel pump circuit to make sure that the fuel pump is not losing power just before the problem occurs (which could indicate bad fuel pump relay or oil pressure switch).<br /><br />Dave

 

[tommays]

Re: 7.4L MPI Engine turns over but immediately stalls

http://www.boatfix.com/merc/Bullet/sbcover.pdf <br /><br />read away<br /><br />tommays

 

[bigbrownbuku]

Re: 7.4L MPI Engine turns over but immediately stalls

i had a very similar problem this summer in a boat with twins of the same engine(only 1 would vapour lock), a lot of troubleshooting later i accidently fixed the problem. if you have a vapor lock problem and it sounds like you do this board isnt going to help. you need to find an expierienced tech that can get hands on on your engine.

 

[muc]

Re: 7.4L MPI Engine turns over but immediately stalls

Might want to buy a 3/8” to 3/8” hose barb connecter and 18” of 3/8” clear hose, remove the fuel line at the water separator and install the clear hose --- look for air bubbles when your running engine. One of the problems with the cool fuel system is that once air gets in it the only place it can get out is thru the injectors and they seem to have a bit of trouble doing that. Good Luke Muc

 

[rodbolt]

Re: 7.4L MPI Engine turns over but immediately stalls

in my area with seawater temps in the 80's and ambient air temps in the 90's we have had some issues with the cool fuel setup. only 2 that I can think of. be careful playing with tubing as sometimes the sction side will become pressurized by the return fuel. next time it happens feel the fuel filter. if its abnormally warm you may have one of the few. volvo and marine power use a seawater cooled vapor seperator. the cool fuel setup allows the filter assy to be the vapor seperator. the marine power G-force set up allows either a return to the tank method of cooling just like a car or a seawater cooling setup in the return fuel line. volvo just runs seawater around the fuel in the VST. merc had a better idea. yes there are a few that engine removal is about the only method of changing the fuel pump. I would eliminate any other source before replacing the pump.

 

[waterone1@aol.com]

Re: 7.4L MPI Engine turns over but immediately stalls

If it comes down to the fuel pump, in most cases it can be done without pulling the engine. The last one I did was in a cramped engine compartment with twin 454 mag inboards, and a genset. If you have a single engine, this should not be too hard to get to. Some folks will gasp or balk at this, but I did not follow the factory proceedure of removing the fuel rail (and all of the injectors). I just removed the two lines going to the fuel/water seperator and dissconnected the two raw water lines going to the cool fuel unit, then removed the mounting bolts and slid the unit out(with the line still attached to the fuel rail and injectors). You can then replace the pump and re-install it. In my opinion this was much better than removing the throttle body,intake plenum, fuel rail and all of that fun stuff. Do what you feel comfortable with.