Cylinders wont fire.

[Confident Noob]

Hi all. Starting a new thread after getting some amazing help from this community and conducting proper testing to narrow down my problem.
Long story short, my Mercruiser 7.4L MPI (L29) starboard engine won't fire up. I've worked past starter and ignition systems. Used a proper in-line spark plug tester and got bright flashing between cap and coil and from cap to individual plugs.
I tried some ether into the intake to rule out a fuel issue, but I got no sputtering after multiple attempts. Got what sounded like a single pop, after a few attempts.
I guess my first question is whether I'm testing properly with the ether? I did two good sprays into the butterfly valve behind air filter. I feel like I should be getting at least a few sputters.

 

[stresspoint]

is this a new thing that just happened or did the motor quit whilst operating ?.
if the fuel pump is activating then check the fuel pressure , spraying starter fluid into the throttle body will tell you nothing.

 

[Confident Noob]

Follow up info: I'm getting a steady cool air flow coming backwards out of my throttle body... and same steady airflow coming out of plug hole with plug removed.... its a breezy day. But this doesn't seem like it should be possible. My brain is hurting.

 

[Confident Noob]

is this a new thing that just happened or did the motor quit whilst operating ?.
if the fuel pump is activating then check the fuel pressure , spraying starter fluid into the throttle body will tell you nothing.

Not new. Engine wouldn't start after dewinterizing. I misdiagnosed starter and spark issues initially, and have moved on from that trying new things. Read several forums saying to spray starter fluid to essentially confirm if you have a fuel problem. If sputtering, then you know fuel supply issue, correct? The fuel pump activates like the other one every time.

 

[Confident Noob]

Follow up info: I'm getting a steady cool air flow coming backwards out of my throttle body... and same steady airflow coming out of plug hole with plug removed.... its a breezy day. But this doesn't seem like it should be possible. My brain is hurting.

Added info: steady air flow coming out of all 8 cylinders when plugs are pulled.
Fully functioning port engine dosen't do that.

 

[flashback]

I'm mystified, but will follow your thread to conclusion..

 

[Confident Noob]

I'm mystified, but will follow your thread to conclusion..

Lol. I'm really hoping someone will jump in with an aha moment about some component I'm not familiar with, but it truly makes no sense to have steady airflow.

 

[flashback]

This steady airflow is something I don't understand..

 

[tpenfield]

You should get intake air flow only ( suction) at the throttle body . Let’s think about the timing chain

 

[dubs283]

I don't know what you mean by "steady air flow"

Is this with the engine turning over/cranking or just static?

If I were guessing the air flow is with the engine turning over then my first test would be compression. I'm thinking tpen is suggesting a timing chain issue. While they do break/jump a tooth it's rare.

Did the winterize service include fogging oil through the intake?

 

[Confident Noob]

I don't know what you mean by "steady air flow"

Is this with the engine turning over/cranking or just static?

If I were guessing the air flow is with the engine turning over then my first test would be compression. I'm thinking tpen is suggesting a timing chain issue. While they do break/jump a tooth it's rare.

Did the winterize service include fogging oil through the intake?

To clarify for everyone, while engine is sitting, not cranking or anything, there is a steady pouring of cool air that comes out of the throttle body, or, from any cylinder with the plug unscrewed. It just seems to be flowing from the breeze... presumably flowing backwards from the exhaust. Yes, I understand how crazy that sounds, lol.
No, the winterization didn't include fogging unfortunately.

 

[dubs283]

While I'm not a fan of ether/starting fluid I would think if everything was sound with the engine it ought to fire off and run at least temporarily.

I use a squirt bottle of gasoline when attempting to test prime an engine or test for a lean condition while running. The engine isn't designed to run on ether, it needs gasoline

Still would be interested in some compression numbers from your engine.

As far as the air flow through your engine your guess is as good as mine at this point

FWIW the 7.4 mpi most often had some small size fuses in a covered harness end/pigtail near the ecm that controls main power, fuel pump, etc. Can't recall if any of the fuses are part of the fuel injector circuit or not. An oem wiring diagram would explain better

 

[flashback]

I think you have some really good LSD!

 

[dubs283]

Does the sea water pump have a mechanical fuel pump attached to it?

 

[Confident Noob]

Does the sea water pump have a mechanical fuel pump attached to it?

I do not think so. My fuel pump is electric, Mercury Quicksilver.

 

[Confident Noob]

While I'm not a fan of ether/starting fluid I would think if everything was sound with the engine it ought to fire off and run at least temporarily.

I use a squirt bottle of gasoline when attempting to test prime an engine or test for a lean condition while running. The engine isn't designed to run on ether, it needs gasoline

Still would be interested in some compression numbers from your engine.

As far as the air flow through your engine your guess is as good as mine at this point

FWIW the 7.4 mpi most often had some small size fuses in a covered harness end/pigtail near the ecm that controls main power, fuel pump, etc. Can't recall if any of the fuses are part of the fuel injector circuit or not. An oem wiring diagram would explain better

I'm going to pick up a compression gauge next, and I'll post those numbers. Kinda concerned with the air flowing through a static engine, that i have stuck valves somehow. I'll also try to find those fuses again. I have the diagram. So far I found a fuse reset push button (little red button) below the ECM. I'm just not sure if all three fuses are reset from that, or if other fuses are separate.

 

[Confident Noob]

I'm going to pick up a compression gauge next, and I'll post those numbers. Kinda concerned with the air flowing through a static engine, that i have stuck valves somehow. I'll also try to find those fuses again. I have the diagram. So far I found a fuse reset push button (little red button) below the ECM. I'm just not sure if all three fuses are reset from that, or if other fuses are separate.

I'm back! And about to start compression testing using the merc instructions. I noticed the instructions don't mention pulling power from fuel system, only grounding the coil. Should I be doing something to stop fuel flowing? With all plugs removed won't this test push a lot of fuel vapor into my bilge?

 

[Bondo]

I'm back! And about to start compression testing using the merc instructions. I noticed the instructions don't mention pulling power from fuel system, only grounding the coil. Should I be doing something to stop fuel flowing? With all plugs removed won't this test push a lot of fuel vapor into my bilge?

Ayuh,..... Move the throttle to Wot,.....
That'll allow maximum air flow, 'n the 'puter will think, "flooded motor", 'n turn off the fuel,.....

 

[Confident Noob]

Ayuh,..... Move the throttle to Wot,.....
That'll allow maximum air flow, 'n the 'puter will think, "flooded motor", 'n turn off the fuel,.....

Ooooooh. Thanks!

 

[Confident Noob]

Ok. Either I'm real dumb (strong possibility), or I'm real screwed.
0 compression/no movement on the guage on cylinder 1 or 3. I tried re-seating guage a little tighter... no change.