Spark Plug ?, What Happened? Some Close up Pictures... Updated

[holgo123]

1993 OMC Cobra, 5.0 l EFI/MPI

I have had the boat out about 5 times since a lengthy transom repair and the last time out, I heard something in the motor kind of pop and then heard an intermittent ticking (like a lifter ticking). I just pulled all the plugs and found the #5 cylinder's (1st cylinder on the right bank from front of engine) spark plug has a glob where the electrode used to be. All the other plugs look great (they are brand new, just a few hours on them...). Is this pre-detonation? Can it happen on one cylinder only?

 

[Bondo]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

Is this pre-detonation? Can it happen on one cylinder only?

Ayuh,.... That's Detonation alright.....

And,... Yes, it can happen to 1, or All the cylinders, for various reasons...

 

[Coors]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

Are the heads carboned up? You might want to try some sea foam.

 

[Don S]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

I would do a compression test before anything else.

 

[holgo123]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

Here are the compression numbers:
1 - 125 lbs., 2 - 135 lbs., 3 - 140 lbs., 4 - 145 lbs.,
5 - 120 lbs., 6 - 140 lbs., 7 - 140 lbs., 8 - 150 lbs.
The pressure built to the reading on the 1st/2nd stroke and held. How does this look? I also checked the timing and it reads dead on 5 degrees BTDC. Any thoughts? Thanks!

 

[Coors]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

Numbers look ok; there might be some carbon in the one, glowing, and setting off the fuel mixture early.

 

[Don S]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

You have low compression and damaged plug on #5 cylinder. I'm thinking you have some lean issues from possibly plugged injectors. A leakdown test would be a good thing to do on #5 to locate the actual problem, But I think you really need to pull the head and have a look. I can almost see part of the piston being missing.
This is a Ford MPI, correct?

 

[holgo123]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

It is a Ford 5.0 l EFI/MPI with about 300 hours on it...

 

[Coors]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

I was thinking piston damage also, but decided to leave that to the pro's.

 

[holgo123]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

I started tearing it down, but have decided to wait and to try and get a leak down tester and check it before I pull the head. It may help me figure out where to look in case the piston is intact. The top of the piston looks like it has more carbon on it than the others from looking through the spark plug hole... What a mess... If the injectors are dirty (getting them cleaned seems kind of expensive, I think I would rather replace them), can they be replaced by regular injectors for a Ford 5.0 l? Do they have to be a certain lb? Thanks for your help!

 

[newport dave]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

I can't believe you still have any compression in that cylinder, looking at that plug you can see what appears to be small bits of aluminum. I think you have piston damage.

I don't think I would bother to do a leakdown, the heads need to come off for an inspection. Once the heads are off, you'll know what needs to be done.

 

[Mkos1980]

Re: Spark Plug ?, What Happened?

Re: Spark Plug ?, What Happened?

I started tearing it down, but have decided to wait and to try and get a leak down tester and check it before I pull the head. It may help me figure out where to look in case the piston is intact. The top of the piston looks like it has more carbon on it than the others from looking through the spark plug hole... What a mess... If the injectors are dirty (getting them cleaned seems kind of expensive, I think I would rather replace them), can they be replaced by regular injectors for a Ford 5.0 l? Do they have to be a certain lb? Thanks for your help!

They can be replace by regular injectors, but make sure the lbs are the same. I know the 5.0 In the mustangs were 19lbs Orange top injectors. Your best bet it to pull one and cross ref it. If they are 19's I would but a whole set. The whole set is about 250 bucks from summit racing. Buying one for 50+ dollars is crazy.

 

[holgo123]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

I pulled the heads and the piston and cylinders look good. Some of the cylinders have a little discoloration, like rust stain, but all are smooth with no grooves... There is some carbon on top of the pistons and the combustion chamber on the head. The valves on #5 (the one with the burned up spark plug) looks o.k. There is some spotting (rust) on some of the valves on the adjacent cylinders. I am not sure where to look now... I am going pull the lifters, can they be tested? It seems like I was having an intermittent ticking (but that was before I changed the plug and I don't think that would cause the detonation issue). Should I go ahead and pull the other head and get a valve job and clean them both up? The inside of the motor is clean! What could have caused the problem? Could an incorrect plug temperature? The plugs I put in to start the season are Autolite #147. Autozone cross referenced them... I just looked them up and they seem to be for cars built in the 70's... Could an injector that may be plugged a little lean out the mixture and overheat the cylinder? Any thoughts? Thanks for your help!

 

[holgo123]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

I forgot to ask... Where is a good place to get the gasket set to put this all back together? Does it take a special head gasket? Also, the injectors are orange with some gray paint... I am going to measure their dimensions and try to identify them for possible replacement...

 

[Don S]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

I would look very carefully at the area I have circled in red. It looks an awful like metal erosion (melted), and metal transfer to the ring.

 

[bomar76]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

Curious as to how you have 2 odd and 2 even numbered cylinders on the same side?

 

[JustJason]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

i know your question is about #5 cylinder... but what's up with the combustion chamber you have marked as #7
To me that looks like rust on the intake valve... and maybe a hint of it on #5 exhaust valve as well.... Tell me its just the lighting... or that you accidently spilled some water one it.

 

[JustJason]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

and after saving the pic to my hd and blowing it up a bit... all of those exhaust valves look awefully clean..

 

[bruceb58]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

Curious as to how you have 2 odd and 2 even numbered cylinders on the same side?

This is a Ford. That is how Ford numbers them.

 

[newport dave]

Re: Spark Plug ?, What Happened? Update w/Pictures

Re: Spark Plug ?, What Happened? Update w/Pictures

I would look very carefully at the area I have circled in red. It looks an awful like metal erosion (melted), and metal transfer to the ring.

I agree with Don, it's hard to tell (can you post some better pictures??), but there may be some damage there.