4.3 mercruiser sparks for 3 seconds

[abe13simp]

Hello all, new to boat world but i have a 2010 4.3 in a tahoe q5 that tries to run for about 3 seconds and then spark dies. I have replaced the pick up sensor in the dizzy,and cap and rotor in the distributor, new ignition coil, and even tried and new alpha ignition control unit and all with the same result.

Looking up posts and everyone says the oil pressure switch is failed but the oil pressure gauge and fuel pump both read and work correctly. It is carbureted and fuel is pumping into the bowls like normal.

So i hook up my timing light to the center coil wire from coil and start the engine and i might get 6-7 sparks from the timing light and the engine does hit a few times but then spark dies away, and turn key off and try to start again and it will not throw any spark for maybe 5 minutes. I wait 5 minutes and restart and get about 3 seconds worth of spark and it all dies again.

Boat was not winterized correctly and engine block cracked, i just installed new engine in the boat and trying to get it running. Thanks for any assistance.

[mmwjr]

Are you consistently getting power to the plus terminal of the ignition coil? Should be 8-12V. If not you may have an issue with either the ignition switch or kill switch.

[abe13simp]

Yes i have checked for key power on +side of ign coil when the key is on and also while starting engine. Where does the grey wire(negative) side of the ign coil, get its signal from? That negative side of the coil doesnt seem the pulse very much, checking with multimeter while cranking.

[abe13simp]

what should the ground side of the coil be because i have 12 volts there as well with the ignition in the run position. while not running that is. tapping the green white wire that goes to ICM to a ground location does not spark a spark plug either..

anyone have a source to a wiring diagram for that engine in that boat so i could just go through it?

[mmwjr]

Originally Posted by abe13simp

what should the ground side of the coil be because i have 12 volts there as well with the ignition in the run position. while not running that is. tapping the green white wire that goes to ICM to a ground location does not spark a spark plug either..

anyone have a source to a wiring diagram for that engine in that boat so i could just go through it?

That’s not ground, the negative terminal of the coil should pulse between approximately 4 and 8 volts, had to see with a meter which will do a rms average. I suggest you look up the manual for the engine under Documents of this site and follow the troubleshooting guide.

[abe13simp]

Originally Posted by mmwjr

That’s not ground, the negative terminal of the coil should pulse between approximately 4 and 8 volts, had to see with a meter which will do a rms average. I suggest you look up the manual for the engine under Documents of this site and follow the troubleshooting guide.

i already downloaded the manual from this site for the 4.3 but the manual is for a 99 that it shows and the manual ends at section 3 and the electrical components start in section 4. does anyone have access to the rest of the manual or know where to obtain?

[mmwjr]

Originally Posted by abe13simp

i already downloaded the manual from this site for the 4.3 but the manual is for a 99 that it shows and the manual ends at section 3 and the electrical components start in section 4. does anyone have access to the rest of the manual or know where to obtain?

The 4.3 is just a 5.7 less 2 cylinders, try using manual 24’s troubleshooting guide.

[abe13simp]

thank you that manual helps a lot. we seem to have everything needed to get it going again but still are only just a handful of sparks then quits sparking. trys to start running but dies cause spark dies. tried a new ICM and that didnt change it either. there are 2 wires up by the carb that we dont know what they go too. the orange pink and the brown go to the transom harness on the other end and the black just goes into a ground block with a bunch of other grounds. added some pics. anyone know what those ring terminals should be on and will it keep it from running?

[mmwjr]

I’ll have to look at the wiring diagram and get back to you. Is this a regular carburetor with a choke or a TKS one?

[abe13simp]

tks carb, not regular choke. Im thinking that is there a trim position sensor that would kill spark if prop is trimmed up?

[mmwjr]

Originally Posted by abe13simp

tks carb, not regular choke. Im thinking that is there a trim position sensor that would kill spark if prop is trimmed up?

Nope, trim limit switch prevents the drive from being raised too high but has no influence over the ignition.

[yahoo82]

Have you checked your battery with a load tester? I had a bad battery once that read 12v but must have had a bad cell. It would turn over but didn’t have enough to produce spark (which I anlways thought was strange that there was enough power to turn the starter but not enough voltage to make spark. The fact that when you wait a little while it works again feels like battery.