Mag 350 MPI won't reach full rpm

Misfire test did not reveal a dead cylinder. Same rpm drop on all cylinders.

how do I check the throttle body? Just manually push it open?
 
Misfire test did not reveal a dead cylinder. Same rpm drop on all cylinders.

how do I check the throttle body? Just manually push it open?
No!

You should not manually open an electronic throttle body.

On a scanner you could check the commanded vs. actual throttle position. That is pretty easy to do on a car with a $200 off the shelf scanner. Not so easy on a marine application.
 
Misfire test did not reveal a dead cylinder. Same rpm drop on all cylinders.

how do I check the throttle body? Just manually push it open?

i this case i recommend you NOT to replace cap and rotor .

no experience on DTS but if you switch on ignition and with throttle only push the lever full forward the throttle body should respond or not ???
 
Cap and rotor are due to be replaced but may wait til off season.
Throttle body plate won’t move with engine off. Gonna start another thread on that topic.

may just have to let it be. Been that way for probably 12 years. Been through several marine surveys.
I will have it on trailer in a few weeks, may switch props and see what happens.
 
Update. I replaced plugs, wires, cap and rotor. Same problem. Also checked all engine parameters against other engine at idle and 1600 rpm in neutral No diff in Params except at 8% throttle I’m 150 rpms off. Ruling out prop issues since the problem happens in neutral too.

Ran compression test today, cold engine all cylinders between 170 and 180. 360 hrs on engine.

gonna do another misfire test today at higher rpm. I don’t know what else to check. Is there any way something could be obstructing the exhaust?
 
Check the fuel pressure and Report back.

Do you have any maintenance history? Has the Cool Fuel 3 module ever been replaced?

Do some research on the Cool Fuel 3 paint issue. You may have paint chips clogging one or more injectors.
 
Fuel pressure 39 or 40. Don’t think cool fuel has been changed but I kinda ruled that out cuz this issue has been there since it was new based on rpm history. Only .1 hrs over 4500 rpm in 12 years. Other engine has 1.4 hrs
 
Cant' believe no one has brought this up. But, what are you using to gauge the RPM's? The tach on the boats are notoriously undependable. I have one that jumps all over. Need to take it out and work the switch on the back. I use the sync gauge to make sure they are the same. So, I hope you are using some other method of measuring your data.
 
I have smart craft vessel view. The gauges show same as my scanner. What switch are you referring to?
 
I dont believe the smart craft tachometers have the switch.

the older tachs had a switch on the back so you could select 4, 6, or 8 cylinder engine.
 
Misfire test at 1500 rpm indicated all cylinders were contributing the same. Hooked up scanner and pressure gauge, went from stop to plane to full throttle. Got same results both engines. 40 psi whole time. At full throttle both eng read 100% throttle and 4.4V on tps.

At this point I’m gonna have to just live with it. If it gets worse I’ll have to take it to the dealer.
 
How old are those injectors ? Ever been serviced? Have your flappers broken loose and blocking your exhaust? How rusty are the insides of your elbows?
 
Look at these pics. First one shows .1 hrs bet 4500-5000. 2nd shows 1.4 hrs. Thats over 12 years. Fist engine only 6 minutes at wot in 12 yeats! Problem was there from day
 

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I wouldn't get too hung up on that info. I would address the questions I posted #32
 
Only my second year with boat so no clue on injectors but doubtful they’ve been cleaned. Don’t know anything about flappers and elbows, but I will investigate.
 
Talked to Merc and they said these are symptoms of the gen 3 paint delam issue. Told me to pull the lid off the pump side of module and inspect. So that will be done this weekend.
 
Just to finish this thread for someone who finds it down the road.
The issue is unresolved. To date I have replaced plugs, wires, cap, rotor, checked fuel pressures, inspected/tested fuel pressure regulator, inspected exhaust riser and water shutters, compression test, misfire test. Had throttle recalibrated and switched pcms.

Just gonna live with it and hope it doesn’t get worse.
 
i feel your frustration, i have twins also v drives, one engine will run 4600-4800, the other wont get over 4000. diacom software clearly shows my timing is being retarded TO 24 DEGREES. but i cant find the cause, im not getting any alarms, fuel economy is bad. been struggling with this for more than a year, swapping parts, compression tests, swapping fuel systems, caps rotors plugs wires, ECM's blah blah blah. starting to think vibrations in the tranny are affecting my knock sensor thus pulling the timing down. although the knock sensor will save me from engine damage, it is a troubleshooting hurdle hard to get past. if only there was a way to bypass the knock sensor to see if my rpms will pick back up, then at least i have a clue. but no misfire, cough, sputter nothing. im thinking about putting a rubber oring under the KS to make it not so sensitive. in the two diagrams, you can see the healthy engine's spark advance is hunting and the week engine is flat lined at 24 degrees. i have to manipulate my throttles to make my sync gauge center up. i guess i will continue to peck at it here and there. it really only bothers me when i have a loaded boat and struggle to get on plane, the stronger engine is doing most of the work.
good engine timing.png
struggling engine timing.png
 

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