MPI turbo issues on Viper between 5100-6000 rpm. Stumbles then takes off again

[PropellerHead]

I have a 2015 Yamaha Viper with a Yamaha dealer installed MPI turbo. I bought it last year and out on the trail I noticed it will hesitate and sort of stumble while accelerating between 5100 - 6000 rpm when accelerating moderately hard. Of course the guy I bought it from said "It does, huh, I never noticed that". When I accelerate slowly it is usually less noticeable or not noticeable. When I aggressively accelerate it does it very briefly Although I think it is harder to notice because it gets past the spot where it hesitates a little faster. Everything seems fine once I am up at high rpm like 6500. The turbo appears to be working because it keeps up with my friends Sidewinder with a 250 tune, but as a Viper it is geared lower so it gets to 80 mph fast but can't top 90 mph ish. It feels like a waste gate opens up too long and it looses most of it's charge. It also makes a slight miss or sputtering sound when this happens. When it does this, if I back off the throttle a tiny bit, it goes away and actually speeds up instead of slowing down and the sputtering sound goes away. If I leave the throttle right there, it runs and sounds GREAT, but trails have corners. Other symptoms: it starts hard or even not at all in very cold weather, and it gets poor gas mileage 9-10 mpg. We reduced the spark plug gap to .20 it was at .28. That and cleaning the air filter seemed to help it run better, but it was not the complete answer and still has all of the symptoms. Its almost like when the waste gate opens, it does so too long or opens too much. Idea's?

 

[xpturbo600]

Set the plug gap at 18 thousandths. My guess is you notice the slight hesitation as the turbo starts to spool, making a pound or two of boost. That point is where the map sensor starts to read pressure and additional fueling doesn't start until sufficient boost is read by the sensor. What is your fuel controller? If the standard dobeck box...try upping the base fuel a step or two and/or bump the transient boost fueling up a step as well.

 

[PropellerHead]

I keep the sled 5 hours North of me so I can't look at it and can't remember off had what brand the fuel controller is but it does have a way to increase of decrease settings. Its credit card sized and maybe 1 cm think. A while back I read a little about it. It has 3-4 distinct rpm zones that can be adjusted on the controller. Each one has specific boost numbers so I will try what you suggest. One thing that seems to conflict with the logic of adding more boost is the sputtering sound which sounds a bit like an old 2 stroke that has the choke still on or partially on and is fouling the plugs. This might mean that it is dumping too much gas in and knocking out spark or igniting it in the exhaust, although I hear tiny little pops/rumbling when this happens not a true backfire which I would think would be the case if a large amount of excess fuel was being dumped into the exhaust. I have never taken any of this apart but if I were to guess I would guess that a waste gate opens, I loose pressure and it stumbles, then if I accelerate, it leaves that zone and off I go. The whole problem only seems to occur between 5000 ish and 6,000 ish rpm or maybe 6500 rpm. From 6500-8000 it is a powerful beast. Thanks for the help. Alex

 

[NOSNOWNOGO]

I had EVO reflash the stock ECU on my viper. Vipers have a terrible stock fuel map with alot of lean and rich spots. When you back out of throttle it goes lean. That might be cleaning the low end over fueling out. I believe dobeck control box is what is being referred to with fuel adjustments. I highly recommend running a good AF guage. AEM is what I run. Yes they don't give them away. The only way to know exactly what is going on and when is to have a clear understanding of what fuel mixture is. Check and monitor fuel pressure as well. I run a digital fuel pressure guage for real time monitoring. AEM as well. I ended up going back to nytro ecu and wiring and put my viper kit in an axys chassis. Whole different kind of monster now. Good luck!

 

[PropellerHead]

Thank you, I will look into getting gauges. If I can get it working without gauges and the expense, I would prefer to do that but it might be the only way to know what is going on. This is my first Turbo and I don't know enough to start making adjustments on the programmer and don't want to loose the rest of my season because I try something that ultimately leads to problems. Thanks, Alex

 

[NOSNOWNOGO]

Completely understand. No way of knowing if it's a lean or a rich stumble without being able to monitor. The main issue I had was AIT Temps. Charge air going into throttle bodies. Innovate guages are cheaper but you need to calibrate. You may simply have a fuel pump going bad or a filter issue. Hence monitoring fuel pressure as well as 02s. Loss of fuel leads to a lean mixture and will cause detonation. Not a road to go down. Nytros had a weaker stock fuel pump so most high hp kits ran a secondary pump with a 1-1 regulator. I'm guessing you are running a 180 kit. One other reason I reflashed ecu was to raise Rev limiter. It's factory set to 9k I believe. Raised it to 10k. Vipers hit fast and they bounce to 9400 9500 quickly. It's so fast you would not be able to see it on display. Would need a data logger. This could also be the issue. If you are able to ease into it. Again would need data to gain more understanding to eliminate. I know alot of people are setting gaps. I've bounced back and fourth and have not seen a difference either way. Clutching, belts, bad or stuck rollers. All could be the issue or play a part. The most important thing to me is monitoring the internal combustion. If it goes sideways it's not a cheep fix. Don't get too discouraged. Any guy running a turbo for any amount of time hits some snags. The performance difference to me makes it all worth it. I have a build in the member builds forum. Vipax. I definitely understand frustration of things not working as quickly as we would like. Hopefully that helps.

 

[NOSNOWNOGO]

Also don't reuse plugs. Install new. I read you reset gap. Not sure if you replaced. Ngk cr9e are what I run. .28 on gap. No issues at 19lbs of boost. I just make sure they are all the same when installing. If I think I have one bad I replace all.

 

[PropellerHead]

Thanks. I think I will leave the plugs gapped at .20 for now because I do think it helped reduce some of the problem. I think it had 2 or more problems and re-gapping it helped one of the problems because it definitely ran better while accelerating hard. If I had to guess, tit's either a mapping issues as it transitions from one range to the next or a waste gate opens and stays open too long. The reason I think it is more likely to be the waste gate is this stumble happens at slightly different rpm ranges not always at exactly 5100. Sometimes it is 5400, sometimes a little higher. If I accelerate gently it does not always do it. My thought is maybe the waste gate opens to dump excess pressure and fuel and can't close again while under that amount of boost. I don't even know what the parts look like so I really am just guessing but maybe the boost is set so high that it relieves the pressure but can't close the gate fast enough. I'm looking for any help I can get from people that understand turbo's because I don't so all I an do is read comments, see if it matches symptoms and if it does, try it. I really appreciate the comments. Thanks, Alex

 

[NOSNOWNOGO]

The Reasoning behind the smaller gap is out of airflow under high boost blowing out the spark. I'm only guessing but I'm assuming you are running a 180 kit? 6lbs of boost? Wastegate could possibly be an issue. Bad actuator possibly. Again the possibilities can go on. K.I.S.S. Something I frequently have to remind myself of. Air, Fuel, Spark. Always go back to basics. A fuel map doesn't get out of adjustments unless it's not able to read sensors correctly. Could be a boost leak. Bad or plugged map sensor. A pressure test can aid in finding. Might be an exhaust leak. That's a simple test. Start sled. At idle plug off exhaust with rag. Don't burn yourself. It should die very quickly. As I said earlier establishing a baseline is the safest and fastest way to start narrowing things down. It shows you where to start looking. A boost leak will cause the turbo to overboost. Hopefully some of what I'm saying makes sense.

 

[PropellerHead]

Thank You, Alex

 

[PropellerHead]

Set the plug gap at 18 thousandths. My guess is you notice the slight hesitation as the turbo starts to spool, making a pound or two of boost. That point is where the map sensor starts to read pressure and additional fueling doesn't start until sufficient boost is read by the sensor. What is your fuel controller? If the standard dobeck box...try upping the base fuel a step or two and/or bump the transient boost fueling up a step as well.

Thank you I will give that a try. Going to be hard to test since the snow has disappeared where I am but I will try that and wait for next season. One odd thing that happens is when its stumbling during acceleration, if I let off the throttle ever so slightly, it starts running smoother, the noise goes away and I actually pick up in speed enough to be noticeable but not that measurable (maybe 1-2 mph). Its like it starts burning correctly. When it stumbles it also runs a bit rough and I can hear what sounds like a very small backfire but since it has a performance muffler I would think any backfire would be loud. Thanks again for your suggestions. Alex

 

[PropellerHead]

Thank you I will give that a try. Going to be hard to test since the snow has disappeared where I am but I will try that and wait for next season. One odd thing that happens is when its stumbling during acceleration, if I let off the throttle ever so slightly, it starts running smoother, the noise goes away and I actually pick up in speed enough to be noticeable but not that measurable (maybe 1-2 mph). Its like it starts burning correctly. When it stumbles it also runs a bit rough and I can hear what sounds like a very small backfire but since it has a performance muffler I would think any backfire would be loud. Thanks again for your suggestions. Alex

I had EVO reflash the stock ECU on my viper. Vipers have a terrible stock fuel map with alot of lean and rich spots. When you back out of throttle it goes lean. That might be cleaning the low end over fueling out. I believe dobeck control box is what is being referred to with fuel adjustments. I highly recommend running a good AF guage. AEM is what I run. Yes they don't give them away. The only way to know exactly what is going on and when is to have a clear understanding of what fuel mixture is. Check and monitor fuel pressure as well. I run a digital fuel pressure guage for real time monitoring. AEM as well. I ended up going back to nytro ecu and wiring and put my viper kit in an axys chassis. Whole different kind of monster now. Good luck!

 

[PropellerHead]

Thank You. I will definitely consider reflashing my ECU. First I am going to put on a AF gauge that I bought. I bought an inexpensive one and I will try that for now. While somehow I want to believe it is a bad waste gate system, when I think through the logic of when the waste gate should be open, (de-accelerating) that is not when the problem occurs. The problem occurs when I am accelerating between 5000-6000 rpm's and not always at the same rpm. When I mash the throttle down and hold it down on a straight stretch, it accelerates extremely well up to 5000 K and from 5-6 it accelerates OK but seems to not be as dramatic, then after 6 its accelerates exceptionally well again. It tends to be harder to notice this because you blow right by those rpms. When I accelerate moderately, is when its noticeable between 5-6K and you can hear it stumble. If I accelerate lightly it does not seem to do it. Thanks, Alex

 

[PropellerHead]

Completely understand. No way of knowing if it's a lean or a rich stumble without being able to monitor. The main issue I had was AIT Temps. Charge air going into throttle bodies. Innovate guages are cheaper but you need to calibrate. You may simply have a fuel pump going bad or a filter issue. Hence monitoring fuel pressure as well as 02s. Loss of fuel leads to a lean mixture and will cause detonation. Not a road to go down. Nytros had a weaker stock fuel pump so most high hp kits ran a secondary pump with a 1-1 regulator. I'm guessing you are running a 180 kit. One other reason I reflashed ecu was to raise Rev limiter. It's factory set to 9k I believe. Raised it to 10k. Vipers hit fast and they bounce to 9400 9500 quickly. It's so fast you would not be able to see it on display. Would need a data logger. This could also be the issue. If you are able to ease into it. Again would need data to gain more understanding to eliminate. I know alot of people are setting gaps. I've bounced back and fourth and have not seen a difference either way. Clutching, belts, bad or stuck rollers. All could be the issue or play a part. The most important thing to me is monitoring the internal combustion. If it goes sideways it's not a cheep fix. Don't get too discouraged. Any guy running a turbo for any amount of time hits some snags. The performance difference to me makes it all worth it. I have a build in the member builds forum. Vipax. I definitely understand frustration of things not working as quickly as we would like. Hopefully that helps.

 

[PropellerHead]

Its still a ton of fun to ride and when a 250 hp Sidewinder and a 2020 Etec 850 can't pass it until I hit my max rpm which seems to be 8,600 or 8,800 on my sled, I can't really complain. Early on, I though it might be the clutch. While it seems to work well, all it would take is a problem with one spot and it would slow down the rate of acceleration and might even cause it to briefly accelerate when I back off the throttle (which it does) because it then can get out of a spot where it is sticking. My guess is, it is flooding the engine at those rpm's. Since that controller has adjustable settings and I think 3-4 different stages it goes through, the one for midrange might be too rich, then when I de-accelerate a tiny amount it perks up and goes faster brirefly, probably because it gets a better fuel mixture. It would also explain why it is sort of stumbling and has a very slight gurgle or popping sound when the problem occurs and then that goes away when i let off the throttle slightly. It only does this when I am on the throttle hard. I would not think a clutch issue would do this, but if it is in need of more power to run well due to a clutch is the wrong position it might sort of stumble, and then correct once I back off the throttle a little. Thoughs?

 

[NOSNOWNOGO]

Have you looked at your clutch weights and rollers? A bad bushing can cause a weight to stick. Bad or broken springs. Helix. Etc. Yes clutching can create alot of issues.

 

[PropellerHead]

I havn't yet due to not having a heated garage where I keep it which is 5 hours North of where I live. This spring I plan to go over everything, clutch, fuel settings at each rpm. The hard part is if I adjust them I don't have a good way to test the sled in warm weather. Time for a heater in my storage building. Thanks, Alex

 

[jim]

Four strokes like a burst of fuel when you thump the throttle...they tend to go lean when you hit the throttle more aggressively. Hence fuel maps will shoot a burst of fuel along with a fast throttle flipper (carb'd motors have an acceleration pump to do this, EFIs use mapping). It almost gulps the air when you do this and can create a lean spot. And this is only amplified on a turbo. That's why it's smoother when you roll on slowly...no gulp of air and fueling keeps up.

But it sounds like a classic lean spot when you start pouring on the coal. Don't be afraid to adjust your turbo boost mapping 1 notch richer for that RPM range. Just write down your base settings you have now and come back to them if you get lost. You can buy gauges and sensors, but I don't think you need to. The reality is, some sensors/motors like one set of numbers and an identical other sled will be different. Go by the tune and feel...not to mention good luck keeping an eye on the gauges when you are thumping the throttle into full boost...objects are closer than they appear at that point!

BTW...9-10 MPG for a turbo is actually pretty good.

 

[Cable810]

Have you figured anything out?? I've run into the same issue. Running lean and stuttering at the same Rpm range.

 

[Cable810]

Not to HiJack this thred but foe future reference years down the road I hope this will help!

I was dealing with a similar issue and I pined it down to a bad turbo...

Here is my thread at TY4STROKE

Viper Miss/Stutter. Wont fire on .02 Gap

After the first ride of the season I'm left with trying to get the sled running right... 2015 Viper MTX Mpi turbo. Between 5100 and 6200rpms there's a stutter and sounds like a miss. 0lbs of boost at around 40-45mph i get a constant stutters and sounds like it's missing as well. Once I get...

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