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

[yearzero]

Hello all, need some help and advice. Got a 01 SeaRay 182 with 4.3 Mercrusier serial number M071272.

Bought the boat from a "boat club" (this was not a club boat, just something the owner picked up to "flip"). The engine has about 350 hours on it so Im guessing it sat around quite a bit all those years. We test drove it on the water and I checked out as much as I could on my own and I took her home about 3 weeks ago. We took the boat out the first weekend and it ran great but noticed that the starboard side riser was running really hot and the steering was really stiff which I knew already but tried to lube it up with no luck. While I did have it out, it ran great. Got up to plane just fine and temp stayed about 168 or so. I brought it back and he agreed to replace the steering cable and manifold. Before I bought it he already replaced the riser/elbow so that was already new.

Two weeks later I go to pick it up and he along with his "tech" was still working on it. This is where it got interesting for me.

While he did replace the steering cable and got a new manifold, he did not bother to order a new 3 inch riser which even to my untrained eyes looked like crap. Full of rust and the mating surface between the exhaust and water passages were not smooth at all. He was also using some orange Permatex stuff all over everything! The manifold gasket and between the spacer and riser/elbow were oozing the stuff all over. Even though this boat club offered to warranty the boat for 90 days I pretty much decided I dont want them working on my boat anymore so I said thank you and took it home. I already know and have on order a new 3 inch riser along with extra sets of gaskets to redo the new manifold and pull off the port side to inspect it.

Now, even tho Im running on borrowed time with that crappy 3 inch riser (why oh WHY would you replace the manifold and not the riser??) We took the boat out on the lake yesterday for a quick ride but could not get past 2300 RPM without backfire. At least I think its backfire as I never heard/been on a boat that did that before. Best I can describe is a loud POPing sound from the engine bay and seat of the pants feel like a loss of power for that fraction of a second. We turned around and put it back on the trailer. Got home and ran it under the hose and engine idles just fine. Only under load at about 2300 RPM out on the lake it was backfiring. Hey, at least the steering feels silky smooth now and pulling back upto the dock with one finger was a breeze

I did some Googling last night and this morning I checked a few things. I pulled the anti-siphon valve off the tank and it seemed fine. The little ball was clean and took very light pressure to push in. I tried to check the pick up strainer but it would not come out the tank. I lightly blew into the 90 degree fitting with my mouth to possibly clear off any gunk off the strainer and heard bubbling in the tank (I am not sure if this was a good idea or not to blow my hot breath into the tank but I figured a little wont harm much?) I checked and double checked the plug wires and cap and they all look good, but the plugs are on my list to replace soon. I went to local West Marine and picked up a new fuel/water separator filter and a bottle of Marine Sta-Bill and put about 10 oz into the tank. I poured the gas from the old filter into a glass jar but it seems like its ok, no water from what I can tell. I also used some CRC carb and choke cleaner all over and into the carb.

The engine continues to run fine at idle and up to about 1500 RPM but Im afraid to run any higher than that with no load in neutral. If I close the choke with my finger the engine dies right away (rules out a vacuum leak??) I also did another compression test and the numbers were the same as when I first got the boat home.. (around 175-180 all around)

I did not check the little filter INSIDE the carb. Could not really find it? Is it in the metal line?

Could ANYTHING with replacing the exhaust manifold cause this issue

Perhaps bad or now fouled gas? That first weekend we had it home I was not really thinking and just went to a local station to fill it up with gas. Im thinking maybe the old gas that sat there now mixed with new gas gummed something up?

Timing is always something people say to check but why would that have changed since last time?

I have not taken it back out on the water as it was getting late and other projects around the house took priority (I still stink of Florida irrigation gray water) but I may try and take her out tomorrow after work.

Any other things to check, think of? Again, could an improperly installed exhaust manifold cause backfire? Or just coincidence that this problem comes up now?

Thanks in advance.

 

[MikDee]

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

The timing could be off, take the Dizzy cap off, & check condition of that, & what's underneath. It should be electronic ignition as well.

 

[yearzero]

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

The timing could be off, take the Dizzy cap off, & check condition of that, & what's underneath. It should be electronic ignition as well.

Thanks for the reply MikDee, that was one of the first things I did. Pulled the cap off and checked every inch of each wire for cracks. Cap was nice and clean inside with no signs of arcing anywhere and the contacts showed what looked like a normal wear pattern. Rotor looked good too. The only thing I saw wrong was the paper gasket under the cap was a little rotted out.

 

[yearzero]

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

Any one else got any thoughts? (bump)

 

[Fun Times]

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

Hi there welcome to iboats! Here is your parts catalog for your engine model: http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=809969+98

The Carb fuel filter is behind the big nut where the fuel line connects to the carb. First remove the metal fuel line then with a 1 inch wrench you'll be able to remove the filter to inspect it. See item #4, 6 and everything in between. http://www.mercruiserparts.com/Show...br=100&bdesc=Carburetor(Mercarb+-+Two+Barrel)

If you are getting a back type fire sound, then it could either be in the ignition system or fuel system or small amounts of water leaking into the cylinders. Blowing air down into the fuel tank is fine to do as a test. One thing you'll want to do is bypass the boat fuel tank and get a 2-6 gallon fuel tank with new fuel line and run it with that to see if you get your power back. Also you'll want to set up a way to test fuel pressure at the Carb to see what your getting. Should be in the 3-7 PSI range. Vacuum test is important to check as well.

If your manifolds are leaking water into the engine cylinders then that could contribute to your symptoms.

It's normal to see the starboard side exhaust system to run about 20 degrees hotter then the port but not much more then that.

Placement and design of the gasket between the manifold and riser and/or elbow is critical for proper water flow cooling of the exhaust. Follow the service manual for installation. Do you have the Manual yet?

Get a timing light with a dial advance knob and be sure the ignition timing if advancing under load.

Hope you find it soon, good luck.

 

[Bondo]

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

Ayuh,.... Change that carb filter, 'n try it,...

It Sounds like fuel starvation to Me,...
If the filter change don't fix it, I'd go for a Carb Rebuild,...

 

[cliffblue]

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

While the timing should not have changed, it would be easy to bump the distributer while wrestling those manifolds off and on. I would check the timing.

 

[yearzero]

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

Thanks everyone. Gives me more ideas to check FUn Times, those links are really helpful. The new riser should be here by today so before I take it out again I'm going to change replace that and inspect the other side as well.

Can't understand how I missed the carb filter but looks easy enough to check out and replace Sounds like a timing light and fuel pressure gauge is on my list of new tools. I had a light once but got left behind with the ex wife. Lol.

Question? I thought I read someplace that the fuel pressure should be a certain value even at idle? Are the fuel pumps serviceable? The more I think of it the more I think it's bad/old gas since the boat sat for so long and I put about 3/4 of a tank of fresh gas in the first day

 

[harleyman1975]

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

It is possible that they got the firing order messed up. It will run without popping until the ign advances then it fires the plug that is transposed when the intake valve is open hence the pop only at higher RPM's so check that. Otherwise Im thinking main jets in the carb might be plugged up some.

 

[Scootimus]

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

OP, does this happen after the engine warms up a bit or right out the gate? I've been having a problem with mine after it warms up and has been running for a bit. Mine will start to backfire through the carb and will do it so much that it causes the boat to come off of plane. If I keep it below 2300 rpm it will usually run enough to stay on plane and get me back to the landing. The last time I was out with my father as a spotter he noticed that water started to leak out between the manifold and the riser under high rpm/heavy load. I ordered a new gasket set and have installed them. We were thinking at it could be possible that since the water was leaking out that it could have been getting in to the engine enough to cause a misfire. We will be testing the boat this week with hopes that this was the issue. Just curious if you could have the same type of issue if they are just trying to seal the hell out of it with the wrong thing.

 

[yearzero]

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

OK I finally got a chance to put the boat back in the water today after replacing the riser and checking/replacing a few other things. Happy to report its no longer back firing but something is still not right as its VERY sluggish and wont go past 3200 RPM.

To Recap, had a old/bad/leaky? starboard riser and replaced it. When I took the old one off I found a PUDDLE of water sitting in the manifold. Not sure if that was causing my misfire/backfire issues but no doubt it was BAD.

As per suggestions given here I also replaced the fuel/water separator, checked the cap and wires, checked the anti siphon valve, replaced the carb inlet strainer filter and finally checked and adjusted the timing. I figure these are all good things to replace anyway since I just got the boat about a month ago. The only thing I have not checked yet was fuel pressure.

When I checked the timing, it looked to be about 1-1.5 degree off so I tweaked it and got it dead on 10 BTDC as per the manual. (yes I made sure it was in BASE timing mode by grounding the pur/white wire).

So now the boat does not backfire and engine runs ok, idles smooth and propels me forward but fastest I can go is about 25-30 MPH at around 3200 RPM and seems to take forever to get up to plane. Granted the water was really choppy today but I remember getting up to speed alot faster than I could today.

Could adjusting the timing to "spec" cause such a drastic decrease in performance? I figure I will play with timing while out on the water and look into renting/buying a fuel pressure setup

To Scootimus, I am sure others will agree that if water was leaking out the gaskets to the outside there is a good chance water was leaking INSIDE as well and based on my experience that led to misfires. How did the risers/manifolds look internally? My risers matting surfaces looked really bad and corroded so thats what probably led to water leaking. As others will say its critical that a good seal is made between those components, which means that the machined surfaces of riser to manifold is solid. When I put the new riser on I lightly sanded the paint off to bare metal and of course used fresh gaskets and torqued everything to spec. If yours were leaking I might suggest taking a closer look at the manifold and risers. I consider myself pretty lucky (and you might be as well) that I found the water leakage before some serious damage.

 

[yearzero]

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

Forgot to add that I noticed two things about when I adjusted the distributor.

First thing I noticed was when I loosened the clamping nut I had to use both hands and lots of arm to twist the distributor. Leads me to think it was never ever adjusted. (boat is a 2001 with about 350 hours)

Second thing I noticed was when backing out the dock as I shifted the engine sounded like it was about to die. I know this is because of the ignition interrupt switch thingy mechanism kills power to release strain on the gears however the other times I took the boat out and the couple times I shifted in/out of gear while in the driveway it did not seem to behave this way.

I could be wrong but makes me think messing with my timing made it worse?

thanks in advance

 

[Bondo]

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

Forgot to add that I noticed two things about when I adjusted the distributor.

First thing I noticed was when I loosened the clamping nut I had to use both hands and lots of arm to twist the distributor. Leads me to think it was never ever adjusted. (boat is a 2001 with about 350 hours)

Second thing I noticed was when backing out the dock as I shifted the engine sounded like it was about to die. I know this is because of the ignition interrupt switch thingy mechanism kills power to release strain on the gears however the other times I took the boat out and the couple times I shifted in/out of gear while in the driveway it did not seem to behave this way.

I could be wrong but makes me think messing with my timing made it worse?

thanks in advance

Ayuh,... I'm guessin' ya mighta moved the controller too slowly, causin' the stumble ya heard,...
When shifted Briskly, you barely notice the stumble,...
On the wagon, it don't work, as it needs the water's resistance against the prop to activate the switch,...

 

[Scootimus]

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

To Scootimus, I am sure others will agree that if water was leaking out the gaskets to the outside there is a good chance water was leaking INSIDE as well and based on my experience that led to misfires. How did the risers/manifolds look internally? My risers matting surfaces looked really bad and corroded so thats what probably led to water leaking. As others will say its critical that a good seal is made between those components, which means that the machined surfaces of riser to manifold is solid. When I put the new riser on I lightly sanded the paint off to bare metal and of course used fresh gaskets and torqued everything to spec. If yours were leaking I might suggest taking a closer look at the manifold and risers. I consider myself pretty lucky (and you might be as well) that I found the water leakage before some serious damage.

There was a little bit of crystals in the exhaust to show that moisture was present. Not a whole lot but it doesn't take much water in a cylinder to shut the engine down. There did appear to be a couple of areas on the gasket that may have been allowing water to seep where it shouldn't have been. I'm hoping that I've caught this in time to avoid any internal damage as I know the hot internals don't like to be splashed with water either. I fired her up and she purrred like normal. Sea trial will be in the next day or two.

Hopefully you can find the issue with your planing and low rpms.

 

[funk6294]

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

Did you replace the sparkplugs? It's possible that when they were changing the manifold that they let the riser hit the plugs and cracked the porcelain. You might also run another comp test to ensure the leaky riser didn't hurt anything. Btw, I am assuming that when you first got the boat it was capable of hitting target rpms.

 

[MikDee]

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

Firing order 4.3 V6, 1-6-5-4-3-2 clockwise, check your wiring. By the way, I've had the same thing happen on occasion when shifting, Bondo explained it well.

 

[yearzero]

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

Ayuh,... I'm guessin' ya mighta moved the controller too slowly, causin' the stumble ya heard,...
When shifted Briskly, you barely notice the stumble,...
On the wagon, it don't work, as it needs the water's resistance against the prop to activate the switch,...

Im guessin yer right. That first time back on the water I was taking it really easy not wanting to push anything at first.

There was a little bit of crystals in the exhaust to show that moisture was present. Not a whole lot but it doesn't take much water in a cylinder to shut the engine down. There did appear to be a couple of areas on the gasket that may have been allowing water to seep where it shouldn't have been. I'm hoping that I've caught this in time to avoid any internal damage as I know the hot internals don't like to be splashed with water either. I fired her up and she purrred like normal. Sea trial will be in the next day or two.

I believe its totally normal to have some water mist or crystals like you describe mixed in with the exhaust out the prop. Remember...after the elbows the water from the manifolds and hot exhaust gasses are actually mixed together as it goes down the y-pipe past the shutters.

Hopefully you can find the issue with your planing and low rpms.

Did you replace the sparkplugs? It's possible that when they were changing the manifold that they let the riser hit the plugs and cracked the porcelain. You might also run another comp test to ensure the leaky riser didn't hurt anything. Btw, I am assuming that when you first got the boat it was capable of hitting target rpms.

I have not replaced them yet but its on my list. I did check them visually and also did another compression test. Got the same numbers all around as when I first got the boat. To be honest, I dont recall what the max RPM was when I first got the boat but I do remember being able to get on place MUCH quicker and seat of the pants tells me I was able to get higher RPMS.

Firing order 4.3 V6, 1-6-5-4-3-2 clockwise, check your wiring. By the way, I've had the same thing happen on occasion when shifting, Bondo explained it well.

Yep, checked firing order and even pulled a wire or two to confirm a change in idle to make sure it was running on all cylinders.

 

[yearzero]

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

Update.....New issue found?? Possible cracked block? I love turning a wrench but Im at the point where I just want to enjoy my boat :grumpy:

So....yesterday I picked up new plugs, cap and rotor....Rechecked the timing.....Then I remember reading that too much oil could cause you not to reach full RPM like I had last time I went out so I decided to drain a little as the dipstick was always showing on the high side. Well...when I pulled the drain hose out and took off the plug hardly anything came out...I disconnected the quick drain hose from the pan and still just a trickle of oil into the bilge and it was milky brown (uh oh??) I cleared it with a ziptie and drained everything out. Both the drain plug/fitting in the pan and the quick drain hose was full of gunk/mud. When I blew out the quick drain hose to clear it to reinstall I did it with water pressure using a small jet nozzle fitting on my garden hose I had what looked like brown POO come out the other end. Needless to say I was not happy to see such gunk/mud and milky brown oil. If you recall as I originally posted above I had a bad leaky riser but I didnt think water could get down into the crankcase?? Can it, or am I looking at a cracked block? Head gasket??

I went ahead and changed the filter and put in cheap 10W40 from the auto parts store and ran it again today. It actually ran better than before...I could get up to about 3900 RPM and power seems to be back but not quite there where I think it should be....It could be the new plugs, cap/rotor....could be I got the timing better....could be the fresh, non agitated overfilled crankcase?? It still backfires a little under load...Mostly when running up to about 3/4 throttle...If I accelerate slowly its fine....If I "floor it" its fine....It only backfires when I set throttle to about 3/4. I figure a carb rebuild is next on my list but now with this milky brown oil I think I have bigger problems to deal with.

Anyway...since temp and oil pressure seemed to be fine while I was out today.. on our return trip back I was playing around with a few WOT runs and almost got up to 4k RPM (I need to check my prop and maybe get advice on that) but then I notice that the oil pressure did DROP from the usual 40 to about 25-30. Even when I got back home and flushed it on the muffs the oil pressure was low to what I usually had. Could this simply be due to the 10-40 auto oil I put in temporally or did I awaken some kind of sleeping dragon inside that engine.

When I got back home I drained the oil I put in yesterday and sure enough it was already like chocolate milk.

What should I do? Go for another jug of fresh oil/filter a few more times to see if the contaminated water/oil cleans itself out or figure the block is cracked and start saving my pennies? Check the head gasket?

One thing that has me baffled is the little plastic hoses that come out the valve covers and run to the flame arrestor. I know they are to vent the gases from the crankcase back into the carb but they seem to be venting an awful lot of moisture. Almost like a steam. When I pulled them both off today water was dripping out. Its obvious to me that where ever this moisture is coming from its clearly dripping back down into the valve covers. Im just confused if this is BECAUSE I ALREADY have water in my engine oil OR is this is what is putting the water IN? Where is this moisture coming from and which way is it supposed to go?

Thanks to all who have replied so far...This place has been a great help but Im starting to wonder if this purchase was a mistake. Hate the idea of having to source a new engine or block after just a few weeks :facepalm:

 

[cliffblue]

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

Hey YZ, I started out with the same oil issues after I bought my first and only 2001 4.3 I/O three years ago. I got it from a guy that bought it as a repo. You haven't said if you had changed the oil before the previous post. I found the same as you on my first oil change, gunk! Not having a pump out unit, I wrapped a clean rag around an air line and pushed around 5 psi of air into the crankcase at the fill tube to motivate the oil out the drain line. When I saw burping at the drain, I knew it was all out. I wasted Quicksilver on the first change but added an oil flush and ran it per instructions before dumping it. I went back with the cheap stuff next, then back to QS 25-50. I believe the oil had almost never been changed. Maybe because the way the dipstick does not go into the crankcase, but pipes into the drain. The oil on it always looked great. I also pressure tested the water jacket to 20 psi that held 24 hours. It has never increased oil level, but always looks milkshake at the end of season oil change. I just finished going through the top end to check intake and head gaskets, but they all looked fine. There was plenty of "gunk" in all the little traps on the top of the heads and in the valley. I had the heads checked and redone. They checked out fine. You can search my name to see some of it. Got it running yesterday. You said the oil was high, is the oil level increasing after running a while? If not, maybe some extended run time will clear the moisture from the crankcase. I now believe my milkshake oil is condensation due to short run times most of the time. Couldn't hurt to rebuild the carb. I had to clear a piece of crud left behind after evaporation from one of my jets. If you have the Mercarb, it's pretty easy. Check the plastic spacer under the carb. I've always had a cold engine stumble till it warmed up. I just found during this last repair that the spacer was warped and I'm pretty sure it was my vacuum leak problem. The new spacer has additional webbing under it. Good Luck! Cliff

 

[MikDee]

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

How do the plugs look? any of them look steam cleaned? That would be a clue to water in that cylinder. The backfire might be another hint.