merc mystery

[imported_dickm]

After 20 min. at cruising speed, motor detonates but idles and restarts.(1998 5.0,carburated) 30 more minutes, detonates and no spark.12V is going to the coil, nothing is comming out.Replaced coil,wires,plugs,cap, ignition sensor, Key switch, lanyard kill switch, and ignition module. Runs great for another 30 minutes. detonates and starts to run rough. I'm guessing headed for no spark. Could corrison in the battery cables be the orignial cause? I followed the manual's troubleshooting chart, Vessel Assist has labeled me a "frequent flyer".

 

[Limited-Time]

Re: merc mystery

I'm guessing a heat related failure, Losing connection somewhere. Does it start and run after it cools down?

 

[cobra 3.0]

Re: merc mystery

Plugged gas vent? Try loosening your gas cap and see if it still does it.

 

[imported_dickm]

Re: merc mystery

first time yes, 2nd time no (no spark,replaced module) ran great, then same thing all over

 

[bruceb58]

Re: merc mystery

You verified no spark when this happens? Did you pull a plug wire off and test it?

 

[searay3]

Re: merc mystery

I also believe you have a poor, heat related connection somewhere. Chasing electrical can be tough. More of a process of elimination than looking for a cause. Start by making sure your batt cables are clean and tight at both ends. Battery and block. Follow them from the battery to the block/starter and look for any rubbing, chafing or even melting near the block. Look for corrosion wicked up into the connections at the ignition/distrib and alt. The big plug where the helm wiring meets the motors wiring can be loose or corroded. A vom and a lot of patience.....

 

[bjcsc]

Re: merc mystery

Keep in mind during all of this that detonation is very bad. It can destroy an engine in a very short period of time, as in minutes...

 

[tommays]

Re: merc mystery

My many experiences with the lean condition caused buy cloged fuel filters points me in a different dirrection


Tommays

 

[Limited-Time]

Re: merc mystery

My many experiences with the lean condition caused buy cloged fuel filters points me in a different dirrection


Tommays

Same here but the loss of spark leads me to the heat related elec. issue.

 

[bjcsc]

Re: merc mystery

My many experiences with the lean condition caused buy cloged fuel filters points me in a different dirrection


Tommays

Wouldn't you notice an increase in engine temperature if that was the case?

 

[DHPMARINE]

Re: merc mystery

What do you mean by detonates? I'm not sure we see the whole problem.

DHP

 

[imported_dickm]

Re: merc mystery

popping and backfiring sounds. This all seemed to start after my outdrive was stuck down, due to a bad connection at the positive terminal on the battery to the trim pump. I was fooling around with the terminals and hadn't disconnected the battery's negative cable. I certainly appreciate the input and I'll keep trying.

 

[Reel Poor]

Re: merc mystery

Replaced coil,wires,plugs,cap, ignition sensor, Key switch, lanyard kill switch, and ignition module.

Did you replace the rotor ?
Is the distributer housing grounded properly ?

 

[imported_dickm]

Re: merc mystery

Local store didn't have the rotor that day, I will replace it. I've been cleaning up the grounds to that area. The post on the block was fairly nasty

i

 

[Reel Poor]

Re: merc mystery

It's possible that the rotor is your problem.

 

[imported_dickm]

Re: merc mystery

thanks Reel, being unwise I thought I had it figured out with some ground cleaning. Same story, towed back in. o..K. How is the distributor housing grounded?I have a new sensor that has an additional ground wire that the original didn't have. The problem condition occurs the same with the new sensor as with the original.

 

[Reel Poor]

Re: merc mystery

If you grounded the black wire from the new sensor you should be ok.

Get the new rotor.

 

[imported_dickm]

Re: merc mystery

failed again, now theory #7. All this seemed to start after an oil change from quicksilver 25-50 to mobil 1, synthetic 15-50. Could the viscosity difference make the sensors shut down the motor after the oil gets hot?. the oil pressure reads normal.temp is fine too.

 

[imported_dickm]

Re: merc mystery

i'm taking the boat to the shop today. The wife is upset I spent so much time on it and were're still not boating