Mercury 80 hp ignition problems

Dia75

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Oct 31, 2013
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Hi, I have an issue with my Mercury 80 hp, I have replaced the spark plugs,CDI/Trigger and the stator and still no spark would the mercury switch (small blue thing with 2 wires one goes to earth) that's next to the switch box be the cause?.. or the rectifier?, hopefully a new battery might solve this? low battery power and slow turn over might cause the lack of spark?

Also the tilt and trim works, but stops half way lifting up, after putting power to the solenoid it will raise all the way, has no issue lowering down completely.. any ideas?

serial number is 8054064

Before.jpgAfter 10.jpg
 

Chris1956

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Mar 25, 2004
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27,036
Re: Mercury 80 hp ignition problems

Well, all those things could be a problem. Disconnect the mercury switch and the rectifier. Tape the yellow wires on the rectifier so they cannot short to ground or each other. Disconnect black/yellow ign killer wire at switchbox. I did not see a black/yellow wire in your picture. Older motors had an orange or salmon colored ign killer wire. Maybe you bought harness with older wire colors?


Clean all battery cables, and check 'em for corrosion under the insulation. Replace any bad ones. Use a second battery in parallel to boost starting motor current. See if spark returns.

BTW most PTT units have a trim limit switch. It will allow trim unit to trim about 1/2 way. Sound familar?
 

carholme

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Re: Mercury 80 hp ignition problems

You certainly have the standard Mercury corrosion evident throughout your wiring loom. In picture 1, one of the wires going to the switchbox ix broken.

Gerry
 

Dia75

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Re: Mercury 80 hp ignition problems

The parts where sourced from a local Mercury spare parts/boat dealership and with the engine serial number, and I did go back to check to make sure wiring colors were correct as what was left of original wiring to compare, I read up on the wiring diagrams and other info regarding this model engine and it did point to a black/yellow wire, although I dont recall one before I replaced the CDI, only the 2 orange wires in the second pic.

As for the tilt and trim there is a switch on the ram arm im assuming this is the trim limit switch, disconnecting this is still wont raise fully, tbh it dosent even get half way.. not enough for the boat to be trailered.
 

Dia75

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Re: Mercury 80 hp ignition problems

You certainly have the standard Mercury corrosion evident throughout your wiring loom. In picture 1, one of the wires going to the switchbox ix broken.

Gerry

Yup lol, pretty much the entire loom was in that state when I got the boat, all replaced now. Boat apparently hadnt been started in 7 or 8 years.
 

Chris1956

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Re: Mercury 80 hp ignition problems

Trim limit switches are wired in series with trim motor. Disconnecting them allows no power tothe solenoids. use a jumper wire to bypass the trim limit switch. Normally a trailer button is used to lift the motor all the way. Do you have one of those? Do you have the three pushbutton PTT panel instead?
 

Dia75

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Re: Mercury 80 hp ignition problems

It does have the trailer button ill look into the wiring on this today, as for the engine not starting ill also disconnect the rectifier and mercury switch hopefully this sorts the issues, getting new battery today.
 

Dia75

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Re: Mercury 80 hp ignition problems

Ok, trim all good replaced a section of wiring that was heavily corroded that was stopping the trailer button from working, and have spark on all cylinders but think now its a fuel issue ;/ drained tank and replaced with fresh fuel/oil mix, im assuming there are rebuild kits for the carbs and fuel pump?
 

Chris1956

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Re: Mercury 80 hp ignition problems

Sure, gasket kit, inlet needle and new floats, for each carb are the way to go. Make sure to clean the idle passages well.
 

Dia75

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Re: Mercury 80 hp ignition problems

well I have spark, carbys cleaned out with compressor, idle screw needles are stainless as are the needles in the fuel bowl regardless it was pretty clean inside and no wear on either so just replaced gaskets.. new pump kit so now bladder is hard. New battery but still slow on turn over still.. replacing starter solenoid when it arrives as previously on removing the wiring loom I damaged it by cracking the casing. Would the solenoid be the issue?.. or the cables from solenoid to battery?.. as these had a lot of weathering.. just put new insulation over them basically.. but would the weather damaged cables be the cause also?.. low resistance and causing them to heat up? or would I knew a start motor rebuild/new motor? Will be doing a compression test on it also, had a tester just wrong fitting is designed for car engines so doesnt seal.. although i got 90 psi on cylinder 1.. lol.. test just leaked past it.. slowly.. im getting somewhere.. I think >.<
 

Chris1956

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Re: Mercury 80 hp ignition problems

The battery cables if corroded, will cause the starter to spin slowly. My battery cables rotted out down to a couple of strands only, under the insulation. So check the entire length of the cables, looking for bulges.
 

Dia75

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Re: Mercury 80 hp ignition problems

Ill be replacing starting solenoid, and considering a new harness is quite expensive for now ill make up two new cables to from battery to solenoid to test.
 

Dia75

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Re: Mercury 80 hp ignition problems

Success!! faulty starter solenoid was the cause, a little Aerostart on first start up just to make sure, and 10 mins running on idle with earmuffs (a new impeller was installed) to adjust air mixture it runs like a dream! :D, considering.. I never actually comp tested it entire time I have owned this boat as it was given to me before a divorce settlement that would have left a fellow bloke to pay its value.
It sat it at a relatives property for 2 years, until recently decided its time to get out onto the water with it.. and discovered how weathered the wiring was.. about $1200 in parts etc, only replaced with genuine Mercury items and a little faith it was just electrical and maintenance, I know I skipped step 1 Compression test.. but the risk going in wallet deep paid off I would say! :p
Taking it for a test run at a lake close by make sure the timing is correct and see what fuel usage it like before it does a fishing trip.

Thanks for the comments on this thread! Till next time happy and safe boating :D
 

Dia75

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Oct 31, 2013
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Re: Mercury 80 hp ignition problems

Another question regarding this motor.. does the stator charge the battery once it is started?.. and whats best way to test it if it is suppose to be charging it..
 
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