Optimax High Rev at Start-Up / Idle Miss

[Action1820]

My 2002 135 Optimax (SN 0T701655) has developed an issue, whereupon starting cold it will rev to 2500 - 3000 with a good puff of smoke, than die. On the second start, it will rev up again, but not nearly as high, whereupon it may die or continue to run. If it does die, the third startup typically doesn't cause a rev up. Once running, the motor has a stumble / cough / miss every 3-4 seconds. Once off idle, that cough seems to go away. Digging into my service manual and these boards, basic symptoms without any testing point towards the fuel regulator diaphragm. Tracker is my second guess, but hard to pin point without pressure readings yet. Is there anything else that jumps out?

I will take pressure readings this weekend at idle / 5 / 10 / 15 seconds after and post the results. Are there any other good ways to test for leaks on the fuel diaphragm / tracker valve? Can I pressurize air side to 80psi, turn key to on to run the pumps, and monitor the fuel pressure leak down? Would that definitely show any breaches? My motor is one of the earlier models that does dump the air pressure 100% at shutdown. Are there any other tests / things I should check while doing pressure checks?

I posted a video to Youtube of the stumble as well - link is below. Engine runs only DFI oil. I also rebuilt the pulse fuel pump earlier in the summer when I replaced the three year old fuel lines.

Thanks for the help!

https://youtu.be/6YfAuhLdxys

Josh

[JOE54]

rev at start up and smoke are a good indication of fuel in air side of system likely bad diaphragm in rail [tracker valve] prob

[Action1820]

Follow up with pressures. Tested with Glycerin filled gauge.

While Running at Idle
Air - 78
Fuel - 110 (Dead serious - gauge only goes up to 100, it was past that)

5 Seconds After Shutdown
Air - 0
Fuel - 10

10 Seconds After Shutdown
Air - 0
Fuel - 10

15 Seconds After Shutdown
Air - 0
Fuel - 10

As stated before, my motor is one of the pre-2003 that always dumps the air when shutdown.

Because of the high fuel pressure, I thought my gauge was acting up. I tested it on a tire that has has the tire pressure monitoring gauge in the car, dead on. I also verified with another air gauge, dead on.

I also tested for air leaks and verified the fuel pressure with the motor off. With shop applied air, the air pressure regulator is blowing at 78. With the key turned on and air pressure holding at 78, the fuel pressure rose to 88 and wouldn't go over. Tried this multiple times back to back, and couldn't get the fuel to climb above 88.

Obviously, the high fuel pressure is alarming. What could be causing that? Blocked passage or check valve back to the VST? Why is it only happening when the motor is running, instead of just pressurizing? I would assume that overly high fuel pressure could be causing the sluggish idle because of overfueling?

Thanks.

[EuropeanAM]

I think I've been working on this with you elsewhere as well. ???

[Mitriton]

I have a 2001 Opti (150hp)that has the same problem but much more severe. Only during HOT weather after 5-6 or so fishing stops when I start the engine in the afternoon during hot weather it will rev to full throttle if I don't shut it down fast enough. It'll do this 20-25 times until the excess fuel is used. That's what I think anyway, then eventually it stops reving but idles very rough until I put it in gear and go. Once I start moving all is fine until the next stop. The problem will reoccur if the stop is longer than 20 minutes or so. Had it at two repair shops and still not fixed. Had the needle valve in the VST replaced and the problem went away for about 50 engine run hours then returned. This summer a diaphragm (not sure which one) in the fuel system was replaced but didn't help. It won't happen throughout the mornings, only in the hot afternoons. Repair shops can't spend all day in my boat so they can't replicate the problem. Mercury says they never heard of such a problem so no help there.

[JOE54]

POST # 2 depressing air scrader at start up will tell if fuel in air side of system MERRY CHRISTMAS JOE

[Mitriton]

JOE54 I don't know what you mean by depressing air scrader.

[JOE54]

the test port for the air press is what I should have said depressing this valve a small amount will relieve pressure and no fuel should be present in air side of system, note : do not depress fuel test port it will be under pressure