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Ztrem

Loss of power, backfiring, not sure what to do.

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So last week was the first time with the boat in the water, no problems, ran great. This week, not so good. While the boat is in neutral, I can rev the engine up to 5-6000 Rpm, sounds perfect. No backfiring when boat is in nuetral. When I put it in gear, there is hardly enough power to get on plane and the boat backfires intermitantly. If I move the throttle back and forth quickly, it seems to help get the RPMs up high enough to get on plane.

So far I changed the fuel filter and changed the distributor cap and rotor. I am not sure what else to do. Any and all suggestions appreciated. I have a 4.3l MPI. Recently had the outdrive removed and serviced, I don't see how that would matter but I thought I would mention it just in case.

And.........I hope all of your mothers, wives, and daughters have a wonderful day today.

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Thanks Halbert. I changed the IAC towards the end of last season. When it went bad, there was a steady warning alarm beep. With this current problem, there are no warning alarms. Also, the engine idles perfectly.

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Wonder if you're down a cylinder. A fuel injected engine can mask a dead spark plug at idle. Try moving the engine cover, and with the engine running, look at the spark plug wires where they connect to the spark plugs themselves for a blue spark where the spark is ground out on the head, or listen for a 'snapping' sound.

I'd also take the dist. cap off; maybe it's gone bad on you from corrosion or an internal failure under the plastic. (there was a MerCruiser recall on their V8 MPI small block distributor caps puking, but it did not include the V6 MPI dist caps for whatever reason.

I take it you have the audio self-check beep when you turn the key to the 'on' position from 'off'? (comes on once or twice, and then goes away until the next time the engine is shut off and then turned back on) If so, and the engine is running rough, then its a mechanical problem such as an ignition component, or a fuel pump has gone south on you...or the shift interupt switch or shift anticipation mode switch has stuck, screwing with the timing.

On the dist cap and wires, did you change out one wire at a time? Mistakes like putting # 4 wire on # 2 terminal on the cap can happen. Wingnut has mentioned it before, but a NAPA Gold dist cap might be worth the price to find the culprit. That and changing out the spark plugs. NGK TR55IX, NGK stock # 7164.

Lastly, take off the water seperating fuel filter, and empty the contents into a container. Allow the fuel from the filter to settle for a few minutes, than come back and see if there is any water in it. Put a new fuel filter back on if you see signs of water.

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Thanks for your replys. I changed the cap and rotor and the fuel filter. I number the plug wires when I remove them, so I think I am good there. When I turn the key, I get the beep, then a whirring sound, then the boat starts and idles fine. When I rev the engine in idle, no missing, no backfiring. Sounds like a Ferrari. Put it in gear and I can't even get up on plane, unless I pump the throttle and build RPMs. The suggestion of the shift switches is intriguing as I did not know the boat even had such a thing. Can you tell me where they are located? I might change them just to make sure. I was thinking next step to look for the arcing plug wires and change the plug wires one by one, starting with the coil wire.

Thanks again for all of your suggestions. As usual, very helpful and much appreciated.

Kevin

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Later MerCruiser Alpha 1 Gen II MPI engine runs a shift anticipation mode. Helps take away a little timing to reduce RPM when it notices that the shifter is heading towards neutral. The shift interupt switch kills the engine for a second to help take away load when shifting into neutral.

I've seen the shift interupt switch be a problem on an older 4.3L EFI above 4000 RPM - ran fine below 4000 RPM (bad switch was messing with the engine timing) I'm just grasping at straws here. Disconnect the shift interupt, and see if the boat will operate properly. NOTE: do it out away from everyone, as it will be a bear to shift!! Located up on top the engine.

http://www.marinepar...16002/12839-290

Lastly, maybe you have some bad fuel or block fuel pick-up. Could always hook up an outboard tank with straight gas (no oil mix) and see if you can get the boat to function properly.

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Had not thought about the gas. I just refueled last week. Boat ran fine prior to refueling. Is there a way to test gas? I am not comfortable running with an exterernal tank. I am not sure how to do that safely.

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I had this problem and it got rapidly worse to the point that the engine wouldn't start. Long story short, the anti siphon valve at the tank was cross threaded (from the factory that way) and it was sucking air. The sealant they used kept it running fine for a few years before it started to break down and let in more air.

Reading codes didn't help diagnose the problem. Old fashion systems knowledge fixed it. I started at the fuel pick up and worked forward in the system until I found the problem. You will have to do the same. It could be any number of things like a cracked pick up tube or clogged pre filter. A quick test to see if there is air in the system is to insert a short section of clear hose before the filter and run the engine. I'm not comfortable doing this because I have never found a fuel compatable clear hose and don't like gas + ignition source near my face.

These fuel injected engines either run or they don't. Air in the fuel system is one sure way to shut down the system.

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Thanks for the comments Ben. Gives me something else to check into. I think I should just buy a new boat :)

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Have you had a code reader hooked up to check for ECU error codes. It sounds to me like a TPS is acting up. It sends the throttle position information to the ECU. Could be it's sending the wrong information and the ECU is putting the engine in safe mode.

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On the Mpi engines, is the timing advance electronic? I ask because it sounds like the timing may not be advancing as throttle is applied.

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Thanks for all of the great comments. As a "do-it-yourselfer", I am going to start eliminating the things that I can do myself. I think first I will drain the gas tank and add some new gas. I have about 20 gallons or so in the tank, so any suggestions on how to do that would be appreciated. If that does not work, I am going to replace the plug and coil wires, then spark plugs, then ignition coil. If none of those work, then the shift interupt switch and shift anticipation mode switch. These seem easy and inexpensive and should be done anyway.

If none of these work, I cry uncle and turn it over to the pros. I guess the one thing I keep thinking about is that the boat ran fine the first weekend out. I did nothing to it. Then this problem started suddenly the very next weekend. It did not come on gradually, getting worse with each outing. The only change I made was to fill up.

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I honestly believe that getting a 3.2 gallon outboard tank and fuel line will be easier and cheaper than to remove the fuel from the fuel tank which may be fine.

What we do in such a case is to remove fuel line from the engine at the water seperating fuel filter. Plug the fuel line with a bolt, etc. Remove the outboard engine quick-connect from the outboard fuel hose, and attach the outboard fuel tank line to the engine.

NOTE 1: if the outboard tank is above the attachment point on the engine, fuel will want to gush from the line due to gravity. Buy an outboard tank that has a quick-attach fitting on the tank itself so you can easily remove the entire fuel line from the outboard tank. (plug and play style vs. permanetly attached)

NOTE 2: Route the fuel line in such a way that the serpentine belt or any pulleys cannot touch or snag the fuel line while underway.

Once the outboard tank fuel line is attached to both the engine and outboard fuel tank, push the primer bulb until you fell the primer bulb fill with fuel. If everything is good and clear, and no fuel is found to be leaking, start the engine, and take it for a short run. (3.2 gallons of fuel will NOT last long!!) I think you'll know in several minutes if the problem is fuel related, or something else.

NOTE 3: To remove the outboard fuel hose, disconnect from the fuel tank, and run the engine for a couple of seconds. This should drain most of the fuel in the line, making for less of a mess when you remove the line from the engine.

As regards engine timing on your particular version of 4.3L MPI MerCruiser, the timing is set by the ECM. I think you should start with fuel, then move on to spark, and if that doesn't cure it, then call in the pro's.

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Thanks Sea Lord. I really appreciate your taking the time to layout a path forward. I am going to give it a try. Just for kicks I looked up the marina where I bought the gas. I wanted to know if they received any other complaints. They said no, but asked if I put a fuel stabalizer in over the winter. I did not. I had less then 1/4 tank and did not think it was necessary. He went on to say that he thinks what may have happened is the fuel separated over the winter, meaning that the gas(heavier) moved to the bottom of the tank and the ethanol(lighter) moved to the top of the tank. So, initially when I ran the boat it was running on the more rich gas that was in the bottom of the tank. When I added additional fuel, this caused the ethanol to get disturbed and be consumed by the enigine as a larger percentage of the gas/ethanol mix as it was not completly mixed with the gas. He thinks the richer(unmixed) ethanol clogged an internal fuel filter. If you are tracking with me, I guess this kind of makes sense. Is there another fuel filter that I might need to change? Does this sound like it might be the problem? I think the external gas tank is still worth trying. At least that will isolate this as a fuel related problem.

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Only other fuel filter on that engine are the screens on the fuel injectors themselves. If it is found the injectors are clogged, they can be cleaned for not that much money.

Some of the earlier (MY 2000-2002?) MerCruiser MPI engines had an in-line fuel filter on the fuel line from the fuel tank to the engine; attached to the boat before the water separating fuel filter on the Chaparral's at least. Mercury part # 35-864572 stamped on the side of it. Merc stopped using it around My 2002; probably found it wasn't needed, and it cost a lot.

Unstabilized fuel, especially if the original fuel had ethanol in it, could certainly go skunky on you. Your boat's fuel tank is vented to the atmosphere unlike your car, so things can go south very quickly. If there is any place on the water where you can get ethanol-free fuel in future, it would be worth it IMO.

NOTE: new 2012 246 SSi WT has a new fuel system installed much like an automotive type, where the fuel can't leak out onto the swim platform when being filled, (actually works) and is not vented directly to the atmosphere. (I forget what the system is called...mandated by the EPA)

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Ethanol in boats causes all kind of problems. Below is a link that will inform you on those problems. If your fuel sat all winter with only 1/4 of tank of ethanol fuel and no treatment like Sta-bil Marine in the tank you have fuel seperation. The only fix is to get rid of the fuel. Once it seperates it will not mix back even with treatments.

http://www.fuel-testers.com/about_ethanol_fuel.html

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On the Mpi engines, is the timing advance electronic? I ask because it sounds like the timing may not be advancing as throttle is applied.

To Duane's point, is the distributor assembly tighen down properly to not allow movement (advance/retard)?

Usually when you get a "backfire" the intake valve is open to allow this to happen. If the valve is open when the plug fires, usually the ignition is firing at the wrong time, hence a timing issue.

Even with electronic ignitions, there must be a point of reference that has to align with engine position.

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If the valve were not seating properly, I would think the backfiring would happen consistently. Instead, it only happens intermmittantly, there does not seem to be a pattern other the higher RPMs and under load. Strange?

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If the valve were not seating properly, I would think the backfiring would happen consistently. Instead, it only happens intermmittantly, there does not seem to be a pattern other the higher RPMs and under load. Strange?

He didn't say the valves werent seating properly. He said check your distributor is tight and he implied that you may want to verify your timing is on par. Most auto engines run at 10 deg. at idle with no advance. Not sure if boats are same, but should be within a couple deg. either way. If your timing is off or not advancing as rpms go up, then under no load you may not have any issues. Yet under load, the engine could bog, backfire, and run like poo.

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Thanks again for all of your suggestions. I am off to the Jersey Shore this morning to see if I can find the source of the problem. I think I will take Shepards advice and try to eliminate something fuel related(bad gas, clogged filter) as the problem. If that does not work, I will move to ignition components. If that does not work, I drop it off at the marina.

Thanks again for all of your input. I will let you know how I make out.

Much appreciation,

Kevin

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Well, had a friend of mine change plugs and wires, also ran the boat on an external fuel tank with new gas. No change, still running very rough, no power, backfiring. Also disconnected switches. No change. I think it is time for the pros. Thanks to all for your suggestions and help. I really appreciate it.

Kevin

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Can I adjust the timing on my own I dimissed(wrongly) timing as the issue because I thought it was electronic and did not have to be adjusted manually. I guess when I think about it the sysptoms are classic bad timing. I am going to be so pissed at myself if that is the problem and I ignored it as a possible issue.

Thanks Bob and Betsy.

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