350 MPI suddenly Cut Out at 3700 rpm.

[scoflaw]

your almost there, sound like a connectivity issue to the injectors. Make sure you have the constant 12volts to them, if so, start tracking and see where the ground signal from the ecm is getting lost

 

[SeaAyeOwe]

I have 12v to the injectors - I am wondering if a shorted injector can cause all other injectors to fail. They are all powered from the same side and I think the ground is pulsed. My train of thought is if one injector has failed on the electrica side would it stop all the other injectors from pulsing - anyone have any experience with this?

 

[sdleo26]

I have 12v to the injectors - I am wondering if a shorted injector can cause all other injectors to fail. They are all powered from the same side and I think the ground is pulsed. My train of thought is if one injector has failed on the electrica side would it stop all the other injectors from pulsing - anyone have any experience with this?

At the risk of stating the obvious, Ty swapping all or one at a time and see if it fires.

 

[scoflaw]

You can ohm them individually

 

[CliffA]

certainly no expert at this but i would think each injector has to be wired to the ECM separately since the receive a ground signal to fire in the proper time...they likely share the same power signal....so since none of the injectors seem to be firing it stands to reason that something is keeping the ground signal from the ECM from reaching 'ALL' of the injectors......could this be a ground wire from the ECM that has a bad connection?....

cliff

 

[scoflaw]

And when you did the noid test all the injectors were disconnected right and you got no signal. My guess is bad connection / broken ground wire to ecm

 

[paulswagelock]

From the manual:

NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine is operating when the short occurs the engine may stop operating and will not start.

starting to think you had a ground wire melt or chafe as others have suggested.

 

[scoflaw]

interesting enough this is, I would think that if a sensor grounded out failed and killed the engine , that it should set a code, but who knows

I suppose you could ohm all your sensors and at the same time check its plug for a grounded condition. I would first make sure the ecm itself has a good ground

 

[scoflaw]

After talking to someone smarter than me, he tells me the 3 wire camshaft position sensor under the distributor cap will shut off your injector pulse. Check the values

 

[SeaAyeOwe]

At the risk of stating the obvious, Ty swapping all or one at a time and see if it fires.

You can ohm them individually

Yes that is my first step today, to measure resistance and compare. I will also be able to check voltage at the plugs as I am going through the process.

After talking to someone smarter than me, he tells me the 3 wire camshaft position sensor under the distributor cap will shut off your injector pulse. Check the values

Thanks scoflo - I assume this means the hall sensor in th diagram. I guess my best option right now is to swap all distributor components across the engines and go from there. This is the problem with not having an understanding of expected readings or a shop full of spares - swapping is my only real option. :grin:

 

[SeaAyeOwe]

certainly no expert at this but i would think each injector has to be wired to the ECM separately since the receive a ground signal to fire in the proper time...they likely share the same power signal....so since none of the injectors seem to be firing it stands to reason that something is keeping the ground signal from the ECM from reaching 'ALL' of the injectors......could this be a ground wire from the ECM that has a bad connection?....

cliff

And when you did the noid test all the injectors were disconnected right and you got no signal. My guess is bad connection / broken ground wire to ecm

From the manual:

NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine is operating when the short occurs the engine may stop operating and will not start.

starting to think you had a ground wire melt or chafe as others have suggested.

interesting enough this is, I would think that if a sensor grounded out failed and killed the engine , that it should set a code, but who knows

I suppose you could ohm all your sensors and at the same time check its plug for a grounded condition. I would first make sure the ecm itself has a good ground

Yes that is my first step today, to measure resistance and compare. I will also be able to check voltage at the plugs as I am going through the process.

Thanks scoflo - I assume this means the hall sensor in th diagram. I guess my best option right now is to swap all distributor components across the engines and go from there. This is the problem with not having an understanding of expected readings or a shop full of spares - swapping is my only real option. :grin:

Guys - I have the service manual but while it has the wiring diagrams I cannot find the ECM ground wire. I have spent hours on the engine and have not seen any broken wires - but today I need to double down on this ground search. Can anyone tell me where to look for the ECM ground or any other ground I should inspect in detail. My engine is the 2005 350 horizon MPI and it is the stern drive configuration with the port engine being the problem.

As I have said I have had both a Mercruiser diagnostic and the Ronda tool on it and no codes are showing up but by now I am trying every single avenue.

 

[SeaAyeOwe]

Guys - I have the service manual but while it has the wiring diagrams I cannot find the ECM ground wire. I have spent hours on the engine and have not seen any broken wires - but today I need to double down on this ground search. Can anyone tell me where to look for the ECM ground or any other ground I should inspect in detail. My engine is the 2005 350 horizon MPI and it is the stern drive configuration with the port engine being the problem.

As I have said I have had both a Mercruiser diagnostic and the Ronda tool on it and no codes are showing up but by now I am trying every single avenue.

Wiring diagrams found on line for those that might need them. Page 4D-30 is the MPI. Normal replace asterisk with b*o*a*t*f*i*x
http://www.*******.com/merc/techbk/96/96hgd4.pdf

 

[SeaAyeOwe]

OK - al injectors are reading about 16 ohms resistance, cheap multimeter that has not been calibrated recently but they are all consistent. Tells me there is no shorted solenoid coil on an injector.
With ignition switch on (not cranking) all injector plugs are reading about 11v-12v - really hard to get a good contact but they are all consistent.
Still trying to trace the ECM ground physical wire to give it a visual but if I have 11 -12v across the injector solenoid it would suggest I have a good ground at the ECM.

 

[scoflaw]

If the ecm is communicating with the scan tool the ground is not your issue. Did u hear me about the camshaft position sensor under the dist,. cap. that can kill the injector signal?

 

[SeaAyeOwe]

OK - I do not know whether to laugh or cry. It is fixed. Thanks to everyone for the suggestions - it helped a lot.

It was the distributor cap and or/rotor. Baffling as to the failure mode but after swapping across the cap and rotor from one engine to the other the fault moved. New cap and rotor and we are all good.

Remember I (and both mechanics independently) had checked spark at the plug and verified we had spark. We chacked maybe two or three but did not check every spark plug. I had checked spark at the coil. Also both mechanics used their diagnostics tool and neither showed a fault code.

Both caps and rotors were changed by my previous mechanic at the end of last season, I ditched him because of another issue I had with him. I just reviewed the invoice and see he replaced them with Mercury parts - except when I went to the store today I see they are AC delco GM parts. I am not sure if it would have made a difference but I bought the top quality part I could get today with brass contacts instead of the white metal ones.

Anyway - I now know my fuel system and ignition system inside out - but I lost 4 days of beautiful boating weather and because I am OCD on this kind of stuff three nights of sleep.

A happy ending at least - my mechanic will take back the ECM and the high pressure fuel pump he had suggested changing out - a total of $2500 Canadian so I am glad about that.

Dave

 

[sdleo26]

Great to hear Dave, glad it worked out for you. I know the feeling well - when I have a problem with anything mechanical/electrical I am consumed with it until it's fixed. I bet you feel great regardless of it being something "simple". It's really hard to find good mechanics; most are ham and eggers with a 100 piece craftsmen tool set. This is just another example of why I try to do everything myself.

 

[Bt Doctur]

Got to hand it to the engineers on this one. 3 year old boat with the new emission package, cats, etc. operated very well the day before, the next day it was a no start. no fuel delivery, no fuel pump pre-prime sound. Everything else worked.
All engine breakers checked, all ENGINE fuses checked, engine relays swapped.

This lone fuse was sitting directly on top of the battery along with it`s spare replacement fuse in a plastic bag on the wire.
Originally thought it to be the bilge pump feed but following the wires it led up to the main wire harness. Fuse rating was 5 amps so it couldn`t be for the bilge pump anyway.

Removing the cover, it had blown the fuse from what I would describe as simply battery vapor corrosion and thats why it blew.The spare fuse also had heavy corrosion on it also and it was in plastic.
Replaced with a jumper and boat now ran.

My fix was to cut away the fuse that was laying on the battery, direct connect the leads to the battery and install a new fuse holder on top of the motor near the other ones on the motor
Local marina wanted to try replacing the fuel pump first, an expensive guess. Guess nobody tries to fix anything anymore.
Just keep throwing parts at it so see what sticks.
Migh have to save and blowup the pic to see it better.

So ,if you have fuses laying on top of your battery, move them to a safer location before you get stranded.

 

[bbrunoner]

Dave. THANK YOU!!!
I have an '08 Hurricane 256 6.2L MPI, one engine, and the exact same thing happened to me. Underway under 3/4 throttle, no signs of hesitation or slow start, and it dropped out plane, dead. Before i found your thread, i looked at fuel filter and separator bowl the and replaced the fuel filter, checked fuel pressure, checked all fuses, inspected harnesses for wear, and put noid lights on the injectors. All looked good. Was ready to give up the boat to my mechanic, forfeiting Labor day weekend, then saw your thread Saturday night. Went out at 7am Sunday morning, threw in my old cap on the distributor (I replaced it 2 years ago) and hooray, it started.

 

[SeaAyeOwe]

Well I am glad the whole trauma has helped someone else - I have lost count of the number of times this site has saved me heartache so glad I could pay it forward just a little.

Dave. THANK YOU!!!
I have an '08 Hurricane 256 6.2L MPI, one engine, and the exact same thing happened to me. Underway under 3/4 throttle, no signs of hesitation or slow start, and it dropped out plane, dead. Before i found your thread, i looked at fuel filter and separator bowl the and replaced the fuel filter, checked fuel pressure, checked all fuses, inspected harnesses for wear, and put noid lights on the injectors. All looked good. Was ready to give up the boat to my mechanic, forfeiting Labor day weekend, then saw your thread Saturday night. Went out at 7am Sunday morning, threw in my old cap on the distributor (I replaced it 2 years ago) and hooray, it started.