1999 Optimax 135 only runs w/key in Start Position

[bryandurkin]

Hello - engine serial #OG960445

I recently had a 4 beep situation after running for an hour or two while bringing the boat to the trailer. I replaced the Water Separator and an external Water Separator (I have seen that both may be an issue but working through troubleshooting - I am open to remove this). Checked the secondary fuel filter and found a very small amount of water (maybe a tbs or 2) and drained this and added new fuel. I have recent tune up, new plugs w/proper gap, fuel w/Mercury additive and have used the boat 3 or 4 times w/o any issue other than the 4 beeps (only at the end of the day)

Now when I prime the engine, prime the bulb I can hear the low pressure run for 2 to 3 secs and it fires right up.

As soon as I go from START position to RUN position it turns off. I have tested the fuel pressure and have 90 on the fuel and 80 on air side - I only have 1 fuel pressure gauge right now and and will get a an air pressure gauge today. It does fluctuate and isn't solid (it's not running just in start position so hard to see). I do not have a low pressure test schrader valve and will get one if I need it. I'm not sure where to start as it seems to fire up immediately and as soon as I turn of start position it dies immediately.

The batteries are 3 months old and have 12.7 & 12.6 volts and are above 12 volts during start.

Any suggestions I'm open - feels like its electrical but clearly it may be fuel related. I'm mechanical but not a mechanic, I have the service manual. Could be TPS? Pulse Pump? High Pressure fuel? I'm not into parts swapping and want to eliminate as much as possible.

Thanks so much.

I will post a video if that's helpful.

[bryandurkin]

Sorry if I wasn't clear - found water in secondary separator and changed both. Prior to this ran fine and just the beep condition.

[Rip Bass]

So,you’re saying at start up when the key goes from the start position to run position,the motor turns off? If so,I would think the switch is bad.

[EuropeanAM]

More than likely a problem in the keyswitch harness. I'd be connecting a separate (transom-mounted or test) keyswitch harness directly to the engine to see if the problem is in the engine OR in the boat wiring.

[bryandurkin]

OK - sounds good I'll check into that! Does the service manual wiring diagram show any service ports for hooking up a remote key start? Appreciate the help so much

[EuropeanAM]

Yes- it connects in the same place the Keyswitch Harness connects (inside the engine cowling). Refer to the Installation and Rigging section.

[bryandurkin]

Thanks so much! After some digging it's an original key switch so it's likely the culprit - it's not as smooth as it should be so I'll go ahead and wire up a new switch. I'll keep you posted.

[bryandurkin]

I thought I would reply so in case someone else has the same issue - 100% fires before I can let off start! I also used the Mercury OEM/Quicksilver part and the colors & functions matched up 100% AND had a low temperature solder ring in the heat shrink connector so the connections are rock solid. Thanks so much.