HELP not getting spark on my Mercruiser 4.3L

[Meyercrew]

Hi, I have a 1992 Bayliner Trophy with a Mercruiser 4.3l I/O. I have had an intermittent issue over the past few years where the engine will die and won't start again. And sometimes Ill go to get underway and it will turn and turn but wont fire up, then ill come back a few days later and it runs fine. I do know that its not getting spark when it wont start. So what ive done so far is new plugs, wires, distributor cap and rotor, sensor in the distributor and coil (last year). after i did all that she fired right up so i shut it down and now no spark again... anyone have any ideas on what else it could be?

 

[achris]

Re: HELP not getting spark on my Mercruiser 4.3L

Hello and welcome to iBoats...

First.... Please Read This Before Posting A Question... How to Ask a Question....

Mercruiser have been using the 4.3l engine in all its various guises since 1984, and there are a LOT of differences. And although the boat is 1992, the engine may not be, so serial numbers are king when it comes to Merc products. You'll find you have 3 serial numbers of importance; engine serial number, drive serial number and transom serial number. Find and record those and use them when posting questions here.

Ok, on to your problem. 2 things I would be checking. All the grounds wires are clean and tight (including a ground wire from the distributor body to the engine block. If there isn't one, add one), and the shift interrupt switch is not causing the problem....

Chris.....

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

I will work on getting the serial numbers. I have considered the interrupter switch, but it seems to do it even when i adjusted that. I also added a ground to the distributor when i installed the new sensor. Also, just for fun i added another new coil and still no fire.

 

[Don S]

Re: HELP not getting spark on my Mercruiser 4.3L

You will have to do this when it won't start, and do it quickly.
If it won't start, leave the key in the run position and check with a multimeter to see if you have voltage to the + terminal of the coil (purple wire).
If you have power to it, turn the key to start and see if you still have voltage. It will be lower, while cranking, so let us know what it is.

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

Well I attempted to get the volt reading and found that my multimeter isnt working, which would explain the 0 volts reading i was getting on every connection. I am still sure im not getting spark out of the coil but I will have to wait until tomorrow to get a new meter. Im going to go enjoy whats left of a very rare sunny day that we get here in Alaska.

 

[Don S]

Re: HELP not getting spark on my Mercruiser 4.3L

How are you connecting your meter, 0 volts if you are doing a dropdown means everything is good.
With your meter set on DC at the proper range, the black lead goes on a good ground (battery negative terminal is perfect) then the red lead goes to what your are checking for voltage.

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

Ok got a functioning meter... got 12 volts to the coil with the key in run. when i try to cranking the engine the volts drop to 9. still no spark coming from coil. the only item i havent replaced so for is the ignition module that mounts to the riser. would it be a safe bet to lean toward that being my malfunction? anyone heard of that being an intermittent failure item?

 

[Don S]

Re: HELP not getting spark on my Mercruiser 4.3L

Try charging your battery and checking connections. You shouldn't be seeing less than 10 volts while cranking.

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

well it was actually 9.8 while cranking and i do have one weak battery but the other is fully charged. I also disconnected all connections and cleaned them last week as part of my initial trouble shooting attempts.

 

[Don S]

Re: HELP not getting spark on my Mercruiser 4.3L

Now that you have a good meter, follow this procedure when it's not working.

.

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

PERFECT!!! That is the diagram Ive been looking for!! THANK YOU!!!! I could only find the thunderbolt V diagram

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

Do you have a complete wiring diagram as well? Just wondering if theres a ground that im missing somewhere. The problem with no spark has now gone from intermittent to permanent. It has now been a week with no spark, usually it would have fired by now.

 

[Don S]

Re: HELP not getting spark on my Mercruiser 4.3L

Here is the wiring diagram. There should be a ground wire, the clamp that holds the distributor down could be what was making the ground for a while if the wire is missing.
Some of the newer distributor sensors have a ground wire on them as well.

View attachment wiring.pdf

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

Any suggestions where I can get the ICM? All symptoms are pointing to that. Ive done some searching but havent had much luck

 

[Meyercrew]

Re: HELP not getting spark on my Mercruiser 4.3L

sorry for the late final update... But turns out it was the ignition control module that mounts to the manifold. found one at a shop here in town plugged it in and she fired right up. Thanks for the help