Crusader 5.7 MPI stumbles after 1 hour run

[RyDrew]

Hi all, new owner of a 2004 Carver 360 Mariner with twin 5.7 MPI's.
Sea trial no problem. First hour and a half of drive home after purchase was perfect at 3,600 rpm. Both fuel tanks registered at 1/4 tank (125 gal each). At this point the starboard engine started stumbling badly and revs dropped way down. The captain thought that maybe the gage was incorrect and we were running out of fuel so we stumbled in on the port engine to get gas. Put in 60 gallons each tank and the gages both went back up to over 3/4. Started right up and we continued the voyage. Ran great again so we assumed problem solved. Ran another hour and the same thing happened. At this point we were only a few miles from home and we knew we had fuel so he dropped the throttle way down on starboard and ran 80% on port engine. After a couple more miles and nearing home port, the starboard engine started running smooth again. We ran the rest of the way at a reduced speed and got into port nicely.

Note: new fuel pumps and fuel coolers installed this past winter by P.O. Only about five hours this season.

I read through a lot of posts here and have seen several similar issues pointing to several solutions. What I'd like to hear opinions on is the best sequence to start the trouble shooting process. Possible ideas from what I've seen here and elsewhere:

1. Fuel Polish
2. Large particle filter/water seperator
3. Small particle filter before pump
4. Anti-siphon valve (not sure if I have one)
5. Fuel Vent tube
6. Fuel pressure
7. Something else?

Thanks.
RyDrew

[bud37]

Question....how was the sea state, smooth or rough, with a lot of rocking side to side for example.

[km1125]

Source of the post Hi all, new owner of a 2004 Carver 360 Mariner with twin 5.7 MPI's.
...
4. Anti-siphon valve (not sure if I have one)
...

You should actually have at least two, if it's a gasoline-powered inboard vessel (I'm sure yours does, that's for the benefit of other readers).

They would be mounted right at the fuel tank, where the feed to the engine connects. Looks like an oversized hose barb fitting. You can take them off and clean them, but new ones are relatively inexpensive so a lot of folks just get replacements and swap them with new (you can always clean the old ones and put them in your 'spares' box). Just make sure you get the correct size of threads and hose barb.

[Viper]

Certainly consider the anti-siphon valves, also, if you have Oberg fuel filters (black hockey puck shaped) chances are they haven't been serviced regularly if at all. When facing the front of the engine, they are typically low on the right side close to the back of the engine. If you have these, the screens should be checked and cleaned or replaced. Even if this doesn't solve the problem, at least you can record when they've been serviced for future reference.

[RyDrew]

Thank you Viper and KM1125. I'll check those. The challenge is that at this point of the season it will be hard to test (and expensive with the problem waiting an hour or more to rear it's head). But maybe I'll see evidence of the problem.

Bud37, it was about average for Long Island Sound, 1 foot seas, with a moderate breeze. After the second stumble, the captain thought it was bad fuel or gunk. I don't think it was bad fuel after filling up 60 gallons fresh gas in both tanks, but who knows.

I'm thinking of getting a fuel polish. Anyone have an opinion? Does it get the junk out?

I'll also change filters along with the suggestions above.

After all that, I'll run up to Deep River for winter and the rest of the winter service.

Any other things to check?

[RyDrew]

Thank you Viper and KM1125. I'll check those. The challenge is that at this point of the season it will be hard to test (and expensive with the problem waiting an hour or more to rear it's head). But maybe I'll see evidence of the problem.

Bud37, it was about average for Long Island Sound, 1 foot seas, with a moderate breeze. After the second stumble, the captain thought it was bad fuel or gunk. I don't think it was bad fuel after filling up 60 gallons fresh gas in both tanks, but who knows.

I'm thinking of getting a fuel polish. Anyone have an opinion? Does it get the junk out?

I'll also change filters along with the suggestions above.

After all that, I'll run up to Deep River for winter and the rest of the winter service.

Any other things to check?

[RyDrew]

Sorry for the triple reply, but the site keeps crashing in the middle of my replies. Same when trying to get to the site

[bud37]

Considering the previous owner changed out some parts, it would be interesting to know why they did that.

As far as the fuel, you could just get the tanks drained/sucked out and start fresh especially if the fuel was old, that may get the tank bottoms clean.

Now that said you did burn lots of fuel and got fresh so you could just change/clean all the filters/screens mentioned including the anti syphons. Won't hurt , it is regular maintenance anyhow.

[RyDrew]

UPDATE:
I reviewed the past 2 years of repair receipts from the previous owner. There was a lot done on the fuel system including:
- new fuel pumps
- new fuel coolers
- new fuel filters