1990 mercruiser 4.3 no spark

[trashboat]

Hey guys I have a 1990 sea ray with a 4.3 mercruiser with thunderbolt IV that has no spark.

Been working on it chasing it down, I've worked through the thunderbolt troubleshooting flow chart.

I only had around 10.5 volts at the coil, so I disconnected the purple and grey wires from the harness, and jumped directly from the battery.

Also have 12v at the wht/red wire from the distributor.

I get spark on my spark gap tester when disconnecting the wht/grn wire and strike it against ground indicating that the sensor in the distributor needs to be replaced.

I replaced it, and still no spark so just to be sure I exchanged it for another one and still no spark.

All of this was done with shift interrupt switch disconnected, not sure where to go with it next unless somehow I got 2 bad distributor sensors. Any input on what to look at next would be appreciated, thank you

 

[ESGWheel]

I am not familiar with these systems so difficult to offer advice. However, a search of this excellent forum yielded a comprehensive post (link) on them and how to troubleshoot. Perhaps that can help. Good luck!

 

[alldodge]

Welcome
Is this a new to you boat, or did this just happen reticently?

With distributor cap removed, crank the motor and does the rotor rotate

Is the ignition module have 2 or 3 wires?

 

[trashboat]

New to me boat, was supposedly running a year or two ago.

Rotor rotates, and it is the 3 wire ignition module red/wht, wht/grn and ground wires.

 

[alldodge]

Verify the rotor is rotating when the motor is cranking

and the rotor looks like THIS

 

[trashboat]

Yes I verified that the rotor is rotating while cranking the engine, and that it is the correct rotor.

 

[alldodge]

Just to verify the issues

With 12V on Wht/Red wire and striking Wht/Grn wire "rapidly" you have spark and it sparks many times and not just once or twice

Rotor rotates and firing order is correct

The ignition module does the same thing as striking the Wht/Grn wire rapidly to ground. So if grounding the Wht/Grn wire many times rapidly will simulate same thing

 

[trashboat]

Correct, grounding the wht/grn rapidly I have spark on my spark gap tester.

Verified firing order, rotor rotates and have correct voltage at wht/red wire, and coil.

Going by the thunderbolt IV troubleshooting diagram everything seems to point that the sensor in the distributor is bad, but that will be the third one I put in it.

Other than triple checking the grounds again I'm not sure what else it could be.

 

[nola mike]

Are you using an Amazon special?

Correct, grounding the wht/grn rapidly I have spark on my spark gap tester.

Verified firing order, rotor rotates and have correct voltage at wht/red wire, and coil.

Going by the thunderbolt IV troubleshooting diagram everything seems to point that the sensor in the distributor is bad, but that will be the third one I put in it.

Other than triple checking the grounds again I'm not sure what else it could be.

 

[trashboat]

Are you using an Amazon special?

If you mean the distributor sensors, the first one was but the one that's in there now is a quicksilver.

 

[alldodge]

As you stated, it goes back to the sensor

To verify, the spark gap tester is on the coil wire with both Wht/Grn wire and when cranking?

 

[trashboat]

As you stated, it goes back to the sensor

To verify, the spark gap tester is on the coil wire with both Wht/Grn wire and when cranking?

I only tried it while grounding the white and green wire, but yes it's connected to the coil and grounded.

I can try it while cranking the engine over later. If there's no spark while cranking but spark when grounding the wire, what does that indicate?

I'm also going to exchange the sensor again, just to make sure.

 

[alldodge]

I can try it while cranking the engine over later. If there's no spark while cranking but spark when grounding the wire, what does that indicate?

The sensor is just a switch. Striking the Wht/Grn is doing the same thing as the sensor. This is the reason it says to strike the wire to ground rapidly several times (not just once or twice)

So if it sparks doing the wire and not the sensor, that just shouldn't happen

Reason to do the coil wire is so the distributor is taken out of the equation other than the sensor

 

[trashboat]

The sensor is just a switch. Striking the Wht/Grn is doing the same thing as the sensor. This is the reason it says to strike the wire to ground rapidly several times (not just once or twice)

So if it sparks doing the wire and not the sensor, that just shouldn't happen

Reason to do the coil wire is so the distributor is taken out of the equation other than the sensor

Replaced the sensor again and have spark now, third time is the charm.

Still won't fire but I suspect that's a timing issue, had it backfire a couple times.

Thanks for all of the input, it's appreciated

 

[Chris1956]

Make sure the spark is happening at TDC of the compression stroke (with the valves closed). If you had the distributor out to replace the sensor, it can go back 360* out of time.

 

[nola mike]

Replaced the sensor again and have spark now, third time is the charm.

Still won't fire but I suspect that's a timing issue, had it backfire a couple times.

Thanks for all of the input, it's appreciated

Still curious if you were using an Amazon special sensor? They can be very hit or miss...

 

[Scott06]

Replaced the sensor again and have spark now, third time is the charm.

Still won't fire but I suspect that's a timing issue, had it backfire a couple times.

Thanks for all of the input, it's appreciated

Turn distributor while cranking. If backfiring yes timing is wrong
reading this wonder if you had a grounding issue on distributor to block . Not sure if third wire off sensor is a ground which would nix my theory… but if clamp is loose …

 

[trashboat]

Turn distributor while cranking. If backfiring yes timing is wrong
reading this wonder if you had a grounding issue on distributor to block . Not sure if third wire off sensor is a ground which would nix my theory… but if clamp is loose …

New sensor was connected the same as the previous two.

Yes it's backfiring while cranking .

 

[alldodge]

Re-check the firing order

 

[trashboat]

Re-check the firing order
View attachment 407271

Verified this today, going to pull the plug for cylinder 1 tomorrow to put cylinder 1 at TDC to set base timing.