5.0L MPI Engine No Spark

[aka4ajax]

Re: 5.0L MPI Engine No Spark



Thanks for your post, i sent it over to the mechanic, however cut out the first bit. Adrian Cronk is the Mechanic and he is the best we have in the country on Mercruiser engines.

He has been on and off this now for over a year, as I can only get back home every 4 months (i am working in Afghanistan). We have tried just about everything and really appreciate all the advice.

I wish though we could actually find the bloody fault.

Just to recap for you all;
On the Mercruiser DDT when you get to the test spark part, the coil delivers a single spark, its clean and strong.
There are no other faults or warnings for the whole system test.

But when you go to crank the engine from the key no spark is generated so no start.

Emergency cut off is fine, battery power is very good, new sensors all round and inhibitor gear interrupt is also correctly set up.

ECM has been tested on 2 other boats now and is good, its only done 20 hours now and that is all whilst we've been working to find this fault.

Someone must have seen this before I am so depressed its been over 18 months now and were still having the same problem.

Please please please help

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Do any of you old sea dogs know anyone at Mercury or Mercruiser I could tap into there knowledge?

 

[dubs283]

Re: 5.0L MPI Engine No Spark

while cranking the engine is there rpm signal on the tach??

if not =

faulty crank positon sensor

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Let me check that one, i actually can not recall seeing the revs go up.

Many thanks I will come back to you.

 

[Fun Times]

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, Have you done any of this yet???

Give this a try, Hook up your timing light to the coil wire (Between the coil & the dist cap) do you see a strong constant flash when cranking??? Now hook up the timing light to each spark plug wire, do you see a rhythm of flashes as the engine turns over???

If you have spark at coil wire, But not at the plug wires then try a new OEM cap and rotor and see what happens. Good luck.

 

[Don S]

Re: 5.0L MPI Engine No Spark

Did you do the tests on Chart A‑2 Main Power Relay Test on page 2-14 of manual 36?

 

[mpeel]

Re: 5.0L MPI Engine No Spark

You said the voltage is reading 12.3 volts (By the way that is only approximately a 60-65 % state of charge). Check the voltage while cranking the engine. If the voltage drops much below 11 volts, spark will be weak or non existent. Running the ignition coil test with the scan tool can be misleading because the starter is not being engaged, leaving plenty of power to run the coil.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Don and mpeel, many thanks we will go back and re-visit these 2 tests.
Neil

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Many thanks were going to try this also

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Hi Neil

Regarding the threads you have sent me - I have already done all the tests mentioned. I am now looking at the possibility of the relucter plate which is situated on the front of the engine in the timing cover which makes the signal with the crankshaft position sensor. The EST ignition systems suffer from bad earth return and the ECM ignition signal is very reliant on good battery earths. I have currently removed the looms from the engine to the dashboard to test, and I have to say that some of the interface wiring you have done - i.e the old instrument wiring - could well be a factor. Regarding the RPM signal - that is something I will be checking when I have re-assembled the loom into the boat. I am also putting together a test loom with a short loom plug and ignition key to prove where the problem is. I shall be going back next week at some point armed with this new information. WE ARE GETTING CLOSE !!!

Adrian

 

[Don S]

Re: 5.0L MPI Engine No Spark

The EST ignition systems suffer from bad earth return

Never heard that before, not that it matters, you don't have an EST distributor. The only thing used in your distributor is the cap and rotor.

I have currently removed the looms from the engine to the dashboard to test, and I have to say that some of the interface wiring you have done - i.e the old instrument wiring - could well be a factor.

All this should have been verified by checking to see if you have power to the coil when the key is in the run position. For that to happen, the Main Power Relay must work. and that should have been checked long before messing with everything else.

I am also putting together a test loom with a short loom plug and ignition key to prove where the problem is.

Hook a test lead from the batteries positive terminal to the purple wire on the round 10 pin harness (engine side) then jump the slave solenoid to crank the engine and see if you have spark.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Sorry FUN TIMES,

I missed off a reply to you; as we are looking at the lead from the coil that goes into the distributor cap and do not have a spark there before it gets distributed, then no need to look past to the rotor.

sorry

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Well everyone, time for an update I guess.
My mechanic along with information from Brunswick Motors have finally found out what is wrong. The ECU is not compatible with my engine, this was swapped out as the previous one got fried when the engine was fitted. I replaced it with a new 555 ECU that I believed was the same but apparently the ECU I purchased is from a newer engine and the software has changed.
Amazing after all this time and even though questions were asked of the supplier no one told me of the software change and the compatibility issues.

So thanks to all for so much help and fantastic suggestions that eventually lead us to have to suspect the ECU.

neil

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

New ECU is on its way from Brunswick motors and should be here by the end of September.
So I will let you know if this fixes the issue.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

Apparently the MPI 5.0l engine i have was manufactured in 2004 even though its only done 15 hours, it went under and hence i needed to replace all the electrics.
But as it sat for a couple of years not doing any work or gaining hours, i purchased a new ECU for engines after 2007.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

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

Sorry all mine is a 2005 model, but check if anyone hears of this again... as the supplier was not aware of the ECU map change.

 

[aka4ajax]

Re: 5.0L MPI Engine No Spark

New ECU due in UK mid September, I will let you know how it goes then.

 

[Volphin]

Re: 5.0L MPI Engine No Spark

Well if that doesn't fix it, crate it up and send it to me for a stern talking to. Then I will pop on a carb and be on my way.

V