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Discussion Starter #1
Hi, my ATV is missing. It will idle all day and never miss. It is happening in the midrange. Most of the time, it is very infrequent. Perhaps a miss every 30 seconds and sometimes you second guess whether it is missing at all. However, there are times where it can miss a number of firing cycles in a row and you can get small back fire. It can happen on rides that are perfectly dry so this is not moisture related. I do feel like there might be a slight temperature correlation. The worst it ever misfired was yesterday during a long climb where I was wondering for a while if it would make it. The view was worth it. I've attached for your viewing pleasure. On very easy terrain at 10 MPH, I can minimize misfiring by running in high range and very low RPMs. Pressing the yellow override switch makes no difference.

The only thing I have done to diagnose/fix the problem is change the spark plug. That didn't change anything. Any thoughts on what I should do next? Or is this a problem you have to take to dealer to resolve?

Thanks in advance......
 

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Any codes?
 

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Is the machine stock?
 

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Discussion Starter #4
Everything is stock. There are no visible codes on display. If there is some way to display codes, then I haven't investigated those.
 

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Discussion Starter #5
I'm trying to test the coil as per the Service Manual. My quad is a H1, but based on the pictures in the Service Manual I would say I have the coil for a H2 on my machine. I have simple spade terminal connectors (one for black and one for red). The coil has never been touched and I bought this machine brand new. My resistance readings closely line up with a H2 coil, but not the H1. I've attached pictures of all sources I am referencing. For instance, the resistance from the positive to negative terminal is 4.7 ohms and when I measure from inside the plug cap to a terminal is 26.1k ohm. If I remove the plug cap as per the instructions and test from the high tension lead to the positive or negative terminal on the coil I get 21.2k ohm. These readings are slightly out of spec for the secondary coil of a H2, but way out of spec for the H1. Based on the readings I'm getting, I'm thinking that the coil isn't likely the source of my problems, however I have virtually no experience testing coils so I don't know how close is close enough. Perhaps with better voltmeter and proper clamps I would be bang on? I suspect there are others reading this that have oodles of experience. Do you think it's worth replacing the coil? If you don't think it is the coil, what do you think I should try and test next? Thank you in advance.
 

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Pull the codes first.
 

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2016 Arctic Cat Alterra 550 XT
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The diagnostic plug is under the seat. I’m going to make a video on this in the future!




 

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Discussion Starter #8
Thank you for the help! I did something stupid. I turned the key to the run position to see if there were error on the display (I wasn't certain what you meant by codes). Unfortunately, I did this with the plug/coil disconnected as I had been testing resistance. This generated an EFI error on screen and stored a SC24 code. There were no other codes. I proved this stores a code by clearing the codes, and then repeating the same actions and checking the codes again. Thus, it's possible my ride on the weekend generated a SC24 code, but I will never know for sure because my unfortunate actions also generated the same code.

I cleared the codes and took it for a 20 ride tonight. The missing was very few and far between tonight. There weren't any real back to back missing like there was on the weekend, but there were random misses. I checked the codes when I got back and there were none (AC00). I'm inclined to think this miss is not accompanied by any error codes, but now that I know how easy it is to check codes, I can monitor more closely.

I felt the ATV almost left me stranded this past weekend, so I am a bit reluctant to keep driving it without doing more testing/fix. Are there idea on other things I should check? Or just start replacing parts and hope for the best?
 

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If it’s missing less since you checked the ignition coil you may have a bad connection. Does it snap on to the spark plug good? You can pull the boot off and check the end of the wire. It might help to trim the end.

Others things to check would be to clean the carb, make sure the battery terminals are tight,




Arcticfrost
 

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Discussion Starter #10
Thank you, I've had this problem for several months now. It kind of comes and goes. So even though it was missing less the other night, I'm not convinced it had anything to do with what I did.

I bought an in-line spark tester. I drove around for 15 minutes with the tester, and of course everything worked perfect. I've the got the tester packed with me and I will install it the next time it is missing bad and hopefully I will be able to see if it is lacking spark at those moments. I couldn't see much of the seal you referenced in the video without taking everything right apart and removing it. However, what I could see when I moved the seal off didn't show any dry rot. I will definitely investigate that more fully if the inline tester suggests it isn't a spark issue. I've never really used an inline tester before.......is a miss obvious or is it easy to miss when it's sparking so frequently?
 

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Test the fuel pressure. I had the same machine and my fuel pressure regulator in the fuel tank in the fuel pump assembly was bad. It should be 43 psi I think - DoorFX knows!. Easiest way to check is at the filter under neath the rear rack. Just pull off the clamp and attached a good pressure tester. You can borrow one from O'Reilly's or Advance auto parts.

My machine slowly degraded over about a year until I had to fix it.

Skippy
 

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Discussion Starter #12
Thank you for all the ideas. I haven't found the problem yet, but I do have new data. We went for a long ride today. It was missing even more than the last ride. At times, it will even stall when idling, which it didn't do before. It starts immediately after it stalls. However, it can go long periods of time with no missing at all. It feels like there is more missing in low range, and not much if I'm heading down a road at speed in high range. That is consistent with my suspicion that the amount of missing is tied to how hard/hot the quad is. However.......

When it was missing really bad, I hooked up the inline spark tester. I was fortunate to be able to witness the spark when the machine was missing real bad and at very low RPM. I almost upset the quad steering with one arm, and not paying attention to the rut in front of me :) None the less, I was quite surprised to see the spark was strong and consistent even when the machine was missing real bad. Thus, I don't think the issue is spark.

When I got home, I ran it around the yard and got it to miss a bit. I pulled the fuel hose off the upstream side of the filter and connected it to a gauge. It read 44 psi when I turn the key on; as soon as it pressures up and the pump kicks out after a couple seconds, the pressure drops to about 38 psi. I started wondering if the filter was plugged, so I connected the filter and observed the fuel pumped through the filter into a catch container. I expected the fuel pump to come on and stay on because it wouldn't reach the required pressure. However, it came on for about a couple seconds (like normal), and then cut out. It pumped a lot of fuel in a couple seconds, so the fuel filter is not plugged. However, I'm left wondering why the fuel pump didn't stay on when pumping to a catch can? I thought the pump would be pressure controlled, but perhaps during starting it is time controlled?

Given that my problem is intermittent, I almost feel like I should "T" in the gauge and watch what the gauge is doing when the engine misses. I haven't done that as I don't have the fittings to try that today.

Any other thoughts?
 

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2016 Arctic Cat Alterra 550 XT
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Around ‘09-‘10 there were a batch of Arctic Cats that had bad fuel pumps. Everything you’ve described tells me you need a new pump. I’ve changed quite a few on AC’s around that year period. It’s pretty easy to do and should solve your missing issue!


Arcticfrost
 

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Discussion Starter #15
Keep the ideas coming. Thank you so much. I teed a pressure gauge into the fuel line just upstream of the fuel filter and routed the gauge up near the handlebars so I could observe it as I drove. I drove around with it until it started to miss. The fuel pressure was 42 to 44 PSI throughout, even when missing. Thus, I believe that rules out the fuel pump. I noted that the missing seemed to correlate to how rough the ground was. So I took it on the highway and there was no missing. I would then lift my butt 6" off the seat and then drop my mass onto the seat and quite often I could trigger a miss. I can't say for certain that throwing my weight around didn't also cause me to feather the throttle. Most of the time this would only trigger a miss for half a second, but on a few occasions I got it to trigger a miss that lasted several seconds. I thought it might be the tilt sensor, so I pulled the wire to the tilt sensor and the quad stayed idling for a few seconds and died. I am going to try and find out how to bypass the tilt sensor for additional testing. I thought I would post this in case someone is watching and has any other ideas to check. My coveralls are on, and I'm hoping I can get this fixed so I can go for another ride tomorrow. Happy Thanksgiving!
 

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Starting to sound like you have a bare or chafed wire in the harness. Most common place is just after the fuse box , where it goes up and over the frame.
 

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Discussion Starter #17
Thank you. I will check that area. I've abandoned the tilt senor idea. I found out it threw a code when I disconnected it, so if this was the problem it should be throwing codes all the time and it isn't. I also ran an unlit propane torch all around the throttle body with the engine idling to see if there were any leaks. There was no change in the idle, so I don't think I have any leaks. The rubber connector between the engine and throttle body uses a singe clamp, so I believe this is the newer version and not the one that dries out and cracks.
 

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Discussion Starter #18
To inspect the wires near the fuse box where it goes up and over the frame will require removal of the fenders. I haven't done that yet. I couldn't feel any problems. I did wedge cardboard between the wiring harness and the frame in case something was shorting to ground, and that didn't make any difference. I also tried idling the quad and moving wires around to force a miss. I couldn't find any wire movement that caused a miss. I wiggled things from headlight to tail light paying extra attention to the throttle body, ECU, main wiring harness.

I will share a few more observation in the hopes it will stir some ideas. It seems like it misses more when it is under light load vs no load. For instance, it can be missing bad while driving, I can put it in neutral coast to a stop and rev to the same RPM and it will hardly ever miss even if I'm throwing my weight around to make it bounce when in neutral. I suspect I'm bouncing more in neutral then when I'm driving at that point. I can then put it back in gear and it's missing bad within half a length of the quad. I have one small incline in my yard (very shallow - maybe 1% grad) and I've noted I'm more likely to miss climbing it then when I'm on the level or going downhill.

Couple questions: I've never used an inline spark tester before I bought one for this quad. Would I see a miss at low RPM? My neighbor who used to work at a car dealership doesn't think I would see a misfire even if it was missing bad. I can see individual sparks, so I've assumed I would. He thinks I should just replace the ignition coil as they do fail fairly frequently and it's a good bet. He thought the resistance was out enough that was what he would do. I've also read threads where guys starting replacing components and it costs them a LOT of money and they still don't fix the problem.
 

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Cat uses what is known as a wasted spark ignition. It fires every revolution so a misfire is going to be hard to see.
 

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Salad,

does seem like an intermittent short. When you replaced the spark plug was the wire screwed all the way into the cap?

Are the wires going into the coil tight and is the spark plug wire tight at the coil? All easy checks.

Skippy
 
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