Mariner 115 surging Please Help!

[impatico]

I have a 84 Mariner 115 on 84 Thermoglass 16ft bowrider.
I bought the boat after a nice test drive and all was good. Took it home and I took it out with my mom and brother for a quick 10 min spin. I let my brother drive the boat while I backed in the trailer to load it back up. long story short my brother rammed the boat into the trailer. put it in reverse and caught the prop on the trailer and the engine cut off.

next time I took it out it ran fine for about 20 mins then while cruising along it fell on its face and hasn't run right since.

now it runs fine at home on a hose, but on the lake it goes up to 1200 RPM and just surges up and down from 1200-1300.
every once and a while it will pick up and get to plane, but won't go full speed at all.

I've tried squeezing the primer bulb while its surging and no change. also cleaned out the fuel system, nothing
tested the spark and cyl 1 is weak, but compression is good on all 6
changed the plugs, and switched the wires around, nothing
new coil, same, new trigger, same, new ecu, same

have the repair manual and tested everything as it says and it all tests fine, which it then says to connect your diagnostic computer, but don't have one.

the only thing left I can think of is the "tone wheel" the magnet wheel under the flywheel that the trigger feeds off of, but I can't even find a listing for it.


Sorry for the novel but would love any help/insight

 

[aussieflash]

Re: Mariner 115 surging Please Help!

Ouch.Id be checking the prop and prop shaft for damage.You may have bent shaft or stripped some teeth.
(i say you,.... but i mean your brother)

 

[MassillonBuckeye]

How "weak" is that spark out of curiosity?

 

[impatico]

Re: Mariner 115 surging Please Help!

don't really know what kind of answer you are looking for so about 1/2 the power as the others???

 

[Faztbullet]

Re: Mariner 115 surging Please Help!

How about posting the serial number as a 1984 115 does not have a ECU and you cannot hook any diagnostic equipment to it.

 

[impatico]

Re: Mariner 115 surging Please Help!

don't have the serial number the boat is an hour away at my parents for the winter. but it is an 84 mariner 115 and I was referring to the switch box as the ECU as it technically is an engine control unit controlling the ignition system, sorry for the confusion, and the diagnostic computer is the quicksilver thunderbolt ignition analyzer part # c-91-62563A1 I have no idea what that is, I can't find much info online as to what it is, but I did find a PDF of an old tool catalog from Mercury with it in it at http://www.vintagesnow.com/Mercury_files/section 9.pdf

 

[Faztbullet]

Re: Mariner 115 surging Please Help!

If you have weak spark on 1 cylinder it either the switchbox or a bad bias circuit in other switchbox. How did you determine it was weak?

 

[impatico]

Re: Mariner 115 surging Please Help!

with one of those spark testers that clip onto the head and plug into the wire, I believe it's an NGK one

I only replaced the one switchbox that triggers the #1 cyl, think I should get another one? I think I did swap the box i took out with the other to test but ive tried so many things I can't remember, but will phone my dad when he is off in an hour or so

 

[Faztbullet]

Re: Mariner 115 surging Please Help!

A bad bias circuit can make a good box act bad or actually damage the replacement, that is why Merc suggests they be replaced in pairs.

 

[impatico]

Re: Mariner 115 surging Please Help!

so what would you recommend? buy 2 more new ones? you don't think it could be the magnet under the flywheel?

can u test it? take the black/white wire off?
also while I have your superior wisdom, should I get 14.4 volts out of the charging system? while running WOT I only get about a .2-.3 volt increase from engine off voltage. max I have seen is 12.3/12.4 ish volts

 

[aussieflash]

Re: Mariner 115 surging Please Help!

Mmmmmm. You took out boat for test....ran good.You took boat out with family....ran good.You slammed boat into trailer and smashed spinning prop into trailer and you think it's an electrical fault????Good luck.

 

[impatico]

Re: Mariner 115 surging Please Help!

you'd think if it was the prop shaft it would be constant, but the problem didn't arise until 1/2 way through the trip after the accident.
I also have run the engine in the yard plenty, I have run it in gear at WOT and the prop spins true

thanks you for your suggestions though

 

[aussieflash]

Re: Mariner 115 surging Please Help!

Prop would have to be tested under load (pushing 1/2 ton boat in water).
Also rebuild carbs if not done.
Definitely test Stator.
Pull plugs and check condition...Black...brown...or whistle clean?they tell a lot of stories.Good Luck.

 

[impatico]

Re: Mariner 115 surging Please Help!

prop runs true in the water too, carbs are fine, stator tests good, plugs fine, but put new in anyway

 

[Faztbullet]

Re: Mariner 115 surging Please Help!

You don't think it could be the magnet under the flywheel?

Nope as it firing the other cylinders.
Intermittent firing on one or more cylinders:

Disconnect the white/black wire between the packs on a 6 cylinder and retest. If all cylinders now fire, replace both packs as there is a problem in the bias circuitry. On all others, check for low voltage from the stator and trigger. Disconnect the rectifier and retest. If the problem disappears, replace the rectifier.

All cylinders fire but the engine will not crank and run:

On 3 and 6 cylinder engines, disconnect white/black wire and check the bias circuit (white/black terminals) resistance to engine
ground. Readings should be approximately 15,000W for standard packs and 9600W for racing units. If the readings are correct on the
packs, index the flywheel and check timing on all individual cylinders. If the timing varies, replace BOTH packs.

Destroyed one or two cylinders (6 cylinder):

Using a DC Voltmeter check the voltage on the white/black (Bias) terminal. With everything connected, run the engine at various
Rpm’s and watch the voltage reading. It should remain steady for a set RPM. Fluctuation in voltage indicates a problem in the bias
circuit. If there is a problem, disconnect everything on the white/black terminal except the jumper from pack to pack. Retest, if the
problem persists, replace BOTH switch boxes. If the problem went away, reconnect the items taken off of the white/black terminal one at a time, retest after every reconnection until you locate the source of the problem.
Thank you for using CDI Electronics.

 

[impatico]

Re: Mariner 115 surging Please Help!

Will do, thanks FaztBullet your the man!