MerCruiser 454 Misfiring . Possible head gasket?

S

SeaingDouble

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My fresh water cooled 454 started misfiring and what looks to be coolant coming out of the exhaust? But coolant is green so I'm not positive as this looks white. When I shut it down I checked the exhaust manifolds and it feels like two cylinders on each side are cool to touch while the others are really hot. I am doubting both head gaskets could go at the same time, so would there be a reason that two cylinders on each bank would be misfiring? I don't think cylinders 2,8,5 and 7 are firing. There is no water or coolant in the oil. It is perfectly clean still.
 
What does the inside of the distributor cap look like?
Can you test run at night to see if there is any arcing between plug cables?
Have the plug wires been fooled with recently to warrant rechecking correct firing order?

Any change in coolant or crank oil levels?

Is there a sheen in the exhaust wake to go along with the "white" (which sounds more like oil)?
 
Sandy, great questions. I initially thought it was the distributor cap so I checked it and sure enough it was very corroded. So I installed a new Rotor and sensor in the distributor. It’s struggled to start but when it started it was running very rough and miss firing. Plug wires are correct, because I did consider that maybe I messed that up when switching the. There is no oil sheen in the exhaust. I have a video of the exhaust discharge I’d like to share but not sure how
 
I am also thinking it could be the exhaust risers. With it being a closed cooling system I’m thinking if it were head gaskets the discharge would be somewhat green in color rather than a strange Bubbley white. Maybe Rall water from the risers are getting sucked into the cylinders and blown back out Causing a strange looking discharge
 
I dont understand the sequence. Was it missing before you did the work and is it doing the same afterward as before? Checking compression will give you a good indication of what is going on.
 
If you think it's antifreeze coming out the exhaust, it will smell like AF. White stuff coming out sounds like oil mixed with water.

If it seems like I missed the point, I'm sorry, it's just that the older I get, the more and more tedious it is for me to read and understand. It's just 'Old Timers' catching up with me.
 
Even after the work you did it still misfires, correct? The white coming out the exhaust is in the exhaust gas, or is it liquid?
I would:
Check the antifreeze in your heat exchanger to see if the level is low meaning the AF is going somewhere...
Pull out the spark plugs and look at them, the misfiring cyls will be obvious because the plugs will be dark, oily or smell like gas. Are any plugs steam cleaned white with rusted electrodes (sign of water in a cyl)...
I next I would do a compression test and at the same time note if any AF shoots out of the spark plug holes. These two bits of information would tell you if it is likely that you had a failed head gasket. However, if the engine has never had a bad overheat, head gaskets on these engines just don't blow that often, a bad overheat or chronic lower level overheats is what does that.

I had a similar issue on my 4.3 a few years back. Reluctant to start, rough running, I checked all the typical causes (ignition, carburation). Pulled the plugs and they looked suspicious....orange cast to the center electrode, a bit of rust on the side electrode of one cyl...Grounded the high tension lead from the dist cap and cranked it over. Sure enough water (salt) shot out of #2 cyl, and a mist of water came out of #1. Took it apart and yes both head gaskets were blown, probably from a bad overheat 3 years before that. I wound up putting it back together with a set of re-man marine heads (originals were cracked in the exhaust seats of the center cyls in each head) new Fel/Pro gaskets, etc.

I think looking at the plugs will tell you a lot. Don't forget to ohm the resistance of your spark plug wires. Rare to have one go bad but it does happen. Dist cap, rotor, wires plugs first then go from there.
 
The mis firing happened first. I checked the distributor cap and it was nasty so I changed it along with the ignition sensor and rotor. When I started again it was no better. That’s when I realized by feeling the exhaust ports that several cylinders are not firing. I’m willing to bet it’s risers
 
Checking the plugs is an excellent diagnostic tool as is doing a compression check while the plugs are out. Orange on the plugs says water is getting into the combustion chambers and why you are getting a miss in that cylinder. The usual culpret for this is a leak in the exhaust riser gasket allowing water into the combustion chamber and causing the miss. This also the result of a head gasket failure. a compression test will tell you which one you have. Low compression in a cylinder indicates a blown head gasket but can also indicate a valve rusted so it no longer holds compression. Diagnosing a problem is like a doctor diagnosing a problem. You have to start with the easy stuff first. A corroded distributor is another direction to follow. The cause may be anything from water spray while running or water dripping from a loose canvass or leaky engine cover.
 
Sorry , I've never posted pics or video here so maybe someone else can advise on that.

When you mentioned the "white" in the exhaust , I was picturing liquid deposits on the water surface by the transom outlet.
But are you really referring to white exhaust "smoke"... which is usually extra-hot water steam?

Can you dip-capture any of it in a clear container and let it cool and possibly separate ( and smell it?)

You mentioned the hot/cold manifolds. How hot do the tops of the risers get to your palm?

The spark plug and compression check should be interesting. Maybe check resistance of all the plug wires to compare?
 
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