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Need help. Mercury Optimax 2005 115hp

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blaprairie

New member
I really need some help with this one. I have two 2005 115hp optimaxs that have no fire. To give a little history, the engines have less than 50 hours of run time. Sat up a few years and I brought them to my local dealer to get started. Well they tell me that the EFI computer on both engines need to be replace along with a few minor other parts that will run me 12k. I find it hard to believe that both computers went bad just sitting there. I last ran the boat about a year and a half ago and everything was fine. I started doing my own trouble shooting. I do not have any fire on any cylinder on both engine. I checked the safety switch and it is working properly. I am a professional heavy equipment mechanic so I do understand the operation of most engines. Not familiar with Mercury electrical. I am looking for some electrical diagnostic information. I am willing to offer any assistance on tractor, dozer, forklift ect.. information in return.
Thanks,
Brandon LaPrairie
 
Re: Need help. Mercury Optimax

I believe it would be the ECU that they told you is fried and while they do retail for about 2K each I can't see how the total bill would approach 12K unless those "minor parts" were actually major.

On the Opti's, unfortunately, if the ECU is shot the motor will not run. The ignition on these is controlled by the computer and it's collection of sensors and the only way they can be tested is with a diagnostic terminal loaded with the Optimax software.

I would definately take it to another dealer even if that means a road trip and get a detailed analysis from the diagnostic terminal.

While it would seem unlikely that both computers would die simply from sitting, a short in the electrical system if the batteries were still connected, static, a lightning strike close by and probably a few other uncommon events could fry both computers if the motors were still wired to the batteries during storage.

Since you are definately mechanically inclined, a service manual and a printout from the DDT would definately allow you to repair these yourself and save thousands in the process (based on what "the shop" wants)...
 
Re: Need help. Mercury Optimax

Neither engine runs?
You hooked up the kill switch right?
Better run, not walk to the next dealer!

Any engine sitting that long is going to be a bugger. The gas is stale and all the pumps and injectors are probably gummed up.
 
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Re: Need help. Mercury Optimax

Thanks for the info galamb. Yes time bandit the gas is very stale. But the problem i am having is lost of fire. I guess I need to deal with this first before attempting to correct the fuel issue. If anyone had any ideas on how i can diagnose the electrical issue it would be greatly appreciated. I just hate to dump thousands of dollars into these engines if i don't have too. Thanks guys.
 
Re: Need help. Mercury Optimax

If nothing has been tampered with, you have a kill switch issue or corroded ground wire. The chance of electrical surge to knock out both ECU mods is not likely...it would blow a fuse.

Check wires in console or control head for corrosion and peel back insulation to make sure.
 
Re: Need help. Mercury Optimax

todieie, I checked the kill switch and it is working properly. all the wiring is in new condition. This boat has been garage kept, just not used very often. I ordered a service Manuel which I should receive next week. I hope the trouble shooting guide will help. I'll up date the posting if I ever find the problem.
 
Re: Need help. Mercury Optimax

Check the easy stuff first. I suspect the ignition switch. Unplug the cannon plug under the cowling that is comming from the control box, that takes the control box out of the picture. Hook a jump button to the start solinoid( red from battery and yellow/red) crank it through with the jump button, a normal motor will fire. Be sure to unplug the spark plug wires cause if it were to start you can't kill it. Check for fire. This will eliminate any ignition switch and kill circuit issues.
 
Re: Need help. Mercury Optimax

Danebramage said:
Check the easy stuff first. I suspect the ignition switch. Unplug the cannon plug under the cowling that is comming from the control box, that takes the control box out of the picture. Hook a jump button to the start solinoid( red from battery and yellow/red) crank it through with the jump button, a normal motor will fire. Be sure to unplug the spark plug wires cause if it were to start you can't kill it. Check for fire. This will eliminate any ignition switch and kill circuit issues.
Click to expand...


That will not work on an Opti, Danebramage. You need key power on the purple wire to wake up the ECM. Also, the kill switch (blk/yel) is an input into the ECM, not to any ign. component. The ECM shuts off the Master Power Relay that feeds all the fuel pumps, coils, and injectors.

And 12K will but two new 115's. Run don't walk.
 
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Re: Need help. Mercury Optimax

The ECM A connector pin 1 is the key power.
The C connector 15, 16, and 24, are the main grounds.
B 23 is the kill switch blk/yel. (ground to stop)

Anyway the batteries need to be strong. The voltage drop can't be more that ~10.5 volts with the starter cranking away. The ECM shuts off.
 
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Re: Need help. Mercury Optimax

The quickest way around this is with a "cheater key". Tech's use a short cable with a plug and key switch to diagnose these problems.
 
Re: Need help. Mercury Optimax

Timebandit, you made a good point with the strong battery. My battery may be bad. It won't take a charge so I have been using a charger to attempt to start. I will try a new battery first. I received my tech Manuel today so I will send some time reading up before I work on it again. Thanks guys for all the posts. It is nice to have this contact. If any one needs any heavy equipment info I am well qualified to give advice. John Deere certified but have experience on most manufactures.
 
Re: Need help. Mercury Optimax

personally if I was faced with a huge expense like $2k for an ECU, I would be searching for after market controllers, they do exist. Even the megasquirt would be worth a go. The automotive and recreational OEM's think they got ya over a barrel with all their proprietary electronics. One of the real reasons for the push to electronics to control engines.
 
Re: Need help. Mercury Optimax

Diceromc, aftermarket parts is a great option. Is there a web sight you would recommend? I can find what I need and it is significantly cheaper I will definitely go that direction. Thanks.
 
Re: Need help. Mercury Optimax

I was able to work on the engines today. Swapped a few parts and was able to get the port side engine to fire. It even started and ran for about 10 seconds. I found the boost pump in the vapor separator not working so I will get one ordered. The help I received from this post gave me a great start on the repair. Thanks again for all the input.
 
Re: Need help. Mercury Optimax

Got one engine too run but it's a little rough. I replaced the plugs and checked the coils. All three are firing but still has a pretty bad miss. Does anyone have an idea of what I could check?
 
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