mercruiser 350 mag wont start/fire

[shankos]

Mercruiser 350 mag tow sport would not start today. Looking for anyones ideas as to why.

The motor is turning over by the starter motor but it does not fire. I tested it this morning and it fired a few times then went to take it out in the water and it stopped working. It was running 7 days ago when i took it out.

I checked the fuel line and it had fuel in it.
I poored some fuel down the manifold inlet directly into motor in case there was a lack of fuel. This did not work so I assume it is not lack of fuel.

I pulled out a lead from a spark plug and stuck a screw driver in it to check if it was getting spark and I could clearly see spark coming out of it. The spark plugs should be fine seeing it was running last week and they are not that old.

So I am out of ideas as to what is wrong. Anyone got any ideas ?

 

[Bondo]

Re: mercruiser 350 mag wont start/fire

Ayuh,... Is it carbed, or Efi,..??

 

[shankos]

Re: mercruiser 350 mag wont start/fire

It is EFI.

 

[shankos]

Re: mercruiser 350 mag wont start/fire

I tried some more things today.

There is no alarms going off via a beep or double beep so I dont think i have a sensor problem.

There is a throttle position sensor that can stop you from cranking the motor unless you have the throttle lever in idle position but i pulled the sensor off and it made no difference. I tried cranking with various throttle range from idle to wide open.

The boat was running yesterday morning and last week so i dont think all my sparks plugs would be the cause of it. If one or two spark plugs broke the motor will still fire would just run rough. I pulled one of out and it checked out ok.

I checked for spark or more of the spark plug leads and they had spark.

I tried cranking it again today and it fired for like 1 second which is wierd not sure why.

I thought maybe something is up with the fuel feeding system. Not sure if the electronic injectors will feed fuel into the cylindars even after i poored fuel down the manifold if they are not functioning. Is this true ?

I tried to see if i could stick a multimeter in one of the injector plugs to see if it was getting a voltage signal but the multimeter would not fit in the small slot that the plug has.

At the moment i am thinking it could be something to do with the EFI system cause the starting system is fine and the ignition system seems to be ok. The fuel pump and feeding system seems to be ok plus i bypassed it by pooring fuel directly into intake manifold. So that is why I am thinking something is wrong with the fuel getting into the cylinders via the EFI system. Not sure what is would be left to be wrong ? anyone got an idea ?

 

[Pete104]

Re: mercruiser 350 mag wont start/fire

Ya got fuel pressure?

 

[shankos]

Re: mercruiser 350 mag wont start/fire

dont know how to test for fuel pressure. Will see what i can work out less ya have some pointers.

 

[shankos]

Re: mercruiser 350 mag wont start/fire

On the fuel rail on the top of the motor there is a crossover pipe from the left to the right side on the engine. There is a valve in this pipe that when i press by hand it causes fuel to squirt out under some sort of pressure not sure how much. But this seems to indicate that there is some pressure of some some degree.

 

[shankos]

Re: mercruiser 350 mag wont start/fire

i also found three fuses and a fuel pump relay and a main power supply relay. I took these all off and tested them by hand with a multimeter and they where all ok. I also tested the plugs from the motor to the relay where recieving power with multimeter and they where doing so.

 

[achris]

Re: mercruiser 350 mag wont start/fire

Very strange that you are getting spark, but it still won't fire with fuel poured down the intake... Try checking the spark timing. Just make sure it is firing at roughly the right time. Getting spark is one thing, getting it at the right time is also just as important. What year is the engine (or a serial number if you have it)? I would like to look in a manual to see what's attached to the systems....

Just something different to try....

Chris.......

 

[Don S]

Re: mercruiser 350 mag wont start/fire

Perhaops this would be a good time if you did a real ID of this 350 mag. Do you have a serial number? While it may be EFI, is it MPI, or TBI, which type MPI (there are a few) and which type ECM.

 

[shankos]

Re: mercruiser 350 mag wont start/fire

It is MPI.

I dont know what type of ECM it has

I am not sure how I could check the timing it is electronic dizzy I assume ya need a computer to check it. I got a timing light but i have not seen any timing marks anywhere.

 

[achris]

Re: mercruiser 350 mag wont start/fire

You have a raised section on the timing cover, just to port of the top of the crankshaft pulley. On the balancer there is a line cast/machined into the surface. When the line on the balancer is lined up with the raised part on the timing cover, that's close to TDC... Run a bit of liquid paper into the line on the balancer a dab on the timing cover. Point timing light and ensure you're getting spark around that area....a bit before TDC is ideal.

Chris.......

 

[achris]

Re: mercruiser 350 mag wont start/fire

Double tap, sorry...

BTW... Your engine is 2003...

Chris.....

 

[shankos]

Re: mercruiser 350 mag wont start/fire

took new dizzy cap, rotor leads and plugs to get it firing. also a new fuel filter.

 

[svxtech]

Re: mercruiser 350 mag wont start/fire

took new dizzy cap, rotor leads and plugs to get it firing. also a new fuel filter.

Flat top cap with the leads coming off either side? There is a service bulletin on those caps.

 

[achris]

Re: mercruiser 350 mag wont start/fire

Flat top cap with the leads coming off either side? There is a service bulletin on those caps.

Would love to see that bulletin... I have the same style dissy and cap on my V6....

 

[svxtech]

Re: mercruiser 350 mag wont start/fire

Would love to see that bulletin... I have the same style dissy and cap on my V6....

"They are junk" :facepalm: . But seriously, mercury had problems with the manufacturing of them, (shorting out internally) after 20 min of run time they start to fail with the replacements. We had a few "You just tuned my boat up and ran great this morning, but now it won't start" Get the NAPA or after market, They still seem to corrode faster than say a TBV or EST cap, but haven't had any short term failures... yet

 

[Pete104]

Re: mercruiser 350 mag wont start/fire

I found Accel cap rotor w/ brass contacts @ Advance Auto parts. Less money than merc too!

 

[Don S]

Re: mercruiser 350 mag wont start/fire

"They are junk" :facepalm: . But seriously, mercury had problems with the manufacturing of them, (shorting out internally) after 20 min of run time they start to fail with the replacements.

Man how things get turned around in only a few years.

That distributor is from GM not Merc. Every marinizer that buys GM engines (Volvo Penta, Marine Power, etc.) use the same distributor.
The problem was not that they were shorting out, the problem was moisture due to not enough vents.

Here is the 2003 service bulletin on the problem.

 

[svxtech]

Re: mercruiser 350 mag wont start/fire

I understand Mercury does not "manufacture" them, I'm not a linguist, no need to nit-pick. There is a more recent service bulletin on them also that addresses the short run time failure though. (last 6 months or so) that is the one I was referencing.