Optimax 115 1.5L Air Pressure Issues

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10-23-2023, 09:38 PM
MrYeates

Optimax 115 1.5L Air Pressure Issues
Hey all,
Optimax 115 1.5L Serial#1B964991

Engine has been running and starting like a top for the last few years since I acquired it. Was cruising around 4.5k RPMS, motor started to bog down, sputtered out and died. Extremely hard to get started again and would surge and not stay running.
Have checked a few of the basics to start off like using auxiliary tank with different gas, spark plugs, spark test, battery, etc.
Started looking into pressures and so far have checked and found this.
- Gauge hooked up to air schrader valve, cranked motor, pressures jump up to around 30-40 (using cheap gauge for now, don't have liquid filled) and watched it immediately fall back down to zero upon stopping cranking. Noticed there was no building of pressure.
- Checked compressor by spinning manually and compressor piston felt normal, could feel air coming out as well.
- Hooked up shop air compressor to schrader valve, pressurized to 90, as soon as I let off, pressure quickly dropped back down to zero, same as when I cranked it previously.
- Kept compressor running, turned motor over and boat started immediately.
- Kept compressor hooked up, pinched the air discharge regulator line, watched pressure build up correctly as outlined in the service manual.
- Noticed with cylinder 1 spark plug out, I could hear air coming out of the hole. The service manual does mention "To aid in starting when the air rail pressure is low and before compressor has time to build pressure, the direct injector is held open by the ECM. This allows the compression from inside the cylinders to pressurize the air rail faster." This happens with both the key on or off.
- I also noticed that with all spark plugs back in, I could hear air coming out around the exhaust hub by the prop.
I'm stumped at this point. Read through the service manual and nothing else is jumping out at me. I've checked the hoses, don't see any leaks. The air pressure is dropping extremely fast, and it sounds like it's coming from the prop hub. Any ideas or has anyone seen this before? What do I check next?
Edit: Found this post here, sounds very similar to my problem. Going to check the compressor valves tomorrow. Note, I did notice when I pressurize the fuel rail that I could feel air coming out of the compressor air line.
https://www.bbcboards.net/showthread.php?t=1193294
10-24-2023, 01:52 PM
EuropeanAM

1. Make sure you're not exceeding 93 psi of air pressure supply.

2. If the air is ONLY leaking from the #1 spark plug opening, it would be the #1 Direct Injector leaking. It should be closed unless the engine is being started or running (completely).
10-24-2023, 03:57 PM
MrYeates

Quote:

Originally Posted by EuropeanAM

1. Make sure you're not exceeding 93 psi of air pressure supply.

2. If the air is ONLY leaking from the #1 spark plug opening, it would be the #1 Direct Injector leaking. It should be closed unless the engine is being started or running (completely).

1. Yes, I have my regulated compressor not going any higher than 90.
2. That's the only spark plug opening I can actively hear air after removing and testing the other plugs. With Spark plug 1 in, then I only hear it coming out of the exhaust. Confirmed no air is coming out of regulator discharge hose. I did have some air coming out of the compressor intake air line and when I plug that line up, the air still bleeds off.
Understood on it being closed, that makes sense based on how the manual says the PCM keeps it opening when cranking to build pressure. I'll look around, but is there a test to confirm if it's being held open? I believe there was something in regards to using an OHM meter to check.
10-24-2023, 04:54 PM
EuropeanAM

Ohm meter checks the electrical circuit- it could be hung open or hung closed and still pass that.

If air is leaking to the #1 cylinder, that injector is leaking. It's the only viable path (sits right next to the spark plug).
10-25-2023, 12:13 AM
MrYeates

2 Attachment(s)

Thanks for the help, I do really appreciate it.

I went ahead, checked the injectors and got 1.3 across all 3.
I did dig into the fact that air was coming out of the compressor intake line a little more when the schrader valve was pressurized as I understood there should be a reed valve in there. I took the compressor apart and found one of the reeds had broken off and was sitting there. The compressor piston looks to be in fine shape at least, there isn't any metal fragments besides the larger piece sitting there.
Bummer. From my understanding then, I'll need to get my fuel rail and injectors cleaned as any metal bits would likely have made it into the fuel rail.
Any idea what causes these reed valves to break? Just random or do I have a cooling issue potentially at the compressor.

Thanks again! I'll likely use your services to get my injectors cleaned and back in top shape and work on the compressor in the meantime.
Attachment 534948 Attachment 534949
10-25-2023, 01:41 PM
EuropeanAM

The most common cause is a malfunctioning or sticking direct injector (which allows raw combustion gases to pass back into the air side). If you found the piece... replace the compressor reed plate and quite likely the #1 Direct Injector to resolve the problem (spark plugs wise as well).