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

[Scott Danforth]

Impeller on a cobra is a 5 minute job

 

[Lou C]

Yeah, its very easy, just use some silicone grease to hold the o ring gasket for the cover in the groove.

 

[Lou C]

Fried my impeller with all the compression testing I guess. She's a mess.

next time when you have to do the compression test just hook up the water hose and leave it on not full blast but like half open. I don't know about the EFI engines but on the carbed engines with the old style distributor, I always grounded the coil lead, you don't want spark sent to the spark plug wires now disconnected with the cyls pumping out fuel vapor!
When I fire mine up for the first time each season, what I do to make sure the Cobra impeller gets water:
Put muffs on, turn on water full
then disconnect the raw water intake hose at the thermostat housing, and fill it with water, that fills up that hose and the impeller housing itself in the upper gear housing. Then reconnect the raw water intake hose to the thermostat housing.
Then start it up! It's always a good idea to check that water is coming out from under the transom mount because if not something is not right. These systems need a lot of cool water in and slightly warm water out, that's how the heat of combustion is removed from the engine and exhaust.
The things that can cause problems:
if an impeller failed, the bits can lodge in the raw water intake hose, especially in the power steering cooler, this will block water flow. They could even get as far as the thermostat housing, but I never had that happen.

Sometimes that o ring gasket in the impeller cover leaks and it can cause an air leak when the boat is on plane. So after I install a new one, I run it on the muffs with the big plastic cover off so I can see that the impeller housing doesn't leak.

If you had a bad overheat, the water tube grommets that seal it to the upper and lower gear housings, can melt and then it will suck in air when the boat is on plane. To fix this you'd have to split the upper and lower gear housings. Sometimes they don't want to come apart and you have to get creative. I have a solution for that one.

BTW those dual inlet muffs with the square cups don't seal so well. The dang rubber is too stiff.
I had better luck with the Merc round ones with the rod that goes through the lower unit intake holes. On the Cobra there's a plastic screen in there (I removed mine years ago, always got marine growth on it) so you might have to drill a hole thru it for the Merc muffs, but they seal the best of all the ones I used. Mine will run at a steady 160* with those muffs.

 

[Larson220]

Yes if it has a crank sensor for EFI, a failing crank sensor could do something similar, on my old '98 Jeep 4.0 when the crank sensor was starting to fail, one sign was the tach and idle would drop and recover, eventually that turned into a higher speed miss, followed by a reluctance to start, ending in a refusal to start. It did not set a code till the sensor totally failed.
I have a 1988 OMC factory shop manual but this model is so much newer that there's nothing that's similar. In the vid it looks like a Ford 5.0 with the EFI system, so I can't help there. If it was the older models with carbs and points, oh yeah I know THOSE things quite well lol!
Post up pix of the engine and drive.
A bang if you have a dog clutch Cobra might be wear on the clutch dogs or fwd gear causing it to slip out of gear under power, but it could be a lot of other things....
Here's a guess on what you might have....

https://www.marineengine.com/parts/omc-parts/omc-boat-parts.php?year=1993&hp=5.0&model=50FAPRJVN

EFI Ford engine, and the last of the Cobra Dog Clutch drives....
the Cobra dog clutch part I am familiar with and they require a good shift cable in good adjustment to last. I have had the same cable on mine all these years (owned 24 years) and it needed adjusting when I first got it in 2002 and then again about 10 years later, I learned how to do the tricky adjustment myself, not really hard. It has required very few repairs, over the years in salt water use and moorage. A few seals, bellows 2x, gimble bearing once, and I rebuilt the trim rams a few years ago.
You need a good OMC mechanic who knows about the EFI engines, I don't, and if I had one that was acting up, due to most of the parts being NLA, I'd simply convert it to a 4bbl carb and Davis Unified Ignition distributor, that eliminates all the headaches of NLA OMC EFI and electronic ignition parts.

Hello,
I was reading thru all these threads and i want to offer some insights. I have a 1994 Larson that has the same 5.8 EFI OMC ford engine. Most all the EFI parts are no longer available, such as sensors and different electrical parts, however, apart from the distributor and the alternator which are marine specific parts. The rest of the system is essentially a Ford EFI system that was commonly used in many other vehicles, such as trucks and even the 5.0 fox Body Mustangs. All the sensors and other related electrical EFI parts can readily be sourced through any online auto parts retailers. Just look up 1993 or 1994 Ford bronco with 5.8 L EFI.
I know how difficult it is to keep these older engines running with these NLA parts that are difficult to impossible to source from regular marine parts retailers. Good luck.

 

[Lou C]

Hello,
I was reading thru all these threads and i want to offer some insights. I have a 1994 Larson that has the same 5.8 EFI OMC ford engine. Most all the EFI parts are no longer available, such as sensors and different electrical parts, however, apart from the distributor and the alternator which are marine specific parts. The rest of the system is essentially a Ford EFI system that was commonly used in many other vehicles, such as trucks and even the 5.0 fox Body Mustangs. All the sensors and other related electrical EFI parts can readily be sourced through any online auto parts retailers. Just look up 1993 or 1994 Ford bronco with 5.8 L EFI.
I know how difficult it is to keep these older engines running with these NLA parts that are difficult to impossible to source from regular marine parts retailers. Good luck.

good to know and I kind of suspected that.
there are options for the alternator and starter (ARCO) and the distributor (DUI).

 

[cameron92]

Would removing the impeller and putting a hose in the hole where it pulls water be enough pressure to run it to make sure there's no clogs? Or do I need to run the housing with impeller

 

[Lou C]

That's not gonna work, if you remove the impeller housing it looks like this:
(ignore the bolts, that's for pulling the water pump plate to replace the seal)
so the 2 large holes at the bottom, are the ones where water comes up from the lower unit and then gets pulled into the impeller and sent thru the transom mount.
If you want to make sure there's no clogs:
remove the plastic impeller housing
get a helper
Test #1 :go up to the front of the engine, disconnect your raw water intake hose at the 'stat housing. Put the water hose in the raw water hose and turn on the water. Have your helper watch, they should see water spurt out of one of those large lower holes in the impeller mount plate
Next
Test #2 re-connect your raw water hose at the stat housing, with the plastic impeller housing off,
hook up the water muffs and turn on full
water should now come out of the other large hole in the impeller plate
that tests for blockages in the water intake in the drive and leaks from the water tube grommets.

if test #1 is not good you have a clog in the p/s cooler you might have to remove it and clean it out
if test #2 is not good you may have to split the drive (not a fun job take it from me, been there done it 2x) and clean out the water intake area in the lower unit. I had such a problem with barnacles and other crap growing on that plastic screen that I remove it about 13 seasons ago and it's been much better. Lastly replace the water tube grommets. If you don't have an overheat, they last a really long time.
You're in freshwater right?
then some of these jobs should be a LOT easier than they are for people like me in the salt pond.
Look at how narly this drive looks, that's 24 years of mooring and running in salt water, but, a good Cobra will REALLY last. Very few problems overall.

 

[cameron92]

That's not gonna work, if you remove the impeller housing it looks like this:
(ignore the bolts, that's for pulling the water pump plate to replace the seal)
so the 2 large holes at the bottom, are the ones where water comes up from the lower unit and then gets pulled into the impeller and sent thru the transom mount.
If you want to make sure there's no clogs:
remove the plastic impeller housing
get a helper
Test #1 :go up to the front of the engine, disconnect your raw water intake hose at the 'stat housing. Put the water hose in the raw water hose and turn on the water. Have your helper watch, they should see water spurt out of one of those large lower holes in the impeller mount plate
Next
Test #2 re-connect your raw water hose at the stat housing, with the plastic impeller housing off,
hook up the water muffs and turn on full
water should now come out of the other large hole in the impeller plate
that tests for blockages in the water intake in the drive and leaks from the water tube grommets.

if test #1 is not good you have a clog in the p/s cooler you might have to remove it and clean it out
if test #2 is not good you may have to split the drive (not a fun job take it from me, been there done it 2x) and clean out the water intake area in the lower unit. I had such a problem with barnacles and other crap growing on that plastic screen that I remove it about 13 seasons ago and it's been much better. Lastly replace the water tube grommets. If you don't have an overheat, they last a really long time.
You're in freshwater right?
then some of these jobs should be a LOT easier than they are for people like me in the salt pond.
Look at how narly this drive looks, that's 24 years of mooring and running in salt water, but, a good Cobra will REALLY last. Very few problems overall.View attachment 417275

Yikes ya mine is a heck of a lot cleaner then that. Flushed out the lines, no blockages or if there was, they've been flushed out

 

[Lou C]

Consider yourself lucky
Freshwater
HOWEVER
there is one thing many people do not know
fresh water doesn't have barnacles, etc growing in it
nor does it corrode steel/cast iron
BUT
it rots wood faster than salt water by a lot
transoms actually last longer in salt water because the organisms that eat wood (causing rot) don't live in salt water apparently. Salt water actually preserves wood. Like an old piece of driftwood on the beach.
this boat is 38 years old and has the original transom and any rot it had (deck, stringers) was all because of rain water. All that we fixed 20 years ago, tore out all the carpet and had it all gelcoated in non skid gelcoat. I hate hate hate carpet in an open boat, it holds moisture and causes rot anywhere there is a penetration (screws to mount seats, etc). Any boat I had that I wanted to keep, if it had carpet the first thing I'd do is rip it all out, and have the deck gelcoated if it was a wood cored deck.