The be all end all "My STX 12f or 15f or Ultra LX is not running right" Thread

[smokeysevin]

I have unplugged every single connector on this wiring harness and nothing looks corroded. Im about to check continuity between all thr wires at the connectors. Could my tip sensor be causing this? Its the only one that looks corroded inside the little black box.

Tip sensor "should" kill all of them not just half but I have not tested that specifically. I have a few spares if you need a fresh one to try.

Sean

[J_0sh]

Tip sensor "should" kill all of them not just half but I have not tested that specifically. I have a few spares if you need a fresh one to try.

Sean

I appreciate it man but I ordered a used one from fleabay it should be here tuesday, it was only like $18 shipped so not to bad. But since my last post i have ohmed my crank, cam and temp sensors all of which check out to be within spec. Ive removed the little white cylindrical connector that goes next to the power cable and added more grounds to the motor but still no start. Im thinking if this tip sensor doesnt fix it ordering another wiring harness. Maybe somewhere somehow something got fried while i was welding on it and i just cant see it. I didnt have a battery in the boat at the time of welding but so idk.

[steve45]

Maybe somewhere somehow something got fried while i was welding on it and i just cant see it. I didn't have a battery in the boat at the time of welding but so idk.

If you had any ground wires hooked up, you may have fried the ECM. Not sure how, but welding does weird things to electronics. If you were TIG welding with a high frequency start, that would probably be worse.

[J_0sh]

If you had any ground wires hooked up, you may have fried the ECM. Not sure how, but welding does weird things to electronics. If you were TIG welding with a high frequency start, that would probably be worse.

So i just got my parts 15 mins ago, installed the tip sensor and nothing. Same things happening. Im about to get on flea bay and order a new harness and ecm. Im out of ideas.

And as far as the welding goes i was using a spool gun and none of the grounds or any electronics were connected to the engine whenever i was welding, im completely lost.

[cnoon]

Hi Sean, I'm finally getting back into a ski that was not working. Here's my post from before "I've got a mystery issue with another 2004 12f. It's a ski I've been frustrated with for a year. It ran great and then wouldn't start one morning and has never run since. I finally got a compression test extension and checked it out. All four cylinders come in at 30-35 psi. I've double checked that I'm measuring it correctly by checking my other skis (which come in around 180psi). Am I correct to assume the only way it could drop on all four cylinders is if the timing chain skipped a link?" I pulled the cover and checked the timing and it looks correct and the chain doesn't appear to have skipped. Before I yank the head off and check the valve seats for corrosion, is it possible that the timing gear can slip on the camshaft? My understanding is that it's pressed on, perhaps without a key. Have you ever heard or come across such a thing? A slip of a few degrees would probably cause across all cylinders compression drop. I do plan to do an in situ leak down test that might indicate valve corrosion, I guess. - thanks, Chuck

[smokeysevin]

Hi Sean, I'm finally getting back into a ski that was not working. Here's my post from before "I've got a mystery issue with another 2004 12f. It's a ski I've been frustrated with for a year. It ran great and then wouldn't start one morning and has never run since. I finally got a compression test extension and checked it out. All four cylinders come in at 30-35 psi. I've double checked that I'm measuring it correctly by checking my other skis (which come in around 180psi). Am I correct to assume the only way it could drop on all four cylinders is if the timing chain skipped a link?" I pulled the cover and checked the timing and it looks correct and the chain doesn't appear to have skipped. Before I yank the head off and check the valve seats for corrosion, is it possible that the timing gear can slip on the camshaft? My understanding is that it's pressed on, perhaps without a key. Have you ever heard or come across such a thing? A slip of a few degrees would probably cause across all cylinders compression drop. I do plan to do an in situ leak down test that might indicate valve corrosion, I guess. - thanks, Chuck

Could be a few things, valve seats corroded, valves stuck in the guides, slipped timing. A leak down test is a good start if you have the equipment for it.

Likely it is valve related if the ski has sat for any extended period of time. If it is, and the valves are stuck partially open you should see higher than normal valve clearance. You can check that just by taking the valve cover off.

The cam gears are pressed on, and are not keyed, I am not aware of the sprockets slipping even under high load and rpm but that does not mean it can't happen. Unfortunately there is not an easy way to check that unless you can degree them with a dial indicator.

Sean

[Crossrip36]

Hey guys amazing thread. Just got my first a ski. A 2006 stx 12f super clean with 90 hours.
i am pretty well versed in marine deisel and can turn a wrench but i know nothing about jet skis really.

I took it to a lake today for the first time and it seemed to run good for about 10 minutes then started losing power.. then it stalled out and idles very rough and continually stalls. Try to throttle up and it will jump and then die sporadically.

II will mention that this problem persists whether the seat is on or off so I think that likely rules out an exhaust issue.

I plan to rule out bad fuel and spark plugs first thing tomorrow but want to be prepared for that not to help. What are some other things I should be looking at?

[steve45]

Welcome aboard, Crossrip!

Start with a compression test. If it's been in storage for a while, could be bad gas, plugged fuel filters, plugged injectors, or something as simple as a bad spark plug.

That model requires higher octane fuel (can't remember what number).

[smokeysevin]

Hey guys amazing thread. Just got my first a ski. A 2006 stx 12f super clean with 90 hours.
i am pretty well versed in marine deisel and can turn a wrench but i know nothing about jet skis really.

I took it to a lake today for the first time and it seemed to run good for about 10 minutes then started losing power.. then it stalled out and idles very rough and continually stalls. Try to throttle up and it will jump and then die sporadically.

II will mention that this problem persists whether the seat is on or off so I think that likely rules out an exhaust issue.

I plan to rule out bad fuel and spark plugs first thing tomorrow but want to be prepared for that not to help. What are some other things I should be looking at?

When you can, pull the ecu and post the numbers on the case. 06/07 12fs are known to eat pistons depending on the ecu. If you have one of the dangerous ones, I can flash it to the 04 tune I use on my 07.

Post back once you have checked the fuel/spark and what Steve mentioned.

As for fuel, I only run fresh 93 octane on 12fs, they are higher compression at 11.2:1 iirc its an extra few bucks but makes me feel better.

Sean

[Crossrip36]

Well I am into a whole other nightmare. Set my torque wrench to 100 checked it on the lug to make sure it was working. Put one plug in and it snapped off before I was even close to 100. Then same thing on the next one. Now I have 2 snapped off plugs in my cylinder.
I wasnt even on 113 i was at a 100. Completely confused and furious to be honest.

[Crossrip36]

I just put 3 of my old plugs in a vice and snapped them all off at less than 100 pounds on the torque wrench. Guessing my new torque wrench is the issue

[smokeysevin]

I just put 3 of my old plugs in a vice and snapped them all off at less than 100 pounds on the torque wrench. Guessing my new torque wrench is the issue

I don't use a tq wrench on the plugs. NGK specifies finger tight plus some angle on initial install, then less once installed again. I don't have a picture on hand but it should be on the box. Make sure to use a light coating of anti-sieze on the plug threads and a light blob of dielectric grease on the wire end.

Sean

[Crossrip36]

I thought I read in the beginning of this thread that the plugs get torqued on to 113 pounds? Anyway problem solved.

Compression test was good 185-190 across all cylinders.

New plugs and 93 octane fuel. It idles much better but now I am noticing a rattling sound coming from the pump area in the back and it progressively gets worse and then stalls. Only does it at idle if I Rev up to 2000 it goes away completely. FYI this is all on a trailer

Can anyone tell me what the idle should be when out of the water? Seems like 14-1600 is the sweet spot but seems really high but then again I am a noob.

[steve45]

Are you talking inch-pounds, or foot-pounds? Service manual says 113 INCH-pounds.

[Crossrip36]

Right inch pounds makes a lot more sense.....haha lesson learned. Anyway I've norrowed the issue down to something that seems common around here. Won't idle with the seat on but with it off runs great.
found a 3/4 inch hole in the blue hose.