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Mercruiser 5.0 Getting Spark from Coil, but No Spark to Plugs

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CaramelThunder

New member
Hey everyone, long time lurker, but first-time poster.

I’m honestly at a loss to what is going on with this engine and I can’t seem to pin down the issue. It is a 2007 Mercruiser 5.0 with a thunderbolt V ignition system and a Alpha I Gen II outdrive. Back in February I was backing the boat off the ramp and was trying to pull up to the dock when it started stalling while shifting. After a couple of attempts of fiddling with the shifter cable length and testing the shifting, the engine died a final time and would only crank, but not start.

Since then, I have readjusted the shift cable correctly and tried to get it to run on a hose. However, it only cranks and would not start. I followed the Troubleshooting tree for this issue in Mercruiser 24 and still have the same issue. I replaced the cap and rotor, ignition sensor, and coil. I hooked up a timing light to the cables and saw that I was getting a spark from the coil to the distributor, but no spark from the distributor to the spark plug wires. I tested the thunderbolt module and I am getting 11v from the red/white wire, bypassed the shift interrupter switch, and bypassed the lanyard kill switch all with no change. I noticed the battery was a bit low, so we hooked up jumper cables to a truck and still no change. We have 12v on the gauge and when it cranks it gets down to 10-11v. I also verified that the rotor was spinning while cranking the engine.

I took some videos to show what is happening if it helps at all, but the file size is too large, so I will upload them to youtube and add the link when they’re up.

I’m wondering if anyone has any insight into what could be happening as I am at a complete loss as to why I would be getting spark from the coil to the distributor, but not from the distributor to the plugs.

Thank you guys!
 
Check the distributor cap, to make sure the contact at the center terminal is there- some can fall out.
 
How are you seeing spark from coil?
Are you using a spark checker?

Maybe verify top dead center on harmonic balancer to timing cover pointer and confirm rotor is pointing to #1 plug wire location. If you do harmonic balancer to pointer, you can be 180* out so if rotor looks to be 180* out of time, you may have to bump the engine 1 revolution.

If rotor is way off then you will have to look elsewhere.

If you are 100% sure you have spark from coil wire then,

1. Possible distributor gear has sheared the pin but shaft still spins just not correctly.
2. Possible timing chain being very loose issue.

To test for spark which includes intensity and "power level" a spark checking device is best so you can see the spark itself.

Many types are available. I like the ones with spark plug wires and a plastic tube with two metal points about 1/2 inch apart where one lead goes to spark source (coil tower or plug wire) and the other lead goes to ground.
 
kghost said:
How are you seeing spark from coil?
Are you using a spark checker?

Maybe verify top dead center on harmonic balancer to timing cover pointer and confirm rotor is pointing to #1 plug wire location. If you do harmonic balancer to pointer, you can be 180* out so if rotor looks to be 180* out of time, you may have to bump the engine 1 revolution.

If rotor is way off then you will have to look elsewhere.

If you are 100% sure you have spark from coil wire then,

1. Possible distributor gear has sheared the pin but shaft still spins just not correctly.
2. Possible timing chain being very loose issue.

To test for spark which includes intensity and "power level" a spark checking device is best so you can see the spark itself.

Many types are available. I like the ones with spark plug wires and a plastic tube with two metal points about 1/2 inch apart where one lead goes to spark source (coil tower or plug wire) and the other lead goes to ground.
Click to expand...
I used a timing like to see if I was getting spark. I'm unsure of the strength of the spark however. I did notice that it was intermittent when cranking. I did check the point of the rotor and it looked on point, but slightly off so I took the rotor off and placed it back on and it looked good. I'll pick up a spark tester and make sure later today. Am I looking for the color of the spark when I do that?
 
CaramelThunder said:
Like the copper piece on the bottom of the connector on the cap?
Click to expand...
It would be at the center- make sure the metal tab on the rotor is raised enough to make contact, too.

Do you have spark if a timing light clamp is on the coil wire? If you do, you should have spark at the cylinders but if not, and if this engine is fuel injected, you should be able to see a code for the Ignition Control module, AFAIK. I was trained for Mastercraft/Indmar engines that used the 'common' Delphi system but the Tech I diagnostic computer was able to read codes from Mercruiser, so....

Do you have the TKS on this engine? I would recommend finding a service manual.

Not to accuse you of anything, but where is the lanyard?
 
jimn said:
It would be at the center- make sure the metal tab on the rotor is raised enough to make contact, too.

Do you have spark if a timing light clamp is on the coil wire? If you do, you should have spark at the cylinders but if not, and if this engine is fuel injected, you should be able to see a code for the Ignition Control module, AFAIK. I was trained for Mastercraft/Indmar engines that used the 'common' Delphi system but the Tech I diagnostic computer was able to read codes from Mercruiser, so....

Do you have the TKS on this engine? I would recommend finding a service manual.
Click to expand...
I do have spark when the timing clamp is on the coil wire. It is intermittent however. It is a carbed engine as well. I will check the height of the metal tab but it was at 1/4in when I put the cap on.
 
CaramelThunder said:
Like the copper piece on the bottom of the connector on the cap?
Click to expand...

The coil wire terminal inside the distributor is the Center terminal, there will possibly be a copper ring BUT the contact surface for the rotor is a Black carbon like round "pimple". Close to the diameter of a pinky finger tip.

The tang on the rotor makes physical contact with that and then distributes the spark to each spark plug wire terminal on the outer diameter inside the cap.
 
Is it the blue arrow or the red arrow? I'm not sure I understa
SIE-18-5431_lg__32077.jpg
nd which part it is.
 
A few things,
The issue occurred prior to new parts installed.
You seem to be unsure if the shift interuptor had any impact prior to new parts and readjusting cables.

You have disconnected the shift interuptor wiring at the interuptor switch so it cannot affect the ignition, correct?

We can believe with all the new parts, that excludes them from being the cause at least at this time anyway.

Pull distributor cap off, try to turn distributor shaft using the rotor, and see if it will spin. It should only move the amount of gear lash at Dist shaft to cam shaft. If it goes further, let us know.
 
kghost said:
A few things,
The issue occurred prior to new parts installed.
You seem to be unsure if the shift interuptor had any impact prior to new parts and readjusting cables.

You have disconnected the shift interuptor wiring at the interuptor switch so it cannot affect the ignition, correct?

We can believe with all the new parts, that excludes them from being the cause at least at this time anyway.

Pull distributor cap off, try to turn distributor shaft using the rotor, and see if it will spin. It should only move the amount of gear lash at Dist shaft to cam shaft. If it goes further, let us know.
Click to expand...
Yes, I bypassed the shift interrupter and was able to eliminate it. I was not able to spin the rotor more than a gear lash.
 
kghost said:
NO,
Thats the rotor, look inside cap
The sping like tang on rotor makes contact with center of dist cap.
The flat tang part of rotor which is what points to plug wire 1 on dist cap does not make direct contact with plug wite terminals inside dis cap.
Click to expand...
Gotcha! I wonder if I need to raise the tang even more than the manual said. That seems like it could be the issue.
 
I would say yes ONLY if that spring tang on rotor is bent down, other wise I have not had to bend one as received.

For now we are just making sure there is nothing obvious. If all these little things check out then we can move on to other possiblities.

Its very difficult to give an exact answer as so many people leave many of these minor details out of their descriptions/trouble shooting.
 
kghost said:
I would say yes ONLY if that spring tang on rotor is bent down, other wise I have not had to bend one as received.

For now we are just making sure there is nothing obvious. If all these little things check out then we can move on to other possiblities.

Its very difficult to give an exact answer as so many people leave many of these minor details out of their descriptions/trouble shooting.
Click to expand...
It wasn't bent down at all. I measured it with calipers after I installed it and before I put the new cap on.
 
A bit more info on how this works, A basic overview.

The coil gets +12 volts to + terminal from Ignition switch,

As the tanged piece attached to the rotor spins thru the sensor/pick up it sends a signal to the Ignition timing module which then fires the coil by way of shorting the Neg side of coil to ground or stops the sensor/pick up from outputting signal to timing module.

When ever the neg side of the coil is shorted to ground it will dump its charge (spark) thru the coil tower center terminal for TB IV and V NON EFI models anyway.

So if the coil has spark then we can assume the sensor/pick up and timing modules are working. We need confirmation on this.

So confirming the coil is outputting spark is very important.

The Interrupter switch shorts Ignition if you will, so this can cause lack of spark as it interrupts it so eliminating this from circuit eliminates a defective switch which you said you did..

As this occurred before troubleshooting started and it is unclear if the interrupter switch was involved when this first occurred, we cannot know what originally caused the issue.

Since, most ignition parts have been replaced, Interrupter switch has been disconnected from system so we can rule that out.

As a test, You can remove dist cap, remove Rotor assembly, find a feeler gauge about the thickness of the rotor metal bent tang that spins thru the sensor/pickup, connect spark checker from coil wire to ground, turn key to on, move feeler gauge thru sensor and the coil should fire each time you do this. Stay away from contact with spark checker so you dont get zapped!!!
 
Correction

As the tanged piece attached to the rotor spins thru the sensor/pick up it sends a signal to the Ignition timing module which then fires the coil by way of shorting the Neg side of coil to ground by way of the timing module.
 
So just to check if I follow, I should hook up the spark checker to the coil wire and ground it out with the spark checker. Then use a feller gauge in the ignition sensor to test for spark at the spark checker?
 
A spark tester will connect to source of spark on one end and to ground on the other end. It acts like a spark plug so to speak and allows you to actually see the spark. Remember, the threads of a spark plug are Ground.

Once this is done, you can remove dist cap and rotor assembly.
Then turn ign key to on, now pass feeler gauge thru sensor and if all is working you should see a spark from the coil wire.

If you ever played with the old point ignitions, its like opening and closing the points. If done manually with power on to ign, the coil will fire every time the points are opened then closed.
 
What I would suggest first.

You said the coil had spark when cranking engine with everything assembled and connected. Do a spark test of the coil first with a visible spark tester.
If that shows spark then we can decide whats next.

If no spark at coil output while everything is connected then we can troubleshoot more.

I am going to send you a message, please reply
 
Update:

After a phone conversation, it appears two things occuured when this issue first happened.

1. The shift cables at bracket were adjusted and adjusted incorrectly causing the shift interuptor switch to be closed.
It must have been marginal as the issue got bad to failure (no start).

2. When he disconnected the interuptor switch for troubleshooting he jumped the wires shorting ignition module to ground as if the interuprer switch was closed all the time.....therefor NO Spark.


He is going to hook up battery, unplug black/yellow from shift interupter and try to start engine.
I say this will solve starting issue and I advised him on how to adjust shift cables and also to look up my procedure on here that i have posted several times.

Next he will update with results.
 
Got one update only so far,

Once he removed jumper from interrupter wiring connector and connector not connected to interrupter switch,
Engine fired right up. This issue is resolved.

Next is to get shift cables adjusted properly which I sent him a link to a prior thread where those were documented. Once this is completed it should stop making the interrupter switch from being activated until it should be. As the cables were adjusted it was causing it to activate all the time when in gear and in neutral.
 
kghost said:
Got one update only so far,

Once he removed jumper from interrupter wiring connector and connector not connected to interrupter switch,
Engine fired right up. This issue is resolved.

Next is to get shift cables adjusted properly which I sent him a link to a prior thread where those were documented. Once this is completed it should stop making the interrupter switch from being activated until it should be. As the cables were adjusted it was causing it to activate all the time when in gear and in neutral.
Click to expand...
Man this guy has it made. He has you doing his posting for him ….
 
Haha... well it would appear that way...

This could have been resolved right away but lack of specifics from him and lack of specific questions from us, meaning not believing thungs said without questioning the EXACT methods.....

A phone call and asking the right questions and pushing for the specific answers was what it took.

Havent heard back so not sure where things stand other than engine is running with interrupter properly out of the curcit
 
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