Mercruiser 5.7 Electrical Troubleshooting

briankerr

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Apr 13, 2014
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Hello Everyone -

We have had our boat in storage for a while and I am trying to get it back up and running today. At first it would not crank, but I found that there was a voltage drop at the starter due to corroded leads. Once cleaned/sanded it would turn over. Next came some flooding in the carb due to a stuck float/needle (I think), that seems to be ok now. So here I am...

I now think I'm not getting a spark. Multimeter at the ignition coil shows 0v across +,- (short/open?), 12v at both + and -. and when everything is disconnected 0 ohm resistance across (read it should be between .7 - 1.7??). I cleaned all leads here too. Haven't moved onto the distributor or plugs yet.... Any suggestions?

photo 1.JPGphoto 2.JPG
 
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Bondo

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Re: Mercruiser 5.7 Electrical Troubleshooting

Hello Everyone -

We have had our boat in storage for a while and I am trying to get it back up and running today. At first it would not crank, but I found that there was a voltage drop at the starter due to corroded leads. Once cleaned/sanded it would turn over. Next came some flooding in the carb due to a stuck float/needle (I think), that seems to be ok now. So here I am...

I now think I'm not getting a spark. Multimeter at the ignition coil shows 0v across +,- (short/open?), 12v +,+, -,-. and when everything is disconnected 0 ohm resistance across (read it should be between .7 - 1.7??). I cleaned all leads here too. Haven't moved onto the distributor or plugs yet.... Any suggestions?

View attachment 228472View attachment 228473

Ayuh,.... Welcome Aboard,.... Are ya cleanin' Both ends of the leads yer cleanin',....

Battery end, 'n starter ends,..??
Battery end, 'n block Ground,..??

Check the big cannon plug that hooks the motor to the boat,...
How 'bout Power at the circuit breaker,..??
Alternator,..?? key On,..?? key off,..??

You'll find the manuals up in Don'S Adults Only section at the top of this forum,...
follow the links,...
 
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briankerr

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Apr 13, 2014
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Re: Mercruiser 5.7 Electrical Troubleshooting

Starter is turning engine, those ends are fine. I'm just not getting a spark and I think it's the ignition coil due to the voltage / resistance reading I'm getting. I get 12V at the + AND 12V at the - of the ignition coil (primary). Do these just go bad when not in use?
 

searay3

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Apr 7, 2005
Messages
655
Re: Mercruiser 5.7 Electrical Troubleshooting

Is that points or electronic? If electronic, look in the stickies at the top of the forum for a troubleshooting guide. 12V is normal at the + coil for electronic. If points, replace them and the condenser. With points, if you have 12v at the +coil, the coil better have an internal resistor for your points to last. Otherwise should be around 9v at the +coil unless your cranking. Could be the prev owner had trouble with the resistor wire and ran 12v to the coil burning up the points. Also, new cap, rotor, etc for no spark situation to start with regardless of type.
 

briankerr

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Apr 13, 2014
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Re: Mercruiser 5.7 Electrical Troubleshooting

Is that points or electronic? If electronic, look in the stickies at the top of the forum for a troubleshooting guide. 12V is normal at the + coil for electronic. If points, replace them and the condenser. With points, if you have 12v at the +coil, the coil better have an internal resistor for your points to last. Otherwise should be around 9v at the +coil unless your cranking. Could be the prev owner had trouble with the resistor wire and ran 12v to the coil burning up the points. Also, new cap, rotor, etc for no spark situation to start with regardless of type.

This is at the ignition coil. 12v at + when ignition on (normal), but I'm getting 12v on the - post as well (normal?) There is 0 ohm resistance through the primary coil (+,-) of the ignition coil, 11k ohm resistance through the secondary coil (normal I think).

If you think this is fine/normal, how should I test the distributor for spark (without a spark tester)?

Thanks
 

Bt Doctur

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19,093
Re: Mercruiser 5.7 Electrical Troubleshooting

Looks like its still a points system so you need 12v at the + side . With the key "on" measure the purple wire red lead to wire, black lead to ground.NOT THE NEGATIVE SIDE OF THE COIL .
It 12v is present, connect the purple wire to coil and read the neg side of the coil for 12v. If Yes, coil should be good. take a jumper from the neg side of the coil and with 12v appplied to the pos side "scratch" the jumper to a good ground. This should produce a spark from the coil tower lead to ground.
If yes,coil is good.
Now on to the points, open the dist cap and put a piece of paper between the points, using the jumper fron the connection on the points, "scratch" to a good ground, cooil tower should produce spark, Yes wire from coil to dist is good, if No wire is bad.
The points may be glazed or or badly ozidized, clean with a nail file or sandpareer to test, is spark is now present ,replace points and condensor
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting

Looks like its still a points system so you need 12v at the + side . With the key "on" measure the purple wire red lead to wire, black lead to ground.NOT THE NEGATIVE SIDE OF THE COIL .
It 12v is present, connect the purple wire to coil and read the neg side of the coil for 12v. If Yes, coil should be good. take a jumper from the neg side of the coil and with 12v appplied to the pos side "scratch" the jumper to a good ground. This should produce a spark from the coil tower lead to ground.
If yes,coil is good.
Now on to the points, open the dist cap and put a piece of paper between the points, using the jumper fron the connection on the points, "scratch" to a good ground, cooil tower should produce spark, Yes wire from coil to dist is good, if No wire is bad.
The points may be glazed or or badly ozidized, clean with a nail file or sandpareer to test, is spark is now present ,replace points and condensor

Thanks for the reply. I opened the distributor cap and had a look. The body of the distributor is a bit corroded, but the points seem fine. I tested for continuity from the coil to the distributor and it was fine. I cranked it and it spun (slow?).

photo 2 (1).JPGphoto 1.JPG
 

Bt Doctur

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Re: Mercruiser 5.7 Electrical Troubleshooting

it spins at 1/2 the speed of the crankshaft. you really cant tell anything by looking. You could have corrosion where the screw enters the dist body causing it to ground out,no spark. Do those tests in that order and let us know what you find.
The orange lead from the condenser look a bit funky.
If you know how to use the "ohms" scale on a meter, connect one lead to ground and the other lead to the bolt on the dist. crank motor, meter should jump from infinity (no movement) to short circuit, (full movement). that will tell you your good inside the dist continuity wise, condenser could still be bad causing no spark
 
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MikDee

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Re: Mercruiser 5.7 Electrical Troubleshooting

The wire going to the points is bent backwards at the distributor pole, that could be broken? or a weak link, and why is there a sponge being used as the rubbing block on the points? It's too flexible, I'd take it off it needs to be rigid like the plastic rubbing block on the points. Yes, that condenser wire looks funky? I'd get new points, condenser, & rotor, then fasten the condenser lead to the points themselves.
 
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Bt Doctur

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Re: Mercruiser 5.7 Electrical Troubleshooting

there felt ,not sponge.
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting

Alright we are making some progress.... Thanks for sticking with me :)

The wires coming into the distributor were grounded to the body from one of the crimp terminals inside. Points started getting power. I put a light on the ignition coil (primary) and it stayed off while cranking. I checked the contact breaker points (near cam) when cranking and noticed they didn't separate enough to alternate (on/off). I took them apart and cleaned them and adjusted the spring felt mechanism. Now when it cranks the test light alternates on/off (it's a bit dim compared to direct 12v connection at battery - problem?) so the secondary (spark) should be firing.... (right?). I still didn't get spark at the plugs... May have to look into the dis. cap points?
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting

New Problem!

So it appears that we were on the right track and fixed the initial problem last night. I believe it was not starting when I was done fixing due to flooding since it started firing first thing today.

NOW... It fires and runs for ~1 second and then dies. I checked that choke opens immediately after starting. I tried removing the grey wire (tach) from the ignition coil, still happens. Checked the fuel filter, it was clean / no water.

Ideas?
 

Bt Doctur

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Re: Mercruiser 5.7 Electrical Troubleshooting

run a jumper from the bettery to the + side of the coil, see if it now runs. If Yes, the resistance wire or the ceramic ballast resistor is open.
 

Bt Doctur

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Re: Mercruiser 5.7 Electrical Troubleshooting

Typically wired like this,.
UntitledXX_zps21fb2ea2.jpg
Purple wire is the 12v that comes from the key switch , usually powers the alt and then the resistance wire picks up and goes to the coil. The other wire comes from the starter solenoid to provide full battery power only during cranking. Once started and with the key in run position , the resistance wire powers the coil.
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting

run a jumper from the bettery to the + side of the coil, see if it now runs. If Yes, the resistance wire or the ceramic ballast resistor is open.

Ran the jumper, it still cut out. Should the other wires be disconnected off the + on the coil for this test?
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting

I also read this is an occurring problem with mercruisers that sit for a while (as mine has) that could be the oil pressure switch, ignition switch, or shift interrupter. Many describe as you have the starter supplying the coil initially, then it dies do to a short in one of these? What are your thoughts?
 

briankerr

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Re: Mercruiser 5.7 Electrical Troubleshooting


NOTE: this is with the + terminal on the coil jumped, but same outcome.
 

Bt Doctur

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Re: Mercruiser 5.7 Electrical Troubleshooting

That is lack of fuel or a carb problem. Do you know how to prime the float bowl?
the pressure switch in the oil circuit is for electric fuel pumps. using a jumper you eliminate an ign switch problem. coil power is supplied only during cranking ,the ign "On" takes over. hot wiring disables that too.
 
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briankerr

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Apr 13, 2014
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Re: Mercruiser 5.7 Electrical Troubleshooting

I primed the float bowl with some gas and it ran *slightly* longer, albeit a bit rough, so it's prob what you said. Since it's been sitting so long, do you think it's time for a carb rebuild (maybe the float it getting stuck up or something)? or do you think it would be a fuel supply problem (I don't have a pressure tester to test the pump)?
 
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