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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 8331
Experience:  39 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Hello, I am having repeated ignition coil failure.... 2001

Resolved Question:

Hello,
I am having repeated ignition coil failure....
2001 Mercruiser 350 MPI Horizon. New plugs, wires , cap, rotor, and ignition sensor. Alternator putting out about 14.3V.
Brand new coils will fail very quicklly, after after a good run at 3000rpm. The engine will begin breaking-up, and backfireing. If I keep running it, the coil will fail completely. Using Genuine mercruiser coils for thunderbolt ignition....No codes showing up on the scanner.
Stumped...can't afford to be replaceing coils every other trip!
Submitted: 2 years ago.
Category: Boat
Expert:  James replied 2 years ago.

Hello, welcome to JustAnswer.

 

When you are replacing these coils, are you testing them to see what is going out on them? Test the primary resistance it should be 0.60-0.80 ohms and the secondary 's resistance should be 9400-11,700 ohms.

Also, are you sealing the high tension lead wire wit dielectric grease?

Finally, does the tachometer in your boat work?

Customer: replied 2 years ago.

AFTER coil failure, I have not tested the resistances....

If the primary resistance is off on the broken down coil, what does that indicate?? Same question for the seconday...

Did not seal the Coil wire with dielectric grease...but don't think that is the problem???

This is a twin engine application, and the one motor is just a coil eating machine...

The engines have two tachs each...the standard type in dash (one for each motor), and a digital sync type tach, stand alone unit, that displays both engines rpms on one screen. Both apear to work fine....

Customer: replied 2 years ago.
Relist: Other.
mechanic offline
Customer: replied 2 years ago.
Relist: Other.
mechanic offline
Expert:  James replied 2 years ago.

You really should be testing those coils. You don't know for sure they are the problem. They may not be getting the signal to fire because of a faulty coil driver. It is very possible that the driver is faulty and cutting out on you when it gets hot.

You need to test the coil's ohms resistance to verify that the coils are actually faulty and not the driver.

What kills coils it too much voltage. There are only three wires to the coil the pink power wire and the two wires that go to the coil driver. Test at least one of the old coils to see if it is, in fact the problem.

That pink wire that powers the coil comes of the injector positive wires. Pull the fuel injector/ignition fuse and replace it as well.

Customer: replied 2 years ago.

I run a charter fishing business...we make long (2.5 hour) runs to the fihing grounds all the time...One of the last failures, we ran 40 miles with a brand new Mercruiser coil just installed. Engine started breaking up, right before we got to the grounds, slowed down, and it completely crapped out...would not even fire up. Replaced the coil, with a spare, and she fired right up...so i"m pretty sure it's the coils crapping outWink

There is two wires on this coil setup....A red to the +side from the ignition, and a white on the - side to the distributor.

Never heard of a "coil driver" before....are you talking about the ECM?? A faulty ECM will show up on the code scanner...currently the engine shows no codes.

Did not realize that there is a fuel injector/ ignition fuse??? This engine is throttle body fuel injected....

Expert:  James replied 2 years ago.
Why don't you give me the serial nuber off the motor so I can make sure I am looking at the correct diagrams for your motor.
Customer: replied 2 years ago.
serial # XXXXX
Expert:  James replied 2 years ago.

OK,

I keep getting knocked off line, so I am going to open this to the other experts so you can get help. Hope this one makes it to you

Customer: replied 2 years ago.
Thanks james...
Expert:  Tan replied 2 years ago.

Hi my name isXXXXX will assist you.

 

Check your grounds on the distributor and the ECM. Usually high voltage or a poor ground in the ignition causes coil failure. Physically remove the grounds clean with sand paper or wire brush. Check the battery connections ground. If you are using wing nuts remove and use nuts and lock washers.

 

Post back with questions.

Customer: replied 2 years ago.

Grounds all seem good...will triple check everything. Just cleaned all the battery to engine grounds, and connections.

Have not put a meter on the batteries when running hard...I've only checked it idling at the dock and had 14.3v. If the alternator is putting out anything more than that when "running hard", say closer to 15v, will that fry out coils??

If I run easy, say 2700rpm, the engine will run fine for at least a few hours, maybe more before showing any symptoms once the coil problems start they will last the rest of the trip. Next day it will do the same thing, good for a while, than maybe "heat up" and run like crap.....If I go out and jump on it from the get go..3200rpm, it will run poorly right away.

 

Joe

Expert:  Tan replied 2 years ago.

Check your battery voltage through the rpm range anything over 14.8 will create problems and 15 definitely. Check that you have a ground connected to the distributor also. Some of the distributors didn't have a ground if yours doesn't add one. The ground should be connected to one of the bolts coming through the distributor holding the sensor in place. Poor grounds cause resistance causing the coil to overheat and burn up. High voltage causes the coil to get hot overheating and burning up.

 

Post back with questions.

Customer: replied 2 years ago.

I just replaced the sensor inside of the distributor cap (ignition sensor)....the new style sensor, came with an additional ground wire. The original one was only a 2 wire setup, this one was upgraded to 3 with the new ground wire going to ground on the motor. Are you saying to add an additional ground to that...the sensor is only held in place with 2 crappy screws, and if I put a connector under the sensor it will throw it out of alignment...maybe attach a ground to the undeside of the distributor by putting a longer screw through the sensor , then putting a ring connector, and a nut on the longer screw where it passes thrugh the housing? Will do this tomorrow, and also bring someone out with me to help test the voltage at cruising speed...

 

Joe

Expert:  Tan replied 2 years ago.
Correct
Customer: replied 2 years ago.

"Poor grounds cause resistance causing the coil to overheat and burn up."

Will adding the extra ground to the distributor housing eliminate (bypass) any other mystery ground problems i may have

Expert:  Tan replied 2 years ago.
All bad grounds add up to resistance. Check all the grounds on the electrical components ECM and brackets.
Customer: replied 2 years ago.
Wouldn't ground problems also show up at lower rpm....or does loading up the motors cause it to become more pronounced?
Expert:  Tan replied 2 years ago.

There is more demand on the components. More demand means it has to work harder if there is any resistance the voltage doesn't flow. Resistance is like turning on the water hose with a kink low flow not so noticeable high flow the flow is restricted.

 

Post back with questions.

Customer: replied 2 years ago.

So pretty much, either resistance (ground), or high voltage (over charging) is causing the coil to heat up....The easier I run it the longer it takes to heat up. I really don't think I'm putting out 14.8+ volts but will check tomorrow....I also bought a Blaster high performance coil to try...

Will ground the distributor housing, check all the grounds on the electrical components ECM and brackets.....

Am I missing anything?? Should I be looking at the ignition switch itself??

 

Joe

Expert:  Tan replied 2 years ago.

Correct, Check your voltage at the coil when running the engine at higher rpms. The higher the rpms the higher the output is on the alternator, if the regulator is failing the voltage can go real high. Check the voltage at the large terminal on the alternator to get accurate alt output the spec is 13.2-14.8. The key switch should have no affect on the coil failing.

 

Post back with questions.

Customer: replied 2 years ago.

The last time I tried to check the voltage at the + terminal of the coil, with the engine reved up in neutral at the dock the numbers were bouncing so fast on the meter that they were illegible...is that normal??

Will check the voltage when running at the alt...

Expert:  Tan replied 2 years ago.

No the voltage should be steady. Check all the connections and the pin alignment in the plugs. The main engine wiring harness and the ECM. If there is a loose or corroded connection this will cause voltage spikes and poor engine performance. Move the plugs around while the engine is running.

 

Post back with questions.

Customer: replied 2 years ago.

Voltage was steady (on coil+) with the engine idling, around 14.3...once throttle was applied, I could not even read the meter. I thought this was strange, so I put the meter on the other engine, and got the same type of scrambled mess reading, off of the coil that never gives me any trouble....figured that this was normal....

I really appreciate your patienceCool

Expert:  Tan replied 2 years ago.

If you are using a test probe the readings will jump around from the probe moving on the terminal ,connect the test lead using an alligator clip. This should give you a more constant reading.

 

Post back with questions.

Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 8331
Experience: 39 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
Tan and other Boat Specialists are ready to help you
Customer: replied 2 years ago.

Not much more to say here I guess....

wish me luck, this has been a thorn in my side for the past 3 months

Expert:  Tan replied 2 years ago.
Post back to this thread if you have further questions after checking. Your welcome..........Thank you.........Tan

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