Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

[pprussell]

Hello,
First, not sure if this is TB IV or V ignition. Any easy way to tell?

Second, the engine is a 1996, 5.7L with 2 barrel. Alpha one gen 2

Boat is a 21' used for offshore fishing only.

Only had it a few weeks, compression good and even on all eight cylinders.

Always started hard but ran OK once going.

We changed all filters, fluids, impeller, cleaned carb with spray, new plugs, rotor, cap.

Sometimes will not start when cold or restart when hot. At those times, spark seems OK from coil wire with gap tester. But cannot get spark from plugs. Then spark comes back at plugs and engine starts again, runs rough, then cleans out and runs OK again. Sometimes happens several times in a row. Sometimes runs for entire day OK, then next day, will not start cold. Sometimes runs OK for hours, then will not restart. Never stalled once while running.

Is the choke working off the ignition electronically? I was thinking it may be an issue. If not, what could fail in the ignition, then work again, then fail again, and have no relationship to hot or cold.

Any ideas would be helpful.

Thanks,
PPRussell

 

[BudL1te]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

Perhaps a new coil would help? Since you are saying you get spark off and on I would rule out choke until your spark issue is cleared up.

 

[Oshkosh1]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

I'd check ALL electrical connections and wires for possible breaks/shorts. Sounds like a bad connection/ground rather than a component issue.

 

[dingdongs]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

a new sensor under cap cured mine after it left me stranded.similar symptoms to yours but checked mine via tbv runthrough when it had a no start situation.would run perfect once started then nothing.

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

Perhaps a new coil would help? Since you are saying you get spark off and on I would rule out choke until your spark issue is cleared up.

BudL1te, Thanks for ideas. We do get a consistent spark on the gap tester when we pull the coil wire from the middle of the distributor, plug it into the tester and ground the other side of the tester to the battery negative terminal.

Do coils ever fail intermittently, in your experience, or just go hard down?
Thanks!
PPrussell

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

I'd check ALL electrical connections and wires for possible breaks/shorts. Sounds like a bad connection/ground rather than a component issue.

Oshkosh1, thanks, that is good advice. I will pull them all, clean, retighten, spray with Boeshield and then continuity check while yanking on them. Should have done that right away.
Thanks!
PPrussell

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

a new sensor under cap cured mine after it left me stranded.similar symptoms to yours but checked mine via tbv runthrough when it had a no start situation.would run perfect once started then nothing.

Good information. While doing the wire cleanup suggested by another poster, think I will replace the sensor. The Mercruiser dealer suggested that, as well. Not expensive part.
PPrussell

 

[NHGuy]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

Also do a little unplug & replug of the TB module in case it has any corrosion on it's contact surfaces.

 

[86 century]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

Have you replaced the cap and rotor

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

Also do a little unplug & replug of the TB module in case it has any corrosion on it's contact surfaces.

NHGuy, that is a really good idea. Thanks!

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

UPDATE
Ok, we changed the rotor, cap, coil, put in the new type sensor in the distributor, cleaned all the contacts and have 12V at the purple wire at the coil and 12V at the red-white wire at the sensor. The sensor had a black ground, the old one did not, we grounded that to the bolt on the thermostat housing, probably dumb thing to do, as I now realize there is a gasket under that cover. Not sure the ground makes a difference, as the old sensor (igniter?) had only the green-white and red-white wires and no ground.

Now, we have no spark at the coil. Before all the work, we had spark at the coil and not at the plugs. So, $200 poorer and making negative progress. Any ideas?

 

[dingdongs]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

have you tried striking the green/white wire against a good known earth rapidly whilst holding the lead out the centre of the dizzy cap close to an earth.there should be spark.(ignition on)
assume the rotor arm was replaced too.

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

have you tried striking the green/white wire against a good known earth rapidly whilst holding the lead out the centre of the dizzy cap close to an earth.there should be spark.(ignition on)
assume the rotor arm was replaced too.

dingdongs,
I will try this. May I impose upon you for clarification? The green white wire exits the sensor (igniter?) at the front of the distributor. Within inches, there is a connector which allows you to separate the wire. At that point, does one strike the end coming from the distributor sensor or the green-white wire continuing on into the harness to earth? Another question if I may. The lead out the centre of the dizzy cap, we separate that from the coil but leave it connected to the centre of the cap? And then we hold the end of this wire close to a known good earth, while stiking the green-white. Correct? And the spark should be at the wire out of the dizzy cap? Not between the green-white and earth? Thanks for any additional help, as this is confusing to the novice.
PPRussell

 

[dingdongs]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

the centre wire has to be connected at the coil.
its the other end you need as this would is where the sparks would be going to each plug if it were connected to the distributer whilst the engine is rotating.because you cant strike the wire at 5000 times a minute you have to just get as rapid as you can with the green/white wire.
disconnect the green white wire out the sensor and strike to an earth is required rapidly.
read this too; http://www.google.co.uk/imgres?q=th...w=123&start=0&ndsp=22&ved=1t:429,r:1,s:0,i:73

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

the centre wire has to be connected at the coil.
its the other end you need as this would is where the sparks would be going to each plug if it were connected to the distributer whilst the engine is rotating.because you cant strike the wire at 5000 times a minute you have to just get as rapid as you can with the green/white wire.
disconnect the green white wire out the sensor and strike to an earth is required rapidly.
read this too; http://www.google.co.uk/imgres?q=th...w=123&start=0&ndsp=22&ved=1t:429,r:1,s:0,i:73

Thank you, we will try this process and report back.

 

[dingdongs]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

there could be a problem with your tachometer too,it will be connected to the -ve of your coil and you could remove the single wire usually grey to take this out the equation too.
look at the shift interrupt switch too as this can sometimes be faulty and will ground the spark.its only meant to work whilst shifting but if a bad connection will stop an engine running too.

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start other times, OK spark from coil

HERE IS THE SOLUTION
We removed, brushed, sprayed and retightened every contact. Still not spark at coil. We replaced rotor and cap, and ignitor. The ignitor was an older style and it had metal parts and fiber parts, and was corroded and a mess. We tossed it and upgraded to the new sealed Mercruiser replacement part that has an integral ground wire, not just the red-white/green-white striped wires like the older part. We grounded it. Still no spark at coil. Then, we found the coil had a stripped thread on one of the terminals. Looked like it was making contact but not able to tighten the nut on the post. So, replaced the coil. Still no spark.
Then, replaced the Thunderbolt IV module with the new, replacement part, and it takes some wiring changes, as again, like the igniter in the distributor (sensor), the new part is upgraded. When the new module was plugged in, she fired right up and ran like new.
Thanks to all for the great input. By following the suggestions, we were able to replace parts like the igniter and the coil which may have stranded us offshore in the future. Now we have more confidence in the boat, and are looking forward to running for tuna in the next few weeks.
pprussell

 

[pprussell]

Re: Mercruiser 5.7L 2 barrel runs then will not start, The rest of the story

Re: Mercruiser 5.7L 2 barrel runs then will not start, The rest of the story

OK, we cleaned every wire and contact, replaced cap, rotor, coil, ignitor (sensor in distributor) and had the dealer replace the computer TB IV module. Ran fine, took it off shore and same problem, resulting in limping to mouth of inlet and stalling a few feet from the rocks in a big swell. Had the Harbor's boat standing by and they took us alongside and brought us through.

Guess what? The coil was bad. We replaced it with the exact same part number that was on there from the prior owner. We had only owned this a short time. Took it back to dealer, and he put on a coil of a different part number from MSD specified for this engine. It ran fine for three hours on the dino at every speed.

So when you replace parts, be sure they are the right ones, not just the same ones!!

Hello,
First, not sure if this is TB IV or V ignition. Any easy way to tell?

Second, the engine is a 1996, 5.7L with 2 barrel. Alpha one gen 2

Boat is a 21' used for offshore fishing only.

Only had it a few weeks, compression good and even on all eight cylinders.

Always started hard but ran OK once going.

We changed all filters, fluids, impeller, cleaned carb with spray, new plugs, rotor, cap.

Sometimes will not start when cold or restart when hot. At those times, spark seems OK from coil wire with gap tester. But cannot get spark from plugs. Then spark comes back at plugs and engine starts again, runs rough, then cleans out and runs OK again. Sometimes happens several times in a row. Sometimes runs for entire day OK, then next day, will not start cold. Sometimes runs OK for hours, then will not restart. Never stalled once while running.

Is the choke working off the ignition electronically? I was thinking it may be an issue. If not, what could fail in the ignition, then work again, then fail again, and have no relationship to hot or cold.

Any ideas would be helpful.

Thanks,
PPRussell

 

[pprussell]

After three new carbs and two rebuilds, problem identified but not resolved. It is the alcohol in the fuel. Turns into a cloudy yellow gel in the carb bowl. Over the winter, there were times when we did not start the boat for up to two months. Even with fresh fuel, that was all it took. There are many opinions on the cause. Basically, the alcohol absorbs water and bacteria live in this organic compound forming the gel. Other folks said it is because we have an aluminum tank. The alcohol forms a compound with aluminum.
A lot of opinions, but so far nobody can tell me how to stop this again. A search on Google shows there are thousands of other boaters, classic car guys and motorcycle and snowmobile folks with the same issue.
Any thoughts?

 

[burtonrider11]

After three new carbs and two rebuilds, problem identified but not resolved. It is the alcohol in the fuel. Turns into a cloudy yellow gel in the carb bowl. Over the winter, there were times when we did not start the boat for up to two months. Even with fresh fuel, that was all it took. There are many opinions on the cause. Basically, the alcohol absorbs water and bacteria live in this organic compound forming the gel. Other folks said it is because we have an aluminum tank. The alcohol forms a compound with aluminum.
A lot of opinions, but so far nobody can tell me how to stop this again. A search on Google shows there are thousands of other boaters, classic car guys and motorcycle and snowmobile folks with the same issue.
Any thoughts?

I ONLY run "pure gas", alcohol free gas in my boat. Very similar engine to yours, 5.7l 2bbl - 1997. It always started hard, had to research and make some major adjustments to the choke. Along the way, I made the switch to the alcohol free gas. It's 91-92 octane, 100% gasoline. Boat starts better, runs better and I don't have to worry about what you are experiencing - phase separation. You're lucky you didn't nuke your engine....when phase separation is severe, it can trash the whole engine.

If you are going to run gas with ethanol in it, you should be treating it with something like Startron or similar. This helps reduce the phase seperation....It may cost more to run the pure gas, but the benefits and peace of mind is more than worth it to me.....