motor went boom

T

Turkj40

Member
Sep 17, 2014
84
Plymouth Ma
Boat Info
320 sundancer
Engines
Twin inboard 350s
big trouble or something simple??? sooooooo i was supposed to be getting hauled in today and as normal I go to start engines one more time before pick up and nothing form my port side. Cranks but wont turn over then boom, blew the exhaust hose off from riser to muff and saw a spark from what looked like the alternator. Should I be worried or do I have minor repairs. voice your opinions to help with my tequila consumption....
 
Usually when someone says that it "cranks" that means that it is turning over. So did it turn over but not start? Need more info like is it a carb or fuel injected? Year? Sounds like a large back fire.
 
2002 400hrs 5.7 MPIs, ran over the weekend for springs first run just fine. this morning i went to start port side and it didn't start, then a big backfire blowing off the hose from right side of engine looking at stern and the mysterious spark from the alternator. im scared to crank it at the moment to see if it happens again
 
So a couple of things:

-How was the engine running the day before?
-Usually a backfire is cause by an ignition issue - mainly timing way off.
-I would guess the spark you saw from the alternator was really the flame blowing out when the exhaust hose came off - you have inboards, so in a 320 thinking vdrives with the engines facing to stern, so alternator is right there where the exhausts are.
-I would pull the coil wire and open the throttle fully so it won't get any spark or fuel and turn it over a few times to make sure it turns over ok. Doubt you did any damage with one backfire, they bark a lot louder than they bite.
-I'm not going to tell you to try starting it again - I probably would, but that is just me.
-The backfire was either an anomaly - not so common with fuel injection vs carburetor - or you have a timing/ignition or a fuel system problem. With a carbureted engine easy to troubleshoot, fuel injected a little more complicated. A lot of times when a flooded engine finally does start it will backfire.
 
they ran great, port was a sluggish start but ran great. as far as the spark from the alternator the hose blew from the other side of the engine. ill start from the top and work my way down to see why its so hesitant to start. more aggravated then anything cause shes still on blocks in my yard...
 
Ignition issue most likely, did you replace cap and rotor this season ? how old is coil wire? you can swap them see if it fires up.
 
Ate you sure the spark came from your alternator? Is your air intake or "flame arrestor" right ontop of your alternator? Mine is and a good enough backfire will throw a flame up into the flame arrestor and if it's a strong enough flame it will break through the arrestor and look kinda like a spark on the outside.
On the other hand it could be like everybody is saying an ignition problem. Let's say your coil is on its way out or the cylinder that caused the backfire has let's say a bag plug or a loose wire boot. All of those problems above would cause a no spark situation in that one cylinder in return letting that cylinder load up with fuel until u get that one lucky spark and boom there goes your backfire.
As said above do a full tune up. Plug wires cap rotor and coil. If you get the motor to run after that have somebody there to check the timing right away but I don't think you will need to after a good tune up
 
This is my opinion only not an expert but have worked on many injected engines.
Everything as stated above with one exception yours being an MPI system means you have individual injectors on each cylinder. Several things could be happening.

1) you may have a bad sensor on a cylinder allowing it to inject to much fuel into that cylinder when trying to start it causing it to flood in one cylinder.
2) injector could be leaking after engine is turned off allowing that cylinder to load up with fuel.

The first thing I would do is.
1) pull coil wire out of distributor.
2) remove all plugs look at each one to make sure it isn't soaked with fuel or fowled. (google a chart for plug condition fowling, burnt, etc and compare your plugs)
3) if all plugs are good then I would either try to start it or do a full tuneup.

With an MPI system you can leak fuel into one cylinder causing detention when the intake valve opens which is easier to troubleshoot than a TBI or carb'd system which will leak into any intake valve that is open.

Again just my opinion someone else may have more knowledge on your issue.
 
First of all thank you for your replies, so motor is running. Did the norm of checking top to bottom. Replaced SP wires, cap and rotor were clean even though I heard that they are notorious for cross firing and plugs are good. So when it backfired the raw water impeller reversed and caused the belt to bind up. Took the belt of turned it by hand clockwise and reinstalled the belt. So from there I removed the ignition and fuel fuses and spun the crank to make sure everything was turning correctly. Installed fuse gave it a quick spin and it gave me a burp of smoke out the top. Now comes the wierd part, the impeller reversed itself again and the belt stopped spinning. Impellers were changed last year, at that point I decided to replace them again and presto she she purrs like a kitten. I know the two thing don't coincide impeller and fuel,air,spark but why did it. Coincidence??? Thanks again
 
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