350 Mag Thunderbolt IV No Spark At Witbs end

"Yikes you won't believe t

"Yikes you won't believe this one. Maybe I am missing something. I was out on a little evening cruise with the wife and lost power. Phoned a friend and got a tow back to marina. Checked gas was squirting into carb, so pulled a plug and noticed no spark.

Just to be stupid, I took a wild guess and replaced the coil ($69). Still no spark. So I broke out the troubleshooting information and followed the flow chart and it seemed to indicate i needed to replace the sensor in the distributor. So, I pulled the distributor replaced the sensor ($69) and was surprised when there was still no spark. Just for the record, there was 12V at the + side of the coil but no pulsing of the negative side. Also, had 12V on red/white. Striking reg/green against ground seemed to produce a spark but it was not consistent - so what the heck, I replaced the computer module (ouch$$) and then by golly still no spark. At first I had a good pulsing on the negative side of the coil but it dissapeared as soon as i put a spark tester on the coil. Checked all grounds, everything seems right...followed the chart again and this time i was definitely getting spark when striking the white/green so the chart said - replace the sensor. Like an idiot, I bought another sensor thinking maybe first was bad out of the box. Same thing happened. As soon as i put my test light on negative of coil i was getting pulsing, but as soon as i connected the spark tester there was no spark and no more testing. Well, now I am at wit's end. I am mechanical and electrical and usually nail this stuff quickly but I am clearly doing something wrong. Also, by the way, i disconnected the shift interrupt switch by removing the associated white/green wire and also took the tach out of the circuit by taking the correct gray wire off the coil negative. Still no sparky. I am stumped. and I know, I violated the rules by replacing parts without being sure. Also replaced the dizzy cap and rotor...HELP brothers....EH Carumba!!!"

"is your kill switch on, also

"is your kill switch on, also check the conections on back of your ignition switch"

"If all the tests show everyth

"If all the tests show everything is working before you try it with the key switch the we need to start there. If not we need more detailed info on what and what you are not doing.

disconnect the main plug/wire harness from the engine. Large connector!

I attached a pic of a 2 switch gizmo to test/run a engine without the key switch or wiring to the dash.

You need to seperate the wiring harnesses as a starting point.

Hook up the wiring as shown and this will let you start and stop the engine from the engine.

Also look very carefully at your grounds and make sure they are clean and make good contact.

Also make sure you have a hose clamp on the large connector you are pulling apart for my suggested testing when you reassemble it. and tighten it enough but not to much. The large connector can and does give weak or intermitten contacts and a hose clamp helps eliminate this potential issue

here is my test apparatus for testing purposes only!! Use good alligator clips on the wire ends... Let us know what if anything this does for you and your results...


"

OH yah

What year is your bo

OH yah

What year is your boat and what ignition is it???

thunderbolt IV or V etc etc

the details the details.........we need details...........

"I've read your post sever

"I've read your post several times to get a sense of what is going on every time you insert the spark tester in the system. You have replaced all the key components of the ignition system and still can't get it running.

It is my WAG that there is a wire cracked w/in the insulation cover. Is your battery fully charged? Is there a ground wire that connects at the spark amplifier module? Remove it and clean the connector and the point it contacts.

Squeeze each wire between two fingernails and run along the length of it while bending and pinching it. Check the coil wire connectors for corrosion under the shrink cover or just cut and replace them. If you find blackened copper wire when you strip it back, use a 400-800 grit piece of sandpaper to clean it by dragging the bare wire thru the compressed sandpaper."

"Thanks for the replies. The

"Thanks for the replies. The engine turns over no problem and there is 12v at the coil so i don't think any problem with the ignition switch. The boat is a 1992 crownline 350 Mag with thunderbolt IV ignition.

Details are that I have 12 volt at plus side of coil. Usually no pulsing at negative. New coil, distributor ignition sensor, cap, rotor, and computer module. Occassionally I will get a pulse on the negative side of coil with a test light then I put in the spark tester in the coil secondary and get two quick sparks when spinning engine and then nothing. Also these are very fat orange sparks, not blue. Again though, normally there is no spark at all coming from coil."

"Here is more information in c

"Here is more information in case it is helpful..sorry for any confusion. The engine turns over but died because of no spark. There was absolutely no spark at any plug, nor the coil. After replacing the coil I started following the Thunderbolt troubleshooting chart (Thunderbolt IV). It led to a belief the problem was the sensor because there was no spark when momentarily grounding the white/green wire. After this, I replaced the computer module and was pleased to get a spark at the white/green wire when grounding it. After reconnecting the white/green wire I put my test light on the negative pole of the coil and was excited to see it flashing when I turned the engine over - thought I was done. Before turning the engine over to start it I put my spark tester in the tower of the coil and saw two fat orange sparks as the engine turned over, then nothing. What a bummer. Then I put my test light on the negative pole of the coil and there was no flashing a (coil was not being pulsed), so i replaced the sensor in the distributor again and repeated the above chain of events.

So where I am now is that all ignition components are new at least once, and still no spark. It seems that if i let the system sit for awhile or disturb it, say by removing the connector the computer or removing a wire, I will get 2 sparks from the coil then nothing again. I will check the grounds and wires as Mr. Casper suggested. Any other ideas would be humbly appreciated."

"Try this : hot wire from the

"Try this : hot wire from the battery to the + side of the coil, Runs,Y or N
I dont know what your using to measure at the + side of the coil but you may be seeing 12V but not able to pass any current from a corroded connection.Per guy, check the ground wire at the amplifier."

"Thanks will try. It's fu

"Thanks will try. It's funny because when I got the new amp it was all painted where my original was not where it was bolted to the manifold. I took the new one and used my dremmel to scrape off some paint, but not much. I checked the ground on the module with my Fluke and it was good, but it could be that the ground is not capable of taking much current so I will remove more paint from the module."

"Larry:

Not that you don&#3

"Larry:

Not that you don't know what you are doing, but did you double check the insulating spacers on the amplifier heat sink bracket? The heat sink bracket doesn't get grounded. Also, did you place a gob of dielectric grease on the back side of it before installation for heat transfer? Or are they not doing that anymore?"

"Actually this whole thing has

"Actually this whole thing has got me wondering if i am any good at all - i feel like i do not know what the heck i am doing Guy. Good point about the module, it is indeed mounted to rubber insulators. There are 3 grounds (black wires) that appear to be in play. One is from the module to the bottom of the distributor - this is an SOB to get at. Another is the wiring harness that connects to the module has a ground wire that is attached to a bolt that connects the module to the manifold via the rubber insulator - but this is a ground I believe. Another ground is for the firing coil in the distributor which has 3 wires - black, red/white, and green/white. Its odd because my original sensor only had the striped wires and no ground, but the new sensor model that superceded it comes with a ground."

most likely that way because n

most likely that way because nobody ever checks rhe ground wire from the dist body.no ground=no spark

In my Merc. manual it shows th

In my Merc. manual it shows the ground wires from the dist. and module connect together at an engine ground stud. Can you find it?

Thanks Guy - I had to leave to

Thanks Guy - I had to leave town for a week and will look when I get back....that is very interesting. I know the ground from the module went to the distributor but did not see a distributor ground..I think i need to pull the distributor out and physically trace all the wires in that area.

just add a 16 ga. ground from

just add a 16 ga. ground from the dist. to the big stud on the back of the engine.