4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

I'm going to throw something very silly out there.... Check you have a V6 rotor, not a V8 rotor.. Just pop the cap off and count the windows in the disc that runs through the sensor... (those slots that run along the bottom)....

Well...I did buy a new Mercruiser cap and rotor but I will double check.

 

[MikDee]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Another thing to consider, I've seen perfectly good Distributor caps not deliver spark on a few cylinders. Did you happen to save the old one?

 

[Bt Doctur]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

achris, stop giving away all our secrets!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I seen that too from some shops.
With a broken outer spring you can almost push the valve open by hand. Its called "exaust reversion"

 

[achris]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

achris, stop giving away all our secrets!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I seen that too from some shops.
With a broken outer spring you can almost push the valve open by hand

Has a broken front suspension spring on the car a while back. Didn't notice it until I was under there changing something... By the rust marks it had been broken a while... :facepalm:

 

[TampaBoater]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

My boat was doing the exact backfire at high rpm after replacing the exaust manifolds. Turns out i had switched two spark plug wires. After i rechecked the order of the cylinders and wires, everything was firing up fine at high rpm, no more backfire. Simple and stupid mistake but worth checking into.

 

[Walt T]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Problems on one side will point to manifolds and risers and / or head gasket. Never hurts to verify basics though.

 

[MikDee]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

A broken valve spring is sometimes hard to see, but if you can push the spring down with your hand, or fairly easily, it's Done!

I've seen a big block Merc with a broken valve spring, it had no compression in that cylinder, because it was off it's seat, so that on intake stroke it would work, but on compression stroke it would empty the cylinder! The marina owner/mechanic, & his head mechanic were scratching their heads? no compression? and asked my opinion. The engine looked clean, so I suggested "Maybe it's a broken valve spring?" Bingo!

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Found it!......Sure enough I just pulled the valve cover and the exhaust spring on number 2 is BROKEN!..cracked in two and looked like the bottom coil wound up a bit. When the valve is up/closed I can spin the spring with my fingers so must not be holding that valve closed tight at all.

Question is...now what? Ive never done valves before. Can I simply replace this one spring without taking the whole head off? I read about using compressed air to keep the valve from falling down into the cylinder but are there any other methods?

Is this part something I can find locally in either an auto parts or boat parts store?

Im still wondering why the rest of the cylinders on that side of the engine don't seem to be working at all. They have spark...I confirmed that many times. Before I discovered the broken valve spring I did another compression test and got around the same numbers I always got. How could a broken exhaust valve on one cylinder kill the power to the others?? Could this broken spring be the cause of water in the oil? Just trying to understand the flow of everything in relation to each other.



Thanks everyone for the help...

 

[Bt Doctur]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

going to pm my cell ,way to much to type and if you miss a critical point your really in a fix.

 

[Bt Doctur]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Damm, I`m getting good at this stuff!!!!!!!!!!!!!!!!!!!!!!!!! Exaust reversion does funny stuff.
http://www.michel-christen.com/ExhaustElbows.pdf

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Update,, first off...a HUGE THANKS to Bt Doctur for helping me out in taking the time to talk me thru the procedure for changing out that broken valve spring. You sir are a true gentleman and the world needs more people like you...those who are willing to take the time to help out a total stranger in need. You bet I will be paying this forward when I get the opportunity.

So I found a local machine shop that was recommended by one of the local marinas and they do a lot of work on boat engines. He sold me a new valve spring for the grand total of 2 dollars....but we chatted quite a bit about my issue and they were pretty stumped as to why only one side of the engine was working. He thought maybe only one side of the carb was not working..perhaps that side exhaust was clogged (mouse critter?) or the most logical was that there is in fact a head gasket failure and water was seeping past everything killing the fire on that bank?

Anyway...I picked up an air compressor from Sears and set that number 2 to TDC and pumped air in.....I heard the air escaping either thru the carb, or exhaust or perhaps the block itself? Is that normal when using that method for changing a broken valve spring? To hear hissing out? This made me second guess if the piston was in fact at TDC so I kept turning the crank till and watching the rotor and valves. At one point I felt the breaker bar snap back so It told me that the cylinder was under pressure.....but I still heard air hissing out?

I did manage to swap out the broken spring and put the plugs back on along with the distributor cap and wires...the motor fired up on the second crank!!

Now to test things I began to pull wires while it was at idle and saw what I thought was good signs... When I pulled off an even plug..(4) I felt a slight change in idle.....not enough to really tell. The big test I did was I pulled off all three ODD sides..(the side that seemed to be only running before and the motor stayed on!... I also felt that the riser was getting warm which tells me that side was firing ok.

It started to get dark and rain so I had to cover it up but Ill do more tests tomorrow and maybe try it on the water...

So in regards to hearing air escape...should I still consider looking at the head gaskets? Taking the intake off and heads and peeking in?

Thanks again!

 

[Bondo]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Ayuh,.... Air excapin' through the Carb, says the intake valve is burnt, 'n leakin',....

Air excapin' through the Exhaust, says the exhaust valve is burnt, 'n leakin',....

Air excapin' into the base, heard through the oil filler/ drain-back ports, says the piston rings are junk, 'n leakin',....

For burnt, leakin' Valves, pull the heads, 'n have 'em rebuilt,...
For leakin' Rings, ya need to rebuild the short block,...

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Another update....Had a chance to put it in the water today and it actually ran pretty good. Hit about 4200 RPM, topped out around 41MPH, got on plane really quick and NO MORE BACKFIRE

Thanks to the help I got here I found a broken valve spring which seemed to make all the difference in the world. Boat runs great now

Now the only thing I need to figure out is the water issue still in the oil. So far since finding the milkshake I have changed the oil and filter three times. When I dumped the oil last...(this morning before taking it out on the water) it was much lighter in color than last.

Now...two things....On this last batch of oil I never ran the boat in the water...just several times in the backyard on the garden hose and no more than 1500 RPM... the other thing is I put about half a can of sea-foam in hopes to break up some of the gunk down there. Do you guys think either of these factors would make the oil much lighter?? its a yellowish cream colored. (Banana Milkshake?)

I am really hoping that the water in there was due to bad manifolds/risers and seeped in past the rings during the boats past history. At the worst just a bad head gasket. Thats what the guy at the machine shop thought yesterday when I picked up the replacement valve spring....He thought that even tho I have great compression all around...that sometimes those 4.3 blocks can leak water just near the bolts for the heads......

So what do you guys think my next step should be??

Change the oil a few more times and see? (remember...I have good compression all around and motor runs great now) Or go ahead and rip the heads off and look with my own two eyes and make sure....

If I do take the heads off what do I need for gaskets?? intake, two exhaust and two head gaskets right??

Thanks everyone!!

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Ayuh,.... Air excapin' through the Carb, says the intake valve is burnt, 'n leakin',....

Air excapin' through the Exhaust, says the exhaust valve is burnt, 'n leakin',....

Air excapin' into the base, heard through the oil filler/ drain-back ports, says the piston rings are junk, 'n leakin',....

For burnt, leakin' Valves, pull the heads, 'n have 'em rebuilt,...
For leakin' Rings, ya need to rebuild the short block,...

I gotcha there but every time I checked compression I got anywhere from 170-180 all around.

One thing I did notice when changing that broken valve spring...While it was compressed down I put a little pressure on the tool and pushed the valve open...I could hear a distinct change in how the air sounded...I could clearly hear it coming thru the exhaust passages..when I pulled the valve back up...the sound changed again.

Perhaps I did not have the piston at exact TDC and either valve was slightly open? I had the pressure regulator set to about 60psi

 

[Bondo]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Another update....Had a chance to put it in the water today and it actually ran pretty good. Hit about 4200 RPM, topped out around 41MPH, got on plane really quick and NO MORE BACKFIRE

Thanks to the help I got here I found a broken valve spring which seemed to make all the difference in the world. Boat runs great now

Now the only thing I need to figure out is the water issue still in the oil. So far since finding the milkshake I have changed the oil and filter three times. When I dumped the oil last...(this morning before taking it out on the water) it was much lighter in color than last.

Now...two things....On this last batch of oil I never ran the boat in the water...just several times in the backyard on the garden hose and no more than 1500 RPM... the other thing is I put about half a can of sea-foam in hopes to break up some of the gunk down there. Do you guys think either of these factors would make the oil much lighter?? its a yellowish cream colored. (Banana Milkshake?)

I am really hoping that the water in there was due to bad manifolds/risers and seeped in past the rings during the boats past history. At the worst just a bad head gasket. Thats what the guy at the machine shop thought yesterday when I picked up the replacement valve spring....He thought that even tho I have great compression all around...that sometimes those 4.3 blocks can leak water just near the bolts for the heads......

So what do you guys think my next step should be??

Change the oil a few more times and see? (remember...I have good compression all around and motor runs great now) Or go ahead and rip the heads off and look with my own two eyes and make sure....

If I do take the heads off what do I need for gaskets?? intake, two exhaust and two head gaskets right??

Thanks everyone!!

Ayuh,.... After the boar ride, What'd the oil look like,..??

Where was the oil Level,..??

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Ayuh,.... After the boar ride, What'd the oil look like,..??

Where was the oil Level,..??

Well, thats the thing...If I check the oil via the dipstick it looks normal...Since day one it always looked a little high but clear and clean. It was not till I drained it that I noticed it was milky. I think looking just at the little bit off the dipstick its tough to judge the color between what clean fresh oil looks like vs milky brown.

When I put fresh oil in this morning I drained till it was barely a drip coming out the quick drain tube, I put only 4 quarts in and by then the dipstick showed it was on the high side of the "OK" mark if not slightly higher.

I would go drain a little out the quick drain into a clean pan but its raining at the moment. Ill post again shortly

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

I just went out and drained a little into a small plastic cup..Oil was milky brown again but not quite as light as I previously described.

As far as the level goes it was about the same level as it was when I filled it fresh this morning..Perhaps a little less but its difficult to get an exact reading depending on the angle of the trailer and this was just done in my driveway which has a slight decline.

I should also mention that during the brief power test this morning on the water..there was again A LOT of steam coming from the valve cover hoses...Thats the water being boiled off right??

Is there some kind of quick down and dirty way to flush bad milkshake out that you guys would recommend? Some kind of additive? Diesel fuel?? I don't mind spending the time changing the oil a few more times but at some point I gotta weigh the costs of oil and filters only to find out I still have a major problem.

 

[Bondo]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

I just went out and drained a little into a small plastic cup..Oil was milky brown again but not quite as light as I previously described.

As far as the level goes it was about the same level as it was when I filled it fresh this morning..Perhaps a little less but its difficult to get an exact reading depending on the angle of the trailer and this was just done in my driveway which has a slight decline.

I should also mention that during the brief power test this morning on the water..there was again A LOT of steam coming from the valve cover hoses...Thats the water being boiled off right??

Is there some kind of quick down and dirty way to flush bad milkshake out that you guys would recommend? Some kind of additive? Diesel fuel?? I don't mind spending the time changing the oil a few more times but at some point I gotta weigh the costs of oil and filters only to find out I still have a major problem.

Ayuh,.... At this point, I don't see a Problem,...

Forget 'bout that tiny bit of water, it's steam off over time at temp,...
Ya Don't need abunch of oil changes, 'n snake oil baths,...
Just Run it,....

It's the oil LEVEL that needs Watchin',....
If the Level goes Up, ya got a Problem,...
If the Level goes down, ya got an oil leak,...
If the Level stays the same, yer seein' Condensation,.... it'll steam off,...

 

[yearzero]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Ayuh,.... At this point, I don't see a Problem,...

Forget 'bout that tiny bit of water, it's steam off over time at temp,...
Ya Don't need abunch of oil changes, 'n snake oil baths,...
Just Run it,....

It's the oil LEVEL that needs Watchin',....
If the Level goes Up, ya got a Problem,...
If the Level goes down, ya got an oil leak,...
If the Level stays the same, yer seein' Condensation,.... it'll steam off,...

Sounds good...thats kinda what Im thinking as well....

My plan now is to go out and "enjoy" the boat once or twice more then change the oil again since I put cheap 20w50 from Walmart in now and replace it with the recommended 25-40 Quicksilver and a better filter.

I will keep a very close eye on the oil level before and after each run and hopefully she's all good....

Got a host of other issues with the boat I can start looking at now ...trim position sender...new prop, trailer brakes... gelcoat on the topside of the hull and of course the most important one of all...a new stereo for the kids to play crappy music on..lol.....But I gotta admit...the sound the boat makes at WOT is pretty cool and was music to my ears today!

Much thanks to everyone here who helped....Great forum and great people!!

Erik

 

[achris]

Re: 4.3 Backfires above 2300 RPM, just put on new exhaust manifold or fuel issue??

Might be worth one change of a high detergent oil (for that I like BP Corse Plus)... That should clean up a lot of the rubbish. But as Bondo says, watch the level, if it goes up, you have a problem. If it stays the same or goes down slightly (that would be the water content boiling off) you're good to go.

Chris......