1997 Carver Aft 355 with twin Crusaders.. 7.4's...

[benica]

Hopefully, I can help another when the time comes...
Today I need some ideas...
Started out on a 7 day boat ride...
Fresh oil, fuel, plugs, wires, filters, 2 new heat exchangers...
First day...average 9 knots around 2300 RPM for...8/9 hours...uneventful day....stopped for fuel and slip.
Next AM....2 hours in...port engine....RPM's drop to 1000 then 2000 then 1000....fluctuating...tried increasing the throttle...throttle wouldn't move up/increase....ran around 1200 RPM and matched the port engine the same and limped along. Got to a marina....mechanic does his diagnosis...replaced the coil and control module....next morning...underway fine.
Port engine no issues. 7 hours in....SB engine...acting up...same symptoms as port. Stopped...mechanic comes out...replaces coil and module also.
Underway...few hours in...SB cutting out....lower the throttles and mosey along...1800 rpm's...
SB acts up still...after a few hours....
Doing research...cause so far... money spent been....questionable...
Engines do NOT overheat....180° area..
Oil pressure is fine..
Transmission issues ruled out.....
1020 hours on engines....
Concensus is.. we all agree to disagree.....
Half say...electrical issue...half say.. fuel injection issue...
Paying a tech...to guess...essentially just swap out parts...wasted money. Both techs hooked up....some code reader with flashing red light and went from that point..
Just before the engine acts up...tried increasing the throttle...gas lever...won't allow me to go up...down is fine....
Suggestions...
Pompano Beach area...
Thank you for reading and potential replies...

[km1125]

What did you do to check the fuel filters prior to suspecting the electrical stuff? I know (or it looks like) you replaced the filters before you started out, but stirring up the tanks on the trip you might have loosened up some gunk and plugged up the new filters right away. Your symptoms (as described) are so very typical of plugged filters.

[Viper]

I agree with km. Fuel delivery is suspect though I wouldn't rule out an electrical/ignition issue either but stick with eliminating one system at a time. Is there more than one fuel filter per engine, and did they ALL get replaced? You stopped elsewhere for fuel so check the filters for water and debris. The anti-siphon valves are also suspect as well as poor ventilation, check the tank vents. Check the position of your fuel valves and ensure they are placed such that each engine is running off its own tank and that the crossover if applicable is closed. Make sure they are centered in the correct position, they may have been bumped against when working on the engines.

If all that checks out, my next thing would be to consider running on a remote tank though running that long before the symptom arises may render that impractical unless it's a very large tank.

When this happens, has anyone taken temp readings in the engine compartment? Have you tried running with the engine hatches off?

I assume you've been running on the main tanks and not the aft auxiliary tank if applicable?

What model 7.4L are we talking about here? That would really help to know what fuel and electrical/ignition components we're dealing with.

[g36]

On my 1997 405 with crusader xli's. You'll find 3 filters on each engine. Heres a post I made way back. I bet yours is the same setup. The round ufo screen is a definite issue clogs easily and can be opened and can be cleaned the other elements are replaced and not reusable..

From fuel selector valves #1 is a black 4" round filter which is this.... https://www.jegs.com/i/Oberg-Filters/706/4028U/10002/-1
Next in line is a water separator filter looks like this ...https://www.westmarine.com/racor-110a-s ... 08664.html and last
There is a inline filter at the tbi....https://www.google.com/amp/s/marineengi ... l-filter/..

All are on stbd side of engine oberg down low,water seperstor mid height and cannister right next to tbi

[bud37]

Source of the post Paying a tech...to guess...essentially just swap out parts...wasted money. Both techs hooked up....some code reader with flashing red light and went from that point..

Basically they can only get any codes in memory doing that........the only way to do it correctly IMO if it is MEFI, is to connect a laptop with the appropriate program and run/record a test so that all the engine parameters can be monitored and analyzed in real time, a very useful diagnostic tool.

I will say , problems like this are hard to pinpoint, step by step is good and there is some good advice above here.

[g36]

97 crusader xli's Mefi 1

[Viper]

Ya that's why I asked for the model number and how many fuel filters there are. If the current owner hasn't replaced it, there's a good chance the Oberg is original from factory.