help with no fire on any cylinder 1984 90 hp mercury inline

[d.r.]

I HAVE A 1984 MERCURY 90 HP INLINE 6 S.N.65714XX that I have been running for a while. It was running great and just lost power and died on me saturday. I had just taken off after running some lines and it died. When i got home i checked the fuse for the ignition power and it was blown. I replaced it with proper20amp and it has held. Put it on muffs and it acted like it was not firing . Removed one plugand saw no fire when grounded . By the way plugs are almost new ngks. That was evening before last. Came back today and it acted like it was going to crank and actually did momentarilly and died. Then it acted like it was not firing again so I pulled all 6 plugs and grounded to the block and couldn't see any spark. I ohmed out ignition switch and it seems ok. I checked power at the switch box white and red wires and voltage seems very low . can someone give a fellow with limited inteligence some help as what might be happening to my beloved merc.

 

[JB]

Re: help!!!!!

Re: help!!!!!

Howdy, d.r.

Welcome to iboats.

"help" is the worst possible title for a post.

Check this out and try again. http://forums.iboats.com/showthread.php?t=250877

Good luck.

 

[ZigZaggin]

Re: help!!!!!

Re: help!!!!!

I am no pro but am going through a similar issue on mine. Originally no fire on #4 cyl. I tested switch boxes by swapping them and spark issue did not follow so both checked out ok. Ended up being dead #4 coil. Replaced that and then next time out was WOT for about 10 min and then she pretty much shut down and would only get up to 2500 RPM. Had a Walleye tournament coming up and not a lot of time so I had a good mechanic I know check it out. Ended up being loose ground wires. Evidently i didn't get em tight enough and they vibrated loose.

Fished the tournament on Sunday and it ran great to our first spot. 5200 RPM and solid the whole way. Shut it down and fished for about 40 min and on the way to the next spot, just as we got up on plane something happened and we dropped to 4000 RPM and 25 mph. Ran that way consistently the rest of the day. Probably not good for it. Maybe a total of 2hrs total run time that day. Took it back to Tom on Monday and no spark on #4 again. Coil checked ok on ohms. I'll let ya know what he finds out. Most likely switchbox.

If yours has no spark on any of the cylinders you'll proabably need a stator because in my opinion its not very likely for both switchboxes to fail at the same time.

 

[narvlebenoit]

Re: help with no fire on any cylinder 1984 90 hp mercury inline

I have a 1981 90 h.p. and one day I had fire on 3 cyl. the next day tryed again and had no fire on any cyl. it was switch boxes check and see if you have fire going to the coils if not switch boxes. good luck .

 

[CharlieB]

Re: help with no fire on any cylinder 1984 90 hp mercury inline

Due to the COST and the "NO RETURN" on electrical parts policies, it is NOT safe to make an assumption that switchboxes are bad and just start replacing parts until the motor runs again.

A systematic process of testing and elliminating suspects is the speediest and most cost effective method of repair.

Download the FREE Ignition Troubleshooting Guide from CDI Electronics.com

Beg, borrow, buy, or build a DVA Adaptor to use with most any volt/ohms meter and TEST your ignition components following the detailed direction found in the CDI Guide.

Prove parts good/bad then spend your hard earned money on ONLY what you need to make it run again.

 

[ZigZaggin]

Re: help with no fire on any cylinder 1984 90 hp mercury inline

Good Post Charlie B. I agree. In response to my first post on this thread... here's a little re-cap. 2 weeks ago the #4 coil was replaced and the boat ran great for a couple days. Started running terrible again and My mechanic found loose ground wires that I didn't tighten enough when I replaced the coil. Ran great again on the test drive.

Fished this past Sunday with it and ran great in the morning but then bugged out and would only go to 4000 RPM. Sounded it like it was starved for gas. Took it to mechanic on Monday ran a quick test. No fire on #4 hole again! Tom fully checked out the entire ignition system. High and Low speed spark, Trigger coils, stator, etc... He called me back tonight and found a faulty switchbox. Beginning to think I have a gremlin in there. Decided to replace both switchboxes with CDI brand replacements and keep the good one for a spare. Hopefully they last.

Also, if anyone is close to Davenport, IA checkout unleymarine.com. Super cool guy who does an honest job! 16 years experience and now he's starting his own shop.