Mercruiser 3.0 diagnosis / serial number decode

[Eric 3.7LX Alpha 1]

Awesome! Glad you got it figured out.

 

[Tube1]

Engine idles great now, but it’s instantly stalling when I shift in to gear. I completely disconnected the shift cutout cable. Not sure what’s going on now

 

[Tube1]

I can get it to shift without stalling but have to move the shift lever extremely fast.

 

[Scott06]

I can get it to shift without stalling but have to move the shift lever extremely fast.

Usually if you were activating the shift cut out going into gear that is an indication that your lower shift cable or shift mechanism needs a replacement or is hung up

 

[Tube1]

I completely disconnected the drive shift cable, and it still stalls putting it into gear. Probably still a carb issue since the drive is completely out of the question now…

 

[Tube1]

I also feel like something may be wrong with my electric choke. When the engine is cold I’m getting the spring-loaded action of the choke plate. After it warms up, the plate bounces around freely like the choke spring isn’t grabbing it anymore. Unless that’s normal operation of it.

 

[Eric 3.7LX Alpha 1]

What RPM is the engine idling at? You disconnected the shift interrupter wire and the shift cable to the drive and it is stalling?

 

[Tube1]

What RPM is the engine idling at? You disconnected the shift interrupter wire and the shift cable to the drive and it is stalling?

Can’t tell what RPM it’s at because tach is broken… that’s another thing I gotta fix. I just got the idle to where it was smooth but not too rich/lean.

That’s correct. Interrupt switch is completely disconnected as well as the drive cable so it’s literally just the engine spinning with zero load on it and it stalls.

 

[Tube1]

And regarding the tach issue- the gauge needle is pegged out at max RPM. I’m getting 12v at the coil terminals, and the gray tach wire is attached to the (-) side of the coil. Haven’t looked into it any further

 

[Tube1]

Small update:

The carb I attempted to rebuild let the boat idle perfectly but stalled at throttle. I was so fed up with it I ordered a rebuilt carb from guaranteed carburetors.

Finally got it in today, and installed it. The boat won’t even fire now when cranking. The float bowl is filled, accelerator pump works with throttle pumps, and I’m getting spark. It’s hesitating like it wants to fire but doesn’t.

The idle speed screw is set two turns from bottoming out. The electronic choke is connected properly and seems to be working (choke plate opens as engine gets warmer cranking). All the linkages look fine. I can’t find a single thing wrong.

After a few minutes of cranking with the new carb I realized my plugs were horribly fouled. I replaced them, and still nothing. Sputters a little while cranking and that’s it.

At this point I’m done with it, and don’t even want to look at the boat anymore. It’s disappointing to say and I appreciate all you guys’s help but this problem is clearly outside my knowledge.

If anyone has any good shop recommendations that can work on these engines in the central IN area it’s much appreciated.

 

[Scott06]

Small update:

The carb I attempted to rebuild let the boat idle perfectly but stalled at throttle. I was so fed up with it I ordered a rebuilt carb from guaranteed carburetors.

Finally got it in today, and installed it. The boat won’t even fire now when cranking. The float bowl is filled, accelerator pump works with throttle pumps, and I’m getting spark. It’s hesitating like it wants to fire but doesn’t.

The idle speed screw is set two turns from bottoming out. The electronic choke is connected properly and seems to be working (choke plate opens as engine gets warmer cranking). All the linkages look fine. I can’t find a single thing wrong.

After a few minutes of cranking with the new carb I realized my plugs were horribly fouled. I replaced them, and still nothing. Sputters a little while cranking and that’s it.

At this point I’m done with it, and don’t even want to look at the boat anymore. It’s disappointing to say and I appreciate all you guys’s help but this problem is clearly outside my knowledge.

If anyone has any good shop recommendations that can work on these engines in the central IN area it’s much appreciated.

Dump some gas down the carb if it fires it’s the carb , send it back get your money back. If properly rebuilt it should run ok out of box

If it doesn’t run u have fuel delivery or spark issue

If you are open to it send your old carb to mikes carbs and have home rebuild it

 

[Tube1]

Dump some gas down the carb if it fires it’s the carb , send it back get your money back. If properly rebuilt it should run ok out of box

If it doesn’t run u have fuel delivery or spark issue

If you are open to it send your old carb to mikes carbs and have home rebuild it

I dumped gas down the carb and the engine sputters, and shakes a little bit like the cylinder is firing. However no amount of cranking can get the engine to actually fully fire and idle.

 

[Tube1]

I'm messing around with testing spark. It seems I now have no spark at any of the plugs, but I do have spark coming off the coil tower.

Hooking an ohm meter to my points... even when the points are open, I'm getting continuity between them when my black wire coming off the distributor is connected to the coil (see pics). Is this correct? When I disconnect this black wire, the points are not shorted when open, and short when touch together.

 

[banderberg]

If you end up sending it back I've heard lots of great things about National Carburetor out of Jacksonville, FL

 

[Tube1]

I've thought about this more and there's definitely something weird going on with the points/ignition coil. I'm going to re-iterate my previous post because it was a bit scatterbrained:

1. I'm attaching an ohm meter between the two sides of the points.

2. No matter whether the points are physically closed, or physically open, my meter indicates a direct short between the two.

3. When I disconnect The black wire that runs from bottom of distributor to my coil (see pic above), step 2 is no longer true. Instead, the meter indicates the points are open when physically open, and shorted when physically closed.

So... basically that black wire going to the ignition coil is grounded to the distributor body for some reason. I don't think this is right. I don't see any physical damage on the black wire that'd be shorting to distributor body. Could a bad ignition coil cause this?

 

[Scott Danforth]

I've thought about this more and there's definitely something weird going on with the points/ignition coil. I'm going to re-iterate my previous post because it was a bit scatterbrained:

1. I'm attaching an ohm meter between the two sides of the points.

2. No matter whether the points are physically closed, or physically open, my meter indicates a direct short between the two.

3. When I disconnect The black wire that runs from bottom of distributor to my coil (see pic above), step 2 is no longer true. Instead, the meter indicates the points are open when physically open, and shorted when physically closed.

So... basically that black wire going to the ignition coil is grounded to the distributor body for some reason. I don't think this is right. I don't see any physical damage on the black wire that'd be shorting to distributor body. Could a bad ignition coil cause this?

The black wire is the points wire

 

[Tube1]

The black wire is the points wire

Ok. So when this black points wire is attached to the (-) side of the coil, it's shorting the points together even when they're physically open. This makes no sense to me.

 

[Scott06]

I'm messing around with testing spark. It seems I now have no spark at any of the plugs, but I do have spark coming off the coil tower.

Hooking an ohm meter to my points... even when the points are open, I'm getting continuity between them when my black wire coming off the distributor is connected to the coil (see pics). Is this correct? When I disconnect this black wire, the points are not shorted when open, and short when touch together.

Then you have an issue in your cap and rotor. If you place the cap end of the high voltage wire (coil to cap wire) 3/8" inch of an engine ground crank it and have spark , but don't have spark at the plugs see if cap and rotor are still making good contact.

Other thing is to disconnect the shift interrupt to see if it is grounds out coil when it shouldn't

here is a points trouble shooting guide

How To: Troubleshoot a Points Ignition System

***Please read through ALL the information before attempting any procedure listed here and before asking ANY questions*** ***This tutorial is designed to explain step by step the proper procudures for troubleshooting a no spark issue for an engine with points ignition. If you are here, this...

forums.iboats.com

 

[Scott06]

Ok. So when this black points wire is attached to the (-) side of the coil, it's shorting the points together even when they're physically open. This makes no sense to me.

if wire is chaffed where it goes through distributor this will happen

 

[Scott Danforth]

Ok. So when this black points wire is attached to the (-) side of the coil, it's shorting the points together even when they're physically open. This makes no sense to me.

The wire is merely a conductor to the points. The points are an electo-mechanical switch. When the points close (path to ground), the coil charges by creating a magnetic field. As the points open, the magnetic field collapses and that is what provides the high voltage from the coil secondary

What is so hard to understand?

There is a sticky on understanding points ignition. I would recommend reading it