1987 85hp force charging problems

hammy_aaron

Recruit
Joined
Jul 13, 2012
Messages
4
Hi All,

This is my first post, as I just recently bought an older boat with the above engine on it.

The charging system is not working. I have run through all of the troubleshooting for the electrical system. I have a good digital voltmeter, and when I check the stator the resistance is within spec. However, when I check the stator to ground, the shop manual says the resistance should be infinity. My voltmeter shows a really high (3000ish) and it keeps climbing, but I dont know what it should read for "infinity"

I have changed the rectifier, checked the circuit breaker, checked the continuity to the battery, and checked all the wiring. The battery voltage is 11.8 with engine off, then bumps up to around 12 at idle, and 12.8 at 1000rpm. That doesnt seem like a high enough rise to charge the battery.

Thank you in advance for all your help.

Aaron
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: 1987 85hp force charging problems

Infinity should be the same as if you were holding the leads and not touching anything, or ""open" circuit. What color stator wires are you checking for the battery charging circuit?
 

hammy_aaron

Recruit
Joined
Jul 13, 2012
Messages
4
Re: 1987 85hp force charging problems

My stator wires are yellow.

To check the continuity I went from the red wire on the rectifier to the red cable at the battery.
 

pnwboat

Rear Admiral
Joined
Oct 8, 2007
Messages
4,251
Re: 1987 85hp force charging problems

What was the resistance reading between the two yellow wires (they should be disconnected from the rectifier)?

I just realized that on a 1987 85HP motor, the battery charging leads on the stator are Green w/Yellow stripe. Do you have any leads that are Green w/yellow stripe?
 

hammy_aaron

Recruit
Joined
Jul 13, 2012
Messages
4
Re: 1987 85hp force charging problems

The reading was 0.6 ohms

There is two yellow going to the rectifier, brown/blue, brown/yellow, brown/blue, brown/yellow coming out of the windings on the stator
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Re: 1987 85hp force charging problems

It seems the rectifier is working. With 11V at stop and 12.8V at 1000 RPM is about right and it should go higher maybe up to 16V at WOT. Remember a simple two speaker stereo alone will eventually drain your battery (unless you have dual batteries) because the charging system is only rated at 7.0 amps at 12V or equivalent of 90 watts at full speed. The engine itself do not use battery power when running. The charging system is more like for the running lights and a little bit for the battery.
 

hammy_aaron

Recruit
Joined
Jul 13, 2012
Messages
4
Re: 1987 85hp force charging problems

Ok.

Thanks a lot. I'm gonna take her out for a run.

Appreciate your help
 

Oldsquid

Cadet
Joined
Sep 16, 2012
Messages
10
Re: 1987 85hp force charging problems

I'm not sure my rectifier is working. I tested with ohm meter and it read 2.6 Mohm forward bias and open reverse bias. Instead of replacing the rectifier with an original bridge, I opted to replace the whole thing. I live in a small town and was unable to find a non-maintenance free battery but I couldn't find one that was recommended. I decided to do a little home work and found a 35 amp bridge and added a 14v zener diode to clamp the output voltage at that level to save the battery. I'll post later for results.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Re: 1987 85hp force charging problems

You should have just started your own thread. Anyways, let us know how it goes with the zener diode. Some people confuses regular batteries as maintenance free batteries because they cannot easily identify the new style electrolyte fill holes (two banks of three holes instead of 6 individual holes). Walmart has mostly regular lead acid batteries. The forward/reverse resistance reading seems to be within range although the forward seems to be a little high. The rule of thumb is to have a ratio of 1:10. Personally, the best way to find out if the rectifier is working is through voltage testing between the input and output.
 
Top