‘02 Amberjack, Mag 350 MPI - Strong Fuel Smell at idle and difficulty starting

[purplehayes]

Hey Gurus....

I haven’t posted in some time... but I need some guidance.

My Port engine is running really rich, there is a strong smell of fuel at idle and residual streaks coming out in the exhaust. (When I start the boat at the dock if I idle it for a while there a build up of oily streaks on the top of the water starts to appear). Not oil though I dont think, I am assuming it is fuel. The engine also does not start well any more. Normally the engine cranks over say three times and then vroom away it goes but this one cranks and cranks then slowly seems to take a spark... Even harder to start it when it is hot. Often if it is the first cold start it starts almost immediately instead of turn turn turn... slow glow... it starts 1/2 way through the first turn

What has been done with it directly for this or indirectly:
Oil Change, Filters and Computer Error code test (all fine)
Changed - Cap and Rotor, TMAP sensor, PCV valve
Initially I put on new IAC valves but ended up cleaning the old ones as the idle became too high with the new ones (not Merc) so IAC has been checked and sorted.

After I did the above I thought it seemed like it was ok for a bit... then I washed down the engine a bit (carefully) and the problem returned. So either it was something that I did and then I messed it up or there is a different issue that I am not aware of. Other searches lead me to believe that maybe my TMAP sensor is toast again but not sure why the new one would drop off line like that. I am currently away from the boat for a week but will try to switch the sensor from the starboard engine and see if that fixes it and if so then know what is what. I have also seen some discussion about vacum lines and fuel pressure return lines or something... but if that is the case then I need some guidance on that as well. Reasonably mechanically aware but I dont spend enough time with the engines on my own to really be able to run with it. I will look through the manuals for the lines and see if I can get a plan.

So ideas and guidance on where to start please.

 

[Espos4]

Sounds like a leaky fuel Injector(s)

When you shut it down, fuel could be leaking from 1 or more injectors causing a VERY rich mixture in the intake manifold. That’s why it takes a while to start a warm engine.

As a test, When trying to restart a warm engine, use the “throttle only” and move the shifter to wide open throttle. This is a “clear flood” request to the ecm. The computer will not fire the injectors while cranking.

YOU MUST IMMEDIATELY MOVE THE SHIFTER TO NEUTRAL ONCE THE ENGINE STARTS!

It starts easy when it sits for a few days because the excess fuel has evaporated and you don’t have that super rich mixture in the intake manifold.

 

[jetpartner]

I have the same issue with my port engine. No computer codes, new injectors, fuel pressure is correct. Only thing that is different is my IAC position when warm. Ignition timing jumps more than other engine. I am leaning towards computer wire harness is bad and when warm resistance causes a hard start problem. The engine runs great once warmed up, no performance issue. I too am confused by the same problem you have.

 

[purplehayes]

Hey Guys,

Thanks for the posts. I will continue to try to figure it out and give the wide open throttle a look on the next warm start.

Cheers

 

[jetpartner]

Hey Guys,

Thanks for the posts. I will continue to try to figure it out and give the wide open throttle a look on the next warm start.

Cheers

1.Put a fuel pressure gauge on the fuel rail, test pressure at idle and with vacuum supply to pressure regulator removed. Fuel pressure should rise with vacuum supply removed, if this does happen your pressure regulator is good. Now put vacuum supply back on let engine idle for a min to stabilize pressure and next turn off engine. Note the fuel pressure right away and compare that to the pressure 5 mins later. Pressure should be within 2 lbs, if a larger pressure drop you have a leaking injector. To find out which injector(s) are leaking then pull the spark plugs, the dark soot covered plug is the cylinder that is getting excess fuel.
2.Check your ECT sensor, when it fails it tells the computer that the engine is cold all the time and extra fuel is sent to the engine. The ECT sensor is not the engine temp sensor.
3. Do not use the wide open start procedure, only open throttle 25-50% this is the range that the computer shuts off the injectors for a flooded start situation.

 

[purplehayes]

Hey guys...

I have to check my settings but I am not getting updates of posts from the thread... but anyway.

Ok so my problem does not seem to be going away at all although I have been trying your suggestions and various suggestions from other areas and have had a mechanic down to the boat as well. I am sure that we will get it sorted but this is boating season and I like to use my boat... and I get pretty frustrated when I am saying sorry to people at the dock when I cant get it sorted or whatever... or want to leave it running for a quick stop when normally I would shut it off to not pour exhaust in the area....

Throttle position at startup, I tried yesterday. The engine turned over and over with nothing at idle then when I pumped the throttle up it exploded to life.... and I quickly pulled the throttle back but it quit. It just never came to life with a good vroom.

Once I did get it started it ran and continues to run great. Smooth... good cruise RPM and WOT matches the Starboard engine nicely 4650 or somewhere there.... I ran a Redline SI-1 fuel system cleaner yesterday and took the boat for a good run. I ran only say 45gallons of fuel for the trip so the concentration was pretty good. Kept the RPM high for the cruise 4000-4200 roughly for 45min each way. Starting on that side after sitting for 3 or so hours was the hardest start that I have had yet... honestly thought I might not get it going.

Fuel pressure was tested by my mechanic as well as the drop.

Anyway... for info... ideas welcome.

 

[cfd95]

Do a compression test.
I had same problem on both motors this year.
Did a compression test .
Starboard 2 cylinders 30 Psi
Port 1 cylinder.
pulled the heads found 2 bad exhaust valves and seats on starboard
1 bad seat on port.
When the motor is idling with dead cylinder the MAP sensor tells the ECM the vacuum is low and to richen the fuel mixture

 

[jetpartner]

After all of my troubleshooting I have to agree with cfd95. I assumed my engine witj 100 hours was healthy and the problem was related to electrical, fuel injection, computer, or sensors. The problem was low compression and low vacuum which told the computer to match fuel demand to manifold pressure. The result was too much fuel and black soot etc. The whole issue was caused by the riser gasket failed and water got into engine causing rusted valves. The net result is zi ended up rebuilding a brand new engine with 100 hours use due to water intrusion