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Sluggish Motor


2Valve
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I just took my 2002 PCM 5.7L equipped boat out of storage and it's not running right.

 

It starts fine but the Idle is a little rough, but seems smoother when RPM's are raised to around 2,000.

Power is definitely down, when accelerating. And there's a different "tone" to the exhaust. Top speed is only 39mph, 4000rpm, where normal is 50mph, about 4900 rpm.

 

I stored the boat last fall with a full 30 gallons of gas, fresh oil, filter and fogging of the motor through the throttle body. (the same routine I've followed for the past 16 years).

The only thing different I can point to is when I dropped it off, I had forgotten to Stabil the fuel. My buddy had some, just enough to treat maybe 5-10 gallons, so my thought is it's the fuel, or maybe fogging the motor fouled a spark plug.

 

Distributor cap and rotor are clean, both replaced last fall

Fuel filter (fuel control cell) is new

Throttle butterflies are opening properly, no binding of cable, etc.

 

Any ideas would be appreciated.

 

2Valve

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I had some similar issues when I got my boat last fall (PCM GT40). Pretty sure the issue was corrosion on the coil where the wire to the distributor cap hooked on. Cleaned that up, and put dielectric grease on all spark plug/cap/coil connections, and that did the trick.
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I just had to do surgery on the muffler on my 196 becuase an intenal part had broken away and almst fully blocked the larger exit pipe. It was running ok but power was way down out of the hole so its worth checking even if its a long shot.
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Since it's probably easier to pull the plugs and check the coil than to pull all gas out, I'd do that first. If you have a way to pump the fuel out easily then do that first. I doubt it's the exhaust since it runs rough at idle, that usually results in an ok idle (maybe a strange noise) and poor high end response. If it isn't plugs, coil, or fuel then we'll go back to the drawing board.
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thanks all. I'll check everything. I'm pretty anal when it comes to 'electrics' cleanliness and dielectric grease but no harm checking coil connections.

 

I'll report back with my official findings. This boat was like a 427 Vette out of the hole, so looking forward to getting it right again.

2Valve

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@"Mateo Vargas" The hard way, you have to pull it out and have a good look inside. There is more info on the CC forum about the problem with some owners doing away with the stock muffler and putting in a straight through setup which you can buy off the shelf. Mine was blocked so badly the muffler blew open and the boat was pumping water and exhaust into the bilge. I suspect it had been partially blocked for a while, this is a potentially bad problem if your out in the middle of a large lake because the boat takes on water with the engine on or off. Its easy enough to repair with a fiber glass kit and a grinder.
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Gas and electronics shouldn’t cause a tone difference. The stretch on this would be the distributor timing slipped and got retarded. You would hear advanced timing in knocks.

If timing is retarded, sometimes the exhaust might seem muddled )if that is a word).

Or check your exhaust system need to be checked as suggested above.

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Get a new battery. At least disconnect it to reset the ECM. Solves many problems.

 

If you have bad gas, go ski it to drain the tank. 39mph is faster than the max slalom speed. Your boat will tolerate some crappy gas. Pull some college kids - they go through the gas! (To their credit, UCLA left me overfull of fresh gas).

 

Sensors, injectors, wires and gas deteriorate over time while not operating - especially if it's moist. Use sometimes helps these issues. Go ski!

 

Of course, I've bonked my prop on the trailer (actually it wasn't me but some insidious gremlin - or kid). Can cause similar symptoms.

 

Or just get a new boat.

 

Eric

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@A_B

I agree. The exhaust tone is just "different", like a poorly timed engine. I have a timing light that I use on my older points and condenser driven engines. I should be able to check static timing and advance operation.

 

Conventional distributor with a lock bolt. Yes, it could have moved.

 

2Valve

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@2Valve : Did you fiddle with the distributor that would lead you to consider timing as an issue, it probably did not move on its own? The advance module would probably be the more likely candidate except you note idle running is rough also which would point me to a misfire. As far as tone, misfire can do that and perhaps not a broken muffler but some unwanted inhabitants decided your exhaust system would make a great winter home which includes their own internal decorations. You might also give the throttle body a cleaning with TB cleaning fluid to get rid of the oil film.
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@DW, There shouldn't be any issue with the distributor as the lock down bolt has never been loose, so you're correct on that assumption. I'm not familiar with the advance module. I was thinking that the ECM used rpm to develop the advance curve?

 

I did visually check both exhaust outlets with a strong flashlight and they look clean with no mouse or other critter evidence.

 

TB cleaning is on my list too.

Thank You,

2Valve

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@2Valve : on advance - it all depends on the marinizer as to what process they use, ECM does have the advance and static timing. Some ECM's or calibrations will also have a limp mode, usually retarding the timing due to some sensor input (like overheating) and a timing retard can change the tone all across the rpm range. Some marinizers use a timing module on the distributor which can be described as a very simple ECM with just a timing advance curve.
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I've had a couple of loss of power issues on my 02. First was a small slit in the hose inside the FCC. I now replace that 2.5" long hose about every 3rd fuel filter change.

 

Agree with OzSki on muffler. My 196 also had a loss of power and exhaust tone change. One riser got warmer than the other. The muffler baffle collapsed creating back pressure. The muffler would also pillow out when the throttle was revved. I bought a used muffler from Art Cozier, but they are repairable if you don't mind the downtime. Installing the muffler is no joy eliminate other possible problems first.

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@adamhcaldwell

I'm going to throw my conventional timing gun at it this weekend. That should tell me at least if advance is occurring.

 

First thing I decided to do is get all the old gas out. Hate to do it. That's 30 gallons that I'll have to dilute in my other vehicles, but it's the most likely culprit in my mind at this point.

 

Thanks everyone for your insight. Much appreciated. Maybe this weekend I'll get some skiing time in also.

 

2Valve

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@2Valve

 

I have also seen a case or two where the fuel pump relay & contacts were super super corroded and the boat ran extremely poorly. There was a voltage loss somewhere in the circuit and the pump wasn't sustaining appropriate line pressure which will lead to really poor spray pattern coming out of the injector nozzles and kill engine performance.

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My 2002 has had poor loss twice. Once was the little hose inside the FCC. The second time took me 4 months to figure out. Changed cap, rotor plugs, wires, even though I did every 300 hrs. Changed fuel filter, cleaned screen in low-pressure pump, took apart gas tank ball check valve for venting, checked timing.

Finally got pissed one Sunday night and took my Dremel tool and cut off the top of the muffler, discovered all baffles had come apart and were blocking exhaust exit. Bought a Fiberglass repair kit, ($ 15) and fiberglassed everything back in place. Runs like a dream.

 

d0qnad71xirx.jpg

 

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@vtmecheng When the baffle failed it was fine at idle. Had adequate power to ski my wife but barely enough hole shot to get me out of the water. Upon removing the muffler, discovered the rubber padding under the muffler was dislodged and a couple of thin spots on the underside of the muffler developed. That is another area to inspect during baffle repair.
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The reason I ask is that @2Valve said the engine seems to have a rough idle, smooths out a bit once he throttles up a bit, doesn't have power at the high end, and has a different tone. Normally engines don't have idle problems due to exhaust blockages unless there is a complete blockage, that's because the volume of exhaust is so low at idle compared to when under load. I'm still thinking it's either fuel or spark related and the best course of action is to start with the easiest things to check and move up from there. Seems easy to check some connections first and the ignition coil is easy to check with a multimeter

 

One shot in the dark that I had happen once on a digitally controlled distributor Chevy engine. The distributor had what is called a pick-up that was under the rotor. It took me months of checking different parts randomly until I just started going one by one through the entire system. Finally found that the insulation on that pick-up part was degrading. Replaced the part and man did that engine come alive again. Point is, sometimes you have to just spend the whole morning/afternoon going part-by-part.

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@adamhcaldwell

 

For pretty much every ski boat a fuel pressure gauge is almost a mandatory troubleshoot tool - particularly on MPI - fuel pump module failure or filter problems are responsible for so many problems that being able to physically watch a gauge can solve. Cheap tool too.

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@vtmecheng

Thanks for the extra information. There IS a connection of some kind on the top of the throttle body and I don't know what its for exactly. I'll check that connection and look at the manual as well.

 

Now, what to do with 30 gallons of fuel. hmmmm maybe a bigass bonfire tonight. :)

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well, the saga continues. I drained the fuel and added 10 gallons of fresh. No change.

 

I then pulled all the spark plugs and discovered plugs 2, 4 were black and wet while all others were clean and new. So I replaced all the plugs. No change.

 

I then grabbed my trusty timing light and hooked up to cylinder 1. Although there's no timing plate with numbers, it appears that idle timing is about 10 degrees BTDC, which is stock.

 

Interestingly, raising throttle barely advances the timing. Like maybe 2 degrees advanced at 2000 rpm.

 

So now I'm trying to understand how the advance work. It appears there's a donut type device in the distributor that can rotate to allow the hall effect sensor to trigger at different points.

 

But I'm not understanding if it's an electrical signal that engages the donut. It can be moved and it stays. Total rotation is about 20 degrees if I had to guess.

 

To re-cap, the engine starts immediately with a slightly rough idle. The engine looks smooth, but if you're in the boat you can feel it shaking.

 

Power is down, with plane out taking almost full throttle. Top speed only 39mph, around 4000 rpm.

 

My gut tells me its an advance issue.

 

Thanks,

2Valve

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I think you are on the right track looking at the pickup coil (donut) in the distributor. I have a 2003 boat with PCM 5.7 TBI and have replaced the coil 5-6 times in 15 years.

 

For troubleshooting I have a new distributor from the auto parts store that I drop in, if the boat runs I order a OEM PCM distributor from ski dim and keep the auto parts handy.

 

You can buy just the pickup coil but trying to change it never works out well for me and I end up getting a new distributor anyway.

 

TomD

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I doubt the advance unit would cause 2 gas fouled spark plugs. When you replaced the plugs you said no change, pull # 2 and 4 back out and see if they are again soaked with fuel. Assuming they are i would suspect 2 leaking injectors.
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I love it when a plan comes together.

 

This morning it hit me. Why would plugs 2 and 4 be black when all the others are pristine? Checking the spark plugs wires and knowing by heart the standard small block Chevy firing pattern since I was a kid (18436572), I quickly found plug wires 2 and 4 were swapped.

 

Please don't laugh. :) God love a small block Chevy though.

 

All 330 horses are back, and I'm going skiing, ba-beeeee!!!!!!

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The wires must have gotten crossed because both leads to the plug are the same length.

Thanks for all your help and getting me pointed in the right direction. Sometimes it's the simplest things.

2Valve

 

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@eleeski

I replaced the plugs last winter just after fogging the motor through the throttle body, and I must have switched 2, 4.

 

In any case, GREAT skiing this morning. Our water is already in the mid 70's.

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