Merc 5.7 idles and then stalls

[Mlevy]

Hello everyone,

Im having a idleing issue with my boat. I have recently re-powered with a 5.7 vortec reman from atk. The issue I’m having is when the boat is cold it starts and idles for maybe 5 mins. Once warm it will run rough and stall. I turn the key off then back on, crank the motor, starts and idles for 10 seconds, then dies.

Things I have checked / replaced with the re-power and diagnosing:

-New distributer
-New plugs
-New wires
-Went through carb Edelbrock 1409
-Metering rods
-Jets
-Orange springs
-float needles & seats are new
-Filters on seats
-Verify electric choke is working properly
-new floats set correctly triple checked
-New fuel pump
-New Sierra in-line filter
-Bypassed the oil pressure switch that controls power to fuel pump
-carb bowl has gas in it
-accelerator pump set on middle hole and get two full squirts on fuel when pumping the throttle so has fuel
-Assuming I have 12v to the purple wire on the ignition coil because it fires up and idles for a little bit.
-Triple checked the timing, set to 8btdc, no vacuum advance.
-fresh gas
-fuel pickup and check valve working properly

Im wondering if the ignition coil is on the way out and quits when it’s warm. I have replaced essentially everything that it could possibly be. When it dies and I give it a little throttle it makes no difference. Just abruptly stalls. Seems like everything points to coil but I have spent so much money on this boat I don’t want to just bust out the wallet and throw more money away.

any help would be great

 

[dubs283]

have you verified there is no spark when the engine dies?

 

[Mlevy]

No I didn’t get a chance last night but plan to today. Everything seems to point in that direction. What would be the best way to go about this with only myself to start the boat and check for spark? Or is it a minimum two person job?

 

[dubs283]

if you can see the engine from the helm you should be able to set a spark tester to be visible while cranking the engine

 

[Scott Danforth]

with the key on, use a remote start switch.

https://shop.advanceautoparts.com/p...YUyVlF5DPdS9fivU4bAaAvZ2EALw_wcB&gclsrc=aw.ds

 

[Mlevy]

Update:

I picked up a inline spark tester yesterday, put it on the coil and ran the boat. It ran in neutral at around 2000 rpm and when it quit I could clearly see the light die and then motor stalled so I am definitely loosing spark.

I plan to check the wiring over again to make sure there are no loose connections and maybe run 12v to the coil with a new wire before I replace but everything is pointing to the coil. It seems to be temperature related. Once the motor is hot and dies the first time then it only runs for a couple seconds and quits again. Let it cool down for a couple hours and it will run until it gets up to temperature again and quit. Most likely no good because the last motor overheated and cooked itself along with the coil.

-Mitch

 

[alldodge]

Assuming I have 12v to the purple wire

Need to stop the assuming and do more testing. Get a voltmeter and connect it to the coil and measure voltage until it dies

Its a 5.7 but what year, or better yet what was the original motor serial number

 

[Mlevy]

At the time it was an educated guess. I do have 12v to the coil and I wouldn't think it would run without it, not great anyways. I think I’m on the right track now, I’ll post back with what I find.

Thanks!

 

[Mlevy]

Put the new coil on tonight and the boat worked like a charm. What an upgrade from the 4.3 vortec!

Thanks for your help everyone!