5.0 MPI problems

Last Dollar

Active Member
May 10, 2011
244
Huntington WV boating the Ohio River and lakes in
Boat Info
Sea Ray 225
Engines
5.0 Mercruiser
Had trouble getting the engine to run yesterday a couple of times. It happens after I run for a while and shut it down. When I restart it acts like it will barely run and eventually quits. It always restarts quickly but no matter where I put the throttle it seems to act like it's starving for fuel, will not rev and then quits. After several attempts it eventually starts to run better and then acts normal. I put a fuel pressure gauge on the rail today and it shows 35/40 lbs continuously. I did not have the gauge with me yesterday when it was acting up so I don't know if it had fuel pressure issues at the time. I'm wondering if there is a pressure sensor issue or some other electronic sensor that is intermittently failing.
 
What year engine? Some of the early 5.0l need to have a booster pump and check valve installed to address vapor lock.
 
A bad fuel pressure regulator can also cause hard hot restarts
 
A bad fuel pressure regulator can also cause hard hot restarts
From looking at online parts diagrams there are two fuel pressure regulators on this 2003 5.0 serial # OM626769. Neither of these are cheap but just wonder which one is the likely trouble maker. One is on top of the intake manifold and the other is on the port side of the engine inside the case that has the fuel pump. Of course one is very easy to see, the other is going to be a lot harder to have access to.
 
I have two of the same engine. My serial numbers are similar so I have the mercruiser parts diagram bookmarked for this engine. Whenever I need something I'm always amazed at the marine markup. This is one of those cases where it's just a GM part that costs between $20 - $60 (high end for OEM) at an auto parts store. Yes people will tell you to always buy the Mercruiser part, but for almost $400 but that's your call. I was referring to the round one on top of the fuel rail between the injectors. Tons of 90s/2000s GMs have these.
 
... the other is on the port side of the engine inside the case that has the fuel pump.

Do you have the fuel cooler? I don't have it on mine -- just the exposed fuel pump above the fuel/water separator.
 
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My 2003 6.2L was having similar problems, it ended up being the fuel pump. Merc is only providing the pump, cooler and regulator as a unit called Cool Fuel 2 (CF2). My mechanic had to pull the motor off the mount to get access. Hopefully your boat has better access.
 
That regulator on the fuel rail doesn’t do anything in the marine application. The regulator on the pump is the one that controls fuel pressure.
 
I'm having the same fuel problems. It turns out the paint is flaking off inside the Cool Fuel Assembly and clogging the filters and fuel injectors. Mercury knows about this problem and is covering the repairs under a recall but there are no parts available currently. My mechanic(Mercruiser dealer) is working with Mercury to resolve and so far Mercury is paying for the repairs.
 
Last Dollar, it’s likely that you have a CF2 fuel pump and vapor lock booster pump. The Cool Fuel 3 (CF3) came out in 2005, and has the paint flake issue that Brite referenced.

it’s a difficult problem to diagnose because the booster pump covers up deficiencies in the main CF2 pump when you are in neutral. My boat ran fine at the shop, but terrible at the lake. My mechanic had to put mine on the dyno to put a load on it to get the fuel pressure to drop. It was solid 40 psi in neutral, but dropped to 20 under load.
 
Update on my problem. I bought a fuel pressure test gauge and hooked it to the port on the engine. Fuel pressure initializes to a little over 40 lbs and then drops back to 35. Engine running it holds around 33 lbs. This problem has not shown up again since that one day on the first weekend out for the season. I shall keep the test gauge in the boat so if it does happen I can test pressure immediately. It ran fine all day this past weekend. We ran 54 miles on the river with repeated stops and restarts all day with no issues. All hot restarts were very good. Engine had plenty of smooth power while underway.
 
It shouldn't be running at 33 lbs., this will cause a lean condition that will eventually bite you in the ass.
 

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