80 HP Merc won't start. Help!

[muttmike]

(reposted as original has someone elses text when I try to read it).<br /><br />What we know:<br />80HP, Model 800, SN: 305***x (darn forgot rest. am at work!), Inline four with a distributor, Single coil.<br /><br />Issue:<br />Engine spins well but won't start. Can detect no spark at plugs.<br /><br />What we tried:<br />Energize coil by jumping power from that rectangular distribution? box (front inside cover)<br /><br />What we got:<br />Sparks!!!! (NOT THE GOOD KIND AT THE PLUGS! THE SHORT KIND AT THE COIL!)<br /><br />The coil appears to be mounted to a plastic plate<br />that isolates it from the block. There are only three wires on the coil: HT lead to distributor, power in from the box thingy and chassis ground.<br /><br />Is the coil the problem (hate to replace it to find other problem caused coil to short)? Could it be the distributor? Other know problems? Can I use a car coil to test with?<br /><br />BTW: the wire insulation is melted/charred on the wires on the ignition and neutral switches. So we cut about a foot off the wiring bundle/loom and have by-passed the neutral lock-out (yellow) to the (_very_ light) orange wire and are attempting to start by adding the red wire.<br /><br />As I said the engine turns over but does not start. There appear to be some wiring issues. We were told that the PO said it was running when he replaced it.....<br /><br />We would appreciate your help<br /><br />Thanks, MuttMike

 

[jeff1]

Re: 80 HP Merc won't start. Help!

OK,THE FIRST THING TO DO IS GET A NEW RECTIFIER.<br />I'D JUST ABOUT BET MY NEXT PAYCHECK THAT ITS BLOWN<br />BESIDES THEY'RE CHEAP AND EASY TO INSTALL.THE RECTIFIER REGULATES THE CURRENT FLOW BETWEEN THE POWER BOX (RECTANGLE THING)AND THE COILS.IF YOU GET FIRE OUT OF EACH COIL,THEY CANT BE BLOWN.SO THAT WOULD ELIMINATE THE NEED FOR COILS...BY THE WAY,DON'T USE A CAR COIL...YOU MAY END UP BLOWING YOUR MIND

 

[muttmike]

Re: 80 HP Merc won't start. Help!

Jeff. You say coils (like we should have 2) I only see one. This rectifier. Does it look like a relay? (1 red in and two (burned) wires out? ;-)<br />-- MuttMike

 

[ledgefinder]

Re: 80 HP Merc won't start. Help!

Serial number does matter here - you probably have the more common ignition (7 wires to the switchbox), but it's possible you've got the oddball (4 wires to the switchbox). <br /><br />Here's a link (big thanks to maxrules) that'll give you the serial numbers, and your wiring diagram if you have the common ignition.<br /><br /> http://www.maxrules.com/oldmercs/Wiring/1966ona/30.PDF <br /><br />There are a couple simple checks you can do. Make sure your mercury tilt switch isn't grounding you (disconnect it's wire). Make user you have 12V on red (all the time) and 12V on white (just when the key is "on" or "start").<br /><br />Beyond that, you have to have a peak reading voltmeter or oscilloscope. Here's how the ignition works. A small coil inside the distributor sends a signal to the switchbox when it's time to fire a plug. I don't know the precise voltage or the waveform, but it's somewhere in the neighborhood of 2 to 10 volts, and you'll get it 4 times per crank revolution. No signal? Then the problem's the sensor in the distributor. If there is a signal, the switchbox is supposed to dump the charge in the capacitor to the coil. It's something like 300 volts, again 4 times per revolution. If you've got a peak-reading VM or a scope, you can easily see what's going on & quickly determine whether it's the sensor, switchbox or coil that's at fault. As a recent poster suggested, you might be able to use a light bulb to get a rough idea whether you're getting signals from the sensor & from the switchbox.

 

[ledgefinder]

Re: 80 HP Merc won't start. Help!

You just have one coil. The later 800/850s have 4 coils.

 

[muttmike]

Re: 80 HP Merc won't start. Help!

Hey Jeff, I think we have a kink in the comm link and it's my fault. When I said I got sparks, I did not mean at the plug(s)! When we tried to energize the coil we got sparks (as in SHORT). This short went away when we disconnected the single chassis ground from the coil to the engine case. Again, only one coil.

 

[muttmike]

Re: 80 HP Merc won't start. Help!

thanks for the link Ledgefinder. It looks closer then any of the diags in the manual we're using.

 

[Bear]

Re: 80 HP Merc won't start. Help!

800 (80,0) 2559001 - 2783252 1969 4 cyl <br />800 (80,0) 2783253 - 2986443 1970 4 cyl <br />800 (80,0) 2986444 - 3186282 1971 4 cyl <br />800 (80,0) 3186283 - 1972 4 cyl <br />800 (80,0) 9004402 - 1972 4 cyl <br />800 (80,0) 4831999 - 1978 4 cyl <br />800 (80,0) 9177626 - 1978 4 cyl <br /><br />If you have 305**** this is it:<br />800 (80,0) 2986444 - 3186282 1971 4 cyl <br /><br />This might help<br /> http://outboardparts.com/mercury/miscellaneous/troubleshootinghelp.htm

 

[muttmike]

Re: 80 HP Merc won't start. Help!

Well we "disconnected" the rectifier: no joy!<br /><br />Could not find the mercury switch (assumed it was SCed by a PO).<br /><br />The test light showed no pulse comming from the little coil in the distributor.<br />We tested by cranking starter and checking all the terminals (to chassis ground) coming from the dist. to the box. Again nary a flicker. Is this a valid test or is the duration of the pulse too short?<br /><br />Another question: the plugs installed are unique to me. There is no electrode or ground finger protruding from the end. Rather the electrode is recessed in the center of the plug. <br /><br />Any other sugestions?<br /><br />Thanks MuttMike

 

[mellowyellow]

Re: 80 HP Merc won't start. Help!

center-fire plugs are correct. you have no spark<br />on all 4? rectifier only sends signal to tach.<br />and sends juice to keep battery charged. <br />doubt it would be no-start problem...but I ain't<br />100% sure...<br />have a manual? get one if not! <br />the troubleshooting section would be invaluable.<br />tried to jump start? by-pass ignition, battery,<br />and starter yet?

 

[ledgefinder]

Re: 80 HP Merc won't start. Help!

Lack of glow on light bulb may not be definitive - the voltage on that sensor is only around 2 to 10 volts. Sorry, I probably suggested a dumb test for the sensor. Tough to decipher these without a 'scope or peak-reading voltmeter.