No spark - Mercruiser 3.0

[arrkerr]

My 1991 Mercruiser 3.0 will no start, but cranks over (now that I've replaced the starter ). I yanked the first plug and held it against a good ground while cranking the engine and I don't have a spark.

My plugs are brand new. The spark plug wires look fine, and electrical connections seem good and tight. The distributor cap had some moisture under it when I pulled it out of storage a few weeks ago, but I left it off for a week (while replacing the starter), and cleaned all of the contact points and the rotor tip.

I'm not seeing much in the way of troubleshooting in the service manual. In your guys experience, are there any easy tests to be done on the coil or distributor? If not, what is the most likely culprit?

 

[arrkerr]

Re: No spark - Mercruiser 3.0

I found this list via google:

Below is a quick list of items which can cause a "no spark" condition from the coil:

1. A bad key switch.
2. A blown ignition fuse.
3. A bad harness connection or bad harness.
4. A bad shift cable.
5. A faulty Shift Interuptor Switch on the shift plate assembly.
6. A shorted tachometer.
7. A removed or faulty Safety Lanyard Switch.
8. A bad ignition coil.
9. Breaker Points worn or not adjusted (conventional ignition).
10. A bad condensor (conventional ignition).
11. A faulty sensor (Thunderbolt or Delco).
12. A bad Ignition Module (actually very rare).
13. A bad timing chain (rotor does not turn).


Looks like a spark tester is the first thing to pick up tomorrow and make sure I'm getting a spark from the coil. I didn't realize they could be connected directly to the coil, eliminating the distributor.

 

[PowerAddict]

Re: No spark - Mercruiser 3.0

if its a points system, try sanding them down abit to get the glaze off. If its not (and also if it is i suppose), have you verified the rotor is turning?

 

[fat fanny]

Re: No spark - Mercruiser 3.0

Download the manual for your engine from the stickies section @ the top of the forum and there are also tips for all your operating systems functionability as well as test the can be performed to verify there operation. Welcome aboard!

 

[Maclin]

Re: No spark - Mercruiser 3.0

Points are hard to clean, so I am not sure what you did there. Filing or sanding them may work for a bit but that removes any hardening on the contact surface and they are not long for the world after that usually. Do the full points replace with dwell and timing check. Same for cap and rotor, once any corrosion starts they go quickly. I mean, I assume you want reliability on the water and not just a spark while in the driveway, I'm just sayin'...

 

[Glastron_V210]

Re: No spark - Mercruiser 3.0

Re: Troubleshooting...here's what I would do.

First, pull the high voltage lead form the input to the dist (Center top). Put a spark plug in it and ground it like before. Do you get sparks? If you do, then you dist cap/high voltage leads are the problem. If you don't then perhaps it's coil or something else.

The way the ignition works is to have a steady 12V applied to 1 sied of the coi, and the points or electronic ignition altenately creates or eleimates a circout to ground. So, turn your key on and look for at 12V on at least 1 side of the coil. If you have it, then your ig key is not the problem, it may be coil or points.

There is a lot of ways to go from here. I like to do this:

1) Remove all plugs or dist cap etc so the engine can't fire and rotate unexpectedly

2) Connect a voltmeter to the side of the coil you suspect is connected to the points or el ignition

3) Rotate the engine by hand.

You should see the voltage on the coil go 12V, 0V (Or close to 0), 12V, 0V if the points are working. If this is happening, you likely have a bad coil. If not, look at the points and wires connecting the points to the coil.


Good luck. Let us know what you find.

Chay

 

[arrkerr]

Re: No spark - Mercruiser 3.0

Here is what I've found. There really isn't a lot to go on in the manual, so I hope you guys can help.

I get no spark coming from the coil directly.

I've checked the coil resistance, primary and secondary. It is within specifications. The manual actually has a bit of an error - the primary resistance should be measured in ohms, the secondary resistance should be set at 1k ohms. They have a foot-note for the DDIS system, but not the distributor system.

At the + side of the coil I'm getting 12 volts with the ignition on.

At the - side I have two wires, one from the distributor, one from the shift interrupt switch/tach. A voltage read from the wire from the distributor reads 12 volts, and slowly drops to about 3 volts as I hold the breaker opened. A voltage read from the + to the ground coming from the tach/shift interrupt switch gives me a steady 12 volts. Does that all sound right?? The shift interrupt switch seems to work - ie: there is no connection through the switch right now, and there is if I manually push it closed. So why am I getting a ground?

Suggestions on where to go from here?

 

[Bt Doctur]

Re: No spark - Mercruiser 3.0

shorted tach, remove the grey wire from the neg side and retest motor

 

[arrkerr]

Re: No spark - Mercruiser 3.0

Yep, runs with the grey wire disconnected.

Unfortunately this probably isn't safe in the water since the grey wire is spliced in with the shift interrupt. But it sure helps (and makes me feel better)!

 

[Don S]

Re: No spark - Mercruiser 3.0

Disconnect the gray wire off the tachometer itself. Until you get a new tach.

 

[SunkenVssl]

Re: No spark - Mercruiser 3.0

ive got power at the purple wire to the coil when the key is on but not spark at the wires....?

 

[arrkerr]

Re: No spark - Mercruiser 3.0

You'll have power on the purple. The way the coil works is that it looses the ground, and the coil emits a huge charge that makes the spark. If your tach is shorted, or your shift interupt is closed, it keeps the coil grounded and it'll never spark.

Disconnect the grey wire and see if you get a spark. You can't drive it like this (you won't be able to dis-engage the drive and go to neutral!), but its a good test out of water. If that works, the grey wire is grounded out from either the tach or shift interrupt - sounds like it is usually the tach, but the interrupt could also get stuck or need adjustment.

If the tach is shorted, just leave the grey wire off the coil and run a jumper wire from the shift interrupt (big switch block on top of your motor) to the coil so that it will be able to go to neutral.

Hope that helps!

 

[barker4684]

Re: No spark - Mercruiser 3.0

I found this list via google:

Below is a quick list of items which can cause a "no spark" condition from the coil:

1. A bad key switch.
2. A blown ignition fuse.
3. A bad harness connection or bad harness.
4. A bad shift cable.
5. A faulty Shift Interuptor Switch on the shift plate assembly.
6. A shorted tachometer.
7. A removed or faulty Safety Lanyard Switch.
8. A bad ignition coil.
9. Breaker Points worn or not adjusted (conventional ignition).
10. A bad condensor (conventional ignition).
11. A faulty sensor (Thunderbolt or Delco).
12. A bad Ignition Module (actually very rare).
13. A bad timing chain (rotor does not turn).


Looks like a spark tester is the first thing to pick up tomorrow and make sure I'm getting a spark from the coil. I didn't realize they could be connected directly to the coil, eliminating the distributor.

Would like to thank you greatly for this post! Spent all afternoon troubleshooting my ‘99 mercruiser 3.0 with no fire coming from the coil and no knowledge of how to finish troubleshooting. Saw this list of things to look for and thought I would run through the easiest first. Found it right off the bat and never imagined the engine would ever even turn over if the kill switch was pulled/off!!!!! Needless to say I have a spare ignition coil now in case it is ever needed! Thanks again for your post! My family now thinks I’m the boat God!