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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16132
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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No spark at the coil on Mercruiser 5.7

Customer Question

I have a mercruiser 1998 5.7 efi bravo 3. Replaced the cap and rotor spark plugs, starter solenoid fuses. Still no spark at coil Serial #0L012408
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.

Did you happen to notice if there was an injector pulse when cranking the engine over?

Customer: replied 1 year ago.
No gasoline spray from injectors.
I disconnected fuel line to carburetor and turned on and fuel shoots out.
Expert:  Jason replied 1 year ago.

The only part of the engine that controls both spark and injector pulse is the ignition module under the distributor cap. That provides both the signal for spark, and for injector pulse. If the injectors were pulsing, then we would get into checking voltages and checking resistances of the ignition coil. But because they are not pulsing, then what you would want to do is replace the ignition module. Does that make sense?

Customer: replied 1 year ago.
it does, let me replace it tomorrow and get back to you
Expert:  Jason replied 1 year ago.

There are no time limits here. And you can post back at any time, before or after putting through the ratings.

Customer: replied 1 year ago.
I'm going to swap the ignition module from my starboard engine which runs perfect on to port engine and see how things go. Is there anything special to do that job? i read online i need some sort of grease... is that right? and if, can i get it in a hardware store?
Expert:  Jason replied 1 year ago.

You don't want to swap the modules. Yes you would need thermal grease, which you would have to get at an auto parts store. But It's also going to throw the starboard engine out of time. And is going to be a big pain in the butt to re-time it.

Customer: replied 1 year ago.
Can i replace it with this one? available at my local parts store
Expert:  Jason replied 1 year ago.

No you would need a marine module. The timing curves between the automotive modules and the marine modules are different. If you tried that it would not advance the timing enough, and the engine would struggle to make power. What you need is this one in this link.

Customer: replied 1 year ago.
that is super expensive...what about the following, they all say marine and replace current Ignition Module #811637 at a fraction of the price. ###-####7Ccid###-##-####7Cagid:13933641889%7Ctid:kwd-98583555169%7Ccrid:60879540769%7Cnw:g%7Crnd:4882458002597555495%7Cdvc:c%7Cadp:1o4&gclid=CLi6x_6Q5sgCFQuraQodAegJlA
Expert:  Jason replied 1 year ago.

The module from Mercury lists for 208. All 3 of your examples should be okay. But I don't dabble in aftermarket parts at all.

Customer: replied 1 year ago.
I replaced IC Module and nothing, engine cranks but doesn't start.
So far:
new spark plugs, rotor, dist cap, starter
ignition solenoid
swapped coil
swapped all 3 fuses
tested pick up coil OK
changed IC module
whats next?
Expert:  Jason replied 1 year ago.

Did you get spark or fuel pulse back, or is there still no spark and fuel pulse? Also, did you use a Mercruiser part, or an automotive part?

Customer: replied 1 year ago.
no spark at coil and no spray/pulse at injectors, nothing changed
Expert:  Jason replied 1 year ago.

Did you get a mercruiser part or automotive part?

Customer: replied 1 year ago.
I found this one locally: clearly says GM marine inboard engine
Expert:  Jason replied 1 year ago.

Got it. Now it's going to be a process of measuring voltages and checking resitances with a volt meter. Is that something you are able to do? If yes, can you open up PDF files if I give you the instructions in that format?

Customer: replied 1 year ago.
I think i have done everything shown in the PDF file you sent.
Ignition Coil Test: done by swapping with starboard engine
Pick Up Coil Test: done, all readings match test instructions
Ignition Module Test: replaced
Whats next...
Expert:  Jason replied 1 year ago.

If you remove the distributor cap and crank the engine over, is the rotor actually spinning?

Did you disconnect the tachometer?

Customer: replied 1 year ago.
rotor spins, i was just checking on that. Regarding tach wire, when this issue started few months ago and the engine didn't start sometimes i disconnected the tach wire ( i think its the gray wire) and didn't make any change, i will try again.
Could the ECM be fried?
Before changing the starter, injectors had a nice steady pulse, now there is nothing, no spark at the coil, what is before the coil that i can check for voltage/power.
Expert:  Jason replied 1 year ago.

This problem started just after changing the starter, nothing else in between?

Customer: replied 1 year ago.
I was having problems sometimes with the port engine. Sometimes didn't start although the starter did crank. One day took a dump on me and engine didn't start anymore. A mechanic came over and check everything and said your starter is fried.(According to him because the starter was already beaten it was taken so much juice out of the batteries that the voltage was lower than what the electronic components need it to fire up engine).I took starter to an autopart store and was checked and sure thing it was toasted.I bought a new one, installed it, cranks nice, better/faster than the old one but now i don't have pulse at the injectors.Which i did have before with fried/toasted starter.
Sometimes i wonder if when connecting new starter if a wire touched the wrong place could have burn something else.
Expert:  Jason replied 1 year ago.

You said you checked/changed the 3 fuses. Using your meter, do you show power into and out of those fuses?

Also, what is the voltage on the purple wire at the coil reading with the engine actually cranking over? (and not just key on)

Customer: replied 1 year ago.
This weekend i did the following:
voltage @ purple wire @ coil with the engine actually cranking over: 10.25v
Disconnected gray wire @ tach: nothing
no rpm gauge movement when cranking
plugged rinda codemate: no errors
From Ignition System Check (service manual 24):
Step 3: rotor does turn
Step 7: 12.28v/11.93v @ terminals
Step 8: 12 volts (gray wire at the electrical box next to riser).
Many steps say "check for secondary spark", not sure what that means.
I will perform more check steps today, will report later.
Expert:  Jason replied 1 year ago.

Check the continuity of the plug wire between the ignition coil and distributor cap next just to make sure it's not a bad plug wire.

Customer: replied 1 year ago.
I will do that this morning, also, in Service Manual #24, Ignition System Check in several steps they mention CKT 3, CKT 121 etc... is there a diagram so i can know location of CKT's?
Expert:  Jason replied 1 year ago.

Page 5G-39

Customer: replied 1 year ago.
i don't know what they mean by secondary spark...
Expert:  Jason replied 1 year ago.

They just mean spark.

Customer: replied 1 year ago.
Where is the 5 way or 6 way harness connector?
Expert:  Jason replied 1 year ago.

Not sure what you mean by that.

Did you follow the instructions I gave you in the Volvo troubleshooting guide to the letter? Go step by step?

Customer: replied 1 year ago.
Im following service manual 24 as you recommended. Step 9A, ckt 121 @ 5-6 way harness connector i believe is BRN/WHT 10 in wiring diagram right?
Expert:  Jason replied 1 year ago.

When I help folks troubleshoot EST ignition systems I purposely gives them the Volvo instructions for troubleshooting it. The EST system is a GM system, made by GM. GM sells that system to Mercury, Volvo, and a few others. There are all sorts of manuals to get troubleshooting instructions out of. You can get them from Volvo, Mercury, PCM, straight from a GM manual and a few others. The Volvo way of troubleshooting this system is the easiest way to do it.

I'm assuming you don't have access to a lab scope/oscilloscope, so what I would recommend you do next is call around to places like auto zone and see if they have a special tool to check GM ignition modules. It's a tool some autoparts stores do have. And then take your new module and your old module down to them and get them tested to see if the are good or bad.

The way this system works is the ECM doesn't take over until after the engine has already started. So when cranking, you should still be getting spark even with a bad ECM.