MER 470 no spark, now I've seen everything!!

[mikesearay270]

Ok. so my 4 cylinder Merc 470 port engine won't start. I am not getting spark to 3 of the 4 cylinders. How is this possible?? Only one of the 4 spark plugs is getting spark. I pulled all 4 plugs and put to good ground. Cranked and only 1 plug arcs. WTF??
I have a twin engine and my problematic port engine has spark from the coil wire to ground, at the points with HT lead 1/4" from good ground with the rotor pulled, and won't arc from the coil HT lead a 1/4" from the rotor spring lead at it's top (good news) so there's no short in the rotor. I've followed the troubleshooting sequence from my Merc service manual and primary and secondary ingition is in order. At this point it should be HT wires or plugs or distributor needing replacement. This engine will crank and occasionally backfire, gets plenty of fuel from rebuilt carb, plugs get wet with fuel. New plugs gapped properly at .035" No cracks in the distrubutor cap to the naked eye. My Stbd engine starts and runs fine. I put the distributor cap and HT wires from my running Stbd engine on my non-starting port engine. Same deal, only one plug will get spark. What IN THE HECK is going wrong??
Thanks,
Bilgerats

 

[stonyloam]

Re: MER 470 no spark, now I've seen everything!!

It could be the the cam on the distributor or the cam follower on the points is worn to the point where the points are not opening enough and your dwell is way off. With the center wire off and near ground you should get 4 sparks from the coil per rotation of the distributor shaft.

 

[EddiePetty]

Re: MER 470 no spark, now I've seen everything!!

.....kinda sounds like either the distributor's bushings or cam are/is worn in the port engine. Try swapping the complete distributor.

 

[mikesearay270]

Re: MER 470 no spark, now I've seen everything!!

Guys. Verified that I was getting 4 zaps of current every 360 degrees rotation. Popped in a new set of points, gapped to .022 (range is .018 to .025). Put the distributor cap back on. Was getting a very weak reading on my spark tester at each of the 4 plugs, but it was spark. When I was about to give up for the night and put tools away, imagine how amazed I was to see my rotor sitting on the shop rag. Reinstalled it and the engine fired right up belching out Stabil Fogging Oil that's been coating the pistons since last Sept. Thanks for the advice. I'm going to put a timing light on it tomorrow night and see where it is. No dwell meter available at this time.

 

[stonyloam]

Re: MER 470 no spark, now I've seen everything!!

Strange, sounds like some ware and the points were a little glazed over. Before I switched over to a petronix, new points were part of the spring tune up. A dwell meter is really handy, this is the one I have: http://www.amazon.com/Actron-CP7605...F8&qid=1340685176&sr=8-1&keywords=dwell+meter

 

[achris]

Re: MER 470 no spark, now I've seen everything!!

.... to see my rotor sitting on the shop rag. ...

Ohhh... :facepalm:... I've done that too many times to count...

Terry... That's a nice meter... I use this one -> http://www.amazon.com/Equus-5568-Pro-Timing-Light-Tool/dp/B000EVU8J8
Unfortunately the dwell meter is a digital number going up and down... I prefer an analog meter for dwell... Much easier to see what's really happening...

Chris.......

 

[stonyloam]

Re: MER 470 no spark, now I've seen everything!!

That is nice, mine is so old school you still have to divide the V8 numbers by 2 to get the 4 cyl numbers LOL. What I do like is the tach function to double check my boat tach especially at idle.