OMC 5.7 won't idle

[79Rude115]

I have an 1990 OMC 5.7 "PWS" model

The engine does not want to idle especially when cold. I find my self with it on the trailer warming for 5+ minutes but even after running across the lake to normal operating temp it still does not idle well, it just barely stays alive at idle after completely warm and occasionally will die.

I think the obvious things are vacuum leak, spark plugs, points, fuel filter. I looked for a vacuum leak but did not find anything that looks out of the ordinary. Any advice on where to start and other items to look at would be appreciated.

One additional issue which I guess could be related is that the tach isn't working properly. I looked at my OMC factory service manual and it advised me to check the connections and the setting on the back of the tach. On the back of the tach I found the setting was pointing to 3 instead of 4 however when I tried to change it the plastic fitting seemed to be stuck and I did not want to force it as I was sure it would break.

 

[Boatin Bob]

Re: OMC 5.7 won't idle

You can always just disconnect the tach to get it out of the picture. Another thing you can check is the ESA module as this will cause an engine to idle very poorly (by design) but it should only happen during shifting from gear into neutral, disconnect it as well to see if that's your problem.

 

[Limited-Time]

Re: OMC 5.7 won't idle

Hows the choke setting?? When is the last time the engine was fully tuned??..............As for the tach, it's possible theres an issue there...................if you disconnect it, that will tell you is you issue is there....................also could be the idle circuit in the carb. I'd go choke, tach, tune-up, then carb.......

 

[Bondo]

Re: OMC 5.7 won't idle

I think the obvious things are vacuum leak, spark plugs, points, fuel filter. I looked for a vacuum leak but did not find anything that looks out of the ordinary. Any advice on where to start and other items to look at would be appreciated.

Ayuh,.... I Agree,....

At Best,.. A Full,+ Complete Tune Up will cure it,....

If Not,.... I'm Guessing the Carb needs a Rebuild......

 

[79Rude115]

Re: OMC 5.7 won't idle

I think I have the tach working now, I was able to get it set to 4 and it is reading correctly at least at idle. I checked the distributor cap and it appears to be original as it has some of the engine paint around the lower edge, it has a bit of corrosion under the cap. The points dont look bad but the spring is a bit rusty.

How do I go about checking the choke setting?

Last tune....dunno, I just got the boat. I also think it could have some old gas in it although i added 10 fresh gallons to it.

 

[79Rude115]

Re: OMC 5.7 won't idle

What all would you include in a full tune? How can I tell what ignition I have i.e. is it a mallory or a Prestolite?

 

[Uraijit]

Re: OMC 5.7 won't idle

What all would you include in a full tune?

Plugs, wires, cap, rotor, points, fuel filter.

I'd also put a little fuel system cleaner in the tank, and replace vacuum lines as needed.

You can use an unlit propane torch to locate vacuum leaks. Just squirt propane around the manifold, and if your idle speed changes you're near a leak. The vacuum leak pulls in the propane, which will cause the engine to idle higher, due to the extra fuel.

 

[chiefalen]

Re: OMC 5.7 won't idle

Yep a full tune up. I would run it in the dark will show you if you have bad wires to the plugs.

Did you check a plug to see how they look?

New dist. cap. New plugs gap right. New wires. new points.

This site has everything you need.

After the tune up spray some carb cleaner around the carb. Same as propane youll hear the difference if theres a leak.

Good luck keep us posted.

 

[79Rude115]

Re: OMC 5.7 won't idle

Thanks for the help gents, I am going to work on it this Sunday, will let you know how it goes. I have a couple of questions regarding replacing the points. The manual says to rotate the distributor shaft until the point rubbing block makes contact with any cam lobe.

How is the distributor shaft to be rotated? Is this done by cranking the engine until you get to the top of a cam lobe?

 

[Don S]

Re: OMC 5.7 won't idle

I would also do a Compression Test, you can't tune an engine with poor compression, and they won't idle very well either.

 

[79Rude115]

Re: OMC 5.7 won't idle

Update - I did the plugs which were horrible looking and not the correct plugs, they were automotive plugs. I also changed the distributor cap, rotor, condenser and points - all appeared to be original except the points.

It looks like I made a rookie mistake, I took it out for the first time since the work yesterday and could only get to about 2k RPM at which point it started back firing.

I guess I did not get the spark plug wires on in the correct positions or perhaps the points gap isn?t correct. I have the OMC manual which shows the correct order of the spark plug wires connection however it isn?t clear exactly where the #1 connection goes in relationship to the cap screw (see attached scanned copy of manual figure 27). The wires also look like they could be automotive instead of marine, they are grey and say something about 8 MM performance - Napa has a marine set for $46


Any advice greatly appreciated

 

[79Rude115]

Re: OMC 5.7 won't idle

bump

 

[79Rude115]

Re: OMC 5.7 won't idle

Is the problem I am seeing with the backfire at 2K RPM likely to be points gap or spark lead connection order?

 

[Bondo]

Re: OMC 5.7 won't idle

Is the problem I am seeing with the backfire at 2K RPM likely to be points gap or spark lead connection order?

Ayuh,....

That's Why I mentioned a Carb Rebuild,....

A High-Speed miss is usually caused by a Lean condition.....

An Electrical miss is usually Constant from idle to WOT.....

 

[79Rude115]

Re: OMC 5.7 won't idle

Thanks Bond-o

There was no high speed miss until I changed the points, condensor, cap and rotor. The boat ran great before that, it just did not idle

 

[Bondo]

Re: OMC 5.7 won't idle

OK,...

Were the Points set properly,..?? Was the Dwell metered,..??

 

[Uraijit]

Re: OMC 5.7 won't idle

Is the problem I am seeing with the backfire at 2K RPM likely to be points gap or spark lead connection order?

Did you check your timing? Did you set your points' dwell, after replacing them? Is your distributor advancing timing, as you increase engine speed?

EDIT: Dang you bondo, you beat me to it!

If you've got your firing order out of whack, it would probably cause running issues at idle, but you should verify that everything's correct. Pull the #1 spark plug, and put your finger over the spark plug hole. Have someone crank the engine over until you feel the air pushing your finger out of the hole.

Then rotate the engine the rest of the way by hand, until the timing mark on the balancer, is lined up with the '0' or 'TDC' mark on your timing cover.

Once it's lined up, pull the distributor cap off, and look at where the rotor is pointing. Mark that location on your distributor cap. This is your #1 wire location. Plug your #1 plug wire into that location, and plug the rest of the wires in in their proper firing order.

After that, set your timing, then points dwell. Then reset timing, and re-check points dwell. Keep going back and forth setting them, until they're both right. Should only take a couple of tries.

 

[Bondo]

Re: OMC 5.7 won't idle

EDIT: Dang you bondo, you beat me to it!

Ayuh,.....

'ell,... 3 Minutes ain't even Close......

Don beats Me by mere Seconds all the time.........

 

[79Rude115]

Re: OMC 5.7 won't idle

I don't have a dwell meter, I just used a feeler gauge and set them to .018 gap at the top of one of the cam lobes. I checked the original points before removing them and they were exactly the same gap.

How do I check the timing advance? I ordered a new set of wires and I am going to make sure they all are connected properly. I have a feeling that I might have all of the leads connected 1 point forward of where they should be however I would have thought that the egine would not even start if that were the case. The other possibility is that I have the wrong distributor cap - I will compare with the original to verify.

 

[Uraijit]

Re: OMC 5.7 won't idle

Ayuh,.....

'ell,... 3 Minutes ain't even Close......

Don beats Me by mere Seconds all the time.........

Yeah, but my post took 3:01 to type.