1999 Optimax 225 Sputters at 2000 RPM after 20 min, won't plane

[hstechfl]

Hello all- hope someone can help with this..

I've got a 1999 225 optimax, Serial #0G826471.

Basically the motor runs fine for about 20 minutes in the water- idles, gets on plane like normal. After about 20 minutes or so, the engine starts to "choke" or "stumble" trying to get on a plane at about 2000 RPM. Some background: just recently changed the compressor, flushed fuel rails, injectors, cleared debris from oil return check valve and connected hoses. Changed fuel filters, plugs. 1150 MCA battery just load tested at 1000 CCA OK. Spark plugs wires seated correct to coils and plugs. Engine temp is OK, water flowing from tell-tale normal, system voltage shows about 13.9.

First thing I did when getting it back was pull the plugs- which looked normal.

My other thought was that its a failing low pressure fuel pump. But checked amp draw of pump and runs between 1-2 amps. Ran for over 20 minutes to see if it would slow down. Still OK.

Here is a video I took of the problem. Its hard to hear, but basically its running at about 1500 rpm. When I give it throttle it wont get past 2000 rpm:



Again- keep in mind that everything runs fine for about 20-30 min before this happens.

Any help would be appreciated!!

[Savage]

Perform a spark test as the problem is occurring.

[hstechfl]

Perform a spark test as the problem is occurring.

Thanks- will try if I can get it out again. Problem only happens under load. Engine runs fine on muffs or in bucket. Are you thinking coils?

[hstechfl]

Just thought of this also- On the new compressor there are 3 wire leads. The old one only had 2 which correspond to the 2 coming from the wiring harness on the engine- so one is left unplugged. Not sure if this is causing the problem but thought I would add.

[EuropeanAM]

Check the temperature of the OUTLET FITTING on the low pressure pump, while the problem is occurring. A hand-held infrared temp gun is a good tool for doing this.

If temp of that fitting exceeds 110 degrees F, the pump is failing.

[hstechfl]

Thanks Don- will try next time Im able to get it to the canal. Could a PSI test on the muffs tell me anything?

[EuropeanAM]

Very likely that you'll never replicate this condition on the muffs.

[hstechfl]

Bummer- That's what I figured Thanks will report back!

[hstechfl]

Should be able to get out there in the next couple days..

Just to stay ahead of the game (since I cant get the boat out often), what would be the next culprit you would test if the low pressure pump were OK? Want to bring as many tools with me next time I get out there. Thanks!

[EuropeanAM]

Check Air/Fuel Pressures using Liquid or Glycerin-filled gauges, and record results for:

-Idle
-Under Acceleration
-5/10/15 seconds after shutdown (restart for each time period).

[hstechfl]

So finally got it out again today..

This time- the problem surfaced right away.

So like Don said in another thread- I trimmed up a little while the engine was bogging. As the RPMs starting rising, I trimmed back down and then up again and the motor broke free. Got it up to 5500 RPMs and motor ran fine. Tried this about 5-6 times and had to trim up every time to get it past the bogging. Dont know what gives since I never had to do this before.

So next I removed the cowling to connect the fuel pressure gauge. Started right up, maintained 90 PSI. Also maintained pressure after shutdown. So I wanted to see what the reading was while it was bogging- but this time- no bogging! Engine took off like it normal, trimmed all the way down. Repeated this process 6 times. Never got the bogging while the pressure gauge was hooked up.

So now my question is now- could it be loosing pressure through the schrader valve? All my readings were normal, but if the leak was from the schrader- the gauge would cover this up (preventing the leak) correct?

[Savage]

Highly Un-likely......But easy enough to test with some spit, or soapy water.

[hstechfl]

Highly Un-likely......But easy enough to test with some spit, or soapy water.

Yup tried this.. didnt see anything unusual.

Forgot to post fuel/air pressures for Don:

Fuel
Running: 90
5 seconds: 89
10 seconds: 87
15 seconds: 84

Air
Running: 80
5 seconds: 79
10 seconds: 77
15 seconds: 76

They were pretty consistent, although the fuel was dropping faster than the air after 10 seconds...

[EuropeanAM]

Just for grins- was the COWLING off the engine?

BTW... those pressures look pretty good.

[hstechfl]

Yup- Funny you should say that because when I took it out- the engine ran fine as soon as I took off the cowling!

Guess it was a coincidence that the problem stopped when I hooked up the gauge..

Anyways still cant find the smoking gun. I ordered a set of carbon reeds from you, guess I'll report back when I get the old ones taken off.

[EuropeanAM]

Check the idle relief boot for nicks, cracks, or holes.

[hstechfl]

Check the idle relief boot for nicks, cracks, or holes.

Checked it last night- looks ok. Sprayed some soapy water around it also. No leaks.

I noticed in another thread you mentioned a worn flywheel could cause problems. Mine is in a little rough shape. It still starts and seems to idle OK most of the time. Could this be a problem?

[EuropeanAM]

What does the LOWER set of teeth look like?

Just to confirm- do you have the plastic flywheel cover (and attenuator/cover) in place when you run it WITH the cowling?

[hstechfl]

Not sure if these are the "lower" teeth, but here is a pic:



Yes- I took the covers off for these pics. But just FYI- would it affect performance if the plastic cover (the one over the flywheel) was removed? Aside from the air filter- does it do anything?

[EuropeanAM]

I would recommend that flywheel be removed, rust removed from the lower set of teeth (wire brush or other hand-operated rust-removal method), then prime and repaint with Mercury Phantom Black paint. Flaky/Rusty teeth can cause a wide array of performance (even starting) problems.

Plastic attenuator and flywheel cover are factored into the airflow for the engine (which is a FIXED figure in the MAP tables of the PCM). ECM/PCM cannot "compensate" for changes in airflow.

Other reason I asked is that sometimes cowling sound-blanket material will come loose and end up covering air inlets (with cowling on).