QUICK HELP! - 98 Johnson 150hp

[mattttt25]

1998 johnson oceanrunner 150hp on a 20' center console.<br /><br />has run great all season. boat and engine sat unused for about 5 weeks. started fine. used to get approx 5000rpm and 42 mph. now i max at 4000rpm and 31 mph. no other symptoms- engine sounds normal, normal exhaust, etc. just maxes at 4000rpm. even sounds "normal" for 4000, but can't get it go higher.<br /><br />where do i start? decarb, new plugs? thanks-

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

^

 

[Hooty]

Re: QUICK HELP! - 98 Johnson 150hp

Happened to me a while back. Enging started in a flash, sounded great, just short on beans. Finally pulled the cowling and there wuz a dangling sparkplug wire. It had been that way for a coupla weeks. I think it's because those V6's run so smooth, you can't tell a dead miss when ya have one. I'd bet ya got one dead hole. Put the muffs on 'er, crank it up and check the temp of the sparkplugs until you find the cool one. That's the one not hittin'.<br /><br />g'luck & c/6<br /><br />Hooty

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

thanks hooty, i thought it might be one cylinder not firing, but i was told i would hear it. haven't checked yet, but i'll check all plugs and compression while i'm at it.

 

[Luna Sea]

Re: QUICK HELP! - 98 Johnson 150hp

"boat and engine sat unused for about 5 weeks"<br /><br />In the water? Is the bottom painted" 5 weeks not moving in the water....... <br /><br />Sorry, had to ask.

 

[Walker]

Re: QUICK HELP! - 98 Johnson 150hp

I'm with Hooty. A 6 can drop a cylinder and its virtually impossible to tell by ear.

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

luna- long story with the bottom, was painted but with defective paint. just cleaned it last week, no change.<br /><br />well, spent some time on the engine. i pulled all the plugs and they looked the same and normal. i checked compression, and got 100 on 5, 80 on 1. did the oil pour down that cylinder and it jumped to 110. so the manual says its the rings. back to that later. i checked each wire with a plug, and saw a spark for every one. replaced plugs and ran the engine, pulling each wire. every pull resulted in a slight change in rpm. finally decarbed and ran the boat. no change- still runs and sounds great, but hits a wall at 4000 rpm and 31 mph.<br /><br />so with all that, i assume the plugs and wires are good and i'm getting good ignition. i find it hard to believe one cylinder with low compression is causing such a change. besides, it could have always been that way.<br /><br />i do have one other symptom. every once in awhile i get a check engine alarm going off. it doesn't last, but seems to go off at higher rpms. i haven't worried much about it, knowing it's a fuel delivery problem. could this be linked to my power loss? could my fuel pump be bad? again, i stress that every time i head out it hits the wall at 4000 rpm.<br /><br />any ideas? am i headed the right direction? what next? thanks-

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

anxious...

 

[dcolpitts]

Re: QUICK HELP! - 98 Johnson 150hp

sounds like fuel, if you have a bulb on the fuel line try pumping it at 4000 rpms see if it helps, also check vent on fuel tanks for blockage. Also if you have a built in tank check the antisiphan valve for blockage, this happened to me a little while back

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

thank you. headed over to the boat to check the fuel system. hope it's something simple. if anyone else has an idea, pls post. thanks-

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

update- i ran the boat yesterday and same results- wot produced 4000rpm at 31 mph. the check engine alarm happened to sound a few times, but turned off quickly. i pumped the primer bulb, but no change. also ran with the top off and air silencer off, witnessing the carbs opening up and at least getting some fuel to each. i then docked the boat and let it run idle. i checked temps with a laser gauge, at the base of the plug and plug itself. all read the same. gave up and drank some beer. talked to some fellow boaters, and one proposed his guess- the check engine alarm (which sounded a few times when the boat was still running well) was telling me i wasn't getting enough fuel to one of the lower cylinders. over time, i scorched the cylinder. now, with 20 psi lost at that cylinder, i've lost 1000rpms and 10 mph. does that make sense? he also said i could have gotten water in the cylinder. when i left the boat sitting for 5 weeks with the engine up, the water sat at the lower cylinder and deteriorated the head gasket at that point. another boater said that the oil test (pouring oil in the cylinder before the compression test, which resulted in a normal reading) eliminated the possibility of a head gasket leak. so...<br /><br />1. does this make sense to anyone? any other ideas?<br /><br />2. if i do have a bad cylinder, will running the engine until the end of the season damage things further?<br /><br />3. this is starting to get beyond my capabilities. what sort of repair costs am i looking at- couple hundred, couple thousand?<br /><br />thanks-

 

[ob]

Re: QUICK HELP! - 98 Johnson 150hp

May be time to take into a reputable shop that can run it up on a dyno and diagnose for possible ignition glitch.The cylinder in question most definately will need to be adressed before it causes further problems.If it were mine ,I wouldn't run it in present condition.

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

ob- are you saying you think its still an ignition problem? could one cylinder with lower compression be causing that drastic of a loss? do they usually go as fast as mine did?

 

[ob]

Re: QUICK HELP! - 98 Johnson 150hp

What I'm saying is that it is possible that there is an ignition problem since nothing has been positively eliminated yet.If carb porting is restricted ,squeezing the primer bulb will do nothing to confirm.However bumping the primer button of the ignition switch may,since it will allow fuel to bypass the carburetors.<br /><br /> I'm not sure what all sensors on your engine initiate the "check engine" light.I'm guessing it's just fuel restriction.

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

ob- yes, according to the manua, the check engine alarm simply signifies a higher pressure in the fuel system- a fuel restriction problem.<br /><br />not at all sure if this has anything to do with my loss of power.<br /><br />can you comment on the low compression on one cylinder? in your experience, will this cause a 1000rpm and 10mph loss, and can it happen "overnight"??<br /><br />thanks again-

 

[ob]

Re: QUICK HELP! - 98 Johnson 150hp

I think the low compression of the one cylinder is a side effect of fuel starvation.IMO the low compression coupled with restricted fuel flow or overheating that caused it could indeed effect the engines performance to the degree that you are experiencing.Other cylinders may be starving as well and their low compressions may soon follow.Just have to eliminate one monster at a time in the troubleshooting process.

 

[mattttt25]

Re: QUICK HELP! - 98 Johnson 150hp

ob- thank you. you're the second person with that opinion. i will try and troubleshoot the fuel problem first.<br /><br />i've decarbed, cleaned the fuel filter. any other easy fixes?