No Spark - 4.3 Liter Mercruisers

mark guthrie

Member
Aug 25, 2009
101
St. Pete, FL
Boat Info
2001 280 Sundancer
Engines
4.3L with Alphas
Hi all,

I have a 280 Sundancer.

Both engines have the same problem. They crank fine, and getting fuel - but no spark.

Is there a separate circuit for the coil? Different than the starting circuit?

I recently replaced some breakers and pulled all of the batteries, could I have left a wire or two off? I thoroughly checked but don't see any.

I also put a jumper from the battery to the coil but no difference.

Any advice?

Thanks, Mark
 
Actually mercruiser web site must have a wiring diagram for the engine, check if you have power to the ecm, there also may be relays involved
 
Hi all,

I have a 280 Sundancer.

Both engines have the same problem. They crank fine, and getting fuel - but no spark.

Is there a separate circuit for the coil? Different than the starting circuit?

I recently replaced some breakers and pulled all of the batteries, could I have left a wire or two off? I thoroughly checked but don't see any.

I also put a jumper from the battery to the coil but no difference.

Any advice?

Thanks, Mark
Here is a link for the wiring diagram
https://www.downloadboatmanuals.com/motors/mercury/mercury-mercruiser-service-manual/
 
I assume you have an EFI engine, I see in the diagram there is an engine circuit breaker that supplies power to the ignition relay, I suspect that is your problem, check to see if you have power there, I have been an auto tech for 40 years
 

Thanks. So power is a separate circuit for the ECM? I tried going to this site, but I can't figure out which one is the wiring diagram, there are many, many links...I tried one and it took me down a rabbit hole. Might not help anyway as I am not great at reading schematics.

Do you know if there is a way to jump power to the ECM?

Just prior to this happening, I replaced many of the original Searay breakers on the main panel, I am wondering if I missed a wire? I looked closely yesterday and don't see any that aren't attached. I also pulled all of the batteries, thought maybe I missed reattaching a wire but that doesn't make sense as anything going to the ECM would have to be on a breaker.

Also, this is happening to both engines, so unless the same power goes to both ECMs, there must be two wires not connected.

I really appreciate your input!
 
The second link down is for 4.3l
Mercury Mercruiser #18 Service Manual Marine Engines GM V-6 262 CID (4.3L) [PDF, ENG, 12 MB].pdf
Do you see a breaker for the ignition, maybe you did noy hook a wire back up when you did your work?

What year is your boat?
 
Behind the distributor you will find a black fuse holder that holds 4 small blade fuses. Pop the top off and check to see if any of the blade fuses are burned.
 
Thanks. So power is a separate circuit for the ECM? I tried going to this site, but I can't figure out which one is the wiring diagram, there are many, many links...I tried one and it took me down a rabbit hole. Might not help anyway as I am not great at reading schematics.

Do you know if there is a way to jump power to the ECM?

Just prior to this happening, I replaced many of the original Searay breakers on the main panel, I am wondering if I missed a wire? I looked closely yesterday and don't see any that aren't attached. I also pulled all of the batteries, thought maybe I missed reattaching a wire but that doesn't make sense as anything going to the ECM would have to be on a breaker.

Also, this is happening to both engines, so unless the same power goes to both ECMs, there must be two wires not connected.

I really appreciate your input!
I just clicked on the link and it works fine?
 
Monitor the voltage at the 50 amp breaker on top of the motor while cranking. If it drops below 11 volts that's your problem.
 
The second link down is for 4.3l
Mercury Mercruiser #18 Service Manual Marine Engines GM V-6 262 CID (4.3L) [PDF, ENG, 12 MB].pdf
Do you see a breaker for the ignition, maybe you did noy hook a wire back up when you did your work?

What year is your boat?

Thanks for pointing out the link. I was able to download it.

It is a 2001 Sundancer.

There is a breaker for the ignition. One of the breakers I replaced. I believe it is the same breaker that powers the starter (from memory). Maybe there was another lead on it that I didn't reconnect, but if there was, I sure can't find it. I wish I had fired up the engines after replacing the breakers to test, but I didn't.
 
Thanks for pointing out the link. I was able to download it.

It is a 2001 Sundancer.

There is a breaker for the ignition. One of the breakers I replaced. I believe it is the same breaker that powers the starter (from memory). Maybe there was another lead on it that I didn't reconnect, but if there was, I sure can't find it. I wish I had fired up the engines after replacing the breakers to test, but I didn't.

I believe the starter is powered directly from the battery switch (thickest red cable in the ER).
 
Yesterday I thoroughly checked the batteries, to see if something has become disconnected. All was fine. Took the opportunity to clean up everything and treat all of the poles with CorrisionX.

I don't seem to have the blade fuses behind he distributor and I don't see a 50 amp on top of the engine (scolaw).

On the main panel there is a breaker for each ignition, when off, the starter does not crank.
 
My 1998 5.0 efi has 3 fusesin the ecm box. Lift the lit and check the fuses there. I know 1 of them is a fuel pump fuse but not sure of other 2
 
Its inbetween the riser and air cleaner cover
Screenshot_20230529_173411_Gallery.jpg
 
Update. Thanks for the input. I got them both started. While troubleshooting, I decided to clean everything up, including the battery terminals. And then charged all night. Guess what, they both started. Ugh...sometimes it is the simple stuff.

Now I have another problem, the port engine is running rough and will die at idle. I am getting some vapor coming out of the throttle body. My mechanic thinks it is getting too much fuel. The good news is that he is coming today.
 
So the reason for no spark was your voltage drop was below 11 volts, enough to crank the engine but not enough for the ecm to fire the plugs.
 

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