08 Dragon - strange intermittent bog

Was riding with friends last Friday and I have an intermittent bogging problem that has gotten worse than the prior ride (and did not exist before that).

Behavior: Wide open climbing or getting into it carving a sidehill, the engine sometimes acts like it is dropping one cylinder, or at least a half a cylinder, as it still pulls enough to let me turn out or cut a different sidehill path and feather the throttle some. This is happening more consistently now than it did last ride out, where it mainly only happened while racing a buddy across a short lake. I did find that when it does it if I feather in and out of the throttle I can usually get past it or get the sled to pull again sometimes all the way through the end of a climb. Straight out WFO from the bottom of the hill with a little run-up before the steep, and after 5-10 seconds - instant bog that won't go away unless you change throttle position. Does not die completely like I said, seems like maybe a 30-50% reduction in power. It is not an instant RPM drop so I do not suspect clutching, also because when the bog is absent it climbs like a champ.

I am not getting a check engine light flash (so probably no DET issue), not hitting the rev limiter (happens even way below 8000 RPM), water temps are fine, KOSO EGTs were showing in the 800-900 range one time that it happened for a prolonged time during an easy sidehill (did not feather the throttle which gave me plenty of time to check EGTs and check engine light). Max EGT shows a little over 1100 degrees F.

Sled details: Chassis has approx 4100 miles on it, engine has a lot less. Carls 860 big bore with pistons / rings replaced late winter for maintenance per Carls. Approx. 1500 on bottom end. Exhaust valves were cleaned and passages checked at that time. Reeds inspected at that time and are fine. Switched out spark plugs for a new set of BPR9EIX Iridium NGK (from a used set) during the ride, no difference. New spark plug caps before the ride, wires look good but are in the protective plastic loom cover stuff so difficult to inspect them completely.

Due to a no-start problems after the overhaul over a month ago, at that time I ended up switching out the stator (which did not help), complete engine harness with injectors (which did fix the problem), fuel pump tested fine at that time, new fuel filter was installed, VR switched out and back to "original" (replacement "good" one). No indication of voltage regulator problems i.e. no flickering of lights, voltage level on gauge is good / normal. I did switch out the gauge with an analog / digital combo gauge from an 05-06 900 but all the lights light up when you start it and it self-checks fine.

Ideas? Even though I did not get a CEL (chk engine light), could there be a code in the computer? I can ask the local Polaris dealer to read out any code.

- Seemed like the SPI fuel filter line was "kinked" on one end when given to me by the (non-Polaris) dealer, I mentioned it and they said "they all come that way". I was thinking poor packaging but at the time I was trying to get the sled just to fire up and was glad to find a filter locally. Maybe this is restricting fuel flow? But if it was, wouldn't I see EGTs spike, or have the DET sensor go off at least due to lean condition? I have another fuel filter without this kink I can put in there to test next ride out (possibly / probably last ride of the year).
- Plug wires - replace them too?
- Could it be a bad throttle position sensor, even though I am not getting a code?
- Maybe the stator I got has intermittent issue(s)? although it worked fine for a number of rides.
- Coils? Seems strange one would go out now but you never know (they were the only thing I did not change out when trying to get rid of the no-start condition after the new top end). I do have a friend who (I believe) has a spare set. Will see if I can get them and switch them out before the next ride (if it happens).
- Exhaust valve selenoid? Easy test - just plug it off...

P.S. Thanks to NapaMatt, sled_guy, PaulAnd, AngerManagement890, DiamondDave, and many others for giving me lots of good ideas when this sled would not start after the new top end (well, it started a number of times in the shop and on the trailer but was giving me a CEL injector issue blink code and finally would not restart at all). While annoying and sometimes dangerous, this problem is small in comparison to that one, at least I am riding.

Wow, no response... I think I dislike the way the polaris forums are organized, in general. All the guys who may have helpful experience with "older" sleds like mine apparently don't look at the "browse all polaris" forum or the older IQ forums very often and don't see when someone is looking for a helping hand...

Oh well. I am gambling on it being the TPS, dealer tech was thinking the same thing based on what I described to him, so they get to look at it and possibly replace it tomorrow.

So I plan on riding next Tuesday (28th)! Guys (and gals) dreaming of their new Axys RMKs can dream while we are still out riding. ;-)

EDIT: They tested and adjusted the TPS and idle today (23rd), said it was out of adjustment but it tests out okay as far as values go. The only trouble code in the computer was a single low voltage(?) code... momentary glitch since I am not getting any voltage issues or indications.

retiredpop said:

I think there is a possibility the TPS is faulty. I have never cut one apart to look at the internal workings of them but I think they have a wiper arm that physically sweeps across the windings of a precision wire wound resistor. Anyway if the wiper arm does not push on the windings with sufficient pressure the resistance will not be consistent and may vary slightly if the throttle stays in one position. When you change throttle position the wiper arm makes good contact again for a while so the problem clears up. That's my theory but if you have swapped out the TPS unit for a known good one then I'm just blowing smoke.

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Thanks retiredpop. I have not swapped out the TPS since you need a special gadget to set it, and I don't have a spare one of those available (and new ones are like $150). Dealer tech said it tested out fine as far as functionality goes and the adjustments were off some so he set all the adjustments (he did sound like he knows what he is talking about as there are low / high voltages and ranges of values he prefers within the factory specs, etc.). I am going to throw a set of ignition coils on it too, that I borrowed from a friend (his spares).

I also brought up the fuel filter line "kink" issue with the tech and he said they have had filter lines come in bent like that and never have a problem with them, and he did inspect the fuel lines for issues and saw no issues. He also said the sled ran out great on the stand.

Hopefully I will find out on Tuesday if the snow at the trailhead has not melted completely... gotta get the stuff swapped out...

Snowbird11 said:

i had a similar problem a while back that ended up being a rusting slp can choking off the exhaust intermittently.

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Thanks for the idea. I have already replaced the SLP can once on this sled and once on another sled due to baffle breakage internally (you could hear it rattling around), this one is still silent so hopefully that is not the problem.

The good news is no cutting out today, I thought it did it once but might have been mistaken. Only thing is now I am not sure if was the TPS since the dealership adjusted it and everything, or if it was the ignition coils which I had switched out. I wanted today to be an epic riding day, and it was.

Bad news is I did get a 5-blink code on the way out from the bowls - exhaust temp sensor. Crossed the creek, got the code, not too worried about it, it went away and did not come back.

Second bad news is Lincoln Bowls are done for the year. A month early basically. Bummer.

NapaMatt said:

hey haven't been on in a while..

So Did the tps fix it?

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Dealer tech said the TPS tested out good, but was misadjusted, so they adjusted it (not just to specs but to his / their [Kurts] preferred range). Also I replaced the ignition coils with a spare set a friend of mine had, wanted the last ride to be a good one, since we were running out of snow early. And it was! Only one momentary / minor bog one time but it might have been the situation I was in, I never had a stitch of trouble otherwise, turned out to be a really good day to end the season...

milehighassassin said:

Kind of a slow time of year around here. Most people are done for the season.

TPS would have been my first suggestion. Clean exhaust valves as well. Check the springs to make sure they are good.

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Just had the engine apart for an overhaul 4-5 rides before this and cleaned exhaust valves and replaced springs with new.

slash said:

mine had the same bog the fuel line not the filter was restricted . made a new one 5/16 ID hose open full flow ends bigger filter.

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Made sure that there were no kinks or restrictions in the fuel lines other than the one I mentioned above in the fuel filter line, dealer tech claimed they have seen lots of them come in with that bend (almost kink) and as long as the line is basically situated straight then the pressure (58PSI) keeps it open and flowing. I did not replace the filter with the kind-of-kinked line (it was already a new filter and the only one I had to put on there when I was trying to get the sled going when I had a no-start issue after my new top end). Fuel filter was not the problem with the no-start (long story, another thread on there already), and apparently not this time either. :becky:

So next season I get to try to figure out whether it was the coils or TPS, I will put my original coils back in, but who knows how far into the season we will have to go before I get to open it up on hills... pray for better snow than we had this year...

Thanks for the input guys. Unless my bog comes back next season, I consider it basically solved...

It's baaaack...

Well, the bog is back, momentary wide open bursts on trails yesterday, and in and out of throttle carving up a clearcut, and it is intermittently back...

This is with the spare set of coils from my friend in place from last year, so apparently not the coils.

Seems like TPS is next eh?

The bog comes on suddenly and unpredictable, one time it will be fine, the next time at full throttle it will act like a miss on one cylinder, but then sometimes kick back in... not long enough for the EGTs to react from what I have been able to see.

I think it is fixed, fingers crossed... was it the fuel pump?

I could reproduce the bog even in our field when there was still snow 3 or 4 weeks ago, with a full throttle burst, almost every time. One buddy recommended taking apart the related electrical connectors, making sure they were clean, and putting in some dielectric grease. I did that, hit them with a small wire brush if there was any doubt and if they were big enough. Thinking back to when I was fighting the no-start after the new top end, my fuel pump sounded odd, even though it had the correct pressure, not a consistent hum when powered up, kinda growly etc., so I ordered a new fuel pump (not assembly, just the pump, way cheaper), pulled it out Wednesday and replaced it, hit the big hills yesterday and not one bog or glitch detected.

Since it seemed better after the TPS was set, I am not counting my chickens yet, but so far so good. I was also down some on RPM due to concrete spring conditions, going to drop a couple grams and go again sometime soon.

HalfBrit said:

I have similar issue on my 08 d8.
did you test it after the dielectric grease and before replacing the fuel pump?
because it is intermittent, connection problems sound likely.

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If I recall correctly I got one ride in between the dielectric grease and the fuel pump replacement... most of the critical connections I could not wire-brush as they were too small and all had rubber seals on them anyway... I added a little dielectric grease to them as a precaution. The bigger ones like the voltage regulator and stator connectors I was able to brush a little but they still had a little older dielectric on them and no visible signs of corrosion. One way to tell for sure on the fuel pump would have been to have a fuel pressure gauge hooked up to it while riding and see if it dropped but the gauge I used last go-around was borrowed and I figured with 4K mountain miles on the chassis and fuel pump and the growly varying sounds it made when powered up, the fuel pump would be a good maintenance item anyway, keep from being stranded should it ever quit in the backcountry.

I recommend powering up your fuel pump with the sled itself not running (there are threads on priming your fuel pump using 12 volts, that will do it) and see what it sounds like, should be steady hum and not varying or growly in my opinion anyway...

Toy Tech said:

I had a full mod on my 2003 RMK 800 that was acting like that. I found that the crank was out of phase and had to replace the crank & got a rebuilt crank. It ran great for 2 rides and started acting up again. I sold it to my cousin and he put a new crank in it and it ran great for him. I don't know if you still have this sled anymore, but you may want to check the crank phase and make sure that both the mag & pto line up properly at timing marks on the mag side. Polaris has always had issues with cranks when you pump out big HP. I've heard of people running big bores hard on Polaris' replacing the crank yearly to keep from going through this pain in the butt.

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Great that you bring this up... I lost the crank late last spring on the way back to the truck. Didn't explode, just made funny noises and can wobble the clutch around by hand... going to replace the crank here shortly, maybe that will fix this old issue for me... thanks for the info!