Both Mercruisar engines won't start

[hdommert]

I have twin 340 rebuild 1986 340 Mercruisar's (454 block) engines. Both engines won't start, wait one will start, oh no now they won't start.....etc. you get the picture. The engines will crank over, there's a spark and fuel will get to the carburator, except that there is no gas smell. A novice told me that I needed a new accelarator pump kit and to add marine engine stabil to the fuel becasue the enthanol is the reason that the engine won't turn over. I still have fiberglass fuel tank. Do I need to replace immediately or can this wiat? How true is this and what else am I missing. Heinz J. Dommert 1986 SF Bright Raven, Summit North Marina DE

[lobsta1]

Heinz, Welcome to the playground. It seems like you have to start with some basic troubleshooting. Are both engines doing exactly the same at the same time? If not, what is different. Are you getting 13V at the start terminal? If you pull the wire off the start switch that is multiplied to all the gauges, do you get the voltage now? What do you get at the positive side of the coil? I don't know your level of expertise, so be please do not be offended when I say start with the basics. I am assuming you have Merc engines with Thunderbolt IV ignition. If so you can go to this link & scroll down to the TB IV pics & troubleshooting section. Al http://www.marinemechanic.com/site/page19.html

[dougl33]

Tell the novice to go away. What were the engines doing before? Running well? Had you just fueled up? Something's going on if they both stopped running at the same time, though I doubt its ethanol related.

[hdommert]

Thanks - All lobsta1 Basics are fine and yes both engines do the same thing. For whatever reason I got the starboard to start but can't figure out for the life of me how or why. I will test the start switch voltage to see whether I get 13V at the terminal. Just for my understanding - how did I go from fuel, spark and air to voltage problem? Are you saying the the ignition is not passing enough juice to the starter? Interesting, I never through of that. FYI - I did read half the script for the new naming ceremony of the boat. That's when the starboard engine kicked-in. If your superstitious maybe I need to finish the naming ceremony and the port side will start! dougl33 Next time I see him, novice is gone - see ya! Heinz J. Dommert 1986 SF Bright Raven, Summit North Marina DE

[Rick]

Heinz, No one here is going to tell you one way or the other whhether your gas tank is ok. It's one of those things where it's the Captain's decision. There's plenty to read within the forum about it for you to understand it better. There is however a few of us who think that post '85 boats will have fewer ethanol problems. I think Al's concern is that if you're dropping too much voltage, the engine's ignition/computer won't work right. My engines have fuel injectors and a computer that stop working below 10 volts. So this is one check that's easy to confirm and a good one to eliminate. Give us more info, we'll help get them going. Rick Ticket 85 SF Merc 454 MPI's Falmouth, MA

[lobsta1]

Not enough voltage = no spark. When you are talking the starter, then that is different problem from no spark. If the motors crank, do they try to start then die when you release the starter switch? If they do you could have a bad resistor wire in the Merc harness. Get a 25' length of at least 14 gauge wire & temporarily run direct from the start switch to the positive side of the coil. This will bypass all the harness connections & the resistor wire. When was the last time plugs, wires, rotor & cap were replaced? Back in the 1980s, Merc wires were notorious for going bad after 3 years. Over 20 years ago, I spent 2 days in Pt Judith R.I. with the local mechanic finally diagnosing a bad coil. Had to come all the way back to Danvers, Ma with a WOT of only 3000 rpm. Called my local mechanic (Doug LeBlanc's cousin) & he said (without looking & just by knowing my boat) "get rid of the wires". End of problem & back up to 4350 rpm WOT. Al

[franklyprice]

Replace them with diesels, that will fix them.. Oh , wait, not everyone can do that. Well, Al's advice is good. You have to rule out problems one step at a time. You need good gas, enough spark to ignite it and lets assume since both engines just started doing this that there is enough compression and the timing is OK. So don't rule out a big slug of water in both engines. If you aren't getting what you want out of jumping the ignition, I would change fuel filters, run it through until good gas is flowing and then you may need to rebuild the carbs, at least suck out the bad gas and refill with clean .

[otf]

If it is both motors that have a problem begin with the things in commmon, voltage, fuel. Chances are there is not one item on both motors that went bad at the same time (such as a coil) unless they are in bad repair. If neither will start and they both crank (they have some voltage) I would lean toward fuel. If it was shut off hot last time it makes sense that something could have crystalized/hardened as it sat and cooled. A smell of gas would imply that the carbs are getting fuel, this is real easy to test with a simple sniff of the intake without the spark arrestor. If they are getting fuel the next question is enough, and is it good? A decent mechanic will be able to smell and look at gas and know if it is "bad". If it has water in it that could be another problem. Ethanol, from my experience, forms inside the intake-on and harms the mechanical portions of the motor (valves, etc). The damage/failure of these is more obvious than just not starting. If they are not getting enough gas it could be filter, fuel pump, pickup. I'd probably check them in that order.

[FidelityJim]

Thunderbolt ignitions eat plug wires, you may see a spark but it's just not hot enough. After going through a couple of sets of Merc. wires I switched to 8mm Accel Hi-Perf and haven't had a problem for 4 years. Also check the sender in the distributors (the thing that the slotted cup goes through) the original ones had steel that rusted and caused timing variations and rough idle. Quite often ignition troubles mimic fuel problems. Clean your flame arrestors with Fantastic and rinse with water, don't use solvent based cleaners. Jim Hart Fidelity:Always faithful and worthy of trust.