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58EFI OMC Cobra engine problem

R

rafeekbesheer

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This engine is in a 1994 4 Win

This engine is in a 1994 4 Winns boat with 200 hrs.
I get a thumping noise at idle and beyond. Had it back fire and blue smoke come out after a hard start pulling a skier. There was black soot on the flame arrestor also.
Any ideas
 
Is it a dull thumping like a h

Is it a dull thumping like a hammer tapping on an avil? Or a higher up tinny tap? Almost similar to a wood pecker tapping on a tree. Can you tell if it follows engine RPM or does it seem faster?
 
"Dull thumping, hard to hear w

"Dull thumping, hard to hear when engine is revving although it does go higher with the engine rpm.
Thanks for taking an interest in this problem."
 
The thumping sound has been th

The thumping sound has been there for a while. Its only until lately that it backfired twice while flooring it to pull up skiers.
 
"I'd suspect that the back

"I'd suspect that the backfire and thump have no correlation. Without being there and actually looking/listening to it and from your description that it's not double time but you may have lower end issues with your engine i.e. rod knock, thrust bearing issues. The backfire I would more suspect would be fuel related. Do you know if your oil pressure is within specification? If it isn't that would be an indication of worn engine components. When you changed the oil last did you see if it a metallic sheen? Again without being there it's hard to give a definitive."
 
"Oil pressure has always been

"Oil pressure has always been good on the dash, never had it measured. No oil consumption either. The oil comes out black when I replace it even though its not used much. Does that indicate anything?"
 
No the color of the oil is no

No the color of the oil is no indication as to the wear. If it's black it's basically normal. I would have someone who knows alittle bit about the motor to listen to what you have. If it is a lower engine issue then yes motor will need to be pulled and it maybe pricey.
 
"Thanks Walt,
I will probably

"Thanks Walt,
I will probably wait for warmer weather until we are out of the freezing range and take to a couple places for input.
Apreciate your help."
 
"Not sure how mechanically inc

"Not sure how mechanically inclined you are but if having a problem determing whether the noise is coming from the engine or the outdrive, one method to narrow it down is to pull the drive off and run the engine. You can run it for a very short time like this but for an extended period you would need to attach a garden hose to the engine supply hose at the thermostat. Doesn't take much work to pull the drive off."
 
"It sound to me that what caus

"It sound to me that what causes the 'thumping' and backfireing is one or more leaking valves. This might be a 'mushroom' valve, defective lifter or perhaps a combination. It should be possible to read out from the sparks which cylinder(s) is/are causing the trouble. A compression test might be of further help. I even suggest Yo make a mark on the front pulley for TDC of each cylinder to determine if You may have one or more cylinder out of timing/double fireing. You may even use a timing light with buildt in rev counter to check for this problem. Put the pick up as close to the spark as possible and whatch for double rpm reading."
 
I suspected a valve or lifter

I suspected a valve or lifter problem from the get go. Thank you for the detailed analysis.
What is involved in repairing this?$$
 
"A 'standard' job on t

"A 'standard' job on the V8!!!
Head gaskets (down both to check), intake/exhaust manifold gaskets, a valve or two, perhaps a lifter. Job itself is no big deal, but You would need a manual to guide You. No special tools needed except a torque wrench and timing light. If valve(s) needs to be changed a spring compressor.
Including lunch and a snooze -one day job. If in a hurry and You know what to do - 4 hrs. It all depends on the mechanic. However if You do it with the boat at sea, do not forget to disconnect and plug the raw water hose, or You end up with a submarine!
Check the part prices at this page, they have probably what You may need."
 
This job is not for me. Do I h

This job is not for me. Do I have to take it to a boat shop or could an auto mechanic do it.
I have all the repair manuals and can get the spare parts needed.
 
"I would preferr a good auto m

"I would preferr a good auto mech that I know befor an unknown boat workshop. The auto mechs seems often to be have better knowledge of the EFI system than a lot of boat mechs. This is a plain forward engine job, and should be managable for almost anyone with some experience."
 
"PS:
I do not know the engine

"PS:
I do not know the engine room layout and boat interior, but sometimes it may be better just to lift the engine out and do this kind of repair outsiede the boat to protect carpets etc. It takes less than 1/2 hour to lift it out, but You would need an alignment tool when reinstalling."
 
"That is reassuring, as I am n

"That is reassuring, as I am not happy with the boat shop I go to.
Have to wait for spring, it gets cold here in Chicago in winter you know.
If u are in Chicago area do u know of a mechanic u trust?"
 
"Not at the moment, but that o

"Not at the moment, but that one brougt us from Norway down here. Just Google 'haffiman' and You may find out more!"
 
"I checked it out[img][/img] T

"I checked it out
That is quite a trip, takes a very determined sailer and understanding family.

I would like to make the change from motor to sail one day. My family didnt want a sail boat 20 years ago as I used to sail my 20' cabin sail boat as a dinghy which scared the sh.. out of them. They swore never again..

Good luck"
 
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