Gen 5 454Mag MPI stalling on plane

[M Kyle]

Recently purchased boat with the 454Mag MPI, 385 h.p. I've had many problems with what i always thought was fuel delivery. After reading many posts on here I alleviated many fuel and electronic components. And yes, it does have that nauti VST. Having said that, I am not convinced it is my problem. I've talked to Mercruiser direct and they suggested that my problem was not likely fuel boil problems in the VST. To date, I've performed or paid to have perform all the the following repairs...new fuel lines, new fuel water separator (x4), new anti-siphon valves (2 tanks, 2 valves), inspected tanks as best as possible, new ignition module, new cap, IAC, MAP, TPS and most recent fuel pump rebuild. Certified Merc mech said that fuel pressure was only 1/2 psi at idle and 2 psi at 3000 rpm and that this was my smoking gun. Maybe so BUT...after the last repair of fuel pump, the boat DID NOT stall at idle, like before. However, it did die at 3500 - 4000 rpm while under way. It did restart without too much objection and did not do it again the remainder of the weekend. BTW, this occurred within minutes of a recent fuel fill. Thoughts anyone?Was it a fluke or problem still remains? Becoming more and more frustrated. Also, while it is a Gen 5 motor it does seem to have some Gen 6 components, for example the ignition system is Gen 6.

 

[alldodge]

Certified Merc mech said that fuel pressure was only 1/2 psi at idle and 2 psi at 3000 rpm

I have a hard time with this statement because, if this was the case your motor would be running real lean if it ran at all. See no way it could run at 3k rpm with only 3 psi. Now if he was talking the low pressure mechanical pump I could go with that.

The first think I would like to know is what is the fuel pressure at the rail?
Next dump the contents out of the fuel filter into a clear jar or baggie and see if something is in there that shouldn't be?

 

[tpenfield]

It is frightening to think what all of that parts throwing has probably cost so far. MPI engines sure are great when they are working right, but a bear when they are not. I am currently working through some issue with my Gen 6 7.4 MPI w/ VST fuel system.

As AD said, the fuel pressure at the rail is supposed to be in the 30-40 psi range. Not exactly sure what the 454 MAG spec is though.

Any codes that were read from the MEFI (ECM) module? I'm almost thinking something electrical given that it dies suddenly.

 

[M Kyle]

Thanks for the responses guys...At ALLDODGE -> I didn't explain that very well about the fuel pressure. In my novice knowledge of the system there is a low pressure side and a post VST high pressure side. The low pressure side wasn't, according to Merc Mech, able to feed the VST adequately with a poorly functioning low pressure mechanical fuel pump. It was the mechanical pump that was rebuilt. Merc specs on the mechanical pressure is 2psi to 8psi...I'm sure that is linear with engine RPM?

ALLDODGE/tpenfield....agreed, the fuel pressure on the rail, as I've been told should be 36 - 42 psi. I assume (very bad to do) that the Merc Mech did in fact run pressure tests there as well and no codes were mentioned in the diagnosis either. Again though, I wonder if it was checked? I'll find out.

A sensor yet to be replaced is the IAT, but at this point I'm done replacing parts. But guys, I want to clear, this adventure in performance problems and fixes has been performed over the last several months. The IAC and TPS were on my own ignorance because I've had problems with IAC on other boats previously. And since they are so close together and not easily gotten to on this GEN 5 MPI, I threw the dice and replaced both. All of the other sensors, cap/rotor, filters etc. were discovered to be performing out of spec or after visual inspection were a source of concern.

I sincerely think that I've had many different "opportunities" of problems on this craft. This boat was owned by an older gentleman who used it about 10 hrs/year for the last 15 years. I think he largely putted around the lake and rarely, if ever pushed this mild performance boat (Victory Advantage 27) What's more is the lack of attention to what I consider 2nd echelon maintenance. Yes he changed oil in the motor and drive, but plugs, wires, cap...those things were largely ignored. The cap for example was so crusty, I can't believe it ran at all.

I changed the name of the boat, from what I hear that's superstitious bad luck!? Maybe I shouldn't have. HA

While the emergency ignition shut-off lanyard has been removed (prior to my ownership) due to their temperamental (so I've been told) nature, I wonder if there is still a possibility of problems there? After all, while running down the lake, it simply "turned-off"

 

[tpenfield]

You might be on to something with the kill switch (lanyard). You could check and even re-do the wiring. You should have a kill switch on that boat and use the lanyard when underway.

 

[alldodge]

emergency ignition shut-off lanyard has been removed

This catches my attention only because you can never know how it was done. Someone may have cut, stripped and twisted them together with some electrical tape. Doing it this way and a bit of time, will corrode the connections. May want to check it out and verify the connection.

Might even reinstall the switch for safety

 

[M Kyle]

Is it possible guys that this boat left the mfg without a lanyard kill switch in 1995? While I did recognize that it didn't have one, it was Merc Mech that drove the point home. I see no evidence (plugged hole in the dash for example) that suggests it was ever there.

 

[alldodge]

Don't know, but the kill switch takes the purple wire from the ignition switch, goes thru the kill switch, and then back to the purple wires behind the helm (gauges and such)