No Spark

[tony203040]

Hello everyone!!

One of my first posts, so I hope there are no issues with it. I know there are a ton of "no spark" posts in the forums but I cannot find any posts with similar issues as mine.

Engine: 2002 Mercruiser V6 4.3L EFI TBI

Symptom: No spark, No start.

I worked to follow the Thunderbolt V Ignition Troubleshooting Flow Diagram. Troubleshooting Steps so far:

1. Performed an ohm-check on the gray cable on the back of the tachometer (to ground). Reading 0.9k ohms.
2. Checked all terminal connections...no visible issues.
3. Used a spark tester from the ignition coil to the distributor...no spark (light).
4. 12V is present at the positive terminal (in reference to chassis ground).
5. Connected multimeter between positive and negative terminal of ignition coil...boat starts (and I have no idea why). Disconnect multimeter, boat no longer starts. Uhhhhhhh...what in the world? LOL.
a. I assume a bad ignition coil (maybe my multimeter is acting as a coil?) Crazy talk...I know.
b. I replace ignition coil...no change...still no spark.
c. Return to flow chart.
6. WHT/RED bullet connector from distributor does not appear to be a bullet connector (on my boat)...it does not pull apart. Throw in the incredibly tight space...I'm not sure I'll be able to perform this test. I get frustrated and revert to my computer.
7. Digging through the forums (including Don S's "How thunderbolt systems work" post), I read that disconnecting the tachometer and shift switch can help isolate and troubleshoot the issue.
8. I am now working toward disconnecting the WHT/GRN wire from the shift switch, as recommended by Don S in his post. However, I believe my shift switch has two purple wires coming out and going to a connector. The other connector (that it is plugged into) has a PUR and a BLK wire.
9. In my tireless effort to just move along, I disconnect the connector completely. I turn the key and the boat starts IMMEDIATELY...and then dies after about 5 seconds. I repeated this three times and it dies out like clockwork.

I know I've gone slightly off course from the flow charts, but does anybody have any ideas? I'm thinking a bad shift interrupter switch or a grounding issue. Any ideas, please let me know.

-Antonio

 

[alldodge]

Serial number of motor please?

Don S was talking about a thunderbolt ignition and being a 2002, you should have EST ignition

 

[tony203040]

alldodge,
Thank you for the info...I figured I was missing something. The engine serial number is 0L610684. I've been using Service Manual #25 (90-861328--1). Now that I take a closer look...that was released in Nov 1999.

Thank you,
Antonio

 

[achris]

.... The engine serial number is 0L610684. ...

...Engine: 2002 Mercruiser V6 4.3L EFI TBI...

Errr, nope. That serial number is for a 1998 engine, not 2002 (by 2002 all V6s were MPI).

It uses a MEFI-1 or MEFI-3 ECM, which are not the same as a Thunderbolt V (completely different in fact), so you can't use a Thunderbolt troubleshooting chart to diagnose it.

Apart from the usual checks (broken/loose wires), distributor cap and rotor, HT leads, coil connections, you'll need some diagnostic software to find out why it's not producing spark. You'll also need the manual, and 25 is the right one.

Most Mercruiser owners/dealers use Diacom from Rinda. You could use a Techmate, also from Rinda, but for the extra money, buy Diacom and be able to monitor in real time. The Techmate is not much more than just a code scanner. The main difference is that the Techmate is a standalone hand-held device, and the Diacom is software and you need a laptop computer for it to run on. I have the Diacom, and wouldn't even take a second look at the Techmate.

Chris.......

Here's how to identify the different MEFI units (note the angle of the side connectors).

 

[alldodge]

alldodge,
Thank you for the info...I figured I was missing something. The engine serial number is 0L610684. I've been using Service Manual #25 (90-861328--1). Now that I take a closer look...that was released in Nov 1999.

Thank you,
Antonio

You have a MEFI 3 with TBI and correct its TBV

Those Wht/Red and Wht/Grn connectors are there and going thru the flow chart in 25 is the right way to go.

9. In my tireless effort to just move along, I disconnect the connector completely. I turn the key and the boat starts IMMEDIATELY...and then dies after about 5 seconds. I repeated this three times and it dies out like clockwork.

Look at page 4-E4 and the Tan/Blue wire for the oil pressure switch (area C item 1). Find the switch which should be behind and below the distributor. Remove the wire from the switch and try starting

 

[tony203040]

Thank you, everyone. I am very surprised to hear this is a 1998 engine...since the boat is a 2002. I imagine an engine replacement occurred at some point in its life. Glad to hear I'm using the right manual...most likely, because I pulled it using the serial number of the engine. Thank you, again!

I am at work this afternoon, but will be home in 3 hours ready to tackle your suggestions and hopefully make some headway. I will let you everybody know what I find out, later today.

Thank you,
Antonio

 

[tony203040]

Here's my latest update:

Did some more troubleshooting yesterday and this morning. Ultimately, I tested the RED/WHT wire on the distributor ignition sensor and there is 12 volts. This would indicate that I have a bad ignition sensor, per the flow charts.

Some side notes:
During my troubleshooting, I used a spark tester between the ignition coil output and distributor input. Had no spark. Interestingly enough, while I was back there, I found a ground wire disconnected. This ground wire was never connected to anything...it's clear it's been disconnected for some time. However, based on location and length, it appears it should be connected to negative lead on coil. I go ahead and connect it. I now have spark coming from the coil (to distributor). Still no start. With ground lead attached, I continue troubleshooting and it still point to a bad sensor.

I open the distributor and found it is pretty corroded all around. I cleaned the area and cleaned the sensor...I think I will reinstall and see what happens before buying a new sensor.

I also purchased a distributor tune up kit today, so I will be installing that, as well.

Any other suggestions or ideas before I move forward?

Thank you to everyone who has responded and provided advice.

Antonio

PS: I did not check the oil pressure switch. I went off on this tangent with the ignition sensor that I never did it. Apologies. I will look to do that now, if I don't lose my mind! Haha.

PPS: I did not purchase a diagnostic kit, yet, either. I will look into that and the associated costs. Thank you!

 

[alldodge]

I used a spark tester between the ignition coil output and distributor input.

Should be from coil output to engine block (Ground)

This ground wire was never connected to anything...it's clear it's been disconnected for some time. However, based on location and length, it appears it should be connected to negative lead on coil. I go ahead and connect it.

A ground wire should never be connected to the negative side of the coil, this disables the coil and can cause issues with other components, even the Tachometer

It was running for 5 seconds and now its not running at all?

 

[tony203040]

Should be from coil output to engine block (Ground)

Thank you...I will adjust my troubleshooting step to meet this requirement.

A ground wire should never be connected to the negative side of the coil, this disables the coil and can cause issues with other components, even the Tachometer

Very well! I will disconnect it immediately. I wish I knew where this wire went, and why it's been disconnected for so long. How many leads should be connected to each side of the coil? Right now, there is one wire on the negative side and one to the positive side.

It was running for 5 seconds and now its not running at all?

This is correct...I returned this morning (with the same shift interrupter switch disconnected) and it no longer started (for that five seconds or so). So, I reconnected that cable and started "fresh" from the flow charts.

Antonio

 

[alldodge]

There should only be one each on the coil

 

[achris]

You have a MEFI 3 with TBI and correct its TBV...

Not quite. There is no separate ignition module. The distributor does have a white/red and a white/green wire, but that's only because that's the same distributor being used on this engine as the carbed engines.

...Very well! I will disconnect it immediately. I wish I knew where this wire went, and why it's been disconnected for so long.

Much like cars, Merc try to make as many items a 'one size fits all' deal, it's cheaper to build things that way. The extra ground wire may not have anything to connect to on your engine, but that same harness is used on different models, and it may be used on one of those. Even my MPI engine has wires that are blanked off and not used. Some of the black wires just have a ring terminal on them and are laying openly on the engine. It's just the way it is.

How many leads should be connected to each side of the coil? Right now, there is one wire on the negative side and one to the positive side....

2 wires on the coil. One is red (on the positive side), and is constant power (when the key is ON). The other is white (on the negative side), and that is the one that goes to the ECM and the ECM switches that between open and ground to fire the coil, just like the old fashion points. Just a lot quicker (for a stronger spark) and with a far greater degree of accuracy.

The ECM controls the coil and the timing curve, there is no separate Thunderbolt ignition module, so using the chart won't help you. To test the coil, remove the white wire from the coil negative and insulate it (so it doesn't touch the engine). Get a piece of wire and connect it to the engine ground, with the key ON, touch the wire rapidly to the coil negative. That should produce sparks. That proves the power to the coil and the coil itself. Remove your test wire and return the white to the coil negative.

Chris........

 

[alldodge]

Get a piece of wire and connect it to the engine ground, with the key ON, touch the wire rapidly to the coil negative. That should produce sparks. That proves the power to the coil and the coil itself. Remove your test wire and return the white to the coil negative.

Don't see any reason to do this, already replaced the coil once, and this would only be testing the coil.

As in previous post manual 25 has a test flow procedure