'87 200 Evinrude tach & mis-fire problems

[bigboat505]

My 1987 200 HP Evinrude started having intermittent tachometer problems last week; the reading would intermittently drop out and then read correctly. Yesterday it read consistently high (5000 RPM instead of about 3000 RPM for the speed I was going). Also yesterday the engine started out running well but by the end of the day it seamed to run very sluggish at cruising speed and would not hold idle ? the engine died every time. I could hardly get the boat on the trailer at the ramp due to the engine dying at idle. When I got home to flush the engine it was very difficult to start and I noticed some cylinders mis-firing intermittently. Does anyone have any ides as to my problem? Is this a power pack problem? If so, why is the tachometer reading strangely? By the way, the battery voltage increases to just under 14 volts with the engine running. If it is the power pack, any idea on how to check which one? Sorry for all the questions but I?m at a loss.

 

[HighTrim]

Re: '87 200 Evinrude tach & mis-fire problems

Welcome to iboats.

Do you have a DVM? You will need to check your Rectifier to start. Check the FAQ for a thread by Joe Reeves.

 

[HighTrim]

Re: '87 200 Evinrude tach & mis-fire problems

Tachometers read off the alternating pulses from the stator. Johnson/Evinrude has three wires coming from the stator to the regulator/rectifier, which is where the tach is connected. Graphed-out, these alternating pulses are a sine wave. Rectifiers take that sine wave and convert it to DC. Alternators only alternate if there is a complete circuit, so when a rectifier fails, the circuit is broken. The electricity from the alternator has to find a place to go, so if it loses connection at the battery, it will find its way out elsewhere, and the rectifier is usually the place unfortunately for you. I really can't explain why Johnson/Evinrude don't fuse them anyone?? Anyways, that is why rectifiers usually fail, loose or corroded battery connections. Connecting the battery backwards also blows diodes in a heartbeat. Loose connections usually take out single diodes, but can do that more than once eventually causing a complete bridge rectifier failure. Swithcing battery leads takes out both sides of the bridge rectifier right away.

All that being said, have you accidentally crossed battery leads? Are your terminals corroded or loose?

 

[bigboat505]

Re: '87 200 Evinrude tach & mis-fire problems

Thanks for the response. Yes, I do have a DVM. I will check the battery terminals mechanical connections. I haven't done anything with the batteries for several months, but it is possible they have worked loose or corroded. I will also check the stater motor end of the battery connections.