Intermittent spark on Mercruiser 350 mag mpi

[Lochlomond]

Hi, help required for a year old issue with my 2003 nag 350 mpi, i have an intermittent spark issue from the coil, this can be trying to start the engine, out at low rpms or even at 4000rpm, i have traced the problem i think to the ecm not allowing the spark

I traced wiring today to find while cranking her and not starting and proving no spark at the coil i did have 12v at both the ignition coil and module so i can only see it as the ecm saying no spark mate

History - i have just replaced the coil & module for new, i have had access to reliable spare parts from same year and model as my engine and have tried the following - The ecm, fuel relay, power relay, neutral safety start switch, crankshaft sensor, HT lead all to no avail

I have had engineers look at it, twice had diagnostics connected with no fault codes or errors to report, at my wits end

Can anyone confirm what all sensors on this engine/year etc have an effect on the ecm to control the sparking as the coil is good, the ecm is good and voltage is there then some sensor must be telling porkies to the ecm

Help

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

What is your engine serial number? Can you post it please, Thanks.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi need to check and post later I can tell you it's om64???? If any good for now

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi need to check and post later I can tell you it's om64???? If any good for now

Well that number is close to being within the service Bulletin number 2003-06 that you will need to tell your Mercruiser dealer about to see if that is your problem or not, My guess is, it is.

Have a look at Google, You may find some info about service Bulletin number 2003-06 somewhere in here for a strting point.
http://www.google.com/search?hl=en&...uiser+service+Bulletin+number+2003-06&spell=1

Service Bulletin # 2003-06, V6 & and V8 [GMEFI] NO START MISS FIRE OR ENGINE CUT OFF CONDITIONS.

Good luck with it.

 

[Don S]

Re: Intermittent spark on Mercruiser 350 mag mpi

Here is the 2003-06 service bulletin.

http://www.4shared.com/document/i5e2WwVR/Mercruiser_Service_Bulletin_20.html

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Well that number is close to being within the service Bulletin number 2003-06 that you will need to tell your Mercruiser dealer about to see if that is your problem or not, My guess is, it is.

Have a look at Google, You may find some info about service Bulletin number 2003-06 somewhere in here for a strting point.
http://www.google.com/search?hl=en&...uiser+service+Bulletin+number+2003-06&spell=1

Service Bulletin # 2003-06, V6 & and V8 [GMEFI] NO START MISS FIRE OR ENGINE CUT OFF CONDITIONS.

Good luck with it.

Hi thanks but having looked at the bulletin it does not cover my engine number Its OM644873 the bulletin stops at OM642305

Also the bulletin is more based arround the distributor as intermittently i lose the spark from the coil i don't see this being a distributor issue

Could you tell me which sensors/parts on the engine would tell the ecm not to send a signal to the ignition module

I'm not a marin engineer but looking at the wiring i'm assuming the engine sensors give info to the ecm which in turn controls the fuel and sparks etc

I reckon the ecm sends a signal to the ignition module which in turn sends signals/fires the ignition coil, as i have 12v at both coil and module i still see this as the ecm not telling the module to fire the coil very intermittently

Having replaced the coil & module and tried a sound replacement ecm i have eliminated both of these i still feel their is a roque sensor giving bad info intermittendly to the ecm

As i have for a very limited period of time an identical engine and a 2003 model at that i'd like to try all the bits/sensors etc first to eliminate this before then looking into the wiring, harness, connections etc

So can anyone tell me a list of sensors/parts i should try to at least eliminate them all

Thanks

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi, you might want to go read that bulletin again, Read the second half near the bottom of the page, There are two completely different parts to that service bulletin, They just seem to run together.

Even though your number is just outside the range it still worth doing the test, As I have seen a couple just out of that serial number that needed the new ECM.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi, you might want to go read that bulletin again, Read the second half near the bottom of the page, There are two completely different parts to that service bulletin, They just seem to run together.

Even though your number is just outside the range it still worth doing the test, As I have seen a couple just out of that serial number that needed the new ECM.

Hi, I'll check and give it a go, what determines an Aplha engine? As i see this part is subject to an Alpha engine only, i'm running a bravo 3 leg?

Cheers

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Oh just to add my ecm part No is 864377-T05 which does not match any ecm part no on the bulletin, thanks

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi, I'll check and give it a go, what determines an Aplha engine? As i see this part is subject to an Alpha engine only, i'm running a bravo 3 leg?

Cheers

Sorry about that, I should have checked it out before I wrote that out.:redface:

Because you have a bravo, You are correct, that bulletin does not apply here.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Sorry about that, I should have checked it out before I wrote that out.:redface:

Because you have a bravo, You are correct, that bulletin does not apply here.

No problem so any idea's? I see you are a mercruiser tech so maybe you could answer 2 questions for me please

1) If i have 12v on both the ignition coil and ignition module and when i crank i do not have a spark from the coil and we know its a brand new coil/module and also i have tried another good ecm am I correct in saying that there would be no spark because the ecm is not telling the ignition module to do its stuff

2) Based on me believing my diagnosis in question 1 to be correct can you give me a list for my engine number of all the sensors which would tell the ecm not to spark the ignition (I ask as i have access to an identical engine from my local mercruiser dealer but he wants to rebuild its got a cracked block and time is running out for me for these parts)

Thanks

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

Hi thanks but having looked at the bulletin it does not cover my engine number Its OM644873 the bulletin stops at OM642305

Also the bulletin is more based arround the distributor as intermittently i lose the spark from the coil i don't see this being a distributor issue

Could you tell me which sensors/parts on the engine would tell the ecm not to send a signal to the ignition module

I'm not a marin engineer but looking at the wiring i'm assuming the engine sensors give info to the ecm which in turn controls the fuel and sparks etc

I reckon the ecm sends a signal to the ignition module which in turn sends signals/fires the ignition coil, as i have 12v at both coil and module i still see this as the ecm not telling the module to fire the coil very intermittently

Having replaced the coil & module and tried a sound replacement ecm i have eliminated both of these i still feel their is a roque sensor giving bad info intermittendly to the ecm

As i have for a very limited period of time an identical engine and a 2003 model at that i'd like to try all the bits/sensors etc first to eliminate this before then looking into the wiring, harness, connections etc

So can anyone tell me a list of sensors/parts i should try to at least eliminate them all

Thanks

Here are some ideas for you.

You have a SENSOR ASSEMBLY, Crankshaft Position on the front cover area. http://www.mercruiserparts.com/Show...br=110&bdesc=Front+Cover+and+Circulating+Pump

You also have a SWITCH ASSEMBLY, Gear Indication that could be out of adjustment.
http://www.mercruiserparts.com/Show...c=Shift+Bracket(BRAVO)(SN-0M659999+and+Below)

You also have a SENSOR, TPS.
http://www.mercruiserparts.com/Show...=Throttle+Body(Mechanical+Throttle+and+Shift)

You may also have a SENSOR, Hall Effect, Camshaft Position that looks like number 6.
http://www.mercruiserparts.com/Show...=50&bdesc=Distributor+and+Ignition+Components

You will need service manual number #31 and ECM 555 DIAGNOSTIC SERVICE MANUAL #36 for your engine.

Here is a parts link to all your engine parts using your serial number.
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=884717

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

1)am I correct in saying that there would be no spark because the ecm is not telling the ignition module to do its stuff

Well there is also a higher chance that the ECM is not seeing a single from either a camshaft position sensor or crankshaft crankshaft sensor or maybe another sensor, Or a bad fuse somewhere, No 12V power or ground somewhere, Things like that.

Have you had your mercruiser guy hooked up a computer to your engine yet to try to see whats going on?

If the ecm can not read the input sensors it can not tell the output sensors what to do correctly.


2) Based on me believing my diagnosis in question 1 to be correct can you give me a list for my engine number of all the sensors which would tell the ecm not to spark the ignition (I ask as i have access to an identical engine from my local mercruiser dealer but he wants to rebuild its got a cracked block and time is running out for me for these parts)

Thanks

See my other post from earlier, That was the best I could come up with for you. You will need to inspect the camshaft sensor under the dist cap to see if yours is hooked up.

I say that because if you look at your number 6 you can NOT buy it separately, But if you look at a newer style engine you can buy a camshaft sensor separately. See if your Merc guy can tell you anything about that.:redface: I think I know why but not positive at this time.

Good luck with it.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Here are some ideas for you.

You have a SENSOR ASSEMBLY, Crankshaft Position on the front cover area. http://www.mercruiserparts.com/Show...br=110&bdesc=Front+Cover+and+Circulating+Pump

You also have a SWITCH ASSEMBLY, Gear Indication that could be out of adjustment.
http://www.mercruiserparts.com/Show...c=Shift+Bracket(BRAVO)(SN-0M659999+and+Below)

You also have a SENSOR, TPS.
http://www.mercruiserparts.com/Show...=Throttle+Body(Mechanical+Throttle+and+Shift)

You may also have a SENSOR, Hall Effect, Camshaft Position that looks like number 6.
http://www.mercruiserparts.com/Show...=50&bdesc=Distributor+and+Ignition+Components

You will need service manual number #31 and ECM 555 DIAGNOSTIC SERVICE MANUAL #36 for your engine.

Here is a parts link to all your engine parts using your serial number.
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=884717

Hi thanks for the info, i have already tried the crank sensor, also the gear indication switch

I will try the TPS now

Not sure that the camshaft one exists the number 6, are you saying here that it looks like number 6 or is number 6 on this drawing, i have this i think but there is no plug connected to it, i'm sure from what i have looked at before is that it is noty in use probably due to the problems they had with it on earlier models

I already purchased manual 31 online i'll try and get number 36 thanks

I'll keep you posted this has gone on so long

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

I have had 2 engineers hook up the diagnostic gear showing no faults, no error codes, no issues in history

I'll ask local dealer about camshaft sensor

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

I will try the TPS now.

The TPS should not keep it from having spark, Try to find the camshaft sensor.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

I will try the TPS now.

The TPS should not keep it from having spark, Try to find the camshaft sensor.

Does this engine definately have a camshaft sensor???

I do not see one on the electrical schematic i have from manual 31!

 

[Fun Times]

Re: Intermittent spark on Mercruiser 350 mag mpi

I will try the TPS now.



Does this engine definately have a camshaft sensor???

I do not see one on the electrical schematic I have from manual 31!

No this engine does not have a camshaft sensor, Because They did not start using a camshaft sensor until 2005 starting with serial number OW390000 and up. That is why we could not buy Number 6 in the parts link under your year/Serial number.

In service manual #36 Page 3A-16 shows a wire drawing of the ignition system without a cam sensor, And page 3A-17 shows a wire drawing of the ignition system with a cam position sensor.

If you get a hold of the ECM 555 DIAGNOSTIC SERVICE MANUAL #36 You will want read page 1A-15, It will help give you an ideal how the ignition system works.

 

[Lochlomond]

Re: Intermittent spark on Mercruiser 350 mag mpi

Finally got this problem licked, cheers for all the inputs and suggestions they all helped and I am now an expert on the Merc 350 mag mpi lol

Traced the fault down to a wonky ignition coil plug, had wiggled the wiring in this area many times trying to replicate the problem before but strangely this time it worked and cut the engine off, half a dozen more times and eureka cut out every time but only if I bent the wires a certain direction and only the pink wire ? (12v from power relay)

So with the plug being part of the loom and not sold separately I decided to solder 3 wires directly onto the terminals on the coil and then use connectors to the loom wires, all fired up, wiggled away no cut out, sea trials yesterday WOT superb ready to enjoy boating again

 

[Joeyd224]

I just had the same problem on my 2002 350 MAG MPI. Stalled just ideling, and at 4500 RPM it started running really bad, finally quit running. We had to be towed in.
No codes from the ECM. My mechanic did a lot of testing. Turns out it was the crankshaft sensor. On the bottom of the motor by the oil pan. The mechanic said it probably got wet from water in the bilge. Replaced the sensor, took the boat out and runs like a different boat.
i thought it was the ECM. That would have been expensive.