• We are no longer supporting TapaTalk as a mobile app for our sites. The TapaTalk App has many issues with speed on our server as well as security holes that leave us vulnerable to attacks and spammers.

Hesitiation/Stumble on throttle stab

bigreis

Lifetime Member
Joined
Jul 10, 2011
Messages
201
Location
Central Minnesota
Country
USA
Snowmobile
2007 Apex RTX
2009 Nytro XTX
I have about 1500 miles so far on my 09 Nytro XTX with a Push Turbo. This is my first boosted sled and overall I am impressed except for a hesitation when going quickly to WOT. I am running 6 pounds of boost, PCV with maps direct from Push, clutching from Push, etc... I was thinking of messing around with the Accelerator pump feature on the PCV to see if that helps with anything. Just curious if anyone has experience with this and if the hesitation is typically due to too much fuel or not enough at rapid throttle increase events?
 

I have about 1500 miles so far on my 09 Nytro XTX with a Push Turbo. This is my first boosted sled and overall I am impressed except for a hesitation when going quickly to WOT. I am running 6 pounds of boost, PCV with maps direct from Push, clutching from Push, etc... I was thinking of messing around with the Accelerator pump feature on the PCV to see if that helps with anything. Just curious if anyone has experience with this and if the hesitation is typically due to too much fuel or not enough at rapid throttle increase events?

Do you have the pod 300 as well? 550cc injectors or stock? Dont mess with the accelerator pump feature, but you should be able to clean up the transition of going from no boost to boost in the map. It is hard to say exactly what is going on without seeing what your a/f is when it happens.
 
Do you have the pod 300 as well? 550cc injectors or stock? Dont mess with the accelerator pump feature, but you should be able to clean up the transition of going from no boost to boost in the map. It is hard to say exactly what is going on without seeing what your a/f is when it happens.

I do have the POD and 550 injectors. I will post some data logs I took over the past weekend later tonight. Thanks for the reply.
 
Do you have the pod 300 as well? 550cc injectors or stock? Dont mess with the accelerator pump feature, but you should be able to clean up the transition of going from no boost to boost in the map. It is hard to say exactly what is going on without seeing what your a/f is when it happens.

I have attached two data logs from yesterday... one at low speed because I am wondering if my aft is something to be worried about at low/no boost condtions. Second is a pull from rolling start to full throttle. I can't recall if I got the hesitation I am usually seeing on this run... typically I notice it most from cruising around 30 t0 40 mph and then stab the throttle to launch off a roller or big bump. I am a total novice at boost tuning but really want to learn, so any help is greatly appreciated... the top link is for the low steady speed and the bottom link is for the full throttle pull. First thing I notice is that I am not even breaking 8500 rpm at WOT... should I take a magnet out of the tip of the weight and rerun a log?

https://drive.google.com/file/d/1Kpk8ucoznW3Ti9rCi1VYJr23ze2viWhA/view?usp=sharing

https://drive.google.com/file/d/1pmyoDmJrXEFa-oeE40Y4ECZiu_Z6F4Ak/view?usp=sharing
 
Last edited:
Bringing and old thread back alive here it looks like. Did you ever figure out what the issue was?

I too am having this same issue with my MPI Nytro. It will fall on itself for a split second when you mash the throttle. It doesn’t matter much whether it’s from a dead stop or while rolling. When it’s pegged it falls on it self for a gazilionth of a second then comes back and pulls hard with no issues there after until you let off the throttle and go to mash it again. I have noticed it will do it most when I’m not in the turbo and driving with gradual throttle changes then mashing it quickly. If I’m feathering/blipping the throttle quickly then mash it it won’t do it at all. It never did this last year however this season I upgraded the fuel system to an external walbro pump and an electronic boost controller. Boost pressures have remained unchanged at 6# however fuel pressure has from the stock 38# to the 43# I have it set to now. I have noticed my AFRs will dump to the 9s for a split second when it does its split second bitch fit so obviously it’s from a rich condition however where it’s coming from I have yet to figure out. I have the gems box turned all the way down so my only other thought would be the increase in fuel pressure coupled with some turbo lag??? Maybe some one else could shed come light.
 
Sounds like too much fuel dump during the accelerator function now, serves like an accelerator pump on a carb... to eliminate a lean bog during that brief transition of added air when the throttle plate is wicked open.
All EFI has to have it, so the stock ECU has it built in based on rate of change and amount of throttle position but obviously calibrated to the stock fuel pressure in order to provide the correct amount of that instantaneous fuel burst. Since you said you now have more fuel pressure it logically is supplying a proportionate amount more during that accelerator zone and is too fat, flogging the cylinders with fuel causing a rich stumble. If it's richer at idle too, that is another symptom of the higher base fuel pressure.
Not sure if the GEMS controller has a zone to adjust that accelerator amount, but I doubt it being a piggyback controller because it would never react quick enough.
Try setting the fuel pressure back to stock so that the factory ECU calibration is complimentary and adjust your GEMS to adjust fuel under boost.
I'd say it isn't a turbo lag, because you said it didn't do it before you upgraded the fuel supply system and you didn't mention you changed anything else.
 
Last edited:
I have about 1500 miles so far on my 09 Nytro XTX with a Push Turbo. This is my first boosted sled and overall I am impressed except for a hesitation when going quickly to WOT. I am running 6 pounds of boost, PCV with maps direct from Push, clutching from Push, etc... I was thinking of messing around with the Accelerator pump feature on the PCV to see if that helps with anything. Just curious if anyone has experience with this and if the hesitation is typically due to too much fuel or not enough at rapid throttle increase events?
Did you ever find the solution to your problem? I'm experiencing the same problem.
 


Back
Top