Mercruiser 3.0 electronic ignition, no spark

[Wade1969]

I have a 1996 Mercruiser 3.0 engine with electronic ignition. Battery was installed with leads crossed . . . Wish I could blame someone else for that Anyway, engine turns over but will not start. Checked all fuses and they appear fine, except for the radio fuse. Voltmeter reads 12 volts coming off the coil to distributor with key turned on (with the kill switch turned off, it reads no voltage so assuming it's not a kill switch issue). Neutral switch appears to be operating properly (checked continuity, switch is open in neutral position).

There's no spark from distributor to the #1 spark plug. I assumed the electronic module was fried so I replaced it. Still no spark. Any ideas on how to test further and isolate the issue?

 

[savetexomabeaches]

Squirt some carb cleaner in the carb and see if it fires (if so, fuel issue)
Switch one of the cables that you are getting fire on to the number 1 plug.. If it fires after switching cables, then you know the cable is bad and needs replaced.

 

[achris]

Wade. 3 different ignition systems were used on these engines in that era. We can narrow that down to 2 as the thrid was points. Of those 2 one was EST (single coil and a distributor) and the other was DDIS (Distributorless digital ignition), which has a 4 posted coil. As you referred to a distributor I am going to assume you have EST, correct me if I am wrong.

When testing for spark, test at the coil, not at one of the spark plug leads. Once you have determined that there is spark from the coil, then check at the spark plugs.

The ignition system wiring should look like this.....



The coil and distributor sensor can be tested with just a digital multimeter. The only other thing to check is that the shift cutout switch is not activated.

(Test procedures below, from the factory manual).... Good luck.

 

[Wade1969]

You are precisely correct on the ignition setup being EST. This was precisely the information I was seeking. I will check all the resistance readings tonight and shall report back.

As for a fuel issue, I had checked that with starter fluid initially so I'm confident it's not a fuel issue.

I'm also confident the neutral switch is operating properly considering when I put it in gear and have key turned on (but not engaging starter), there is no voltage from the coil. When I move the shifter back to neutral, I have 12 volts from the coil. I performed a similar test with the kill switch and it seems to be operating properly. Hoping it's my coil or the wiring harness from the coil to the distributor as it has a small resistor in that line. I bought a replacement, just in case off eBay for $35.

 

[achris]

I'm also confident the neutral switch is operating properly considering when I put it in gear and have key turned on (but not engaging starter), there is no voltage from the coil. When I move the shifter back to neutral, I have 12 volts from the coil..

That doesn't sound right. The neutral safety switch in the gear shift selecter box only disables the starter motor from engaging, there should be 12V at the coil (with the key ON) regardless of the gear shifter position. Just be sure the shift cutout switch (which is different to the neutral safety switch) isn't flipping across when you put the gear selector in gear. If in doubt, turn the propller CCW (backwards) as the gear selector is moved to FORWARD....

Chris....

 

[Wade1969]

Chris, you are precisely right . . . Coil still reads 12 Volts with key half turned (not starting) with boat in gear. Ok, I've tested this thing every which way and still no luck. Pick up coil tested good. I bought a new HEI module and a new wiring harness from coil to distribution which has a resistor in-line. Bought a new coil just for giggles also. I've got no spark from Coil but 12 Volts going into coil with key turned half on. I unplugged the power plug from the coil and there is 12 volts at the plug with key half on. The voltage drops to about 9.5 Volts once I begin cranking it. This seemed low to me . . . grasping at straws here but thought I might have a ground somewhere. I disconnected all the wires from the alternator in an attempt to isolate some issue with the voltage regulator, etc. Same result, 9.5 volts suppling coil while cranking. Most of the wires behind the motor is wrapped well in electrical tape but I don't readily see any fuses or anything. Is 9.5 volts to the coil indicative of a problem. If so, any ideas what is causing that? Could a wire have overheated and melted the isulation off the wire and be grounding out at startup? Keep in mind, I never tried to crank the engine with the battery connections swapped.

Thanks,

Wade

 

[achris]

WAG here. Try disconnecting the gray tacho wire. See it you get spark. The reversed battery terminals may have burnt out the tacho and its killing spark.

Chris......

 

[Jimbeam21]

Wade1969 i would love to hear your fix as i have the same exact problem your having thank you

 

[Wade1969]

I'm not seeing a gray tach wire in the engine compartment. Can I just disconnect the tach under the dash to test?

 

[Wade1969]

I pulled the plug on the tach under the dash but that did not change anything. Volts going to coil dropped to 9.5 while cranking. Still no spark. I have a friend with a little newer boat but with the same motor so planning to check it out this afternoon . . . Mainly to check voltage to coil. May swap HEI modules to see if mine is working although my guess at this point is that the problem is occurring prior to the coil. I will advise the team of my findings but certainly, if someone has ideas then please chime in

 

[Jimbeam21]

Have you checked the pickup coil? Yet

 

[Wade1969]

I did check the pickup coil but it tested normal. I had suspected that may have been the issue so I bought one in advance. I guess I will have a box of spare parts when this is all done.

 

[Wade1969]

Well, no luck in troubleshooting the problem so I guess it's going to the shop

 

[Wade1969]

Well, I did not take it to the shop but bought a mercruiser repair manual instead. So, to recap, battery was installed with polarity reversed and key was turned on such that gauges powered up only, no attempt to crank the motor as the full gauge needle moved backwards so problem was evident. Reconnected battery correctly then starter would engage flywheel and turn motor over but no spark. The first problem I identified was no continuity from center pole of distributor cap to center of underside of distributor cap. Replaced both cap and rotor button. The second problem I identified was a bad ignition module located under distributor cap. I have a 1996 Mercruiser 3.0LX but a 1992 Chevy S10 Blazer uses the same module . So, it now cranks and runs. If your boat will still not crank, then disconnect the shift interlock wire plug from the distributor and try to crank it. If it cranks and run with the shift interlock plug disconnected, then the repair manual indicates to replace the "magnetic shaft assembly". I found a spark plug test light and a multimeter (ohm meter and volt meter) to be invaluable in the process of diagnosing my electrical issues. Happy boating!

 

[R055]

They got the mercruiser repair manuals for free to download in one of the stickies in this forum.

 

[Wade1969]

Well hell, I spoke too soon. I took the boat out and it would not idle well. At WOT, it would only turn 4,000 rpm and top speed of 25 mph. Kept back firing. I checked the firing order 5 times over and changed the spark plugs but no fix. I'm thinking it must be the ignition module since it's not a mercruiser part. So, I'm going to start with that and see what happens next. Lessons learned: always buy New OEM parts

 

[bigcountry70]

Did new module correct?

 

[Eric 3.7LX Alpha 1]

Did new module correct?

Wade1969 hasn't been on here since this last post. You should start your own thread for your engine and problem.