After tune up blues!

[Mad Gringo]

My 35' Silverton 1997 wit twin 454"s xli's ran very well. Mechanic talked me into tune-up, and as I have never had that done in 5 years of owning boat I went with his call.


Day after tune-up - took for test run, no throttle response port engine, back to dock, "reset throttle response sensor", took for test run, seemed to work.


Next voyage, before pulling into harbor, slowed down from 3200 rpm, went to go back to 3200 and no response from port throttle, but in few seconds it caught up.


On way back from trip, same thing happened.


Back to dock, mechanic says new wires and plugs were bad, plug tip broke off in engine. Starboard engine appears fine. Mechanic can not seem to get engine timed.


New plugs and wires (again) says boat is good to go. Go for 45 minute ride. Same problem with throttle, not all the time but some times. Now starboard engine missing and backfiring.


Make it back to dock. Mechanic tries everything , gets starboard engine running right. Port engine now has no compression in 2 cylinders.


How did I get here?


Thanks for listening.

[Suijin]

Every mechanic’s nightmare: work on an engine and then have some coincidental and unrelated problem surface that at first glance appears the result of their work.

Not saying it isn’t, particularly with both engines now misbehaving.

I would find a different mechanic as a first step. If your current one screwed up you don’t want them continuing to work on your boat. If they didn’t that should be revealed by the second opinion.

[a64pilot]

No compression in two cylinders is bad, real bad, that’s no tune up fix.
Are they adjacent cylinders? If so could be you got lucky and it’s a head gasket, but need to find out what it is soon and do not run the engine

[Mad Gringo]

Did not have that problem before tuneup! Boat ran smooth, new wires, plugs were put in and then replaced as mechanic said they were faulty. Could not time the engine after that.

[jimbunyard]

A little late, but 'if it ain't broke, don't fix it'...

Time for a new 'mechanic'.

Did you 'loose compression' in the engine with the 'broken sparkplug tip'?

It's a bit odd even if that is the case, as a broken piece of plug could cause that symptom (though rather unlikely), but not in two cylinders.

If your engines are injected and computer controlled I would expect this to be an electrical problem, and even if they are carbureted with electronic ignition this may be the case.

That the engines were running well before would tend to disprove the idea that one suddenly developed 'low compression', but of course stranger things have happened...

[Cadence]

Just out of curiosity, did his tune up involve adjusting valve clearance? A screw up there might hopefully be the cause of lack of compression.

[a64pilot]

Pretty sure 454's are hydraulic adjusters. I guess that wouldn't stop someone though, there is an initial adjustment.
I'm betting head gasket, assuming they are adjacent cylinders, blown head gasket from too far advanced timing leading to pre-ignition or maybe even detonation

[model 10]

You need to see it to believe it, but a little object like the end of a spark plug will travel all through the cylinders, valves and intake manifold doing damage and never leave until you take the head off and remove it.

[jimbunyard]

Originally Posted by Ecos

You need to see it to believe it, but a little object like the end of a spark plug will travel all through the cylinders, valves and intake manifold doing damage and never leave until you take the head off and remove it.

How? Think you have it backwards, you have to believe it to imagine you see it...




Even hydraulic lifters can be over-tightened and cause leaks through the valve train. Good call, certainly something to check if they were fooled with....

[Mikado]

Instead of guessing what is causing the low compression ask the mechanic to do a cylinder leakage test. Will clearly identify the source of the low compression and then you can address the problem.

Good luck,

Jeff

[model 10]

Originally Posted by jimbunyard

How? Think you have it backwards, you have to believe it to imagine you see it...

Well I've seen it a couple of times in aircraft engines. Once a 1/8" pipe plug in a Lycoming 6 cylinder engine fell into the intake port of one cylinder and bounced around between 3 other cylinders. It took out spark plugs, valves and piston tops. A kind of fun part was after thinking the part had left the engine I installed new spark plugs and ferried the plane back to my shop and it started missing again on final approach. It is also common thing with racing engines. It has to do with pulses in the intake system, valve overlap etc.

[Cadence]

Originally Posted by a64pilot

Pretty sure 454's are hydraulic adjusters. I guess that wouldn't stop someone though, there is an initial adjustment.
I'm betting head gasket, assuming they are adjacent cylinders, blown head gasket from too far advanced timing leading to pre-ignition or maybe even detonation

If the OP can afford to feed a pair of 454s I'm sure he can hire someone to solve the problem,

[seabreez]

Originally Posted by Mad Gringo

My 35' Silverton 1997 wit twin 454"s xli's ran very well. Mechanic talked me into tune-up, and as I have never had that done in 5 years of owning boat I went with his call.


Day after tune-up - took for test run, no throttle response port engine, back to dock, "reset throttle response sensor", took for test run, seemed to work.


Next voyage, before pulling into harbor, slowed down from 3200 rpm, went to go back to 3200 and no response from port throttle, but in few seconds it caught up.


On way back from trip, same thing happened.


Back to dock, mechanic says new wires and plugs were bad, plug tip broke off in engine. Starboard engine appears fine. Mechanic can not seem to get engine timed.


New plugs and wires (again) says boat is good to go. Go for 45 minute ride. Same problem with throttle, not all the time but some times. Now starboard engine missing and backfiring.


Make it back to dock. Mechanic tries everything , gets starboard engine running right. Port engine now has no compression in 2 cylinders.


How did I get here?


Thanks for listening.

Clearly not an experienced mechanic. Must have screwed up something. Ask around for a good mechanic and investigate this further. Which cylinders are defective or lack compression? This sounds like a screw up and lack of honesty... I hope you solve this soon and let the forum know what caused the problems. I work often on 454's and they are very good engines. I wish you were closer to here...

[GordMay]

Greetings and welcome aboard the CF, Mad Gringo.
I can understand why you're "Mad".

[Mad Gringo]

Having the cylinder leakage test done today. Two bad cylinders next to each other, with one cylinder being the one that lost its spark plug tip due to bad detonation leads everyone to believe it is the head gasket. will know by days end!


Thanks