TBV ignition electronics troubleshooting....

i am troubleshooting my Thunderbolt V ignition system due to a sudden loss of spark a couple weeks ago....can someone describe the current flow and operation of the hall effect ignition sensor located inside of the distributor?.....i have the new design sensor that is encased in resin and has 3 wires including white/green, white/red and black.....i have the color wires connected properly with the bullet connectors to their matching wiring harness wires and the black wire connected to ground.....

things i have checked so far....i have 12V on the white/red wire and 12V at the positive (and negative which is normal) coil terminals with the ignition key in the 'run' position but i get no spark at the coil...i have been working on this issue for the past couple weeks and out of frustration i started throwing parts at the problem and replaced the hall effect sensor twice, the coil twice, and the expensive ignition module once and still no spark....i have been through the TBV troubleshooting tree numerous times and always get stuck with no spark from coil....i have verified the throttle lanyard kill switch is good, the shift interrupt switch is good, the neutral switch is good, the 50 amp breaker is good, the ignition switch is good, the coil HT lead wire is good, the tach is not grounded out, and the rotor is turning when the engine is cranking over.....

this past w/e i even spent $50 talking to two different certified marine mechanics on the 'just answer' web site about the problem....we spent 2 - 3 hours working on the problem without getting anywhere.....their final suggestion was to replace the TBV system with a simplier Delco EST system for about the same cost as i paid for the TBV ignition module alone.....i prefer to keep the original TBV ignition system and since i have already spent so much monely on new parts i really don't want to spend another $350 for the Delco system....

i have a strong suspicion that the hall effect sensor and/or distributor are not grounded properly and not allowing the sensor to 'pulse' on the white/green wire as the distributor rotor is turning....as stated earlier i have the black wire from the new sensor connected to ground....i do not have a separate wire for a distributor ground....should there be a distributor ground wire?....should i add a ground wire to the distributor?...where would the wire connect to on the distributor?.....does this even make a difference?.....

for what it is worth the testing method in the Mercrusier manual for the hall effect sensor is inaccurate...the manual states to check the continuity between the white/green and white/red wires with an ohm meter and if the sensor is good you should see a reading of at least 100 ohms....i have checked three sensors (two of them brand new) and none of the sensors show any continuity at all between the two colored wires....i don't mean a '0' ohm reading...i mean absolutley no continuity at all.....either i don't know how to use an ohm meter (but i do) or i have 3 defective sensors (unlikely) or the mercruiser manual is wrong.....

normally i am pretty good at troubleshooting problems but this one has me (and two certified marine mechanics) stumped......

thanks...
cliff

Are you using the merc manual and following the chart for TB V
page 4B-17 http://www.*******.com/merc/Servmanl/18/18B4R2.PDF
replace the *`s with b,o,a,t,f,i,x .Use no comma`s

Bt Doctur said:

Are you using the merc manual and following the chart for TB V
page 4B-17 http://www.*******.com/merc/Servmanl/18/18B4R2.PDF
replace the *`s with b,o,a,t,f,i,x .Use no comma`s

Click to expand...

yes, that is the troubleshooting tree i am using....i did some research on the internet last night about hall effect sensors and how to test them....they are actually quite simple....with the ignition key in the 'run' position i have 12V going into the sensor via the red/white wire and i have a good ground via the black wire....i removed the rotor wheel and checked the voltage on the green/white wire and i have 0 volts on the green/white wire as expected....when i interrupt the magnetic field in the sensor i maintain the 12V on the red/white wire and i get 4.5V on the green/white wire.....this tells me the sensor is working by pulsing properly as the teeth of the rotor wheel spin through the sensor and interrupt the magnetic field.....

i suspect i have an unwanted ground somewhere....with the ignition key in the 'off' position i checked the wires going into the ignition module and knock module with a test light to see which ones showed a ground....the single black wire from the ignition module does show a ground as expected which is good....however to my surprise i found all of the purple wires and the tan/blue also showed a ground.....since the purple wires are positive power wires to the ignition module and knock module i am thinking there must be a ground on one of the wires which is causing the coil not to fire....as i look at the wiring diagram for my engine (Mercruiser Service Manual 24) it looks like possible locations for a ground on the purple wire include the alternator, carb electric choke, oil pressure switch, starter solenoid, and electric fuel pump......

does the fact that i found the purple wires grounded at the ignition control module indicate a ground somewhere or do these wires normally show a ground until the engine starts?....if there is a ground somewhere any suggestions on the best way to track it down?

thanks for any help....

cliff

Cliff after looking at service manual #24 it looks like the only way to isolate it would be to disconnect the wiring harness connector to see if the purple wire is grounded at the engine side or the helm side of pin #5 , if it's the engine side I would disconnect each purple wire one at a time to see if it's grounded same with helm side. I'm definately no expert on wiring but it doesn't show purple going to any ground unless it's shorted somewhere.

Bob & Sue said:

Cliff after looking at service manual #24 it looks like the only way to isolate it would be to disconnect the wiring harness connector to see if the purple wire is grounded at the engine side or the helm side of pin #5 , if it's the engine side I would disconnect each purple wire one at a time to see if it's grounded same with helm side. I'm definately no expert on wiring but it doesn't show purple going to any ground unless it's shorted somewhere.

Click to expand...

thanks....i too am no expert at troubleshooting electrical problems, but i am definetly getting better at it as i am working through this issue....i was wondering if i can simply unplug the purple wire connector at each component on the purple wire circuit one at a time and see if the ground signal from the test light at the ignition module wiring goes away....would this work to identify the component and/or its wiring as the source of the ground?....

cliff

after rereading your reply i think you answered my question about disconnecting one component at a time from the purppe wire circuit.....i will try that as a next step to see what i come up with....

thanks...

cliff

That's how I'd do it each component like the oil sender would go to ground with a short I don't see any other way to isolate which component it is. Maybe someone else knows of an easier way. Good Luck

thanks....i just printed out a copy of the wiring diagram and used a highlighter to isolate the purple wire circuit....that makes it much easier for me to follow the circuit in question.....sometimes looking at a wiring diagram can be intimidating until you break it down into individual circuits to see how they all fit together.....

cliff

I like a good mystery.

To answer your first question regarding Hall-Effect sensors. Effectively they provide a signal to the amplifier to trigger the coil. In the old days, a set of points signaled the coil to fire by triggering a ground connection. Amplifiers and Ignition Control Modules work together to advance and retard the coil firing based on a few sensors. One input is the knock sensor which retards the advance when the engine is running.

In a points system, a knock sensor is useless because the points are triggering the coil and the advance is controlled mechanically (centrifugal/vacuum).

So, it would appear all the component testing you have done is correct....yet the coil does not fire. I am suspicious of the neutral safety switch and the kill switch. Something is telling the amplifier not to send the signal to the coil. Assuming you have continuity between the coil and the amplifier and you have continuity between the distributor and the amplifier.....it is the only item left. Alpha models have a netural safety switch, Bravos loop the two black wires together. On some models the neutral safety switch is tied in only to the starter circuit not the ignition.

You mentioned you tested this....how did you test that part of the circuit?

-John

PlayDate said:

I like a good mystery.

To answer your first question regarding Hall-Effect sensors. Effectively they provide a signal to the amplifier to trigger the coil. In the old days, a set of points signaled the coil to fire by triggering a ground connection. Amplifiers and Ignition Control Modules work together to advance and retard the coil firing based on a few sensors. One input is the knock sensor which retards the advance when the engine is running.

In a points system, a knock sensor is useless because the points are triggering the coil and the advance is controlled mechanically (centrifugal/vacuum).

So, it would appear all the component testing you have done is correct....yet the coil does not fire. I am suspicious of the neutral safety switch and the kill switch. Something is telling the amplifier not to send the signal to the coil. Assuming you have continuity between the coil and the amplifier and you have continuity between the distributor and the amplifier.....it is the only item left. Alpha models have a netural safety switch, Bravos loop the two black wires together. On some models the neutral safety switch is tied in only to the starter circuit not the ignition.

You mentioned you tested this....how did you test that part of the circuit?

-John

Click to expand...

thanks John....i have not checked every component on the purple wire circuit for a ground short yet, such as the alternator, oil pressure switch, carb choke, and fuel pump but i have checked the normal suspects...that is my next step, removing the purple wire from each one of the remaining components one at at time and seeing if the grounding to the purple power wire to the ignition module goes away....as i understand it if the neutral safety switch is tripped the engine should not even trun over, much less start....i verified this by disconnecting the bullet connectors for the wire on the neutral switch....with the wires disconnected the engine would not turn over...with the wires connected the engine cranks over normally and at a good speed....as for the throttle kill switch i checked the continuity between the wires from the switch as i flipped the toggle on and off....the continuity made and broke as i flipped the toggle back and forth telling me the switch was working OK.....i have continuity between the distributor and the ignition module (i don't believe the TBV system has an amplifier)...i have verified 12V on the red/white wire from the hall effect sensor in the distributor back to the connector at the ignition module.....i assumed (and maybe wrongfully so) that the presence of 12v at the red/white wire from the ignition module also means i have 12V going into the module from the purple power wire.....i have not actually verified the presence of 12V at the purple wire as it enters the ignition module...i have also checked the shift interrupt switch by confirming there is no continuity between the two wires from the switch when the throttle is in neutral...i also verified the interrupt switch is working properly by measuring the continuity between the two wires as i manually rocked the switch back and forth....as the switch was rocked the plunger in the switch would become compressed and i would see continuity on the ohm meter....when the switch is at rest and the plunger is extended there is no continuity in the wres....i even disconnected the white/black wire from the interrupt switch and tried to get the coil to spark but could not.....

any other ideas on what to check would be appreciated....

cliff

Cliff,

You are far more patient than I am.

You need to verify Wire #9 Purple has a solid 12 volts on it with the key on.

It should based on your pick up test but I want to make sure we aren't dealing with a broken or corroded connection.


-John

PlayDate said:

Cliff,

You are far more patient than I am.

You need to verify Wire #9 Purple has a solid 12 volts on it with the key on.

It should based on your pick up test but I want to make sure we aren't dealing with a broken or corroded connection.


-John

Click to expand...

if it were not the end of the boating season I would not be quite as patient in resolving this issue.....that is why I decided to start throwing parts at it a couple weeks ago, hoping to resolve the problem quickly to get a few more outings on the boat.....now it looks like our boating season is over since I have other things planned for the next 3 or 4 weekends......since I have the time now I want to use this as a learning opportunity concerning the ignition system......


it is almost dark here in SC now and raining a little so it will be tomorrow evening before I can check the actual voltage on the purple power wire to the ign module.....

cliff

OK, so this morning before leaving for work i decided to check the voltage at the purple wire supplying power to the ignition module.....with the key in the 'run' position i do have 12V at the connector pin for this wire....i also reconfirmed i have 12V on the red/white wire from the ignition module to the hall effect sensor in the distributor....i could not recreate the ground on the purple wire at the ignition module that i mentioned in a previous post....when i checked for ground on the purple wire this morning it was not there....weird.....

cliff

Cliff,
I am looking at the merc service manual #24 you have the same engine as mine with 0L0 serial # , carbed. Have you followed the troubleshooting tree on page 1C-9 specifically important note at the bottom about grounding WHT/GRN wire 2-3 times per second? I have re-read your posts don't see anything about testing the coil with a spark gap tester you can pick one up at Harbor Fr cheap or any auto store. That's about all I can think of right now but it's early here on the west coast, maybe it's as simple as a coil or coil wire. We're going salmon fishing in a couple hours today, either sat or sunday I'll be at the marina doing some maintenance greasing coupler, changing OD oil, I can speak to a couple merc certified mech from Sea Ray their only a couple miles from my boat and let them read this post to see what ideas they have.

I agree with Bob. With 12 volts confirmed on wire #9, following that procedure should cause the coil to fire. Effectively, that procedure bypasses the ignition sensor. As a practical question....what work did you do to the distributor?

-JD

Yes , i have followed the troubleshooting tree several times and understand the instructions for grouding the green/white wire.....i am using a brand new spark gap tester and have it inserted into the HT lead from the coil tower and clamped to a good ground source.....i have verified the continuity of the HT coil wire with an ohm meter......i even tried using a heavy gauge wire inserted directly into the coil tower and held the end close to a ground source....when i used a jumper wire to ground the negative terminal of the coil i only got a VERY weak spark....the spark is not strong enough to even register when using the spark gap tester.....

i did not do any work in/on the distributor other than changing the hall effect sensor.....i did verify with my test light that the distributor body and shaft do have a good ground.....

here is a link to the discussion i have had with the certified marine mechanics on the 'just answer' web site....it details what i have done and tested to this point.....

http://www.justanswer.com/boat/80eha-need-help-troubleshooting-mercruiser-tbv-ignition-problem.html

thanks for all the help so far, and good luck with the fishing!!!

cliff

one thing that i don't think makes a difference but i will mention it anyway just in case.....i am not installing the new coils into the mounting bracket when i am testing the system....i am just sitting the new coils on top of the engine and connecting the purple wire to the + terminal of the coil and the coil wire from the coil tower to the distributor or a spark gap tester....i am leaving the grey wire for the tach disconnected from the - coil terminal.....i don't believe the TBV system requires the ignition coil to have a ground for the body of the coil....the older ignition systems required the body of the coil to be grounded either by a separate ground strap or through the mounting bracket.....the wiring diagram does not show the coil body having a ground...the body of the coil is painted with a thick black paint so i do not see how a mounting bracket could ground the coil anyway....and there are no terminals on the coil body to connect a grounding strap.....

right or wrong?

cliff

I hate to keep sending you back to do more testing but lets make sure the coil works. Since it is loose, you can do it off the boat with a car battery. Just put 12 volts to the + side of the coil and connect a ground wire to the - side that you can use as a trigger. Connect the spark gap tester to the - side of the battery and strike the ground wire from the coil to the same ground. When you do that the coil spark gap tester should really light up.

That way you can clearly determine the coil status and visually see spark gap tester light up. Mounting should not make a difference but this test will clearly show you whether or not that is an issue.

It is a good idea to be using six feet of wire or so....throwing sparks around a wet cell battery is never a good idea.

Once we have confidence in the coil and the spark gap tester, we will circle back to the ignition module. In order to trigger the coil, the ignition module "senses" a ground connection via a Hall Effect field. Think of it as a magnet passing close to another magnet. This signal is amplified (that's where the word came from) internally in the ignition module and used to trigger the coil. By intermittently grounding the wht/grn wire, you effectively create the same effect without the distributor pickup in the circuit. The fact that you got a very weak spark when you did the test means we need to eliminate the coil as a problem.

-JD

Have you performed a voltage drop test on all of your grounds, especially the main engine/block ground?