No start condition Mercrusier 4.3 L

[achris]

...The coil + side to ground on the motor was 12 volts. When I put the negative lead on the coil negative and positive lead to the coil positive, I had nothing. Key was turned to on.....

That would be correct. The negative side of the coil doesn't go to ground. It's just the side the ignition module switches (to generate the sparks). Have a read of this....

http://forums.iboats.com/forum/engi...-mercruiser-thunderbolt-ignition-systems-work

You should find something in there that will point you in the right direction...

Chris........

 

[Watkinsj]

My engine serial number is attached in picture this is a 2 bb carb with mechanical fuel pump. I ran through the check list you sent Chris, helped a lot! I was getting spark in the ignition coil tower when the green white wire was disconnected from ignition switch and tapping ground with green/white cord from ignition module. I guess this indicates the new ignition switch I just purchased is bad, never buying another Sierra part again! Checked the resistance in my coil and found all three of my coils are low! Crazy that all three are bad.

 

[achris]

My engine serial number is attached in picture this is a 2 bb carb with mechanical fuel pump. I ran through the check list you sent Chris, helped a lot! I was getting spark in the ignition coil tower when the green white wire was disconnected from ignition switch and tapping ground with green/white cord from ignition module. I guess this indicates the new ignition switch I just purchased is bad, never buying another Sierra part again! Checked the resistance in my coil and found all three of my coils are low! Crazy that all three are bad.

Could also indicate the sensor in the distributor is faulty. Run a wire directly from the battery positive to the coil positive, then crank the engine, see if you get spark.

All 3 coils reading low indicates the meter may not be that accurate in the lower ranges. Is it a good quality meter, like a Fluke, or a electronics shop $10 special?

Chris........

 

[Watkinsj]

Hi Chris, just want to let you know I bought an in-line spark tester and checked every cord. The light lit up on every wire. I have 12V to the ignition coil and the positive lead from the ignition sensor. I ran the green/white wire test on a brand new ignition switch, both of the new ignition switches cause a spark from the coil tower. I have not done a compression test as I don’t have the tool. This boat has a emergency switch for man overboard, when I pull the cord the engine turns over yet doesn’t start, same with it connected as with it disconnected. There is also a 50 amp breaker on the mercathode thingy on the engine, could this be faulty? I am grasping at straws at this point and way out of my league. May have to take it in to a boat mechanic.

 

[achris]

The 'man-overboard' switch only kill the ignition, not the cranking circuit. So having the cord out will not stop the engine being cranked, all it will stop is the sparks.

If you ran a wire direct to the coil positive and you get sparks when you touch the white/green wire to ground, but not when it's connected to the distributor sensor, then either the sensor, the shift interrupt or the tacho is faulty. Disconnect the tacho wire (grey) and the interrupt switch from the circuit and check with the white/green connected to the sensor. Still no spark, it's the sensor...

Chris.............

 

[Watkinsj]

Thank you Chris, where does the grey tacho wire go? I am getting spark in the wires but when I pull a plug and install into end of wires I can not see a spark shoot from the gap of the spark plug, I have grounded the plug as well. When I install an inline spark tester it indicates spark is present on all wires. With all wires connected the correct way, not jumping from positive to the ignition coil, spark is present. I have tried 2 new ignition sensors installed in the distributor, I really don’t think I could have got two new sensors that are faulty. It must be the shift interrupter or a tacho short.

thank you so much for taking time out of your day to respond to me! It must feel like talking to a brick wall haha but I do appreciate your help!!

 

[achris]

Pull the cap and check it and the rotor. Sounds like you're losing spark somewhere in the line.

 

[Watkinsj]

Hi Chris, I pulled the green and white wire coming from the instrument cluster (plug that goes to engine) and disconnected the grey wire also going to the cluster. And the engine finally acted like it wanted to start! It would not keep running but I could hear it almost catch! The distributor cap and rotor are new as of 2 days ago. I am guessing it’s not the cap and rotor. It must be something in the tacho wire and cut off switch. Still not sure where to go from here.

 

[Watkinsj]

Anyone know where I can go to get the correct service manual for a 1989 Mercrusier 4.3 L engine? I can not find anything it’s frustrating!

 

[Chris51280]

its in the sticky in the engine section
https://forums.iboats.com/forum/eng...s/338200-miscellaneous-mercruiser-information
its number 6. same as mine

 

[Watkinsj]

Thank you, the service manual # 7 is what I need for the engine. So another update, after messing around with the wires, I removed the white/green wire from the connection point to the distributer ignition switch and ignition module. Also removed the grey tacho wire from atop of the ignition coil and when cranked I hear the engine almost start-up. This was different than the cranking before. I put a trickle charger on the battery and took two days to charge the battery fully. When I checked the battery it was reading 12 V, is this to low to start the engine? Also I checked continuity between the grey and white/green wires and am getting a reading so, no breaks in the wires.

My next check will be compression but this engine ran great 2 weeks prior to this and the compression was checked when I bought the engine (2 months ago). Everything was within the 180 psi range.

 

[Chris51280]

12v is on the very low side. After charging 2 days, it should have more like 12.6. Take the battery to a parts store. They can load test it.

 

[Chris51280]

Do you have power on the purple wire at ignition on to the TB IV module? Maybe run one directly to the positive of the battery.
Do you have a good ground on the black wire? TB IV and the Distributor? Maybe run one directly to the negative of the battery.

 

[Watkinsj]

I do have full voltage at the purple wire with the key in the on position. Once I put the trickle charger on the battery it was slowly going up and the last I saw it was at 12.48 V and this morning the charger green light was showing, so must be fully charged now. I did check for 12 V at the white/red wire and I have full voltage. Also 12V going to the ignition amplifier (purple wire). I connected the black wire from ignition sensor to the ground at which the ignition amplifier (TB IV) goes, same location. I have yet to run a positive wire straight from the battery to the coil and the same for any ground. The main ground off the battery goes to the engine block stud in the back.

 

[Watkinsj]

Well I figured out the problem I created for myself. After just about giving up I tried to see if I could open the throttle linkage up all the way and try cranking it over and just slightly opened it and tried starting it up. One crank and bam it started right up. So Apparently it was just not getting fuel and air like it needed. Albeit she was running rough and extremely rich. I had black smoke come out of the exhausts and the vapors were irritating my eyes. Does this mean my float level is set to high in the carb?

Thank you for everyone's help! Just feels good to hear it start up again!