5.0L MPI Engine No Spark

[aka4ajax]

Hi All,
I have been using this site for years now and found all the answers to my various little faults without ever needing to post a question. Well that was up until now.....
I have a no spark issue with my Mercruiser 5.0l MPI engine. It turns over at speed and has a fully charged cranking battery.
I have recently had the ECM tested on another boat and that is fine, i also have swapped out the crank sensor as i thought it was the culprit, but still no spark.

On the coil i am getting 12v if i take an earth of the engine, but only 9.6v if i use the white and green wire from the coil driver. i think this is ok....

The intterupt switches on the gear link is all new and working correctly so not that.

Basically i am stumped and would like any help of you guys.

thanks in advance, Neil

 

[dirtyoldman]

Re: 5.0L MPI Engine No Spark

Hi All,
I have been using this site for years now and found all the answers to my various little faults without ever needing to post a question. Well that was up until now.....
I have a no spark issue with my Mercruiser 5.0l MPI engine. It turns over at speed and has a fully charged cranking battery.
I have recently had the ECM tested on another boat and that is fine, i also have swapped out the crank sensor as i thought it was the culprit, but still no spark.

On the coil i am getting 12v if i take an earth of the engine, but only 9.6v if i use the white and green wire from the coil driver. i think this is ok....

The intterupt switches on the gear link is all new and working correctly so not that.

Basically i am stumped and would like any help of you guys.

thanks in advance, Neil

This uses a coil pack, correct? If so, that's the next thing I'd check.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Many thanks for your post.

I have been looking at it the wrong way i think. Your idea of checking the Coil and coil driver is my next challenge tomorrow.

Do you know the resistance of the coil or any way of testing it?

I am thinking of removing it and setting it up in my garage using a 12v supply and try to see if it generates a spark if i manually break the circuit a few times.

Neil

 

[Don S]

Re: 5.0L MPI Engine No Spark

What is the Mercruiser serial number of your engine. There are several setup in the different years, all are not the same. And no, year isn't close enough. Need serial number.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Thanks for your Help;

The serial number is OW613114
Date is Dec 2005
Family is FM9XM05.0GME
Fel is 16.0 gKWhr
Disp is 5.0L

Hope that helps work out what it is.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Ok this morning i have taken off the coil and coil driver pack to look at the resistances across the primary and secondary windings.

I am getting 12v battery power to the A and B connectors to the coil and coil driver, when i pick up the ground off the engine. There also is continuity between the white/green wires and engine block.
when i test the voltage at the A connector using the power +ve and the white/green wires i am getting 9.6v which is also correct i believe for this system.

Looking at the coil windings, i have continuity between the primary and secondary winding pins. This i think is not right....!
Also doing an Ohm reading between the +ve and the two windings one at a time i am getting zero resistance on the meter for both windings. This can not be right, i would expect around 10 Ohms for a automotive coil, so should this be similar?

Looking like coil is short circuit.... any one agree?

 

[Don S]

Re: 5.0L MPI Engine No Spark

I would strongly suggest you test your system per the OEM service manual instead of testing it your way. Those coils are almost $200 US.
Go up click here you can download the manual. #36 is the one you want for your system.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Thanks for the advice.

I used the 555 diagnostic manual to arrive at my decision to test also, as i had gone through the various stages i was able to check without the Mercuiser Diagnostic tool. Which basically asks me to check for the voltages at the coil and driver as i did.

I will download the manual you have linked for me to see if it gives a better option and method.

Thanks.

Yep same manual as i used.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Well i replaced the coil and still no spark.

when running the diagnostic test using the tool. on the test coil part, it does give a good spark at the start and end of the test and does not show any faults.

also all other tests do not show any faults.

To recap, i have now replaced the ECM, crankshaft sensor, Oil pressure switch, interrupt switches and coil. **** what else can i look at????

My mechanic has checked the earths to the ECM and engine, all is good. Also made sure the helm cut off switch is good.

Please if anyone has any ideas please help.

 

[dirtyoldman]

Re: 5.0L MPI Engine No Spark

Well i replaced the coil and still no spark.

when running the diagnostic test using the tool. on the test coil part, it does give a good spark at the start and end of the test and does not show any faults.

also all other tests do not show any faults.

To recap, i have now replaced the ECM, crankshaft sensor, Oil pressure switch, interrupt switches and coil. **** what else can i look at????

My mechanic has checked the earths to the ECM and engine, all is good. Also made sure the helm cut off switch is good.

Please if anyone has any ideas please help.

What is your battery voltage when cranking? Have you checked the fuse to the ECM and any fusible links there might be? Does your dash gauge show oil pressure when cranking?


I'm really reaching here. I don't know the mercruiser MPI system very well, but assume they took GM's and made minor modifications.

 

[wire2]

Re: 5.0L MPI Engine No Spark

....
Looking at the coil windings, i have continuity between the primary and secondary winding pins. This i think is not right....!
Also doing an Ohm reading between the +ve and the two windings one at a time i am getting zero resistance on the meter for both windings. This can not be right, i would expect around 10 Ohms for a automotive coil, so should this be similar?

Looking like coil is short circuit.... any one agree?

An ignition coil is connected internally like an autotransformer; that is, one end of the primary is tied to one end of the secondary. That gives a spark a return path. That's normal, so there will be continuity.

Ohmic resistance of the windings should not be zero, I expect you may not have your meter on the R x 1 scale?
Primary should be approximately 1 Ω, depending on type, secondary will be much higher due to 100 turns of very fine wire.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

When i plug the engine into the Mercuiser test tool and run the diagnostics everything comes back as ok. i even get a spark from the ignition coil on at that point of the complete test.

The voltage of the Battery is 12.3V and I am getting the correct 5V at the sensors.
The ECU is returning ok with 100% power available, but i still get no spark during normal cranking.

Help

 

[Bt Doctur]

Re: 5.0L MPI Engine No Spark

try removing the tach lead.tach might be killing the spark

 

[TJDave]

Re: 5.0L MPI Engine No Spark

This may be way out there and not even apply to a marine engine but,......

I was having the same issues with my 93 Ford pickup. Same size fuel injected motor and year as my boat. I tried everything to track down a no spark issue. ECM, coil pack, battery and alternator checks, wiring, etc. etc. etc.
It was very frustrating and I was about to drive it off a cliff. A mechanic buddy told me to check the magnetic pickup inside the distributor. We replaced it, it fired right up and have had no problems since.

Just a thought.

 

[Don S]

Re: 5.0L MPI Engine No Spark

There is nothing in the OP's distributor but a rotor.

 

[dubs283]

Re: 5.0L MPI Engine No Spark

what i would do is isolate the engine wiring from the boat wiring by disconnecting the 10 pin harness at the engine

this way you can jump the ignition and starting circuit at the engine harness and remove the boat wiring from the system - check your manual wiring diagram for the proper pins to jump to get spark and crank

if you now have spark, your problem is with the boat wiring, if no spark, engine wiring/component issue

my WAG is, seeing as how you have not mentioned checking the cap/rotor assy, your problem may be there

the flat cap/rotor assy on merc MPI engines is notorious for massive corrosion issues

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Hi All I am back and still have not fixed this problem yet, i work away hence i have left this for so long but to recap:

No spark at distributor when cranking the engine.
So far have new coil, new oil and water sensors. New crank sensor and now new engine harness. My mechanic also has just replaced the engine harness also.

When running diagnostic test on Mercruiser tool and getting to the spark test, the coil delivers a single spark so good.

But when then cranking over the engine no spark is delivered......
Battery power is good, 5v at ECM and ECM also taken onto other boat and tested ok.

What can this be?

 

[dirtyoldman]

Re: 5.0L MPI Engine No Spark

Hi All I am back and still have not fixed this problem yet, i work away hence i have left this for so long but to recap:

No spark at distributor when cranking the engine.
So far have new coil, new oil and water sensors. New crank sensor and now new engine harness. My mechanic also has just replaced the engine harness also.

When running diagnostic test on Mercruiser tool and getting to the spark test, the coil delivers a single spark so good.

But when then cranking over the engine no spark is delivered......
Battery power is good, 5v at ECM and ECM also taken onto other boat and tested ok.

What can this be?

Does the rotor spin when the engine is turned over? I had that happen once on a ford, siezed oil pump broke the gear on the bottom of the distributor.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Yes distributor spins fine on crank and all is clean.

 

[dirtyoldman]

Re: 5.0L MPI Engine No Spark

You need to take this to a real mechanic. I'm not sure what tool he used, but you need to be able to look at all the sensors on the engine on a chart and understand what the readings mean. I'm thinking you have something obscure going on , like a harmonic balancer that slipped and isn't on the right spot on the CPS, so the computer is getting no signal. I don't know how else to diagnose this - that's how it's done on the automotive MPI systems when these things happen.