Middle Cylinder Not firing and Getting Random Codes - 2004 GTX SC

[FlashHole]

As the thread title says, the middle cylinder doesn't seem to be firing. It is getting gas and spark to all cylinders. Compression on cylinders 1&3 are right at 140, but the middle cylinder is 120ish. That's obviously not ideal, but I wouldn't think it is low enough to keep it from firing all together..........Or is it?

The other symptoms are as follows:

The beeper works, but is intermittent. The beeper itself tests out ok when hit with 12 volts.
The red LED flashes and the screen displays check engine. That is consistent.
It throws random codes with p0344(CAM) & p1200(TOPS) being the most consistent. But random enough that I not sure I should trust anything it says.

The random codes makes me wonder if its a bad ECU, but I'm not sure if that would also cause one cylinder to completely misfire or show low compression. Unfortunately, I don't have another ECU, nor do I have BUDS or CANDOO. Other than swapping out the ECU, is there a way to definitively test it?

I guess I'm just wondering what my next course of action should be??? I'm no jet-ski mechanic, but I do want to learn, so any insight or suggestions would be greatly appreciated.

 

[skiasylum]

Download a service manual and do a leak down test. The service manual will guide your next steps with the results of the leak down.

 

[FlashHole]

Thanks for the response!!!

I do have the manual, as well as a leak down tester. There's nothing to put a wrench on, so how do I rotate the engine by hand? And how do I keep the cylinder at TDC once I hit it with air? Won't it just push the cylinder down?

Also, would a miss-firing cylinder due to mechanical issues cause the myriad of random codes?

 

[FlashHole]

That cylinder in question happened to be at TDC, so I did the Leak Down test. It's leaking into the crank case pretty bad. So I'm guessing that the Rings are either stuck or worn out.

So my question remains......Would a dead cylinder cause the computer to throw random Fault codes? I don't mind pulling the engine and seeing what I can figure out there, but I'm not sure this thing is worth doing engine work and replacing the computer.

One thing I found interesting is that when I went to turn the engine over using the Super Charger nut, it would only turn a little bit and would then spring back. Didn't matter which way I tried to turn it. I would think that with the plugs out, it would spin relatively freely. Seems like something is binding up.

 

[ski-d00]

Would a dead cylinder cause the computer to throw random Fault codes?

Yes, under the right circumstances but they aren't random. It won't throw the code until it is running and the reading from the sensors aren't in alignment with each other. Low cylinder pressure can change rpm, manifold pressure, TPS, CPS, etc. to have misaligned readings from where it expects it to be which will throw codes. However, 120psi is not really low for a SC motor and I would expect it to run just fine with your values.

when I went to turn the engine over using the Super Charger nut, it would only turn a little bit and would then spring back

The SC is geared up so that it spins around 35k+ max rpms so that when you're turning the SC the flywheel isn't moving that far, around a 5 to 1 ration of engine rpms. If you continue to turn the sc more than 1 revolution without releasing pressure, it will eventually slip forward instead of backwards. You should always turn the SC nut CCW since it is a left-handed nut and you don't want the impeller nut to loosen.

The simplest way to turn the engine over is to turn the drive shaft or bump the starter.

Compression on cylinders 1&3 are right at 140, but the middle cylinder is 120ish. That's obviously not ideal, but I wouldn't think it is low enough to keep it from firing all together..........Or is it?

The engine will not keep itself from firing on a single cylinder as it has no idea what the compression is on any cylinder and will always maintain spark and fuel to each cylinder equally meaning it won't sense a bad cylinder and change spark or fuel delivery.

Does the engine run? Does it misfire? Does it rev up? In limp mode? Need a little more info on the actual running characteristics to advise what the next steps are.

 

[FlashHole]

Yes, under the right circumstances but they aren't random. It won't throw the code until it is running and the reading from the sensors aren't in alignment with each other. Low cylinder pressure can change rpm, manifold pressure, TPS, CPS, etc. to have misaligned readings from where it expects it to be which will throw codes. However, 120psi is not really low for a SC motor and I would expect it to run just fine with your values.

The SC is geared up so that it spins around 35k+ max rpms so that when you're turning the SC the flywheel isn't moving that far, around a 5 to 1 ration of engine rpms. If you continue to turn the sc more than 1 revolution without releasing pressure, it will eventually slip forward instead of backwards. You should always turn the SC nut CCW since it is a left-handed nut and you don't want the impeller nut to loosen.

The simplest way to turn the engine over is to turn the drive shaft or bump the starter.


The engine will not keep itself from firing on a single cylinder as it has no idea what the compression is on any cylinder and will always maintain spark and fuel to each cylinder equally meaning it won't sense a bad cylinder and change spark or fuel delivery.

Does the engine run? Does it misfire? Does it rev up? In limp mode? Need a little more info on the actual running characteristics to advise what the next steps are.

All of that makes plenty of sense to me.

To answer you questions: Yes, it will run, but it runs rough and has a hard time staying running. It is not in limp mode, at least not to my knowledge. I have yet to be in the water with it, so I'm not 100% sure on that. Yes, It revs up.

To be clear, when I say random, I just mean that I don't necessarily get the same codes every time. At first, it was the crank position code. Then it was the cam code and the blow by valve code, then a couple others. They seem to come and go. The check engine and flashing red light is consistent.

I decided to order a Spline/Impeller tool so I could properly spin the motor. It came today, so I took the super charger off and pulled the drive shaft so I could manipulate the engine more precisely while doing the leak down test. Cylinders 1&3 tested nearly perfect. The middle cylinder(#2) tested right in between good and moderate(39 or 40%). It leaks out both the exhaust and intake valves, as well as into the crank case. The majority of the air seemed to be leaking out of the exhaust valves. I'm hoping that means I can get by with just yanking the head, instead of the whole engine.

I also think there is enough compression and cylinder health for this thing to run on all cylinders. The cylinder not firing at all is surely being caused by something else. I've moved around the coils and plugs, and even put new plugs in it, and the misfire didn't move cylinders. I also pulled the fuel rail, and the injectors all seem to be spraying the same.

One other thing I noticed while doing all this, and I mentioned it before, is that when I'm turning the engine by hand.......it will spin easily in parts of the rotation, then it gets harder to spin, like it is binding or pushing through some compression, then it will get past that point and spin easily again for about a half rotation. I have no clue if that is normal or not. In my mind, it should rotate freely and smoothly throughout the whole rotation, especially since the plugs were out, but I really don't know. It seems to turn over just fine with the starter.

So, where do I go from here is the question? How can I rule out something electrical or ECM related? I'm fairly mechanically inclined, so the thought of pulling the engine and rebuilding it is somehow less intimidating to me than troubleshooting the electronics. Electricity is like wizardry to me


ETA.....And whoever posted on the internet to put a wooden dowel down the spark plug hole to tell when the cylinder is at TDC is giving very bad advice. It snapped the dowel right in half and I spent several hours fishing out bits and pieces of wooden dowel rod.

 

[skiasylum]

You’re correct in your assumption the engine should turn over evenly with the plugs out so you are probably dealing with a mechanical issue for sure. Did you do a wet compression test on #2? The 2004 is pretty straight forward electrically with a combo mpem ECM. We are missing the history of the ski, like did it ever run and what’s it like cosmetically. The value of a good 2004 GTX is around $3000 so you’re going to probably be in the hole after you fix it but that’s normal. Your ECM on eBay is $600 used and no way to test because you don’t have a good running ski. So when you rebuild and start it and it runs like crap what then? Is it your recent work or was it something pre existent. Definitely a project ski.

 

[FlashHole]

You’re correct in your assumption the engine should turn over evenly with the plugs out so you are probably dealing with a mechanical issue for sure. Did you do a wet compression test on #2? The 2004 is pretty straight forward electrically with a combo mpem ECM. We are missing the history of the ski, like did it ever run and what’s it like cosmetically. The value of a good 2004 GTX is around $3000 so you’re going to probably be in the hole after you fix it but that’s normal. Your ECM on eBay is $600 used and no way to test because you don’t have a good running ski. So when you rebuild and start it and it runs like crap what then? Is it your recent work or was it something pre existent. Definitely a project ski.

Here's what history I have on the machine. I picked this thing up, on a good trailer, for a whopping $400. I figured the trailer alone is worth that. The seller said it ran when he parked it a year ago, but isn't that what they all say?

Cosmetically, the ski is pretty ugly. It is oxidized and has a little dock rash but the hull itself is in solid condition, the hood is in great condition. I'm really not concerned about the cosmetics. I figured that if the engine was good, then I'd tackle the cosmetics.

Mechanically, and all the pieces are there. But, If there is any sort of serious engine damage, then there is absolutely no question that this ski is worth more parted out. Having said that, one of the main reasons I bought it is to learn how to work on them as a hobbyist. In the end, I'd prefer not to have 5k in an 2k ski, but if I ended up with 3k in a 3k ski, I'd be perfectly fine with that. So, I don't really mind throwing a little money and time at it, providing I gain some knowledge and end up with a working ski. I just don't want to throw money at it blindly. But yes, your assessment of the financial situation is absolutely correct. I'm at the crossroad of sell now and make a little money, or keep going and very likely loose a little money.

Not sure what you mean by wet compression test. If you mean, putting a little oil in the cylinder and seeing if it bumped up, then yes, and it did a bit. I was hoping it was just stuck rings. It may have been partly that, because the middle cylinder did go from about 105 to a consistent 120 after I let it soak, but I don't think it's getting any higher than that. And that's starting to sound like the least of its problems.

Any ideas why it would be binding up? There's no knocking. No metal rubbing that I can hear. No metal shavings in the oil or oil filter. The rocker arms and valve springs all look like they are working as they should, at least from the top.

And where should I go from here? Pull the head to have a look at the valves and piston tops, and see how it spins from there. Or should I pull the engine and just start tearing it down until I find the problem or create one? Like I said, if I pull it all apart and end up with a pile of parts, I can just sell the trailer and all I'll really be out is some time and the cost of some specialty tools. I'd much rather win though

 

[skiasylum]

I’m guessing it sank, ingested water into the engine and hydro locked on a restart attempt and bent a rod. You usually get what you pay for.

 

[FlashHole]

I’m guessing it sank, ingested water into the engine and hydro locked on a restart attempt and bent a rod. You usually get what you pay for.

Indeed you do.

A bent rod is what I kept going back to. I just couldn't figure out how one would bend without there being some other obvious signs of a catastrophic event. I hadn't thought about a hydro lock. That actually makes perfect sense. Time will tell. I am probably going to pull the engine and tear it apart to have a look. I may or may not ever put it back together.

One other question. When you bend a rod, what other parts usually goes with it? Any chance of that being it?