2008 WaveRunner troubles

[Jgorm]

A compression test can fool you. A real test is a cylinder leak down test. If there is a problem area it will narrow it down

How so? My take is if there compression is good, there is no need to leak down. If the compression is bad, do a leak down. The leak down is a bigger pain. Tdc on compression for every cylinder. Even when i did my leak down it was hard to tell where where the air was escaping.

 

[Jgorm]

Guy at greenhulk also suggested could be ecu? I think I’ll swap the ecu from other one and see what happens.

Unlikely, but possible. Ecu is the first go to for people that don't understand efi.

 

[Neutron]

How so? My take is if there compression is good, there is no need to leak down. If the compression is bad, do a leak down. The leak down is a bigger pain. Tdc on compression for every cylinder. Even when i did my leak down it was hard to tell where where the air was escaping.

Compression test uses a check valve in the hose allowing the ring compression to pump up the gauge. Showing your rings only are possibly good.
In using leak down you can find a leaking valve or gasket etc..
As much as a pia it is to do is the only sure fire way to find out if all is sound.
I have seen numerous times where compression test passed great but failed leak down. Usually a head gasket or exhaust valve.
When you set the gauge at its 100%, then attach to the cylinder if the reading drops and you have it at tdc with valves closed then you just use a stethoscope to listen in the intake, exjaust, and dipstick tube.
If no stethoscope you use a long screwdriver to your ear
I can say with 100% certainly that you can have a compression pass and leak down fail result

 

[Jgorm]

Won't a valve or gasket leak fail to produce proper compression? I think it also depends on what % you consider failing. I could see 10, maybe even 20 still building compression, but not ideal. My bad cylinder was leaking 50%, but still made 100psi, half of cylinder 1 and 4. I see what your staying, but that's probably not bad enough to cause a miss.

 

[Neutron]

I have seen it cause a miss on at least 5 cylinder head problems all with exhaust valves leaking.
I am not saying its the problem here but it is a possibility. A proper leak down result will rule this out.
YES a bad valve or gasket can still give you a positive compression reading.

 

[the MfM]

run it in the lake again. Give it a chance to burn off that seafoam you added.

 

[Midnight2V]

Something to look at is the engine electrical harness connector to the #3 coil. It's entirely possible there is an intermittent electrical fault in the connector due to a badly landed or partially pulled out wire. Its a possibility on virtually all coil-on-plug platforms, automobile, boat, or PWC...and it typically occurs during a plug change when someone puts just a little too much force on the connector wires while disconnecting the coil from the harness. If that was the case, you could switch coils between cylinders and the coil previously on #3 would fire just fine on any other cylinder.

 

[Pinhacker71]

I’m going to try switching coils from my other ski and see what happens. If that doesn’t work, swap ecu from other. If still not working I’m taking it to the shop. I’m going to lake tomorrow for a week and was hoping to bring skis along. I guess it’s just the boat this time and skis will have to wait. Thanks for advice.

 

[Ronnie]

As a last resort try switching the rectifiers between skis. Hopefully it’s not the ecu ($1,200 new, $500 used). Rectifiers are around $70.

 

[Pinhacker71]

Okay. Update. Took ski to Yamaha dealer. Tech said exhaust was loose and could be causing the problem. Ski sounded great and he doesn’t think there is an issue. Says take it home and run it. Well, still low power. No difference at all. I took the ecu from my other ski and swapped them. Other ski ran fine with ecu so that is not the problem. I notice that when I open the gas tank for the poor performing ski that it make a big whoosh sound compared the the ski that runs well. Could there be a fuel pressure issue? I pulled plugs and they all looked ok this time. All spark when I crank engine. Should I try to pull fuel filter out of tank? Where is rectifier located. I can try switching it out with other one. Yamaha dealer is over an hour away and not terribly impressed with them. Would love to solve this myself. I wonder if it’s fuel starved. I’ve gotten better advice from this forum than greenhulk.

 

[Midnight2V]

A whoosh like a vent out or a suck in? Try running the ski with the cap cracked open. If your gas tank is pulling a vacuum it could be a clogged tank vent. That could fuel starve the engine. If it is pressurized, it could cause a rich condition.

 

[Ronnie]

Here is pic with the rectifier in it. It is part 18 and costs $115 at yamaha sports plaza, I bought one off of eBay for about half the above cost. Link to the web page is also included.
https://www.yamahasportsplaza.com/oemparts/a/yam/5003a0d2f870021f60a11cdb/electrical-1

 

[Neutron]

Greenhulk seems to only be interested in high performance upgraded skis. Not much interest in helping folks with stock ski problems and advice

 

[boudin]

A bad rectifier just won't charge your battery. If you are seeing 14v at higher RPM, then it's not that.

I'm not aware of any history of bad ECUs with the VXs, only with certain years of HO motors.

Check:

(a) Check fuel pressure either with a fuel pressure gauge or by swapping the sending unit from the other ski's fuel tank. Not an easy job due to limited vertical space. Also be careful of the fuel level sender arm. You must wriggle the sending unit sideways to get it out of the tank.

Keep in mind with good fuel pressure, you can still have a flow problem at higher RPM. Swapping with a known good unit will tell for sure.

(b) Swap all four injectors with the working ski. (Easiest to just swap the entire rail/fuel hose assembly.)

-Greg

 

[Pinhacker71]

I’ve swapped injectors and no change. I’ll check to see if it’s a vacuum or pressure tonight.

 

[Jgorm]

I'm voting for a clogged tank vent.

 

[Pinhacker71]

How hard is it to get to the vent? Do I have to pull the fuel tank out?

 

[Jgorm]

I doubt it. Look at the top of the tank and find the vent line.

 

[Midnight2V]

I recommend simply cracking open the fuel fill cap so that it isn't air tight and run the ski. If it is still running bad, it's not the vent line, that will save you the trouble of having to chase it down for nothing if it turns out not to be the issue. If it runs great, then you know you've found the issue and you can focus directly on it.

I missed the posts about seafoam being used. If you haven't burned all of your seafoam laced gas off, you need to make it a point to do so since it can potentially cause your engine to run poorly all on its own. If the plug isn't getting wetted anymore, you might be chasing a ghost at this point.

 

[Pinhacker71]

Seafoam should be burned off. Gonna try cracking gas cap before I pull things apart. I will also switch rectifiersa and batteries just to eliminate that as a possibility. Thanks for advice.