AllDodge

While there are some issues with the plugs, a good cleaning will have them back to where they need to be for now. The plugs are just showing how well there working with what there given to burn (so to speak). The stuff on the plugs could be stuff being added to the gas (additives and the like). Incomplete burning of fuel or things such as antifreeze or other leaking in.

There has been some good comments to have a look.

Edit: looks like I took to long to respond, others said similar

JohanSweden

The injectors has not been serviced.
Did a leak down test last year with good results. No compression test yet.
I had some issues with my previous exhaust this year that was leaking water. (CMI exhaust).
Changed them to EMI thunder exhaust in late season this year. No problem with water after that what I know..

Something is wrong yes..

Havent pressure tested my new exhaust (EMI Thunder) but my previous exhaust (CMI exhaust) leaked as I said. Thats why I changed to the EMI and I dont think they are leaking.

Yes I will clean them up for a test later.
But doesnt it look like the #7 is missfiring or something?
Its all black.. and when I describe my problem with the missing/spitting engine at 800-1500 rpm range, doesnt it sounds like it could be a problem with the spark plugs/wiring or something..

boatnt

Replace the spark plugs,if it runs ok after spark plug replacement clean your injectors

underpsi68

Yes a couple plugs look like they have oil on them imo. I personally would change them, not clean them.

A couple of plugs look like they have some kind of build up on them?

You had a leaking exhaust? I'm wondering if water got into the valves, valves seats, cylinder walls or rings? Compression test, leak down. I would also put a scope in the spark plug holes and try to get a look of any thing looks funky.

JohanSweden

Is the NGK PZTR5A-15 replacement plugs for the AcDelco plugs?

Yes some build up on some of them. Looks like rust/salt or something.

My CMI exhaust leaked and then I swiched to the EMI exhaust. Could the build up on them have come from when it leaked with the CMI and then been left? I have run the boat with the EMI thunder a couple of times after so it has a few hours with the EMI and the same spark plugs..

SCANDINAVIAN

I tired NGK plugs on my 496HO a few years back and they only lasted for 1 season ap 40 hours. My first set of Delcos had over 200 hours on them and still running strong before I changed . Perhaps I just got a bad set of NGKīs but Iīll stay with the Delcoīs for now. They donīt like water though, had to change them (almost new) after my CMI-leak experience.
If you donīt buy new plugs shift the current plugs position (after cleaning them) by moving the badest ones to the cylinders where the best plugs were and vice versa. Then you probably can determine if it is the plugs that are bad or something else related to the specific cylinder(s) giving you fouled plugs. Also like someone wrote earlier in this thread, borrow one of these small cameras that you can check inside the cylinder with, the rust on the plugs can only come from water.

JohanSweden

I will try this too thank you.

Can the rust on the plugs came from when the CMI leaked?
I mean, I changed the exhaust to EMI Thunder instead. And I have droved the boat a couple of hours with the EMI thunder exahust. Shouldnt the rust/dirt on the plugs have vanished or something?

Ryan00TJ

Follow the above advice......
I would also compression check the cylinders. With the amount of rust and saltwater corrosion on those plugs, I bet your valves and seats aren't much better. Your ohm readings on plug wires are fine. You could still have a cracked boot/wire that could arc. That needs visual test to check.

I use AC 41-983 plugs on my 496, keep the .060" gap. Don't buy from amazon, ebay etc. Lotsa fake plugs out there. Rockauto sells real AC plugs.

Ryan00TJ

More than likely the leaking CMI's caused this issue. Once rusted they will stay that way.

1. Compression test cylinders to get a baseline. If your plugs are rusted, likely your valves/seats are the same.
2. Replace plugs, run boat a couple hours and recheck plugs.
3. At that time/hours, have your fuel injectors serviced.

JohanSweden

No, when I look in at the cylinders from the plug hole with a flashlight I see its rust in there..
To see if there is a cracked boot/wire it needs to be dark to check?

Is it these plugs from this site? The 41-983 is the plugs that I have.
https://www.rockauto.com/en/moreinfo...eQ73GK2A%3D%3D

Yes, I think the CMI caused this.

I will test that