3.0 merc weird firing issue, need some direction NOW WITH PICS

[silverlakez400]

I have a 1990 Cobia Spirit 180. It has the 3.0 mercruiser in it. It doesn't have a distributor like I expected it would. It didn't run good at WOT, and the tach wasn't working. With it running, I pulled all the plug wires of one at a time, and the #1 cylinder wasn't firing on the plug side, but it was getting spark at the other end. So I replaced the wires, and it worked great!!! I gained 10 MPH. But now it's back to running like crap, and the tach that was working great on one lap of the lake was acting up again. So I checked all the wires again, and got a healthy shock on each one for my efforts. I pulled the plugs, and it looked like they were burning kind of clean. I checked a bunch of crap, found that my negative terminal was messed up on the battery, replaced the battery. Then I wondered about my firing order. I have it with 1-2-3-4 and every place I check has it 1-3-4-2. I didn't change anything on that end. Why would it work good for a while, then not run right after a while? And is 1-3-4-2 the correct. Any insight? I'm also going to take everything apart one at a time and clean it and put it back together. Because everything seems to have at least a little corrosion.

Dallas

 

[silverlakez400]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

Also, I did wiggle every wire looking for a loose connection. That's when I found that my ground wire was loose on my battery. It was also hot enough to leave a burn blister on me. But even after changing the battery and making sure they were tight, nothing changed.

 

[Bt Doctur]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

coil pack looks like 1,2,3,4 but firing order is 1,3,4,2

 

[Speed1v8]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

You say negative cable gets hot try changing the whole cable because it might be burned up not getting all the juice it needs first of all. check your wires that they didn't come off the connection inside were the plug touches. That happen to me.

 

[silverlakez400]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

Okay, so the first pic is of my neighbors boat's mercruiser blue box. Mine has a spot for one, but it doesn't have it.

The bundle of wires look like they should go to the mercruiser blue box if I had one, but they are just bundled up near my pump for the trim in the rear of the boat.

The other pic is of what one of my power supply cable's looked like from where it hooks to the battery. I snipped it off for today, and got it down to clean cable. I'll be putting a better end on it.

idea's? thoughts? is this normal? and should all my battery cables have the heat shrink so that there is no expesed wiring at all? or do I leave it open for me to see if I have a corrosion issue? I know on my charger, I had them all closed up, but that was on an old car.

 

[Don S]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

What spark plugs are you running in it?
Here is some info on the DDIS system you may need.

View attachment DDIS.pdf

 

[silverlakez400]

Re: 3.0 merc weird firing issue, need some direction

Re: 3.0 merc weird firing issue, need some direction

That diagram is exactly what I needed.

I also noticed without the boat running I have good power on one of the gauges terminals, and VERY weak power at the other terminal that isn't the ground. So I thought I'd see if it changed while it was running, and a wave came by and I blew my ignition fuse. So I'm going to have to wait until tomorrow.

But I'm pretty excited to see what a new negative cable will do.

 

[Speed1v8]

Re: 3.0 merc weird firing issue, need some direction NOW WITH PICS

My negative cable got the hottest couldn't touch it. Also got my red wires hot as well because of the negative wire this can happen with plug wires as well.

 

[silverlakez400]

Re: 3.0 merc weird firing issue, need some direction NOW WITH PICS

so did changing your cable help at all? did you have it 100% covered except for the end you bolt on? thanks.

So I believe this is looking to be much more electrical than anything else,, would a mod please move this to that section? thank you.

Don, it has champion spark plugs in it. It's not what I put in it, but it is all that my dad has run in his truck, and they last just under 200,000 miles in that and his other cars.

 

[Don S]

Re: 3.0 merc weird firing issue, need some direction NOW WITH PICS

Don, it has champion spark plugs in it. It's not what I put in it, but it is all that my dad has run in his truck, and they last just under 200,000 miles in that and his other cars.

Boats don't like Champions for some reason. I have cured many rough, poor running conditions by replacing the Champion plugs the customer installed.

Post your Mercruiser serial number of your engine.