1987 mercruiser i4 mcm165 b624357 ignition problem

[DixieSpeed]

as the title says i have a '87 i4 165. i have tested everything i read about in the mercruiser needed to know section. the starter slave solenoid works, it puts 12v to the starter and it cranks, it puts power to the coil but not much. thats where i believe my problem is. the engine turns over but will not catch. it gets fuel but no spark. i've tested the coil and it gets 12v through the purple/yellow wire from the starter slave solenoid. when the coil has the grey wire and the black wire hooked up it doesn't get grounded to provide power. there was a spare wire hooked on to the valve cover bolt by the previous owner, i believe it was to hook on the alternator kit. i used it to ground the coil but then the coil only gets 3.6v to the coil from the slave solenoid. i don't know whats up with that grey wire other than i read somewhere its to the tach or hour meter. its most likely my problem but thats why i'm writing this, cause i'm no expert. thank you for any help.

 

[Don S]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

You don't ground the coil, just because it says - doesn't mean it's a ground.
If you have a wire going from the - terminal of the coil to ground, take it off.
The gray wire goes to the tach, and shift interupt switch. The other wire goes to the distributor.
Temporarily unhook any wires to the - side of the coil except the one to the distributor and try it.

 

[DixieSpeed]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

i just disconnected the random wire and set it aside. i took off the grey wire and tested for power at the coil with just the black wire hooked up. nothing. i get full 12v to the purple/yellow wire but only when using a grounding stud. no voltage with the black wire to the distributor.

 

[Don S]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

One more time. You DO NOT ground the coil terminals.

Have you done the ohms tests on the coil?

 

[Don S]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

I'm beginning to think your problem is you need to replace your points.

 

[DixieSpeed]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

ohms test for the coil results. between the - and the top post is 5.69 on 20k setting. between - and + is 1.3 on 200 setting. i recently replaced the coil thinking it was bad and i ohm tested both and these numbers are half what they were for the old coil.

 

[DixieSpeed]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

im looking into doing a digital conversion to eliminate the points.

 

[DixieSpeed]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

i took the cap off to check out the points. the black wire from the the points to the coil had a 2" flat spot and the insulation looked burnt. the points and the condenser looked alright, used but alright. i went to a second engine i received when i purchased the boat to look at the points on that one for comparison. the points on the second engine looked brand new and had a good black wire for the coil. i swapped out the points and condenser and still nothing.

 

[DixieSpeed]

Re: 1987 mercruiser i4 mcm165 b624357 ignition problem

after talking with Dt Doctur for about 15 minutes i got a good spark to happen. i had the point gap set to about 3 times at large as it should be and the points also needed a bit of sanding. now my problem is in a different area, too much water in fuel to burn. but i can handle that one by draining the tank, cleaning the separator out, refuel the carb with a shot of good fuel and it should start right up. thanks for your help Bt Doctur and yours too Don S!