Mercruiser 350 mpi hydraulic locking

[scoflaw]

I had an 8.1, in a truck, with a bad crank sensor that would run poorly and fart and pop, which could cause water to get sucked back into the cylinders.

 

[andrewterri]

QBhoy, After reading everything I thought it might have jumped the timing chain too because I did this on a 302 and had a similar noise. However, it would be banging and hitting the value(s) (Assuming we are talking about an interference engine) whether fuel and spark are present or not.

Thought timing if it is firing against itself but Chris said timing is set off crank sensor. Were you able to put the computer on it? Maybe a failed crank position sensor?

 

[Scott Danforth]

Pressure test the water jacket. This will answer the crack question

plug in Rinda and see what is going on. This will answer most of the other questions on sensors

Measure the static dimension, it will answer the riser question.

Use a timing light to see timing at idle (it should be about 8ish)

 

[scoflaw]

Last I heard this thing don't run

 

[QBhoy]

Hi

Thats a Tub. That would definitely need spacers in the exhaust to raise the riser height. Probably 3" spacers at a min. Or if your dry joint they have differnt configurations. taller risers, different sized spacers to achieve what you need.

You should look at the current exhaust setup.

Hi.

Thanks for relying. It has the high mpi dry joint risers. Also worth pointing out that it’s a fair machine. Manages 50mph gps. Good going.

 

[QBhoy]

Hi all.

I really and honestly can’t thank you enough for all the replies on this. The owner is also following with interest.
Next move is to pull the inlet manifold off her and perhaps the port head. See what’s going on.
One thing is for sure. It took water in initially for sure. Whether that be by means of exhaust side or inlet, is in sure. Not ruling anything out. It doesn’t appear to take any in now with water and manifolds off. Only seems to lock up when fuel and ignition is on, but no further sign of water.
Ive has water ingress before on a few of my engines. By means of riser/exhaust wear and even once by cylinder head on one of the V’s. This is a different thing. It’s not the usual starter clunk noise with water lock. And you’d imagine that if it was a cylinder head issue...it wouldn’t have water ingress to all 4 cylinders on that port bank ?
Anyway. I seriously suspect that water ingress initially by whatever means was serious enough to not only throw the belt off it...but as some have suggested...perhaps throw the timing seriously out too. Perhaps by diz damage and cross firing or otherwise.
Further investigation to follow and can’t thank you all enough so far. Keep it coming please !!

 

[QBhoy]

Last I heard this thing don't run

It doesn’t. Will turn over as fine as you like with plugs in and kill switch off. Enable kill switch (fuel and ignition) and it instantly locks. Almost like opposing pistons fighting against each other.

 

[muc]

Before tear down.

Compression test. Fully charged and good battery, charger on battery so reading stay consistent. Watch gauge for 5 compression strokes, paying close attention to how much the needle moves on each stroke.

Pull the other exhaust manifold so you can see into all the spark plug holes. Turn the engine over by hand and watch that all pistons come up to the same height.

While your doing this check to make sure the timing mark on the dampener lines up when #1 is at TDC.

Crank engine with plugs out and all spark plug leads grounded, with a timing light connected to #1 and see how close timing is to what it should be. Unplug the fuel pump while your doing this. No need to be dumping fuel in the cylinders.

Almost always a bad idea to tear down a engine without having a good idea what your looking for.

 

[QBhoy]

Before tear down.

Compression test. Fully charged and good battery, charger on battery so reading stay consistent. Watch gauge for 5 compression strokes, paying close attention to how much the needle moves on each stroke.

Pull the other exhaust manifold so you can see into all the spark plug holes. Turn the engine over by hand and watch that all pistons come up to the same height.

While your doing this check to make sure the timing mark on the dampener lines up when #1 is at TDC.

Crank engine with plugs out and all spark plug leads grounded, with a timing light connected to #1 and see how close timing is to what it should be.

Almost always a bad idea to tear down a engine without having a good idea what your looking for.

Thanks Muc. Appreciated. I’ve done some of the above but worth me saying again that it’s an MPI engine maybe.

The other bank was dry as a bone. I’m really suspecting there is a timing issue now...as a result of the initial hard stop by water ingress. Almost as if opposing pistons are now working against each other when fuel and ignition is added. She will turn over as sweet as a nut with fuel and ignition removed. No sign of water ingress now with exhaust and risers removed.
Advkce might be to strip the inlet manifold down and check in the V. Also check the head and gasket...but I maybe think that water being in all 4 cylinders might suggest a common source like a manifold ??
right now. She only locks or stops cranking when the ignition and fuel is added (by means of the kill switch being flicked to operational position). With the kill switch off and plugs in...she will crank over as fast and smooth as you like and without any further water ingress.

 

[QBhoy]

Before tear down.

Compression test. Fully charged and good battery, charger on battery so reading stay consistent. Watch gauge for 5 compression strokes, paying close attention to how much the needle moves on each stroke.

Pull the other exhaust manifold so you can see into all the spark plug holes. Turn the engine over by hand and watch that all pistons come up to the same height.

While your doing this check to make sure the timing mark on the dampener lines up when #1 is at TDC.

Crank engine with plugs out and all spark plug leads grounded, with a timing light connected to #1 and see how close timing is to what it should be. Unplug the fuel pump while your doing this. No need to be dumping fuel in the cylinders.

Almost always a bad idea to tear down a engine without having a good idea what your looking for.

Really appreciated Muck. Taken what you have said onboard.

 

[andrewterri]

Sounds like you have a good path to take to figure this thing out. I am curious to find out what the computer is showing. I would suspect the knock sensor would be showing data if two piston are firing opposite.

 

[QBhoy]

Sounds like you have a good path to take to figure this thing out. I am curious to find out what the computer is showing. I would suspect the knock sensor would be showing data if two piston are firing opposite.

That’s a good point Andrew. I’m not even sure the thing is even perhaps close enough to firing to show such a thing. Certainly there are no faults showing on the VesselView.

Cant thank you all enough once more for the input. I’ll be sure to reply as we go. Having another go at it perhaps tomorrow.

 

[muc]

but worth me saying again that it’s an MPI engine maybe.

Don't get to caught up with the fact it's a MPI. It's still just a engine. Just has a different way of delivering the fuel and triggering the spark.

Iv'e had more than a few boats brought to me disassembled because the owner and his buddy's couldn't figure out what was wrong, so they just started tearing it apart hoping to find something that looked wrong. It can get expensive when you try to do it that way. Don't be that guy. Troubleshoot this thing.

If you think it's a mechanical problem --- start with what I suggested.

If you think it's a spark problem ---- start half way through what I suggested.

You think it's a computer problem ----- (no codes showing in vessel view and engine won't start) sure, hook up a scan tool and see what you see. Who knows, it might show something

 

[achris]

You can separate fuel and spark....

If you want to crank it with just fuel and no spark, pull the connector that goes into the coil driver.


To isolate fuel and remain with just spark, pull fuse B on the engine. That will be the one with a red/purple and pink/lt green wires going to it.

Chris......

 

[highfigh]

Ask the boat owner WHEN it overheated, not IF. Ask WHEN it froze, not IF. Ask how long it ran while it was overheating and if he doesn't know, assume it was for far longer than is survivable.

The belt that came off- does that drive the raw water pump? If so, he cooked the water shutter in the exhaust if he was at WOT for any length of time.

Have you determined if it has any leaking valves/valves in wrong position or gaskets? Do a compression test on the bank that has problems.

Pull the lanyard or fuel pump fuse and harness from the ECM that controls the coil(s) and pull the plugs-

Connect an air hose to each cylinder (one at a time) and allow compressed air to enter- doesn't need to be full tank pressure (would probably keep it around 30psi)
Listen for where the air escapes- it may not (valves are closed) or it may come out of the intake or exhaust. Bump the starter and listen to any changes- if it never stops coming out of the intake or exhaust on those four cylinders, it may be a bad gasket or valve, although it could be a bad head/bolt. Repeat this for all four cylinders.

I went through an overheated engine that was run far longer while overheating than the owner said- he told me he shut it down immediately. He lied. Killed the water shutter, ingested water/bent a valve, melted both exhaust bellows, water pump upper, water pocket cover and plastic water tube. All because of a bad raw water impeller. In your case, the belt would serve the same purpose WRT the overheat.

 

[QBhoy]

Wee update for you all. Hate it when posts go unresolved, so thought I’d update.
Managed back to the boat after a good while not being near it.
Its now apparent that the distributor cap and internals have been damaged with the shock of the engine locking up (still presuming either exhaust to riser gaskets failed or flappers after full throttle and slowing down to a standstill immediately). The shock was enough to throw the serp belt off too, if you remember.

Ordered new gaskets (and Intake manifold gaskets just in case) and a new diz unit too. Always suspected this was a tooth out previously too.

Looks like the general consensus of the guys on here were correct in assuming the timing has had a shock or disruption. Excellent guys. Power of the forum !!

ill update as we go and thanks again.

 

[QBhoy]

Conclusion at last !

First of all. Thanks so much for the great advice as per usual on here. Best forum out there for sure.

The boat is now running as never before. Basically what happened is as follows;

when the boat overheated last year (previous post)...it partly damaged one of the exhaust flappers. This allowed a bit of water to come back into the engine. It did so in such a way and violently enough to knock the belt off the engine but now it turns out it also damaged the distributor too. The rotor was barely hanging on and most of the internals had cracked. The plastic internals had broken top allowing cross firing to different cylinders.
New whole diz unit and timing set up. New flappers and manifold riser baskets and good as new (after a fiddle with the diz). I know I know the ecu controls the timing after setting up the diz between the marks...but it still needed a little tiny fiddle anti clockwise to get right afterwards. Literally a couple of mm.

Thanks again all !