7000 misfire at idle

[captainruss99]

You guys have the vast Yamaha experience, so I figured I'd ask. I'll try to make this as short as possible. I have a 16 7000 cat, that just developed a random backfire/popping from the muffler, and rough idle, when it is acting up. First noticed it at the tail end of a long weekend ride. Ran perfect for 700 miles, then the stumble/ popping at idle. When I drove away, it cleared up, ran fine, till the next stop. Now, when I start it in my garage, it will act up right away. When revved up a bit, it will smooth out. It is not a dead skip. It felt like a weak coil, or a bad plug. The plugs were only 2000 miles old, but I threw a new set in, and tried a used but 'good' coil in each hole, with the same results. The plugs removed looked perfect. I've owned the sled since new, has 8700 miles now. I am a mechanic by trade, and it is a very well maintained unit. Use K100 fuel treatment. The valves were done 2700 miles ago. I posted some shortcut procedures on the 'valve adjusting' discussion a couple of years ago. There are no codes. It has the latest flash. The throttle cable seems to be adjusted properly. I did a search, but most issues were under power, not idle related. With all the experience you guys have with the Yamaha Vectors and Vipers, I was wondering if this is a one off, or a more common problem. I ride with many Vipers and Vectors, but we have not seen this before. Thanks for your time.

 

[74Nitro]

Seems like an intake leak.

 

[Snowfun]

Could you have some bad fuel? Try putting some Sea Foam in the tank to see if that makes any difference.

 

[captainruss99]

I did add some k100 to it. My buddies gassed up with me, and had no issues. Feels electrical. I'll bring home some some equipment tonight and test some more.

 

[Goober01]

I had a problem on my cat 7000 after many dollops and alot of time I replace the ecu and problem cleared up. So I took the old ecu apart and it had water in it and ruined the inside

 

[captainruss99]

This was at a dealer for 2 weeks, they couldn't find a reason. They talked with Cat tech, they couldn't give an answer either. I tried a lot of "known good" parts, to no avail. The dealer tech said they tried another ECU, from a good running sled, with the same results. I hope they are telling the truth. It is a very reputable local dealer. I will keep digging, this has cost me most of my winter. I had to borrow a Skidoo Ace to go on a 4 day trip. Took some ribbing there. Will add more when I get more info.

 

[74Nitro]

Compression or leakdown test the engine.

 

[mbarryracing]

You mentioned you had had adjusted the valves 2700 miles ago, I recommend checking them again especially cyl #1 where the MAP sensor solely gets its signal from. If that cylinder has a tight valve now, the MAP sensor will receive a wompy vacuum signal which subsequently affects how all the cylinders run and will produce exactly what your experiencing.
This past fall I had worked on a Viper that after it had a turbo kit installed by a different shop was exhibiting the exact same gremlin, misfire at idle and had been at several dealers and shops that couldn't figure it out. Was told the head was gone through when they installed the turbo kit so as everyone else did, I also assumed it was electrical. I went about swapping out one at a time from another good running Viper all the coils, spark plugs, MAP sensor, ECU, crank sensor, and all 3 fuel injectors and it still had that misfire gremlin. Even went as far as to check that the reluctor ring for the crank sensor on the pto stubshaft hadn't spun. All cylinders had good leakdown but after finally doing a valve clearance check myself I found one of the cyl #1 exhaust valves had almost no clearance. This apparently was causing a weird pressure pulse, and after I corrected the tight valve clearance it ran perfect.

 

[captainruss99]

I ran a compression test, leakdown test. Changed the entire throttle body assembly with all the sensors/injectors. Re-checked the valves. Tried another wiring harness, called the dealer tech again to verify, he did actually try my ecu on another sled, and that sled ran perfectly. He really does want to know what I find, and will talk over things with me. So if you follow the flow, we verified the ECU, changed the whole harness, the crank sensor, complete throttle body assy, plugs, coils, checked fuel pressure, a steady 45 when it's acting up. Strange thing is, sometimes when you start it it runs great, and you think it's cured, then after a while, it starts breaking down. Other times, it will act up right away. I'm under the impression the stator only runs the charging system on these engines, and has nothing to do with the efi system, other than providing the proper voltage. Am I wrong here? Thanks for the tips, I'll keep digging. By the way, the dealer tech said he also checked the reluctor.

 

[captainruss99]

Have you guys heard of valve seats coming loose on these? similar to what some dodge engines did a few years back? They would float around then re-set themselves. just wondering.

 

[74Nitro]

Are you able to point an infared gun at the header pipes to see if it is specific to a certain cylinder.

 

[captainruss99]

I tried it earlier, couldn't find enough room. Today I removed the tank and exhaust shield. Placed the tank on a couple of 2x6 pieces to raise it up a bit. Strapped it down w/a ratchet strap. Now I can easily reach each pipe with the infared gun. My gun happens to be at work, so it will happen tomorrow. While I had it all apart, the valve cover was exposed, right there, and I decided to check the valve clearance again, just in case I may have mis-read the feeler gauge before. I hadn't. All exhaust are between .009 to .010" , intakes are .006 to .007" which are in spec.. Sometimes you need to triple check. Thanks again to those trying to help.

 

[74Nitro]

Have you checked the timing indicator on the stub shaft?
I don't think it would cause your problems, but.....

 

[mbarryracing]

While you have it apart, inspect the #1 cylinder PTO side intake boot and the rubber line to the MAP sensor. Anything that could affect the vacuum signal to the MAP sensor as the vacuum is the highest at idle with the throttle plates closed.
Not sure if the IAC circuit could cause that.

 

[captainruss99]

I do think I've eliminated spark as an issue. I tried an automotive neon type spark tester, and when it stumbles, the light never flickers, on any cylinder. I had previously checked the boots for leaks, when I was changing the throttle bodies. The dealer said he checked the timing indicator. The infared test showed no real difference in temps. I guess it's such a minor stumble, not a full blown cyl drop, that the temp variance is minimal. Tomorrow night I will give it a running compression test, and compare all 3 cyls.. With the tank raised up and set back a bit, I have much more room to work. I'll keep digging.