NEED HELP Marine Power 340 running like crap

[adamsjstt]

This really sounds to me like old gas chunks in the line somewhere. Have you pulled all the fuel lines and cleaned them out? Especially the line from the tank? You say you drained the old gas. Did said gas sit for an extended amount of time with no stabilizer? When you drain a tank is when the floaties can get sucked up into the system.

It would be a real pisser to find out it was something simple after checking all the hard stuff first.

I will be starting with fuel lines and pumps first when I get to the boat. Not sure how long the gas was in the boat, I just bought it , I need siphon out all the old gas before I put it in the water.

[adamsjstt]

Anyone know if you can plug these motors into a normal automotive scanner? And where is the plug in location?

[NICKYPOO]

Not sure how long the gas was in the boat, I just bought it , I need siphon out all the old gas before I put it in the water.

Make sure to blow out the pick up valve on the tank itself. It should have a check valve on it that you'll have to contend with.

It ain't pretty but, sometimes all the boat needs is a quick blow job. Just be careful not to take a load in the face when it comes shootin' out.

[adamsjstt]

Started at the fuel tank, checked the pick up tube and check valve and the hose going to the low pressure pump, every thing is free and clear. Low pressure pump seems to be working fine, plenty of fuel comming out. High pressure sounds good but i will check pressure when i get a gauge (tomorrow). I am going to ohm test the wires, not sure of any other way to check the wires. And the paddle wheel on the bottom spins free and nothing is broke

[adamsjstt]

Ohm tested the wires #1 972 #2 975 #3 793 #4 798 #5 724 #6 713 #7 never held steady it bounced around between 17.00K ohms and 35.00K ohms #8 558 so it seems to me that #7 wire is bad. Also did another compression check with all plugs removed and #1 175 #2 162 #3 150 #4 160 #5 155 #6 155 #7 145 and #8 165. So I will start with plug wires and go from there

[Dunker]

I had a similar problem about a month ago on my 2006 marine power 340hp. The engine would idle fine but when I started to get going it would have a slight sputtered and almost sounded like some popping or slight backfire from the exhaust, I still seemed to have full power but just didn't sound or feel right. Once I started going through everything I noticed the black plug on my knock sensor was broke and the plug on the wire going to the sensor was not able to clip in securely, and I guess was not making a good enough connection. I went and got a new knock sensor (I think it was around $60) and the boat has ran perfect since (i have put about 30 hours on it so far with no more problem. Not sure if this could be your problem but you may not want to overlook the knock sensor.

[NICKYPOO]

I had a similar problem about a month ago on my 2006 marine power 340hp. The engine would idle fine but when I started to get going it would have a slight sputtered and almost sounded like some popping or slight backfire from the exhaust, I still seemed to have full power but just didn't sound or feel right. Once I started going through everything I noticed the black plug on my knock sensor was broke and the plug on the wire going to the sensor was not able to clip in securely, and I guess was not making a good enough connection. I went and got a new knock sensor (I think it was around $60) and the boat has ran perfect since (i have put about 30 hours on it so far with no more problem. Not sure if this could be your problem but you may not want to overlook the knock sensor.

I hope it is something simple like that.

[adamsjstt]

I hope it is something simple like that.

Thanks nickypoo im keeping my fingers crossed.

I cut the ends off wire number 7 and ohm tested again and it ohmed at 486 so i replaced the ends and put it back on. Also I heated up the knock sensor ( it seems to be solid brass) and filled the threaded hole, where the bolt goes, with solder while keeping if hot i threaded the bolt into the sensor, let it cool and unscrewed the bolt and now i have a brand new set of threads, starts up a little sooner but I will have to wait till this weekend to lake test.

[adamsjstt]

Just got back from the lake. Boat is running better but still not 100%, I think mostly from the knock sensor, originally plug 2 and 8 where burning different than the rest ( a little on the black side) side I swapped them with plugs 6 and 4 to see if it was the plug or the source going to the plug, and now I can say it is the source going to the plug ( or the cylinders themselves) because it is still the plugs from cylinder numbers 2 and 8 that are burning black and the original plugs that where in cylinders 2 and 8 ( and now are in cylinders 6 and 4) are burning a light tan color just like the other 6 cylinders.

Can this be a injector issue?
Is it common for a injector to flow to much fuel and cause the cylinder to run rich?

The engine idles rough, of idle it spudders a little and then seems to clean up a little, at low speed it sometimes surges, holds speed fine and at WOT it is turning around 4000 RPM's at 35 MPH
Any Ideas?

[lohe]

You can swap injectors on the cyclinders and see if the problem follows.

[adamsjstt]

You can swap injectors on the cyclinders and see if the problem follows.

Never thought of that. I will give it a try. THANKS
Any other ideas????????

[scoot18]

May not have anything to do with anything. But I heard you say a few times that the exhaust sounded like it was restricted. '?' Is the impellar in good shape, are you sure that you have good water flow through the engine and exhaust? The reason I asked is because my water strainer got clogged with silty muck and mud from a shallow area one time and as soon as I accelerated to get on plane, I could immediately tell something wasn't right. The exhaust sounded funny. Now I'm thinking that if possibly the impellar isn't pushing enough water, or there is a restriction in the water path, if there isn't enough water passing over the coolant temp sensor, the ECM may be making uneccessary adjustments for temperature because of an inaccuracy there. Just a thought; may be way off base. But since the impellar is a normal routine maintenace item, if it's old or original, may as well put one of those in too.

[adamsjstt]

May not have anything to do with anything. But I heard you say a few times that the exhaust sounded like it was restricted. '?' Is the impellar in good shape, are you sure that you have good water flow through the engine and exhaust? The reason I asked is because my water strainer got clogged with silty muck and mud from a shallow area one time and as soon as I accelerated to get on plane, I could immediately tell something wasn't right. The exhaust sounded funny. Now I'm thinking that if possibly the impellar isn't pushing enough water, or there is a restriction in the water path, if there isn't enough water passing over the coolant temp sensor, the ECM may be making uneccessary adjustments for temperature because of an inaccuracy there. Just a thought; may be way off base. But since the impellar is a normal routine maintenace item, if it's old or original, may as well put one of those in too.

Checked impellar and it looks good, no mud or restrictions

[adamsjstt]

So i swapped injectors with cylinder 8 and 6 and after a trip to the lake i checked the plugs again and it is still cylinder 8 ( and 2 but i made no changes to number 2 )that is burning black (rich) so the problem did not follow the injector. Leaving me stumped. Any IDEAS???????

[mls6722]

could you have crossed plug wires?