1987 OMC Cobra 5.0 idles rough

[doublegimp]

Engine idles extremly rough, and will die at idle or when shifted into gear at idle. The engine will not rev up when in neutral but operates fine when at higher RPM's while in gear. Any help would be greatly appreciated.

 

[danond]

Re: 1987 OMC Cobra 5.0 idles rough

When was your last engine tune-up?

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

I just got the boat and engine ran fine ont he test trips, last tune up was a year ago.

 

[danond]

Re: 1987 OMC Cobra 5.0 idles rough

If your carb hasn't been rebuilt recently I'd start there. Cheap to do and good insurance.

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

Should have mentioned this first as well, at idle and just above when the engine is rough there is a wistle. Goes away once the engine is in gear and given throttle. Would a carb cause the engine not to rev in idle yet allow it to in gear?

 

[Boatin Bob]

Re: 1987 OMC Cobra 5.0 idles rough

Your OMC has an ESA (electronic shift assist) module, it stumbles the engine when shifting out of gear (causes it to drop in RPM and run rough by pulsing the distributor). It's possible it may be activating, you could try unplugging it as a test to see if it's the problem. Look for a black module attached to the shift brkt just to the left and rear of the carb (facing the engine) It will have to wire harnesses coming out, follow the 2 wire one to the plug and unplug it (should have a purple and a grey wire in it).

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

I'm heading to the lake in a few I'll give that a check. Can the boat be run without this for the weekend if it ends up being the problem?

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

OK, started boat and idled rough. Removed the spark arrestor and tried it again, same thing, checked the choke and it was operating properly and moved freely. I stopped the engine and disconnected the ESA, started engine and it ran perfectly. Shifting was next to impossible though it was hit or miss. Out of curiosity I cleaned the terminals of the ESA plug and hooked it back up and the engine ran fine in neutral at the dock. While still tied up I shifted back and forth a few times and on the third one when going from rev. to fwd. the engine started running rough again. Because the ESA is a digital box I have a pretty big doubt that it is causing this, it should either be good or bad. So I when back and retraced the wires and I think I uncovered the problem. There are 2 switches one to engage the ESA and one to bypass it once you are in gear. Both switches are operating properly based on continuity checks and testing while the engine was running. But there are contact posts on the shift arm that operate the bypass and they are adjustable. My guess is that these are slightly out of adjustment. The ESA engagement switch is almost always on at low throttle/RP M's (under 1000) and the bypass switches it on and off once you are in gear. Does this make sense, anyone have an idea about the proper way to adjust these?

 

[Don S]

Re: 1987 OMC Cobra 5.0 idles rough

You need a new lower shift cable. It won't release the activaging arm.
Very common problem on OMC and Mercruiser Alphas. Except the Merc will die completely. The ESA unit on the OMC stops spark to half the cylinders, in Merc it kills all spark.

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

Didn't even think about that, if there is too much play in the cable it would cause these issues. How hard are these to replace? Is there any adjustment in them before I go and replace it?

 

[Don S]

Re: 1987 OMC Cobra 5.0 idles rough

It's not a problem of too much play, it's a problem of them being hard to move. Physically changing the cable isn't the problem, getting it adjusted properly is going to take an OEM service manual for your particular model in order to get it where everything works together.
To change the cable, you do have to remove the drive and disassemble the cable to get it out.

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

I have an OEM service manual for it, I will have to look it over see if I think I can tackle it. I would really hate to have to take it to the shop but I may end up having too.

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

OK, update on what I got. Checking with the previous owner before doing anything, the shift cable was brand new 2 years ago, they readjusted the shift mechanism and figured it was cheap insurance to replace the cable while adjusting everything. Cable pull on the shift cable is 2.2lbs so the shift cable is good. After readjusting everything the unit shifts into fwd and about 70% of the time is very hard to shift back to neutral, it just sticks and doesn't want to go into neutral. Same with rev, it doesn't want to go back into neutral. The good news is I think i isolated the problem, the ESA shift interupter switch only activated the ESA 4 out of 10 times that manually threw it. I'm assuming that if the ESA isn't dropping the RPM's of the engine shifting is very difficult or impossible. I ordered a new ESA and shift actuator switch. One other note, the shift actuator arm does not move all that much, not really enough to throw the switch, is there any way to decreas the spring thension on it?

 

[bruceb58]

Re: 1987 OMC Cobra 5.0 idles rough

Not sure where or when you are doing the testing but if you are doing this out of the water, the ESA may not be engaging at all. It is really only needed coming out of gear. Coming out of gear will only be a problem when you are in the water because of the water load on the prop holding the dog clutch gears together. It is the force of trying to shift with the load on it that causes the ESA to engage. That is why you won't see it on land. If there isn't enough force to cause the ESA to engage on land, that is a good thing. Means your cable is operating freely. A binding ESA will cause the ESA to always be engaged and also hold the ESA in the interrupt position.

One more thing. You need to pull the drive every year for inspection and maintenance. When you pull it off you will find the bell crank that the shift cable attaches to in a cavity filled with a white gunk if the boat is used in salt water. Cleaning this area out and filling with grease will help your shifting a lot.

 

[doublegimp]

Re: 1987 OMC Cobra 5.0 idles rough

I made initial adjustments on shore but dropped the boat back in the water to check everything out. The ESA itself is working fine, the switch that activates it appears to be not working. I never have a problem getting into gear from neutral it is only coming out of gear back into neutral, when I try to do that the control just sticks I can pull hard and it won't do anything. The ESA is original to the boat so I figured i would update that when I ordered the new switch just rule out anything going wrong with it.

 

[Boatin Bob]

Re: 1987 OMC Cobra 5.0 idles rough

Give this site a read, some very good info about shifting problems, cable replacement and adjustment. There is a service bulletin in there as well about the spring on switch actuator.

http://www.hastings.org/~stuart/cobra/

 

[sundowner205]

Re: 1987 OMC Cobra 5.0 idles rough

Hi guys...i'm a little confused here...i have an 1989 Four Winns with a 5.7 Cobra. I recently began experiencing extremely hard shifting but INTO gear. Yesterday the boat actually stalled out twice while attempting to shift into gear with the throttle almost pegged. The engine runs perfectly once in gear. I read the Hastings site yet i still have a couple of questions...

1] I read on other posts that the ESA is used primarily to get the engine OUT of gear and i have no problem with shifting into neutral, however the OMC service bulletin herehttp://www.hastings.org/~stuart/cobra/sb4038.jpg states that a bad ESA will cause hard shifting...if so does the ESA not assist in getting the boat INTO gear as well? so can i rule out the ESA or no?

2] If the ESA is not bad then what is the possibility that it is the shift interrupter switch?

I'm pretty sure the lower shift cable is good because when out of the water the boat goes into gear with no problem...could the shift interrupter switch be sticking causing the ESA to stay activated and thereby stalling the boat?

The boat is moored and it is storming like a banshee here rite now; just trying to get some things narrowed down for tomorrow...thanx in advance.