1990 3.4L 250HP diode question

[Capt Randy]

I ohm tested my diode on the motor while I was replacing the stator and trigger. It is open in BOTH directions. What would this do to the performance of the ignition or charging system?<br /> PS, anyone ever bought one? I can't find one online. Was just wondering how much$$$$

 

[Trent]

Re: 1990 3.4L 250HP diode question

If your rectifier is open both ways it can cause the tach not to work and the battery will not charge. Mercury p/n 62351A2 web page

 

[Capt Randy]

Re: 1990 3.4L 250HP diode question

Trent,<br /> Thanx for the reply. The link was very helpful. However, I am refering to the diode (not rectifier) that is inline with the blk/yel wire (kill circuit). I found the part (#83-42551a1) in the link you supplied. I don't want to fire up the motor with 800.00 worth of new switchboxes, stator and trigger and have a problem due to this open diode. Anyone know what it do?? I think it is related to the speed limiter (which is disconnected).

 

[ronmold]

Re: 1990 3.4L 250HP diode question

Where exactly does that diode hook to? Saw it also in the parts diagram but for a 3L not a 3.4L. If from the rev limiter it probably allows the limiter to shut down only 1 bank of cyls. but the ign. sw. to shut off both. Just a guess on my part.

 

[Capt Randy]

Re: 1990 3.4L 250HP diode question

Dasboot,<br /> The diode is in the wiring between the lower switchbox and the rev limiter. The lower switchbox is the one that is disabled if the RPMs exceed 6,000. My limiter is removed. This diode may have been open for years. Should I replace it, or not install the blk/yel to the switchbox, or hook up the blk/yel without the diode!?!

 

[Capt Randy]

Re: 1990 3.4L 250HP diode question

...Anybody want to chime in???

 

[Paul Moir]

Re: 1990 3.4L 250HP diode question

Sure, <br />Did you test it with a digital meter? If so, testing it on the ohms scale is a mistake. Use the diode (looks like -|<- ) test function. In one direction you should read infinty, in the other you should read less than 1 volt, depending on the diode.<br /><br />I can't count the number of times people on this board have followed the manual, or people's suggestions here and replaced a perfectly working diode or rectifier because neither one understood how to test them. The manual publishers particulairly should be ashamed. <br />For God's sake, it's the twenty-first century already! People have digital meters, not ones with 9v batteries or a pile of vaccum tubes!<br /><br />Please pardon my rant...

 

[ronmold]

Re: 1990 3.4L 250HP diode question

Y - off the blk/yel to both switchboxes. Thats how the rest of Mercs are wired that don't have a rev limiter. Paul is right you must check diodes with a meter on "diode" or a 2k range to test them properly.

 

[Capt Randy]

Re: 1990 3.4L 250HP diode question

I will re-check my DVOM at the shop when I open up tommorrow. I used my old digital at home, read open both ways. Used my newer Fluke at the shop, and it read open one way, but had continuity with the setting on highest (2m?). I think the diode is in fact to facilitate the speed limiter, and without it(diode and limiter)I am OK!!