Help! Bought a 1993 Four Winns W/ 5.0 OMC Cobra Motor and Drive - Losing power after crusing

[cameron92]

I have it hooked up to the hose that comes off this which leads to the intake on the thermostat.

 

[cameron92]

I have my pressure tester hooked up this way. That line leads to the freshwater intake. My tester has a bladder on it. If I cover my hand over where the hose came off I can hear water bubbling somewhere but no pressure holds.

 

[cameron92]

I figured it out I had it open going back to the drive. Capped it off and now pumped it up. It's holding 15lbs psi

 

[cameron92]

What's the next step if the cooling system is good?

 

[Lpgc]

So the engine coolant circuit is holding pressure?

The other way water can get into oil is if the exhausts are leaking water into the engine via exhaust ports. If there's such as a problem the water can get past piston rings into oil but the water can also cause hydraulic lock of the engine cylinders (which can damage valves, piston rings, pistons, cause cracks, etc), dilute the oil film on cylinder bores (so cause rings to overheat and lose springiness / lack of compression), cause bore and piston scoring, cause excessive valve wear.

My engine didn't seem to have water in the oil but it did have a cracked exhaust allowing water into cylinders and suffered most of the above (but not cracks in the block or heads). I had to buy new exhausts, new valves, have the heads re-seated and skimmed, new pistons and rings, hone the hell out of cylinder bores to remove scratches. At least the crank, bearings and cam were still good but I did also put in new lifters and pushrods. Parts were cheap from RockAuto, did all the work myself except for the head work which I got a machine shop to do.

 

[cameron92]

So the engine coolant circuit is holding pressure?

The other way water can get into oil is if the exhausts are leaking water into the engine via exhaust ports. If there's such as a problem the water can get past piston rings into oil but the water can also cause hydraulic lock of the engine cylinders (which can damage valves, piston rings, pistons, cause cracks, etc), dilute the oil film on cylinder bores (so cause rings to overheat and lose springiness / lack of compression), cause bore and piston scoring, cause excessive valve wear.

My engine didn't seem to have water in the oil but it did have a cracked exhaust allowing water into cylinders and suffered most of the above (but not cracks in the block or heads). I had to buy new exhausts, new valves, have the heads re-seated and skimmed, new pistons and rings, hone the hell out of cylinder bores to remove scratches. At least the crank, bearings and cam were still good but I did also put in new lifters and pushrods. Parts were cheap from RockAuto, did all the work myself except for the head work which I got a machine shop to do.

Yeah it held 15 psi. It's slowly crept down over about 5 to 10 minutes but I think that was the plug I was using to pressurize the system.

I had to leave town for a few days so I put a bunch of WD-40 penetrating fluid in all the cylinders. Going to retest compression when I get home. I guess the next step would be to pressure test or acetone test my manifold likely the one with the low cylinder compression.

Heading up to a cottage on Saturday, was really hoping I could get the boat at least going to enjoy sometime on the water. But that leaves me Thursday night and Friday to get it going.

Would you be ordering any parts right now if you were in my situation or would you just abandon bringing the boat to the cottage.

 

[Lpgc]

If the engine cooling system presssure test crept down over 5 or 10 minutes I'd be doing it again and making sure there were no leaks at the plug... Creaping down is exactly what would happen if there were a small leak.

Yes I would also be testing the manifolds. The worst thing that could happen is you go to the expense and effort of fixing up / rebuilding the engine (if engine problems are confirmed) but re-use manifolds that were leaking water into the engine thus breaking the rebuilt engine again... you'd still need new manifolds but would need to rebuild the engine a 2nd time.

I wouldn't order any engine parts until I knew exactly what was needed, though if the manifolds are strongly suspected I might order and maybe even fit them to see how it runs with them and see if the compression figures come up.

Something I meant to mention earlier, you said there was a bang.. If the bang wasn't transmission related it could be a backfire from the engine. It might backfire if the mixture gets extremely lean or if the igntion system fires a plug on a cylinder's compression stroke, the latter could possibly tie-in with the tacho suddenly reading higher than actual rpm.

If/while you've got the manifolds off it might be worth trying to look at the bores using a bore-scope through the spark plug holes, any scuffs on the bores (maybe from water diluting the oil film) might mean you'll need to pull the engine to rebuild it with a rebore or at least a hone anyway.

I think there's still a lot of diagnostic work to be done before you'll know what's causing the problems but water in oil, low compression readings, the tacho suddenly reading high with drop of power, the smell of rubber burning and the bang give you/us a lot to think about.

 

[cameron92]

If the engine cooling system presssure test crept down over 5 or 10 minutes I'd be doing it again and making sure there were no leaks at the plug... Creaping down is exactly what would happen if there were a small leak.

Yes I would also be testing the manifolds. The worst thing that could happen is you go to the expense and effort of fixing up / rebuilding the engine (if engine problems are confirmed) but re-use manifolds that were leaking water into the engine thus breaking the rebuilt engine again... you'd still need new manifolds but would need to rebuild the engine a 2nd time.

I wouldn't order any engine parts until I knew exactly what was needed, though if the manifolds are strongly suspected I might order and maybe even fit them to see how it runs with them and see if the compression figures come up.

Something I meant to mention earlier, you said there was a bang.. If the bang wasn't transmission related it could be a backfire from the engine. It might backfire if the mixture gets extremely lean or if the igntion system fires a plug on a cylinder's compression stroke, the latter could possibly tie-in with the tacho suddenly reading higher than actual rpm.

If/while you've got the manifolds off it might be worth trying to look at the bores using a bore-scope through the spark plug holes, any scuffs on the bores (maybe from water diluting the oil film) might mean you'll need to pull the engine to rebuild it with a rebore or at least a hone anyway.

I think there's still a lot of diagnostic work to be done before you'll know what's causing the problems but water in oil, low compression readings, the tacho suddenly reading high with drop of power, the smell of rubber burning and the bang give you/us a lot to think about.

Add in a dry power steering pump as well lol. Looks like I'll be learning how to rebuild an engine potentially. There's a first for everything I guess.

I guess I'll tell my wife very well unfortunately be no boat for this cottage trip . Unless I can figure out the issue and patch it up in a day lol.

 

[Lou C]

I'm in agreement with Lpgc here, I would make sure that your results from the air pressure test are consistent, and even though we didn't see evidence of water in your manifolds or exhaust ports, it's still a good idea to test them. So, the only parts I'd order are the gaskets for the manifold to head joint and the manifold to elbow joint because when you do put it back together those have to be replaced anyway.
Better to take the time now to get it right vs trying to get it done fast and winding up being frustrated.
And, with the rubber burning smell and "bang" you also may have some other work to do....don't lose hope, you will get there but the time it takes is hard to predict. For the outdrive and shifting issues, see if you can find a good local shop that will still work on Cobras, there are none really around here except my local boatyard guy who has known me like 25 years.
I would not be putting this boat in the water till I knew it was right.
BTW my top end engine overhaul took me months, just making sure that I was doing each step correctly, consulting with mechanics and machine shop guys.
Went from this:

to this:

 

[Lou C]

also there is an excellent list of informational articles right on this site:

MUST HAVE Technical Information for DIYers.

MUST HAVE Technical Information for DIYers. (< An @ Work Safe Search Version Of ^^^) If you have NEVER posted in this forum before, please click on How to ask a question link first. 1. How to Ask a Question .... Please Read This Before Posting A Question... 2. Miscellaneous Mercruiser...

forums.iboats.com

 

[cameron92]

How long should I let the pressure test go for? And what's an acceptable loss

I also ordered a smoke tester, figured it'd be good to try that as well. How would I operate that? Same way as the cooling pressure system?

 

[Scott Danforth]

the water jacket should hold 15psi forever

 

[cameron92]

the water jacket should hold 15psi forever

Okay a smoke machine will give me much more insight then

 

[Lou C]

It's important to see that the cooling passages hold pressure, however, the possible advantage of smoke machine is it will show you where the leaks are.
I used it to check a new installation of a 3" Gibson cat back exhaust on my 2007 Jeep Grand Cherokee 5.7. Sounds great (LOUD) and no leaks!

 

[Scott Danforth]

Smile machines are a constant source of pressure. You need to use a shut off valve with a gauge on the engine side.

Pressurize, shut off valve, should hold 15psi.

If it doesn't hold pressure, then re-apply pressure and listen for leaks.
If it sounds in the exhaust, look at the exhaust and heads.
If it sounds in the intake, look at the intake manifold and head
If it sounds in the valve covers, look at the block

 

[cameron92]

Video here

See the video link above. just bought this boat, guy assured me on God that all was good as I was bringing my 1.5 year old out.

I'm not sure what's happening. I'll be crusing along and all of a sudden the rpms on the gauge will rise, then the boat comes to a stop, rpms drop (I'm not touching the lever).

It'll also do the same thing if I give it full throttle. Also when taking off after it happens sometimes there's a faint bang.

Spun Coupler? Misaligned shift cable? Engine issue? I'm lost. How do I test.

Changed to old prop seller gave me, same issue. Drained drive, a bit of metallic on the plug but no shavings.

It just occurred to me that the previous owner installed a new distributor cap. He mentioned something about timing being out but he had a mechanic look at it. Wondering if that relates to my original issue.

 

[Lou C]

Not sure; these models are very different than the older ones like mine in that you have a ECM that runs the EFI, not sure if it also controls spark advance or not. This is why I’m not a fan of old EFI boat engines; when trouble starts you don’t have a starting point for diagnosis unless a modern scanner works with these 30 year old systems. Rather have a carb & stand alone distributor; much simpler & parts are actually available!

If you wind up being able to fix that Ford engine or find another I’d get rid of both the EFI system & that oddball distributor and install either a Holley or Edelbrock 4 bbl and an aftermarket electronic distributor. Learn how to clean and rebuild carbs and leave the problem of NLA unobtanium parts behind. Chasing that stuff is a huge waste of time!

 

[cameron92]

Not sure; these models are very different than the older ones like mine in that you have a ECM that runs the EFI, not sure if it also controls spark advance or not. This is why I’m not a fan of old EFI boat engines; when trouble starts you don’t have a starting point for diagnosis unless a modern scanner works with these 30 year old systems. Rather have a carb & stand alone distributor; much simpler & parts are actually available!

If you wind up being able to fix that Ford engine or find another I’d get rid of both the EFI system & that oddball distributor and install either a Holley or Edelbrock 4 bbl and an aftermarket electronic distributor. Learn how to clean and rebuild carbs and leave the problem of NLA unobtanium parts behind. Chasing that stuff is a huge waste of time!

And that's a relatively straightforward swap? I'm very familiar with carbs. I fix and flip small engines on the side and 90% of them just need a carb clean. Have an ultrasound and cleaner and everything needed.

I know I'm getting ahead of myself here, should be able to recheck compression this afternoon after a two-day soak. Also got in a smoke tester and a leak down tester. Might pop the valve covers off to see if any valves are rusted and seized if the soap didn't work.

 

[cameron92]

And that's a relatively straightforward swap? I'm very familiar with carbs. I fix and flip small engines on the side and 90% of them just need a carb clean. Have an ultrasound and cleaner and everything needed.

I know I'm getting ahead of myself here, should be able to recheck compression this afternoon after a two-day soak. Also got in a smoke tester and a leak down tester. Might pop the valve covers off to see if any valves are rusted and seized if the soap didn't work.

Numbers improved!

Port
125
110
110
100

Starboard
125
125
125
120


I had the throttle closed, for these but the numbers are looking better I think

 

[Lou C]

Not bad ideally you want a warmed up engine & throttle wide open, I think they’d be higher then. Next leak down test and what did the air pressure test show? If all is good test your manifolds & try running it again. See if you still get water in the oil. Air pressure test is really the most important