89 4.3 OMC cobra stalling at WOT

[Ellhills]

hello all,

A few months ago I bought a 1989 4.3L OMC cobra. First time I took it out, it ran great for the first lap, second lap it started misfiring, third lap, it stalled out and shut off, keep in mind this was all at WOT. idling was fine. after it shut off it was a pretty hard start for it afterwards. got it loaded back up and took it home to work on it. replaced the spark plugs (yes they're properly gapped), replaced fuel filter, took a look at anti-siphon valve- good, all fuel lines good, and did a carb rebuild. second time taking it out, still misfiring however ran longer at WOT this time before stalling again and shutting off. took a look at fuel filter while trying to start engine and while it was running.. it was dry. Got back home and decided to replace fuel pump. I installed the same fuel pump that it had before which was a Holley. Third time taking the boat out, ran great all day long, no misfires, no stalling, we were skiing, tubing, and everything with it. just went to take it out last weekend, got on the river, let it warm up, and then decided to go WOT. After about 5 minutes going, it stalled out AGAIN and shut off. to add, it also wouldn't turn back on and took about 10 minutes till the engine finally fired. we ended up just idling to the sand bar and hanging out there for a while. started it back up at the end of the day when we went to leave and noticed it sounded a lot louder and realized.. to top it all off, a golf ball sized hole burned through my exhaust manifold hose. I'm very new to boats, let alone inboards, but I'm just stumped on this one.. head gaskets? ignition module? bad coil ignition? I'm clueless. also any ideas why the exhaust leak occurred? thank you!

 

[itsathepete]

Has it run hot at all. Sounds like poor water flow. Probably needs an impeller maybe a new thermostat. Running hot can cause ignition issues too. Good idea to put in new points and condenser and check/clean distributor cap. Sounds like you have your fuel issue sorted

 

[itsathepete]

And test the ignition coil with an ohm meter

 

[Lou C]

An 89 might still have points ignition, have those been changed? The dwell angle is set first then timing then idle speed.
This is a long shot but a defective tach can short out the ignition. You can try disconnecting the tach lead at the coil.
Also about the burned exhaust hose, the 86-90 models used the one piece batwing exhaust manifolds. These have relatively small water outlets that are easily clogged. If you’re in freshwater you can take these off & rod the openings out with a coat hanger. The water outlets on the thermostat housing sometimes clog and can be cleaned out the same way.
Might need a new impeller which on the Cobra is easy to change.

 

[itsathepete]

An 89 might still have points ignition, have those been changed?

89 definitely had points. I had one until a few months ago

 

[Ellhills]

Has it run hot at all. Sounds like poor water flow. Probably needs an impeller maybe a new thermostat. Running hot can cause ignition issues too. Good idea to put in new points and condenser and check/clean distributor cap. Sounds like you have your fuel issue sorted

The distributor looks like it has had new points in it at one point, doesn’t hurt to switch them out though, and as far as I can tell, it doesn’t run hot, can’t give you an exact number of where it’s at but I’d say around 220°? You think I could have an internal leak somewhere where the water ain’t getting all the way through the engine?

 

[Lou C]

220 is waaay too hot!
These have a 160* thermostat and an open cooling system they normally run at 160-175*F.
Here’s mine in a couple pix
You may have:
Stuck thermostat
Worn impeller
Clogged up manifolds
Clogged water outlets on the thermostat housing

With the engine running on the water hose you should see water being exhausted from the bottom of the transom mount right in front of the lower unit…

 

[Ellhills]

220 is waaay too hot!
These have a 160* thermostat and an open cooling system they normally run at 160-175*F.
Here’s mine in a couple pix
You may have:
Stuck thermostat
Worn impeller
Clogged up manifolds
Clogged water outlets on the thermostat housing

With the engine running on the water hose you should see water being exhausted from the bottom of the transom mount right in front of the lower unit…

Okay I will hook it up tonight and look at what I can see, and 220 was a guess comparing The temp gauge to a 4.3 chevy v6 motor in a vehicle. I don’t have any numbers on my temp gauge But it sits above the temp symbol I’d say about 3/4 to the top, if that makes sense.

 

[Ellhills]

220 is waaay too hot!
These have a 160* thermostat and an open cooling system they normally run at 160-175*F.
Here’s mine in a couple pix
You may have:
Stuck thermostat
Worn impeller
Clogged up manifolds
Clogged water outlets on the thermostat housing

With the engine running on the water hose you should see water being exhausted from the bottom of the transom mount right in front of the lower unit…

Also to add, the impeller was replaced last year, is it possible that it’s bad already?

 

[Lou C]

Probably not but make sure that someone didn't put a 195* thermostat in there. The stat on these are held in with a rubber ring that can get obscured with rust, you have to dig it out with a pick. A good test on temps is to get an IR Temp gun. Then take a reading of the intake manifold right under the stat housing, I have found that it reads about 10* less than the dash gauge. So if I get 160 on the gauge it will read about 150 there, etc. Your manifolds should be around 90-100* at idle and not more than 135-140* after coming off plane and should cool back down after idling for a while. My engine usually runs at the temps you see in the gauge in the pix, only time it might go a bit higher is right after coming off plane, it will go up to 170 or at most 175 but will cool back down to 165 pretty quick.
Here's a pic of how those small water passages on the original manifolds can get clogged:

These have long been NLA, and here in the salt pond we have to change them every 5-7 years, so I converted mine to the 2 piece style used later on by both OMC and Volvo, notice how much bigger the cooling passages are:

 

[Lou C]

You should see water being exhausted like this.....right in front of the big anode on the lower unit....
View attachment Cobra running on the water hose.MOV

 

[itsathepete]

What Lou C said

 

[Ellhills]

You should see water being exhausted like this.....right in front of the big anode on the lower unit....
View attachment 364303

Alright so I got home late last night so I didn’t get a chance to take a look at the thermostat or anything but I got the muffs on it and it seems to have good water flow being exhausted through that hole. How can I tell if the thermostats bad?

 

[itsathepete]

Remove the thermostat and put it in a pot of water on the stove with a thermometer. See at what temp it opens

 

[Lou C]

it should open at approx 160*F

 

[Ellhills]

Alright, thanks for everyone’s patience. Finally got to the thermostat and everything on the boat. Looks like the metal lining that in around the impeller spun and shaved the fins of the impeller.. so that’s option 1 that will be replaced. Option 2.. the thermostat looks like it hasn’t been changed since the boat was made. O ring broke in half when I squeezed it together and thermostat was rusted onto the housing, so that’s getting replaced as well, also realized I’m going to need a new intake manifold cause thats all rusted up inside of it too, if anyone has any advice for any of this, how to make sure it’s done right, or anything it’d be a great help.. thank you!!

 

[itsathepete]

Alright, thanks for everyone’s patience. Finally got to the thermostat and everything on the boat. Looks like the metal lining that in around the impeller spun and shaved the fins of the impeller.. so that’s option 1 that will be replaced. Option 2.. the thermostat looks like it hasn’t been changed since the boat was made. O ring broke in half when I squeezed it together and thermostat was rusted onto the housing, so that’s getting replaced as well, also realized I’m going to need a new intake manifold cause thats all rusted up inside of it too, if anyone has any advice for any of this, how to make sure it’s done right, or anything it’d be a great help.. thank you!!

when the cage around the impeller spins, it can damage the housing. You may need to replace the whole unit. Raw water cooling will cause some rust in the manifold. How bad is it? Big chunks coming off?

 

[Ellhills]

when the cage around the impeller spins, it can damage the housing. You may need to replace the whole unit. Raw water cooling will cause some rust in the manifold. How bad is it? Big chunks coming off?

Yep I kinda figured so I just got an entire new impeller kit with the housing and gaskets and everything and as for the rust in the manifold, yes there are chunks flaking off if your looking into the intake manifold, I’ll grab a picture of it today and put it on here when I head over that way.

 

[Ellhills]

when the cage around the impeller spins, it can damage the housing. You may need to replace the whole unit. Raw water cooling will cause some rust in the manifold. How bad is it? Big chunks coming off?

Yea this is what I’m working with, thinking this is going to have to get replaced sooner than later