No spark, ignition sensor?

I'm troubleshooting no spark issue on Thrunderbolt IV 4.3L Merc.
Have good spark when striking wht/grn wire against ground. That's all. Otherwise the engine is dead. Cranks but no spark from coil to tester. Tach and interrupter disconnected.
Need following info:

- what is the ignition sensor resistance (I get no reading, also on a second (used) unit) - both dead?
Engine ran yesterday no problem, but before it ran I had the same issue - no spark - for more then an hr. What made it work? ...God knows.

Possible culprits:
- ignition sensor
- ignition module
- instrumentation wiring
- intermittent - broken wire to the module

all voltages present. ~12V at the coil, ~4.5V red/wht module wire.
Again, have good spark from coil tower to spark tester when striking wht/grn wire against ground.


How to test the ignition sensor (currently disconnected)? I've read here that ~100 Ohm, is this correct? Sensor has 2 terminals (screws).
2 sensors that I've got give no reading between terminals. Are both dead?

What VDC values should be present on V6 14 ignition module terminals.
This is a typical Alpha 1991, 4.3L engine with Thunderbolt 4 setup with a triangular base - riser mounted module.

Re: No spark, ignition sensor?

unplug the connector at the module on the riser, spray some type of cleaner/lubricant on the connector and reinsert,and retest.

Re: No spark, ignition sensor?

Instead of trying to invent your own way of troubleshooting the Thunderbolt system, might try using this chart from the oem service manual.
If you head up to the Adults Only sticky at the top of the forum, you can even download a manual.

Re: No spark, ignition sensor?

Don's troubleshooting guide is the best way to find your problem accurately. Before I used it I was doing like you chasing wires with a meter and scratching my head. With the guide I quickly diagnosed a faulty coil and repaired the boat in no time...

Re: No spark, ignition sensor?

Possible culprits:
- ignition sensor
- ignition module
- instrumentation wiring
- intermittent - broken wire to the module
- Also could add bad rpm gauge to the list.
- Try removing the gray wire off the back of the gauge.
- Also try Don's test.

Re: No spark, ignition sensor?

Thanks guys. I've seen the chart and generally followed it with some modifications as flowchart doesn't cover all possible scenarios. One of them is a bad connector that gives all the positives when troubleshooting yet when it comes to firing up the engine ultimately fails.
Did some further troubleshooting today and found the culprit - wht/red wire not connecting well enough to the module. You wiggle it and ignition dies, wiggle again and it works. Bt Doctur had a good hunch - so was mine.
Your thoughts must have guided me... LOL. Happy I narrowed it down.

When it comes to troubleshooting "the chart" is very basic and totally useless troubleshooting bad sensor and module issues. So were some posts indicating falsely 100 Ohm sensor impedance. I happen to own 2 boats, both mercs so I got the sensor from the other one plus I had one spare complete distributor incl. sensor and module (thx to Ebay). Checked today all 3 sensors and all of them give no reading - indefinite resistance/impedance. So "100 Ohm myth" goes into the garbage bin. But in the process I found out how to test the sensor my own way.
The flowchart is like taken out straight from Faraday times (or his lab). No technical info - VDC's on specific wires or resistance. That makes things time consuming and nonconclusive. If this is best Mercruiser support could deliver then to hell with them. I did better just by looking at schematics.
Snoski, as you have seen I covered it all, so it was ultimately and literally down to "chasing a wire". Just hoped for a detailed electrical info here.
I've read here some posts where guys have replaced the module, then sensor then found a true reason for malfunction. All based on "chart troubleshooting".
Hope you understand where I'm coming from.
Thanks again, we all learn from mistakes hopefully made and documented by others, haha.

boat teck said:

Possible culprits:
- Also could add bad rpm gauge to the list.
- Try removing the gray wire off the back of the gauge.
- Also try Don's test.

Click to expand...

Covered that - "Tach and interrupter disconnected." but thanks anyway.
Btw. what is "Don's test"?


For future reference:
some V6-14 module resistance values (may help checking if it's OK)
gnd to wht/red - 1.28 kOhm
gnd to wht/grn - 11.22 kOhm
gnd to gry - 8.17 kOhm
gnd to prp - 1.18 kOhm

my measurement, between black module wire ("-" meter lead) and other ones ("+" lead).

Re: No spark, ignition sensor?

Btw. what is "Don's test"?
When it comes to troubleshooting "the chart" is very basic and totally useless troubleshooting bad sensor and module issues.

Click to expand...

Ayuh,.... Don's Test, is by the Book,....
And, you've already stated that, that's just Bullship, so don't worry about it....

Re: No spark, ignition sensor?

"...Did some further troubleshooting today and found the culprit - wht/red wire not connecting well enough to the module. You wiggle it and ignition dies, wiggle again and it works. Bt Doctur had a good hunch - so was mine....."

Isn't the problem you found covered in the very first step from the chart ?

Re: No spark, ignition sensor?

Maclin said:

Isn't the problem you found covered in the very first step from the chart ?

Click to expand...

that is exactly what i thought

the t-bolt IV system is quite simple and there are a TON of em out there

the main problem merc has had with them throughout the years is the ignition sensor

the new, solid black, potted sensor is what i put on ALL t-bolt igniton systems if the sensor in the distributor is anything but this one, even if just doing a tune-up

the old style, two piece sensors WILL fail eventually, its only a matter of time

as far as ohms testing, i have never done any on these igniton components

the flow chart for troubleshooting is very good and seeing as how this system has been around scince the early 80's, i would say this igniton system is quite good for stock applications

Re: No spark, ignition sensor?

Maclin said:

"...Did some further troubleshooting today and found the culprit - wht/red wire not connecting well enough to the module. You wiggle it and ignition dies, wiggle again and it works. Bt Doctur had a good hunch - so was mine....."

Isn't the problem you found covered in the very first step from the chart ?

Click to expand...

Simple answer: NO
you test and all OK, try to start the engine, dead, test again: OK

chart troubleshooting is not totally bull, just damn primitive
* no sensor test
* no conclusive module test

browse through forum and you'll find cases where good modules were thrown in the garbage based on a chart test

on the other hand... what do you guys do when the subject is not covered in the book?
There is always a BETTER WAY. Keep looking.

PS. if Don's test is "by the book" then it is not Don's, don't you think?

Re: No spark, ignition sensor?

First sentence from top block of troubleshooting chart:

"Check all terminals at Distributor, Ignition Module, and Ignition Coil"

proxyx said:

Did some further troubleshooting today and found the culprit - wht/red wire not connecting well enough to the module. You wiggle it and ignition dies, wiggle again and it works.

Click to expand...

Still having problems understanding how your problem isn't covered in that first sentence. Sounds to me exactly like what it is saying to check.

Feel free to think you re-invented the wheel if it makes you happy!

Re: No spark, ignition sensor?

Simple answer: NO
you test and all OK, try to start the engine, dead, test again: OK.
Intermittent wire in the connector.
How do you check intermittent wire... you bend, wiggle, stretch all cables at all points, inch by inch? Is this what you do? Is this what "Check all terminals at Distributor, Ignition Module, and Ignition Coil" means? And if ok at the time of testing you never go back because you checked it?

Re: No spark, ignition sensor?

For someone that has been on this forum for less that 2 full days, your "I know more than anyone else" attitude sure shows through.

Drop the attitude, and you might get along a little better around here.

Re: No spark, ignition sensor?

proxyx said:

Simple answer: NO
you test and all OK, try to start the engine, dead, test again: OK

chart troubleshooting is not totally bull, just damn primitive
* no sensor test
* no conclusive module test

browse through forum and you'll find cases where good modules were thrown in the garbage based on a chart test

on the other hand... what do you guys do when the subject is not covered in the book?
There is always a BETTER WAY. Keep looking..

Click to expand...

PS. if Don's test is "by the book" then it is not Don's, don't you think?[/QUOTE]When I said do Don's test, All I ment was if you do the tree test in post Number 3, http://forums.iboats.com/showpost.php?p=2302459&postcount=3. That Don was nice enough to go find your engine year and post up a chart that Should/Would make your life a little easyer to understand your engines Basic 'IGN' electrical system so you can find out why your engine has no spark. But I guess the only problem with the test is you would just need more Experience with intermittent electrical problems to keep in mind as your looking for and testing the electrical wires, ect, For any condition they may be in. And you now have found out the hard way like we all have in the past that it can be tricky to find out what wire or wires or sensors are bad. That is why most people would take there stuff to a service shop Because they should have the Experience by now to know what to look for while testing for anything. Sorry you feel the test was of no help to you, But I am thinking if you had the Experience with intermittent electrical problems and you had started with the varry first box in the tree, Then if you had the Experience it sounds like you would have found the problem a lot faster, But look at the bright side because now you know and understand how the basic system works, You will be ready for the next time, Or maybe help a freind out some day while out at the lake when his boat is not starting. PS in the end I think you Owe every body a big thank you for trying our best to help you out for free with our Experience we tried to pass on to you, Because more then likely there will be a new problem around the corner that you may need or want our help with next time, After all it is a boat, And that stands for, ( brake out another thousand)

Re: No spark, ignition sensor?

boat teck said:

PS. if Don's test is "by the book" then it is not Don's, don't you think?[/QUOTE]When I said do Don's test, All I ment was if you do the tree test in post Number 3, http://forums.iboats.com/showpost.php?p=2302459&postcount=3. That Don was nice enough to go find your engine year and post up a chart that Should/Would make your life a little easyer to understand your engines Basic 'IGN' electrical system so you can find out why your engine has no spark. But I guess the only problem with the test is you would just need more Experience with intermittent electrical problems to keep in mind as your looking for and testing the electrical wires, ect, For any condition they may be in. And you now have found out the hard way like we all have in the past that it can be tricky to find out what wire or wires or sensors are bad. That is why most people would take there stuff to a service shop Because they should have the Experience by now to know what to look for while testing for anything. Sorry you feel the test was of no help to you, But I am thinking if you had the Experience with intermittent electrical problems and you had started with the varry first box in the tree, Then if you had the Experience it sounds like you would have found the problem a lot faster, But look at the bright side because now you know and understand how the basic system works, You will be ready for the next time, Or maybe help a freind out some day while out at the lake when his boat is not starting. PS in the end I think you Owe every body a big thank you for trying our best to help you out for free with our Experience we tried to pass on to you, Because more then likely there will be a new problem around the corner that you may need or want our help with next time, After all it is a boat, And that stands for, ( brake out another thousand)

Click to expand...

Long story... I'd love you stand by my side, maybe you'd pick up something. There's no such thing as experience with intermittent cabling problem as this is exactly where experience stops. But I see what joy it gives to some like you to point out mistakes after the problem is solved. Upset you couldn't claim any credit? Where were you before? You haven't even read my post carefully as your "tips" were answered by me in the initial posting.

Don S said:

For someone that has been on this forum for less that 2 full days, your "I know more than anyone else" attitude sure shows through.

Drop the attitude, and you might get along a little better around here.

Click to expand...

First of all I said thanks, TO ALL. Second it seems that some guys attend the forums like this not to help but rather come down on you like a bunch of wolves. Usually after the fact... safer this way.

I said from the beginning and it clearly transpires in my post that I'm familiar with "the flow" so bringing this up, although appreciated, was not gonna help me. I also clearly said what I need in order to move forward:
conclusive sensor test method (not answered), VDC values (not answered).
In the process I developed my own ways which address both.
No one also answered my question about sensor impedance/resistance.
So all this I had to figure out myself. And I did. Appreciate the willingness to help though.
Length of time on the forum has nothing to do with anything. Ppl come and go as problems arise. That's the nature of things. Doesn't mean someone is a dummy because never used your forum. It may actually be the opposite.

What set me on a wild goose chase was that on 2 occasions that I recall reading the poster unequivocally stated that sensor has to show about 100 Ohm resistance. Confirmed by others... turned out to be BS.

Last remark: if ppl never questioned authorities we'd be all sitting by the fire... set by lightning. So boat teck you wait for lightning, I like to make my own fire.

Re: No spark, ignition sensor?

proxyx said:

How do you check intermittent wire... you bend, wiggle, stretch all cables at all points, inch by inch? Is this what you do? Is this what "Check all terminals at Distributor, Ignition Module, and Ignition Coil" means?

Click to expand...

Well, um, Yes

A person's interpretation of this, meaning what is a thorough test for what is described, comes with experience. Each of the steps in any troubleshooting flow chart are macros to be executed according to the technician's abilities and knowledge.

Testing is an art to some degree, you found a problem that some owners may have traded a boat in for after many unfruitful and expensive trips to the shop. You should feel great satisfaction in that.

Many that post here do not wave their credentials around all the time, or even ever. Sometimes the sage advice seems rather terse in nature. Since you are looking for instant creds I suppose I could give some of mine and relate my experiences from a previous career as an avionic technician one by one, for example finding cold solder joints that show voltage potential but fail when any real current is needed, but who wants to read thru all that each time.

Re: No spark, ignition sensor?

Maclin said:

Well, um, Yes

Testing is an art to some degree, you found a problem that some owners may have traded a boat in for after many unfruitful and expensive trips to the shop. You should feel great satisfaction in that.

Click to expand...

... and yet got sh%t for this, haha. You being bit sarcastic but I don't mind. Broken connector, wire, cold solder etc. can drive you nuts if all you have is a chart like this. I wonder how many good sensors and modules were thrown away by "pro" mechanics. This boat is on the market right now... with committed buyer sitting on cash and waiting. I had very limited time to fix it. As I said expected better info from Merc.
Thanks to those who expressed their support and understanding.

Re: No spark, ignition sensor?

Uhmmm... your testing a hall effect sensor, not an outboard CDI trigger. 2 different things, and you don't resistance check hall effect sensors. You need to know what your testing, how it works, and why your testing it. You obviously do not, and are just just putting a meter on things and getting meaningless numbers.

VDC values (not answered).

Click to expand...

Sure it was, in post #3 (Don's post) The Merc flowchart. Its right there in the middle. you need 1 to 12 VDC on the white/red. All your doing is turning on the magnet and sending your reference voltage down the line.

conclusive sensor test method (not answered),

Click to expand...

Sure it was... Follow the flowchart. Works everytime. Okay... i'll humor you. There is a different way to do it. My $500 Fluke will see the pulse but not count it, so you really need a $2K+ sillyscope to do it. Ground the neg and put your positive on the white/green (which is the reference signal return wire) You should count 8 switch pulses every 2 revolutions of the motor. If you don't then you have a bad pickup/reluctor or don't know how to use a sillyscope. Don't take my word as gospel though... I only did it a few times in boat school. And because I don't (although I should) own a scope, I use the flowchart every time and it works for me just fine.

No one also answered my question about sensor impedance/resistance.

Click to expand...

I sorta touched on this in my first sentence. But there is no measurement for resistance because all you'd be measuring is a coil of wire around an iron bar. If the wire was broken/an open you'd read infinite but it still can make an electromagnet. If the electromagnet happens then that's half of what you need to make it work (the other half being the reluctor)

browse through forum and you'll find cases where good modules were thrown in the garbage based on a chart test

Click to expand...

Why would it end up in the trash??? I've followed the chart and at times it's started leading me to the pickup... only to have a bad box in the end. If I pull out the old sensor and replace it with a known good one and I ultimately find out its a box I put the old sensor back in. Like I said before... I don't own a scope, but I do keep a $30 pickup in my box for "testing purposes".

But in the process I found out how to test the sensor my own way.

Click to expand...

Just curious... what test did you find that Don, Bondo, and myself do not know about?

As I said expected better info from Merc.

Click to expand...

And I'll finnish with this. All Merc factory service manuals are written in a fashion that they assume the reader has been through tech/Merc school. You will find this to be true for pretty much any manual that comes from the factory... wether it be a boat, a car, an electric clothes drier. They do skip steps from time to time assuming that you have had technical training. If you think Merc manuals need better info... thank your stars your not sticking your nose in a Volvo manual.

Glad you found your problem... And welcome to Iboats

Re: No spark, ignition sensor?

I thought you were the owner, sorry, my post was not meant to slight mechanics. Not all are equal to the tasks they are handed, but you did find the problem, and did learn more about what "check wiring" entails. You are right in that many "pros" throw stuff at it, sometimes that works but in a case like this experience would win out.

Re: No spark, ignition sensor?

Quote:Long story... I'd love you stand by my side, maybe you'd pick up something. There's no such thing as experience with intermittent cabling problem as this is exactly where experience stops. But I see what joy it gives to some like you to point out mistakes after the problem is solved. Upset you couldn't claim any credit? Where were you before? You haven't even read my post carefully as your "tips" were answered by me in the initial posting.


1- There's no such thing as experience with intermittent cabling problem Sure there is,You just need to know when and where to start looking, And you did that and found it.


2- But I see what joy it gives to some like you to point out mistakes after the problem is solved. No joy at all, Even if you where still trying to fix it I would still said what I said up there, Maybe in another way, But about the same.


3- Upset you couldn't claim any credit? I am not the type of guy that wants any credit really, Because if I wanted to, I could have gone in to grate detail to help you out some, And it would have looked like a book, Because I have done that in the past here on the fourms and gotten more credit then I would ever want, So now I have cut back some and just like to help out a little here and there when I feel like it or if I think of some thing that might help some one out, Even though I know I really do not half too help out here, Because every one eles that post up info does a better job then I do. So no I do not need or want any credit at all, I could care less about it. Playing here just passes some time away is all while I get better.



4- Where were you before? You haven't even read my post carefully as your "tips" were answered by me in the initial posting.Yep you where right I over looked your writing of you already unhooking the tack and the shift interrupter switch. Sorry about that, I guess it was experience thinking and not enough reading. I Should not have posted to try to help what was already there:redface: It might not happen again


5- In the end I think I am happy you got your boat running right that is all that matters with or with out the fourms