Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Ironhorse]

My Ultra is an '01 with M&M FI. Although it was dyno tuned and ran very well, every now and then it had an occasional exhaust pop while shifting. Nothing too disconcerting, just a loud single pop. From another thread, I learned how to adjust my TPS via voltage readings. I changed the voltage from .38 to the recommended spec at .61 volts. So far the bike seems to be running a bit better and I have not experienced an exhaust pop.

Is it possible having the TPS off may have been the cause of this?

[hd-dude]

To answer your question, possibly. If the TPS is off and it thinks the throttle is open the ECM will deliver the fuel to the injectors based on that setting. Another thing that happens (I found myself doing this) is when shifting you need to roll the throttle all the way closed or again the ECM will continue to deliver the fuel per the throttle position.

[Ironhorse]

To answer your question, possibly. If the TPS is off and it thinks the throttle is open the ECM will deliver the fuel to the injectors based on that setting. Another thing that happens (I found myself doing this) is when shifting you need to roll the throttle all the way closed or again the ECM will continue to deliver the fuel per the throttle position.

Is that what's happening, by not closing the throttle all the way, the ECM reads the fuel in the system, leans it out to compensate, and that causes the occasional pop? Or do I have that backwards? Would it also be safe to say that if the TPS was lean at .38volts vs .61volts, then the bike was running lean across the board, and the ECM was contantly trying to richen it?

Thanks

[hd-dude]

I'm not sure of the voltage level you had causes a lean or rich mixture. If the throttle is not closed all the way it would be adding fuel thus creating a possible rich mixture for a short duration during the shift, If the pop is coming from the exhaust that would explain it.

[Ironhorse]

I'm not sure of the voltage level you had causes a lean or rich mixture. If the throttle is not closed all the way it would be adding fuel thus creating a possible rich mixture for a short duration during the shift, If the pop is coming from the exhaust that would explain it.

Okay, I'll work on closing the throttle ALL THE WAY when shifting now.

Could having my TPS out of adjustment also contibute to less than ideal fuel economy? In other words if the misadjustment of the TPS was sending voltage signals to the ECM telling it the throttle position was in a "lean condition" across the board, would not the ECM try and compensate by increasing fuel thereby causing low mpgs #s?

Thanks

[arcticdude]

The 01 manual talks about adjusting the TPS but doesn't give any specific values.  It only indicates to use the original value found when tested BEFORE removal and adjust to the same values after installation.  But it does state "Best performance will be obtained using the original voltage value, but if the value is not reliable due to sensor damage, the use 0.275v (275mV)."  This is referring to installation and adjusting to a "throttle fully-closed".  So by adjusting yours and increasing the voltage, you should be increasing the fuel delivered by the injectors- ECM "sees" higher voltage from "more open" throttle and delivers more fuel to go along with more apparent air flow.  Of course, the BPS (or MAP to the car guys) will not sense a higher load, so it will tell the ECM to limit the amount of added fuel.
As for attempting to relearn to "fully close the throttle" on shifting- that's not needed.  You only need to close the throttle enough to cause a negative pressure sensed by the BPS, which will shut off-essentially- the fuel to the motor.

FWIW, my 01 did the same occasional pop.  From several sources (some I believe and some I don't) the all concurred the M&M FI was just that- M&M's.  It wasn't sophisticated enough to quickly adjust the FI.  BUT- your SERT should be able to fix the pop.  Find a good tuner.
Hope this helps.

[Ironhorse]

Thanks for all the response guys.

Let me "spin" something else into this equation.

I have one of those Alpha N digital fuel processors, the one from Gary Betherum at World Thunder Express. Gary installed it when he did my dyno tune. And even though he did a great tune, and got the bike to run better than before, it was not, I hate to say, "perfect". There was that occasional "pop" while shifting, a low idle when cold, and mpgs in the low 30s.
 
So I got the idea to check my TPS voltage. Using the SERT data mode, I checked and adjusted it per the instructions in HD Service Bulletin M-1101 dated April 25, 2000. The TPS read .38. I adjusted it to .61.
 
When I fired the bike up, it idled fast and high when cold, and then dropped down to about 950-1000rpms when warm. I rode the bike all day today, and not a single pop while shifting. I purchased gas and on the remaining fuel I had used, I averaged 35mpg, so the fuel economy is coming up too. I think/hope I resolved my outstanding issues. I just need to see better fuel economy to really know.
 
Here is my hypothesis (Wild Ass Guess) on what happened. The bike was dyno tuned with the TSP in a lean setting. The lean setting was across the board. This lead to the low idle when cold, and the occasional pop when shifting. The O2 digital fuel processor read the lean condition, and made up for it by making the ECM add more fuel across the board. When it was unable to accomodate rapid changes, like during a fast shift, sometimes the exhaust pop occured. This overall enrichening lead to poor fuel economy. By adjusting the TPS, the fuel processor now reads proper burn, and minimizes fuel usage. And it no longer pops.
 
What do you guys think, plausible?