05 350mag mpi power issues!

[Yamanator]

Hi guys, my name is Jim and im in Northern Mi. I'm a new member and that's because im having serious issues with my 05 Crest tritoon with the 350mag motor. I have tried just about everything you can do to solve the problem with no luck. The boat starts up and idles just fine, can put it in gear and cruise all day but as soon as I throttle up it starts having a surge or a slight popping out the thru hull exhaust! I am not getting any alarms and I am not getting any codes that I think pertain to the problem. Yes I even bought a scan tool to check for codes! Here is a list of things I have done to try and resolve this.
plugs
checked all wires
cap
rotor
map sensor on intake
coil
fuel regulator
took out fuel pumps and cleaned and to check for paint chips from gen 3 system, nothing.
8 new fuel injectors
new fuel pickup line and check valve

I checked the fuel pressure and it was high, it's supposed to be 38 to 43psi and I had 55 to 60psi. This is why I did the fuel regulator change. After that it seemed like it might have been worse. Put the old regulator back on after testing it to make sure it was good and am going to double check pressure today.

I am at my wits end with this thing, any help or suggestions are greatly appreciated.

 

[Bt Doctur]

If the cap has been replaced then try a compression test . If that comes back good then cross firing from the wires , bad exaust valve, valve floating from broken spring.

 

[tpenfield]

:welcome:

At least you know that the problem is none of the stuff that you replaced. There sure seems to be a bunch of MPI/EFI engine issues this year, more so that I recall in the past.

You might have to get the diagnostic computer hooked up to it and run the boat and throttle it up to see what is going on.

 

[alldodge]

Popping thru the exhaust you might have a bad or weak exhaust valve/spring. The fuel pressure being 50 to 60 was high and now its back under control but you don't know what caused it to go high?

Do you have access to a scanner?

 

[Searay240sd]

Agree with a compression test. I would also hook up a vacuum gauge. How old is the fuel? I would also double check your connections on the injectors? What brand are the injectors? Check the fuel pressure while you are accelerating. Triple check to make sure you have the correct firing order.

 

[Yamanator]

Was not able to check fuel pressure today, rained here all afternoon. Will try to do that in the morning. Yes I have a scanner and am just getting like 5 standard faults that dont pertain to my engine. Fuel is brand new and have doubled checked wires for hook up. I have a new crank positioning sensor but really dont think that's it since it starts and runs good at startup everytime. We did a test on each cylinder as we were driving at 1600rpm and disconnected each fuel injector one by one, the motor died the same amount for every one! Does anybody think it could have something to do with the IAC or throttle body? Heard of the valves sticking and screwing up on them....

 

[achris]

IAC failures usually set a code, so no code tends to suggest it's not that.

 

[alldodge]

Also if the popping was coming thru the intake then its running out of fuel

 

[Yamanator]

Guys, is bubbles in the fuel normal?
trying to upload a little video and it's not working.
We tested fuel pressure today and it is spot on at 40psi now, but we noticed a bunch of bubbles in the drain tube when purging the system. Is that normal?

 

[alldodge]

bubbles in the drain tube

Which drain tube

 

[Yamanator]

The one on the gauge when you purge it into a can! We were watching it flow and it had a lot of little bubbles flowing in it.

 

[Yamanator]

[No message]

 

[alldodge]

That is the gauge bleed valve/hose for the gauge. This can have bubbles in it from pushing the valve button. If the button is not pushed, then there is a problem with the gauge, not the motor

 

[Searay240sd]

Was it 40 psi though out all rpm ranges?

 

[Yamanator]

No, was at 38psi at start up and idle, as soon as I put it in gear it moves up a little to 40psi. When I get on the gas it moves to 43 to 45psi and then the regulator works and you can see it drop back to 40. It's actually the best it's been, I guess all the clean up on the gen 3 cool fuel system helped it. Now this darn thing seems like it's running with a major vacuum leak! I know it doesn't have that but that's how it feels when you are trying to accelerate. Still no warning horn or any faults on the scanner. Fuel pressure is good and everything has been checked ignition and fuel wise.

 

[Searay240sd]

Do you have a vacuum gauge? The fuel pressure regulator works off vacuum. While under way the pressure should not drop at all. It will return to it lowest number when the vacuum is the highest. I think a compression test is next to make sure mechanically the engine is healthy.

 

[alldodge]

With the popping out the exhaust a compression test would be an easy test, otherwise you need the motor scanned

 

[Yamanator]

Vacuum is good, I have a scan tool and it reads barometric pressure along with manifold pressure and everything is within normal range. Fuel pressure was great throughout the run, did everything it was supposed to do while throttling up and back. I am not getting the popping out the exhaust anymore, it now just seems like it runs with a bad vacuum leak! I know it doesn't have one but that's exactly how it feels when accelerating.

 

[alldodge]

Compression test