HELP-3.0 OMC Cobra Engine Trouble

[gregsalky]

Here is one for you pros. This is a tough one. I have a 1987 Bayliner with a 3.0 ltr 4 cyl OMC Cobra I/O. The problem I am having is that when the motor gets up to operating temperature the boat literally just dies. When and if I can get it started again as soon as I put it in gear it dies again like it is starving for fuel. The boat starts fairly easy and has a slight, almost unnoticable miss or sputter every now and then that I can't seem to clear up with timing/tune up, etc. I replaced the carburator thinking that was it and that didn't work. I replaced the fuel pump and same thing. I went electrical and took out the points and put in a electronic ignition conversion kit and it now starts easier when it is cold but same problem when it gets up to operating temperature. After listening to a few people who put their two cents in they thought maybe a wire was breaking down when it got hot so I replaced the entire engine wire harness and that didn't solve anything. It still literally shuts down after it gets up to operating temperature. When I am cruising, right before it gets ready to die it starts surging/missing. Then it dies. When it cools off it will start right back up and run fine until it hits operating temperature and it goes ka-put again. I changed the coil, wires, switched plugs with the old ones I keep as spares and same problem. I did a compression check with the engine both hot and cold and all cylinders are within their specifications and no two cylinders have a variance of greater then 25%. There is no water in the oil. I did have a crack in the block when I bought it ( the previous owner told me it was the exhaust manifold gasket-he was lying or wrong) that I had a machine shop weld up. A friend made the suggestion at something inside might be still cracked and when it is cold it is closed and when it gets warm it opens up and causes my problem but I can't imagine what it would be. The crack was on the exhaust side of the engine or right side if looking at it from the front. The only thing I haven't replaced is the entire distributor. Could this be a problem? What about valves, head, etc? That I am not schooled on. I am at my wits end and don't have any other ideas and have sunk a ton of money into this thing and it still doesn't run right. My wife is about to kill me for spending what I have and the kids are anxious to get back in the water. Any and all help/suggestions will be greatly appreciated. Thanks in advance. Greg

 

[PINESOL]

Re: HELP-3.0 OMC Cobra Engine Trouble

a shot in the dark here ... but try the coil ... check for spark when it dies while warm ...

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

And this.

http://forums.iboats.com/showthread.php?t=167561

 

[Boatin Bob]

Re: HELP-3.0 OMC Cobra Engine Trouble

How about vapour lock, fuel getting too hot? Check for gas being squirted down the carb when you push on the throttle.

 

[Dakota47]

Re: HELP-3.0 OMC Cobra Engine Trouble

hook up a remote fuel tank straight to the carb.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

a shot in the dark here ... but try the coil ... check for spark when it dies while warm ...

Thanks for the reply. Already changed the coil.

 

[mikeinnc40]

Re: HELP-3.0 OMC Cobra Engine Trouble

How is the timing advance looking when shot with a light?
Also try a vacume gauge and adjust the carbs.

Mike

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

Pull the plugs next time, and spin it over, to see if water shoots out; is the oil overfull, and milky?

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

If not, lack of fuel, or vapor lock, would be next. If you are getting spark at the plugs.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

Oil is clean and right where it needs to be. I will try pulling the plugs tomorrow. Good idea. Thanks.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

I know this is going to sound weird but before the aftermarket electronic ignition conversion the timing was right on and the mark was steady. I tried messing with the timing today to check it since I took the points out and put the electronic ignition in and the mark is WAY off towards BTDC. It is way past 10 degrees BTDC and when I tried to bring it back to where the OMC specs want it and it stalls out. The carb is brand new and right on the money. Played with the mixture screws and put them back at the factory settings where it ran the best. Where should I check the vacuum at and what am I looking for? Thanks for your help.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

How about vapour lock, fuel getting too hot? Check for gas being squirted down the carb when you push on the throttle.

Thanks for the info. I'll try checking this also. The metal fuel lines do run right up the motor to the carb.

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

Do the fuel check, then go back and look at new dist- that may be a problem.
You threw parts at it, without diagnosing the original problem(s).
Time to start over, fuel first.
Then dist. (and wiring of it)
It will work, eventually. But one thing at a time needs to be eliminated.

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

Set it back to tdc, and re-install points dist; see if it will run . and plugs wires in order. You have a manual, right?

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

Do the fuel check, then go back and look at new dist- that may be a problem.
You threw parts at it, without diagnosing the original problem(s).
Time to start over, fuel first.
Then dist. (and wiring of it)
It will work, eventually. But one thing at a time needs to be eliminated.

If it is not the fuel you think that the mechanical part of the distributor could be bad? Like I mentioned, I took out the original points/condensor and replaced them with an aftermarket electronic ignition conversion kit, wires and all.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

Set it back to tdc, and re-install points dist; see if it will run . and plugs wires in order. You have a manual, right?

Same distributor different guts. Checked the order of the wires and they are ok. It ran with the points before the conversion. With the new electronic ignition it starts easier when cold, thats for sure but made no difference when it got to operating temperature and started acting up.

 

[Coors]

Re: HELP-3.0 OMC Cobra Engine Trouble

I think the new parts are in the way of diagnosing the original problem.
Do the fuel test, eliminate that; then check on the dist, which seems to be off-timed.
One thing at a time.
Until someone smarter chimes in.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

I think the new parts are in the way of diagnosing the original problem.
Do the fuel test, eliminate that; then check on the dist, which seems to be off-timed.
One thing at a time.
Until someone smarter chimes in.

I will work on this tomorrow. Thanks for all of your help and suggestions. I really appreciate it. I'll update thread tomorrow.

 

[bruceb58]

Re: HELP-3.0 OMC Cobra Engine Trouble

My guess is going to be the ignition module. Time the engine when it is cold and then check the timing right after it dies. You can still check the timing even if it isn't starting, Just crank the engine and use your timing light.

 

[gregsalky]

Re: HELP-3.0 OMC Cobra Engine Trouble

My guess is going to be the ignition module. Time the engine when it is cold and then check the timing right after it dies. You can still check the timing even if it isn't starting, Just crank the engine and use your timing light.

I did a compression check again both cold and hot. Average cold psi was 120psi across the cylinders. Hot was the same. Ran it till it died and pulled the plugs to see if water was coming out of the cylinders. None found. I'm going to keep working on this thing till it is right. Please keep sending suggestions. Thanks to all for your help.