Mercruiser 7.4L MPI Fuel Pressure Issue

I have a 1998 7.4L MPI Mercruiser. It recently started having issues with starting after it's been running for a while. It starts fine the first time and runs like a champ. After stopping, often it will not start again. I put a fuel pressure gauge on it and noticed that when it starts (the first time) the pressure is about 32psi. After stopping it and then attempting to restart, there is no pressure. I disconnected the fuel pump and checked the voltage at the pump when I turn the key... seemed to be fine so I assumed it was a fuel pump issue so I replaced the fuel pump. Got it all back together, started it a few times and it seemed to work. Took it out on the lake and it ran like a champ. Stopped it for a swim and the problem came back (i've learned to just leave the fuel pressure gauge on it so I can watch what's happening). Anyone have any ideas? I'm wondering if it's a fuel pressure regulator issue? When I swapped the pump I put the old one back on... thinking I should have replaced it too.
Thanks for the help.

Re: Mercruiser 7.4L MPI Fuel Pressure Issue

most likely your fuel pressure regulator,,,
whe the fuel pressure regulator goes bad, it is worse when hot and after a short time of sitting then trying to start.
when it is cold, a bit better since the engine needs more fuel.

Re: Mercruiser 7.4L MPI Fuel Pressure Issue

Ayuh,... You have checked,+ changed the fuel Filters,..?? Right,..??

Re: Mercruiser 7.4L MPI Fuel Pressure Issue

remling said:

I have a 1998 7.4L MPI Mercruiser. It recently started having issues with starting after it's been running for a while. It starts fine the first time and runs like a champ. After stopping, often it will not start again. I put a fuel pressure gauge on it and noticed that when it starts (the first time) the pressure is about 32psi. After stopping it and then attempting to restart, there is no pressure. I disconnected the fuel pump and checked the voltage at the pump when I turn the key... seemed to be fine so I assumed it was a fuel pump issue so I replaced the fuel pump. Got it all back together, started it a few times and it seemed to work. Took it out on the lake and it ran like a champ. Stopped it for a swim and the problem came back (i've learned to just leave the fuel pressure gauge on it so I can watch what's happening). Anyone have any ideas? I'm wondering if it's a fuel pressure regulator issue? When I swapped the pump I put the old one back on... thinking I should have replaced it too.
Thanks for the help.

Click to expand...

Hi.
I have 2000 7.4L MPI, having exactly the same problem you describe. Have not solved it yet.
Check out the service bulletin "MCSB 98-04", at www.marinemechanic.com/site/page19.html.

Re: Mercruiser 7.4L MPI Fuel Pressure Issue

Hello,

I unfortunately have the same problem over the past 4 years on my 1999 Chapparal with a 7.4L MPI engine. I have also been very frustrated. My engine only has 135 hrs. since I do not feel comfortable taking the boat out very often. I agree, when I take the boat out it runs great. Then after driving around the lake a bit, we go to the sand bar for about 4-5 hrs. When I start the boat, it starts for about 20-30 seconds and then cuts off. I hook up a fuel gauge to the schrader valve and notice no fuel pressure even though I can hear the fuel pump cycle on. I drain off the fuel and see a lot of air in the line. It usually takes about 20-30 minutes of just turning the key and turn off (cycling the fuel pump) and priming off the air bubbles. Then all of a sudden the fuel pressure raises to 32-37 psi and the engine starts. It runs great after that till I turn if off again.

If anyone know's what is causing this problem, I too would be very interested. It is costly to pull the engine to get to the fuel pump if that is not the issue.

Thanks,

Jeff

Re: Mercruiser 7.4L MPI Fuel Pressure Issue

I am currently having the same problem with my 99 Nordic. It too has a 7.4 Mercrusier. This past weekend, the boat would start fine when cold, but not start again once it was hot. What did you do to solve the problem or have you? I don,t want to start buying parts without a plan. A mechanic friend told me it was possibly the fuel pressure regulator. I would appreciate any help. The boat has been reliable up to now.... Thanks!

I have a 7.4l MPI in my 2000 Bayliner. I am having the same issue. The boat ran great for two seasons after I bought it (used). The tank always get's topped off with no ethanol unleaded. This year we took it out and ran it for a couple of hours and all was fine. I shut it off for about an hour and then it wouldn't start back up.

The seawater pump is new, and the engine temperature never goes over 175 F. I took it in and my mechanic tested the pump and replaced it. I also changed the water seperator filter.

I took it back out and all went well all day long of pulling tubes and skiers- no problem. Many startups and no issues. Later in the day we drove a short distance to do some swimming. When we went to leave the motor fired right up and upon acceleration it died and would not start. I noticed it back firing. I tried WOT- nothing. I pumped the throttle very fast while cranking at it would almost start. We towed it back in..

Next morning it fired right up.

My plan is to monitor the shrader valve on the fule rail and note the pressure. Anyone with a suggestion or solution? It seems a lot of folks are having this issue.

Hello,

It's been almost 4 years since my last post. I did create a solution but never found a root cause. I did not want to pull the engine on a boat that has about 175 hours. I do not use the boat a lot other than to tour the lake and then hang out at the sand bar. I spoke with Mercruiser experts directly and they could not even help me on this issue.

Since the issue was basically that the fuel line acquired air once sitting, I disconnected the line from the tank to the gas/water separator and put a hand primer pump (basically found on pontoon boats) in-line and reconnected to the gas/water separator. After sitting at the sand bar, I would prime the gas line. I can definitely feel that the line needs priming after sitting. Once primed, the engine starts like a gem and runs normally. No fuel pump issue and I did not want to burn out my fuel pump trying to figure out what is wrong with this lousy design. Mercruiser experts could not even help me on this issue.

I am not sure if it is the fuel regulator but the design is so bad on my boat that you must pull the engine to check the fuel pump and fuel cooling system. I am living this way till one day a solution is found or I need to pull the engine for some reason.

This is a very old thread, and while you are one of the original posters by the rules it can only be opened back up the original poster. If your still having the problem start another thread. BTW I see the issue as vapor lock