Absolutely frustrated with this Mercruiser engine

[370Dancer]

18436572
My friends 2012 205 bow rider with a 5.0 Carb'd engine just couldn't get on plane after she had a "tune-up". Then she had another mechanic go over it who said the carb need rebuilding. That engine simply stalled at a given RPM and wouldn't allow the boat to nose over and get on plane. I rebuilt the little Mercarb for her but after apart it was clean; didn't need anything.
It didn't make sense.
Then going over the spark plug wires I noticed cylinders 4 and 6 wires were swapped on the distributor.
This was last Friday and Saturday.
Runs like a new boat....

@Hoplite808 - her engine's idle sounded smooth but under acceleration sounded just like yours in the video. Check your firing order on the plug wires.

The yard "mechanic" actually did this to me when changing out a distributor in 2017 during the repower. Took a while to discover as I didn't look at the wiring assuming they did it right.
1-8-4-3-6-5-7-2

 

[PlayDate]

The yard "mechanic" actually did this to me when changing out a distributor in 2017 during the repower. Took a while to discover as I didn't look at the wiring assuming they did it right.
1-8-4-3-6-5-7-2

Some of us label the wires just so this doesn't happen. It is a simple mistake but I doubt that is the OP's engine problem. He has been through this engine at least 15 times taking the wires off and putting them back on.

 

[jonl21]

This needs to be fixed or my 3rd party anxiety over this will keep me up at night. God bless the outpour of advice.

 

[Scott215]

Might as well put #1 on compression stroke and see where the rotor is, and recheck all wires. 18436572. Hey you never know because they used to make a 6- 7 cylinder swap cams for chevy years ago . Prob not your issue. Racers swore it would make more power . So the ground cams to match

 

[km1125]

I downloaded the video and striped the sound off, and did a FFT on it (fast fourier transform) which shows the frequency peaks of the engine. In the first part of the video while camera is pointing at engine there isn't anything significant but I can see freq peaks at 68ish and 135ish hz and a ton of mechanical/background noise which I would expect. 135hz would be just over 2krpm firing frequency and all the engine noice, cams, etc. for all 8 cylinders. When you turn away I would suspect you are just getting the engine intake/exhaust noice and the 135 hz drops away and the peak is the 68hz, so just 4 cylinders of intake/exhaust noise. It could be nothing, a sound recording from the back of the boat (just exhaust) would be better for this analysis. It does sure sound like a 4cly engine struggling though...

One other reason I think it's running on 4cyl is the whole safe mode argument. What that ECU was designed (stone ages of controls) there is no ETC (electronic throttle control) or individual fuel injector control (just the 2 injectors). They wanted a simple way to provide limp home and dropping one of the injectors is the way they did it. That provided about 2krpm which is in the manual as an indication of safe mode active.

So, I think you are getting 4cyl of power for some reason:
1. Power to only one bank of injectors (ECM thinks its firing but they really aren't opening up). Remember, ECM fires the injector bank by going to ground. It could even be that a corroded connector makes it look like there is 12v on the high side of the injector, but when trying to pass current, there is some voltage drop on a connector and not enough current (energy) to open the injectors.
2. Exhaust restriction on one side
3. Fuel blocking on one bank.

Back as a kid we had a blocked fuel filter and idled the boat to shore by pouring gas down the carb (from a beer can stolen from parents fridge). Can you get a can of starting fluid (ether) and squirt it into the engine while it's struggling at 2krpm? If it jumps some in RPM like it's making more power, that to me would provide a clue that it's fuel.

I'll attach the FFT for those that are interested! I did knock sensor calibrations on a couple packages, got pretty good doing FFTs using excel. It's amazing what is available for free now vs 20 years ago...

Excellent analysis and it's amazing what you can do with just a low-quality video (and accompanying audio). I did something similar when one user was reporting a knocking sound with his outboard. Could clearly tie it to once per revolution and if the video and audio were better quality, I probably could have pinpointed exactly where in the rotation it was happening.

With better quality audio someone could do this with the OP's case, especially if there was a recording BEFORE it got to the cut-off RPM. If it was recorded as it ramped up from, say, 1200 RPM, to full throttle you could sample the audio and see if all cylinders were firing at 1500 and then some dropped out as it hit 2,000. And it would be better if the recording was using a higher sample rate rather than a "mostly compressed" MP3 to fit into a video file.

 

[aerobat77]

I think we start to enter vodoo science trying to analyze exhaust pulses on a v8 from this video - especially when a crossplane v8 goes thru firing 2 cylinders after each other on one bank at a time of its firing order ( 8-4 and 5-7 is firing on same bank - thats the brabble of a v8 ) .

Lets be honest :

we all failed here
we failed as boaters and we failed as men .

We can do some further vodoo science and dig in the dark while he is dumping further $$$ following the hints but in fact its impossible to tell if this is mechanical or electronics problem from here.

 

[Hoplite808]

I think we start to enter vodoo science trying to analyze exhaust pulses on a v8 from this video - especially when a crossplane v8 goes thru firing 2 cylinders after each other on one bank at a time of its firing order ( 8-4 and 5-7 is firing on same bank - thats the brabble of a v8 ) .

Lets be honest :

we all failed here
we failed as boaters and we failed as men .

We can do some further vodoo science and dig in the dark while he is dumping further $$$ following the hints but in fact its impossible to tell if this is mechanical or electronics problem from here.

As Thomas Edison once said, I have not failed, I’ve just found 10,000 ways that do not work.

 

[Scott215]

Consider just cutting your loss and selling the boat buy something smaller that runs just to get out on the water maybe a few years down the line step back up to a bigger boat this thread is killing
,me I haven't even got out yet I'm hoping to get out this weekend.

 

[aerobat77]

As Thomas Edison once said, I have not failed, I’ve just found 10,000 ways that do not work.

Yes , maybe its time for us for a patriotic pants down tribute with a 'wannabe clubsearay expert' stamp on our foreheads

 

[scoflaw]

Engine has not been verified mechanically sound. That would be a starting point

 

[Hoplite808]

Was able to get down to the boat today and used a test light since I couldn’t find a noid light and confirmed both injector banks are pulsing at idle. I couldn’t test it under load as I was by myself. I also checked spark wire configuration again for good measure and they are still correct.

 

[unsalted]

Was able to get down to the boat today and used a test light since I couldn’t find a noid light and confirmed both injector banks are pulsing at idle. I couldn’t test it under load as I was by myself. I also checked spark wire configuration again for good measure and they are still correct.

Any way to rig a remote camera?

 

[Hoplite808]

Any way to rig a remote camera?

I have to stand in the engine bay and touch the test probes to the unplugged injector wire plug while its running. I can't be at the helm and in the engine bay at the same time.

 

[aerobat77]

I,ve suggested it already to you : is it really not possible to find a lonely spot in the marina where you can tie up the boat on several clamps with good ropes and rev it in gear ? Of course somewhere where the prop wash does not disturb others , of course with a sober brain and carefully looking if anything holds / its safe .

2000 expected rpm,s are not that armageddon force created by this !

You can pulse test the injectors under load AND more important : if the engine revs here also to 2000 exactly you know its not mechanical but electronics introduced .

Other question : do you really have no buddy in the marina who can help you for 15 minutes ???

 

[Hoplite808]

I,ve suggested it already to you : is it really not possible to find a lonely spot in the marina where you can tie up the boat on several clamps with good ropes and rev it in gear ? Of course somewhere where the prop wash does not disturb others , of course with a sober brain and carefully looking if anything holds / its safe .

2000 expected rpm,s are not that armageddon force created by this !

You can pulse test the injectors under load AND more important : if the engine revs here also to 2000 exactly you know its not mechanical but electronics introduced .

Other question : do you really have no buddy in the marina who can help you for 15 minutes ???

The marina I'm at only likes to collect money from boat owners but never spend any money of their own for maintenance. They won't even spend money to evict the abandoned boats that have been there for years. As such the deferred maintenance program they have adopted has left the facilities in need of a few repairs. If I hadn't broke out my own tools and paid for the light bulb and replacement parts myself there would still be no working lights on the pier. Last year we had the gangway collapse and for several months there was no electricity or access to the boats on the pier unless you had a tender or wanted to swim. They did the bare minimum there and the gangway is about to collapse again even though we have all made many complaints. The diver I hired to clean my bottom confirmed with me that only 25% of the anchor chains of this floating dock are still connected and none of them look good. I stay here because slip fee wise it's more affordable than the state run harbors here who want three times as much and are in even worse condition in most cases and offer absolutely no security. I had this boat in a state harbor for a month when I first bought it and caught a homeless guy onboard trying to steal my batteries once. The State Harbormasters response was that it sucked to be me. On my previous boat I had in about 2010 at a state harbor here while recovering from being severely injured after a guy tried to murder me by running me over with an F150, I was notified that the pier had collapsed and they needed me to come down immediately. Sure enough the whole pier was under water and my boat was at the end of said pier. Even though I was in a back and neck brace and walking with a walker they forced me to then and there swim out to my boat and move it immediately or face fines. That pier is still underwater to this day. Anyways, I don't trust my current pier to survive me putting my boat in gear and revving the engine while tied up to it and I haven't got really anywhere else to go. I am on the waitlist for a slip at my yacht club but they don't expect me to come up on that list for at least 8 more years right now and I keep getting bumped lower on the list when a racing sailboat wants to get a slip.

As for your other question I have really weird work hours as a first responder and I'm off work when most everyone else has to be at work. No one was there today when I had time to work on it.

 

[Ericinmich]

I think we start to enter vodoo science trying to analyze exhaust pulses on a v8 from this video - especially when a crossplane v8 goes thru firing 2 cylinders after each other on one bank at a time of its firing order ( 8-4 and 5-7 is firing on same bank - thats the brabble of a v8 ) .

Lets be honest :

we all failed here
we failed as boaters and we failed as men .

We can do some further vodoo science and dig in the dark while he is dumping further $$$ following the hints but in fact its impossible to tell if this is mechanical or electronics problem from here.

Hmm, it wasn't vodoo when I did it at a race track to get a hint in how fast the competition was revving their engine (Indy 500)... also used ffts to calibrate knock systems in vehicles that many here have driven! But you are correct, it is hard to understand.

This engine is not a flat plane crank... Not sure why you suggested that.

 

[Ericinmich]

Hmm, it wasn't vodoo when I did it at a race track to get a hint in how fast the competition was revving their engine (Indy 500)... also used ffts to calibrate knock systems in vehicles that many here have driven! But you are correct, it is hard to understand.

This engine is not a flat plane crank... Not sure why you suggested that.

They Indy engines were though!

 

[aerobat77]

Thank you for your explanation hoplite808 !

Indeed you seem to live in a difficult enviroment and the story with the collapsed pier is just incredible .

However : its truly not a good idea to tie it up on a questionable floating pier but do you have not a lonely spot of a concrete pier somewhere ? Anything solid enough to moore it for few minutes for a load test ?

Look , we try to help but you will not get anywhere if you are not help yourself a bit . If it would be me i would have done it long time ago since when you are able to test the injector pulses under load we can definitely judge if you have a 4 or 8 cylinder under load . When this question is answered and after all the things you have done already we could say if its electronic ( if indeed only 4 ) or if it must be something mechanical ( if all 8 ) .

 

[aerobat77]

This engine is not a flat plane crank... Not sure why you suggested that.

Its a crossplane like i have written , never said its a flatplane.

I mentioned it because the crossplane V8 has its typical 'rhytm' where indeed you can judge the overall rpm,s from this rhytm frequency . But judging at 2000 rpm if all cylinders fire or not , especially when it finally goes thru one underwater exhaust is vodoo science for me.

 

[Hoplite808]

Thank you for your explanation hoplite808 !

Indeed you seem to live in a difficult enviroment and the story with the collapsed pier is just incredible .

However : its truly not a good idea to tie it up on a questionable floating pier but do you have not a lonely spot of a concrete pier somewhere ? Anything solid enough to moore it for few minutes for a load test ?

Look , we try to help but you will not get anywhere if you are not help yourself a bit . If it would be me i would have done it long time ago since when you are able to test the injector pulses under load we can definitely judge if you have a 4 or 8 cylinder under load . When this question is answered and after all the things you have done already we could say if its electronic ( if indeed only 4 ) or if it must be something mechanical ( if all 8 ) .

I really do appreciate everyone's help here. I'm not ignoring anyone's advice I just have limitations with what I am personally capable of. If I can't do it I'm not going to risk injury or worse trying.

As for the pier story you can see on google maps that the pier is still collapsed. The 500 pier is still just the concrete piles and nothing more. My boat was in the third to last slip on the north end of the pier when it collapsed.