PLEASE HELP! 4,3LX suddenly backfires + more

[SeaRayViking]

Hi - hope some one can help.

Our merc 4,3lx 205hp sailed nicely last season but after five months out of the water -of winter storage. We now have a huge problem!

When starting it runs but backfires thru the carb - hard...It's worst in low rpm but you can hear it's rather rough when it runs at about 3000rpm also.
We checked wires, distributor and the plugs. Plugs are OLD but looked ok. (we didn't change them, though)

PROBLEM:
We had a boat mechanic at the boat this morning, and he stated it was a VALVE-problem!!?? He started removing plug-wires from the distributor one by one and then concluded that is only runs fine on 4 cylinders. VALVE-problem he said. ???
He told us we must remove the entire engine and remove the cylinder-heads and replace two valves. (he didn't check the carb or the plugs)
AN EXpensive operation (3000 $)

what do I do??

 

[Bondo]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

Ayuh,......

My Guess is,.....
Change the Fuel Filters,..... If that doesn't clear things up,....

Do a Complete Tune Up......

 

[Haut Medoc]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

I hardly believe that your valves went bad from sitting....
Was there any evidence of water on the plugs?.....
Do what Bondo suggests, filters first, then tune up.....
It sounds like water in your gas to me....
Dump the separater into a clear container & see what it looks like.....
Anyone look at the dist cap & check for moisture there?.....
If the condition persists, then it would be time for a compression check....​

 

[Don S]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

Do the compression test to find out if the valves are bad or not. Without a compression test, I don't see how that mechanic could say all the valves went bad suddenly.
I would stronly suggest you pull the distributor cap and look inside. I would bet it's full of moisture.
New cap and rotor (Do a full tuneup like Bondo said) and it will probably run fine.
Have a look at this thread http://forums.iboats.com/showthread.php?t=192804

 

[newport dave]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

Popping through the carb can be a sign of a stuck exhaust valve(s), and it can happen when the engine sits for a period of time with water in one or both exhaust manifolds.

But when they don't do a compression test and they are pulling plug wires to diagnose a miss, they lose my confidence. As stated before, check for moisture under the distributor cap as it can cause similar symptoms. Hope that's all it is.

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

Hi again,
Thanks very very much to the four of you for the quick answers! I'm quite new at this, so it's a big help! Good point from all of you
I'll rush down to the boat tonight and get busy.
Thanks again!
SRV

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Hi again,

WE changed the plugs, cleared distributor and wires and fired it quite hard, and now i starts great and the hefty backfiring has totally ended! Really Nice...


But:
One of the cylinders stille "pops" a bit thru the carb (not blows or fires) and makes the enginge run a bit rough. When i remove the plug-head from that specific plug the engine runs great on 5 cylinders. It clearly doesn't ignite properly on that cylinder.

Is it still possible that it can be an ignition problem?
We really don't hope it the ignition valve:-(
Can it be exhaust valves (even though they shouldn't effect the ign,)

Thanks again for you help!

 

[Haut Medoc]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Hi again,

WE changed the plugs, cleared distributor and wires and fired it quite hard, and now i starts great and the hefty backfiring has totally ended! Really Nice...


But:
One of the cylinders stille "pops" a bit thru the carb (not blows or fires) and makes the enginge run a bit rough. When i remove the plug-head from that specific plug the engine runs great on 5 cylinders. It clearly doesn't ignite properly on that cylinder.

Is it still possible that it can be an ignition problem?
We really don't hope it the ignition valve:-(
Can it be exhaust valves (even though they shouldn't effect the ign,)

Thanks again for you help!

If you can isolate it to a specific cylinder, you need to do a compression test.......
There is the posssibility of water leaking into a cylinder, through a bad exhaust manifold/riser.....
But you need to do the compression test first to eliminate valve train issues first.....
How old are the risers & mans......
The reasons I keep coming back to this is because it is something that can happen over winter....
Do the compression test.....

 

[BRG25]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

What do you mean by "cleared distributor and wires"? I would replace the cap and wires....

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires + more

Hi,
Thanks a lot again folks.!!
by clearing wires i just meant that we've checked that they we're all totally ok - and they were. But This one cylinder is still popping and making engine run rough.

We're doing the comp test on saturday - we hope it turns out in our favour (meaning no valve-error....)

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

If you can isolate it to a specific cylinder, you need to do a compression test.......
There is the posssibility of water leaking into a cylinder, through a bad exhaust manifold/riser.....
But you need to do the compression test first to eliminate valve train issues first.....
How old are the risers & mans......
The reasons I keep coming back to this is because it is something that can happen over winter....
Do the compression test.....

Finally we managed to do the compression test, and sadly it confirmed our fears; one cylinder had poor compression and yet another one had VERY poor compression, s? we're actually dealing with two bad cyls...

I guess there's nothing else left to do, but to get the engine out of the boat and fix the valves (or piston rings) - or is there?.

too bad (and expensive), but thats life.
Thanks again for help and suggestions, SRV

 

[Bondo]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

I guess there's nothing else left to do, but to get the engine out of the boat and fix the valves (or piston rings) - or is there?.

Ayuh,.....

Blow compressed air into the offending cylinders thru the compression tester fitting,+ Listen.......

You should be able to tell if it's the Valves, or the Rings.....
If it's just the Valves,....
You can pull the Heads,+ leave the motor in to boat......

 

[Haut Medoc]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Ayuh,.....

Blow compressed air into the offending cylinders thru the compression tester fitting,+ Listen.......

You should be able to tell if it's the Valves, or the Rings.....
If it's just the Valves,....
You can pull the Heads,+ leave the motor in to boat......

I agree, & a good remanned head won't cost too much, it should be very doable with the engine in the boat, if it turns out to be bad valves, in fact I'd replace both heads if I were pulling the intake.....

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

I agree, & a good remanned head won't cost too much, it should be very doable with the engine in the boat, if it turns out to be bad valves, in fact I'd replace both heads if I were pulling the intake.....

Hi Haut & Bond. Thx for replys!!. We'll arm our selves with heavy tools and start working this weekend. I've finally acquired the original merc manual - so i'll put the mechanic on stand-by untill we're totally sure what's gonna happen.

Thanks

 

[Bondo]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

in fact I'd replace both heads if I were pulling the intake.....

Ayuh,......

If it comes to Replacing the heads, if your's can't be rebuilt,....
I'd spring for the matching Intake,+ Slap on a set of Vortecs for the extra 20hp......

 

[Tail_Gunner]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Hi again,

WE changed the plugs, cleared distributor and wires and fired it quite hard, and now i starts great and the hefty backfiring has totally ended! Really Nice...


But:
One of the cylinders stille "pops" a bit thru the carb (not blows or fires) and makes the enginge run a bit rough. When i remove the plug-head from that specific plug the engine runs great on 5 cylinders. It clearly doesn't ignite properly on that cylinder.

Is it still possible that it can be an ignition problem?
We really don't hope it the ignition valve:-(
Can it be exhaust valves (even though they shouldn't effect the ign,)

Thanks again for you help!

SeaRay before you do anymore id get a new cap and rotor if you have a rotor....or you can try the following....Dist caps can and do fracture like glass leaving minute hair like cracks which are sometime's not visible even to the human eye......and if this has occured the current will jump to those crack's which are short's... elec is always looking for a way to escape..

Take off the cap, use a well insulated screw driver....have someone turn the motor over and place the screw driver between the center ignition coil button and the individual plug contacts....The voltage will jump to make the bridge and if there are any cracks you will see it jump there to..

It works but there are times even that wont show up a cracked or pourus cap..

Umm it could be a schocking experience......

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Ayuh,......

If it comes to Replacing the heads, if your's can't be rebuilt,....
I'd spring for the matching Intake,+ Slap on a set of Vortecs for the extra 20hp......

We finally got a closer look. And we can see, at the bad cyl is actually missing the push rod for its valve. Just the one - but it's gone! It must be broke into pieces and have slid down below.

Question is now: Can a push rod break without the valve, to which it's connected, being broke or stuck? ... ... if so: How do you replace a push rod? Can it be inserted from the top?
If the valve is stuck, can one loosen it without removing the cyl head?

AND - might sound like a stupe question, but; how riscy is it to "not go look" after the broken pieces from the broken rod???

Loads of questions, i know, but now when we have eye contact with the error, we really want to get it done,

Thanks!

 

[Bondo]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Ayuh,.....

At the Very Least,....
You've Got to pull the Intake, to dig out the broken pieces......

 

[SeaRayViking]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Ayuh,.....

At the Very Least,....
You've Got to pull the Intake, to dig out the broken pieces......

Finally it all comes together. We pulled the intake and the bad cylinder head. Pieces from the broken push rod have been picked up, we've gotten the head remanned and gaskets are in place. Tomorow we will reassemble our engine, tune-up and adjust things and - hopefully - get back on the water soon.


Thanks to all for the tips and advices!

SRV

 

[Bondo]

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Re: PLEASE HELP! 4,3LX suddenly backfires (NEW issues!)

Ayuh,....... You're quite Welcome,....... I always Love a Happy ending...........