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

[Maclin]

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

Backfiring can indicate bad valve sealing, probably time for a compression check.

Backfiring can also indicate a lean condition, what is condition of the carb? What do the spark plugs look like?

The steam from the valve cover vents is from moisture in the crankcase getting boiled off. A little every so often after it has sat a while is ok, but should not be constant. Indications of water in the oil but you already know that.

The low RPM's and lower level of power could be a timing issue.

 

[Maclin]

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

By "timing issue" that includes mechanical or electronic advance not working, depends on the type of ignition.

 

[Volphin]

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

Well you found out that the motor was oil starved. I'd change it with cheap o stuff a few more times after each day and see how it looks. If the block is cracked, $1500 or so will get you a short block you can install in a weekend.

 

[yearzero]

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

chcliffb, this IS the first time I changed the oil...PO said he had just done it but not sure if he really did or just said that to sell the boat.. Like you....each time I checked it the oil looked great...just seemed to be high which is why I went to drain some out and led me discover the milkshake. I like the idea of using air to force out the oil and maybe Ill try that next.

MikDee...since the plugs are new they all look OK except for number #4 which looked a little wet...I remember even when looking at the old plugs the number 4 looked different than the others. If there is a problem I bet its around that cylinder.

Maclin...I did a compression check before and got around 170-180 on all 6 cylinders. I will check it again. The carb seems ok but given the limited history and my guess that the boat sat for a while I plan on dong a rebuild this weekend.

Thats a good explanation of the steam and makes sense now...Lots of oil in the water means it has to boil off....Question is why is there so much water?? As far as timing goes I am pretty sure Im doing it right.... I ground the pur/white wire and start it up...set it with the light and unground wire. Is it possible the computer/controller thingy is not advancing it when it should be?? Is there a way to check that?? Run it under load at high RPM on the water and use the light while my wife steers the boat?? I have the Thunderbolt V BTW

Volphin....Good to know my thought of using cheap oil to flush it out is sorta the way to go...Are there any other methods of flushing engine oil that I might want to try? Since I am in Florida I already figure IF I do need a new block Ill probably get a long block from Rapido and pick it up myself to save shipping....(if they do that?) Not sure how Id be able to get it done in just one weekend...lol....My biggest unknown is how to pull the engine off the boat on the trailer...I can rent a hoist but they wont go as high I think? Rig up a hoist to my garage ceiling? Might just do as much as I can at home then pay a shop to yank the old one and drop the new one in.

Thanks to everyone again...At least this gives me a little hope.

 

[funk6294]

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

If you need to rent a hoist to pull it I was able find a high lift hoist from Ahern rentals that was easily able to pull the engine out and over the side. And I think it only ran 20-25 bucks a day.

 

[Walt T]

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

Backfire, then no power, saw puddle in manifold, milky brown oil, owner said he changed the oil no reason to doubt that, Well gee seems pretty obvious fellas. Owner changed the oil because he knew darn good and well what was going on. Manifolds/ Risers hopefully the only thing wrong, and the very first thing I would check.

They saw him comin..

 

[yearzero]

Seems like starboard side of engine has no spark??????

Seems like starboard side of engine has no spark??????

Ok, so Ive been trying different things to troubleshoot my low WOT RPM/power and backfire issues....I replaced the plugs, cap, rotor, fuel water filter and carb filter. I did NOT replace the wires because the store I went to did not have them in stock and they checked out ok. I tested each one with a multimeter. I dont remember exactly what it was but somewhere around 9-11K ohms on each one. I had also checked timing and attempted to check fuel pressure but didn't have the right fittings for the pressure gauge I rented today. My original thread is here discussing this along with some other issues.

http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/4-3-backfires-above-2300-rpm-just-put-new-exhaust-manifold-fuel-issue-643928.html

Anyway....today I had the engine running on muffs and even tho I had previously checked the plug wires I decided on a whim to yank one while the engine was running...TO my surprise the idle speed did not change much at all. I began to systematically check each wire. What I found was any of the wires on the starboard side of the engine (2,4,6) could be pulled off the distributor cap with little to no effect on idle speed. To be sure I SWAPPED WIRES from one side to the other..(changed both plug and dist. ends of course to maintain proper firing order) I could actually pull all three off the starboard side and it will still idle. The RPM seemed to increase but it still ran.

If I pull a single wire off the port side. (1,3 or 5) The idle drops and runs rough. (er?) If I pull another one the engine dies. Its like the engine is only running off the port side.

I took an old plug and plugged into 4 and then 6 and held it to a ground and saw a spark....It did look rather weak but so did the other side (cylinder 3) and it was one of the old plugs. Bad coil maybe but wont explain why it only seems to produce power on 1, 3 and 5?

What could be the issue with this? Cant be normal? Seems like that whole side of the engine is not grounded but that cant be possible? There is a different brand of exhaust manifold, riser than the port side but I cant see how that would have anything to do with it.

Could this engine even run on only 3 cylinders? That would certainly cause loss of power/backfire and makes me think its something really simple.

Thanks in advance for any help and ideas!

 

[achris]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

So, I have that it's a V6... But WHICH V6? Carbbed? 2 bbl or 4, Thunderbolt IV or V or TBI or MPI????? We do ask people to provide engine model, year and Serial number. As there are so many different variations of similar engines it does make it different without my crystal ball (in for it's 50,000 guess service).... V6s have been used by Merc since 1983...

Chris.....

 

[yearzero]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

So, I have that it's a V6... But WHICH V6? Carbbed? 2 bbl or 4, Thunderbolt IV or V or TBI or MPI????? We do ask people to provide engine model, year and Serial number. As there are so many different variations of similar engines it does make it different without my crystal ball (in for it's 50,000 guess service).... V6s have been used by Merc since 1982...

Chris.....

Sorry Chris My bad, I just assumed since I referenced my original thread that info was already known and this problem has me so spooked I could not wait to post this puzzle hoping someone can help...lol

Its a 2bbl 4.3 Thunderbolt V S/N M071272 2001 Sea Ray 182

 

[achris]

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

By "timing issue" that includes mechanical or electronic advance not working, depends on the type of ignition.

Merc 4.3s have never had mechanical advance....

 

[achris]

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

....why oh WHY would you replace the manifold and not the riser??....

Because it was cracked, and leaking water into the engine... the old style 'wet-joint' ELBOWS should be checked every couple of years with a view to replacing at 4-6 years.... Dry-joint elbows appear to be lasting a lot longer. I am just about to replace my originals (8 years old). One of the other boats with the same year engine has just replaced his, also 8 years old... And they just clog up on the exhaust side of things, no rust or damage to the gasket surface areas...

Chris.....

 

[Bt Doctur]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

I would think a good compression test would be next. you need spark, fuel, compression to make horsepower
Has this motor ever been overheated? Has this motor ever had the heads removed?

 

[achris]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

That's ok... I look at over 200 threads a day so I tend to not remember too many individual ones, and it's just easier to ask (or for you to post) the make, model, year and serial number in the relevant thread each time. It also makes it easier for new people to understand that we do ask this in the opening post... Often I will refer back to the OP for these details if the thread starts getting long and it does get a bit frustrating to have to scroll down looking for the information... anyway....

As the coil is common for all plugs if you are losing spark on one side (of the engine) it could be the rotor, dissy cap, leads (unlikely to be only 3 and all on one side) or a bent distributor shaft.... The firing order is 1,6,5,4,3,2.... Check you have the right leads in the right holes... That could also give the impression some sparks are not there.... Especially if the engine sped up when you disconnected one of the leads....

Chris....

 

[Bt Doctur]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

Reading the previous thread on this motor I believe it has valve seating issues from the water found on the even side of the motor.
Betting the comp test comes back bad on 2,4,6

 

[achris]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

It looks like this and the other thread are crossing over, so I am going to merge them....

Mod....

 

[yearzero]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

I would think a good compression test would be next. you need spark, fuel, compression to make horsepower
Has this motor ever been overheated? Has this motor ever had the heads removed?

Boat is new to me as of about a month ago so I don't know if its ever overheated. I did a compression check twice during all this and get around 180-170 all around. Ill check compression again tomorrow.

I should note that the very first time I took the boat out the day I brought her home it ran fine. No backfires, got on plane real easy and felt fast. (compared to the Catalina 22 the family and I are used to being in...lol) Spedo was not working at that time so I could not record a top speed and cant remember what my max RPM was. I had brought the boat back to the place I bought it to replace a bad steering cable and he also changed a bad manifold and thats when these problems started. Due to what I feel is bad workmanship, lack of training ect...I choose not to bring it back to him and tackle the repairs myself. For what I paid for the boat I aint' mad yet but I do want to work all these things out sooner than later. IF there are any major expensive repairs then I will go back to him and ask for some kind of compensation and/or have him honor the 90 day "warrantee" that I did get in writing but thats a conversation Id like to avoid if possible. Unless Im looking at laying out thousands for a new engine I feel better fixing these things on my own.

 

[yearzero]

Re: Seems like starboard side of engine has no spark??????

Re: Seems like starboard side of engine has no spark??????

Chris..thats just the thing...they have spark....I verified using an old plug held to ground. I saw (and FELT! lol ) spark. I double..triple checked firing order...I even verified TDC of number one using the "finger test" while cranking the motor by hand to find where the rotor was pointed.

Bt Doctur, that side of the motor is the one that had the bad manifold and where I saw water sitting. I don't remember if I mentioned this before but no. 4 plug looked a little spotty compared to the others. Valves or compression are the only logical thing to blame at this point but like I said...I got good numbers all around. I just went to the garage and got my notes...1=178, 2=175, 3=172, 4=180, 5=180, 6=175

UGHHH if it weren't night time Id go out there right now and do another compression test to make sure. This is killing me!

 

[Bt Doctur]

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

one of the posts mention a lot of vapor coming out the vent. I had a V8 doing the same thing . slight discoloration of the oil , no power,etc.
I found a busted exaust valve spring.it was allowing water to be sucked into that cylinder.
Easy to test for, remove the valve covers ,get a small hammer and TAP ,NOT HAMMER the rockers looking for a soft one.
If those number remain the same then this motor should run good .

 

[achris]

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)....

 

[yearzero]

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

one of the posts mention a lot of vapor coming out the vent. I had a V8 doing the same thing . slight discoloration of the oil , no power,etc.
I found a busted exaust valve spring.it was allowing water to be sucked into that cylinder.
Easy to test for, remove the valve covers ,get a small hammer and TAP ,NOT HAMMER the rockers looking for a soft one.
If those number remain the same then this motor should run good .

Taking off the valve covers was something I was thinking of doing soon anyway so Ill try that first thing tomorrow morning. Im a little confused, how would a broken valve spring let water in? Assuming there is NO more water in the exhaust manifold due to cracks? Or is it by the design of these systems there is always a chance of water getting sucked way back down there if valves were not closing properly?

I have actually never really worked on valves/rockers before so what would a soft one feel like? Just not as stiff as the others? Would a broken spring be easily seen by eye? Number 4 is my top suspect right now. That spark plug looked different from the others and even after I put the new ones in last weekend and pulled it it looked funny.

Thanks for the advice. Ill post my findings tomorrow.