Low RPM Misfire/Hesitation

At the risk of posting some info for a second time, I decided to start a separate thread on the hesitation/misfire my bike does at low RPMs. Some of this info is also in the CO Adjustment thread I posted a while back. If any of the Admins think it is inappropriate, take whatever action deemed necessary. No problem.

Like a lot of guys here I have spent a fair amount of time screwing around with my bike right after getting it. I played with the CO adjustments on the bike trying to smooth the idle. Bought a PCIII and hooked up my 5 gas. I learned an awful lot since I’ve started messing with it, and have the fuel mapping very close to how I want it. I no longer have a surge at low cruise speeds and still get 40-44 MPG pretty reliably when running slab. The only thing still killing me is the miss/hesitation at around 1700 RPMs. I’ve read posts here with cures ranging from PCIIIs to throttle cams. If you followed my thread on CO adjustments you already know I have been trying to figure out what the problem is.

Here is what I know:

The reason my bike misfires at 1700 RPMs, whether accelerating or cruising, is that it is seriously over-fueling due to unwanted acceleration enrichment. The computer appears to be overreacting to a noisy TPS signal, because removing the TPS signal fixes the problem 100%. Adjusting the TPS to higher and lower voltages moves the miss to different RPMs, but doesn’t make it go away.

One of the reasons we have a TPS on our bikes is to act as an accelerator pump. As the throttle opens, and engine vacuum drops, the engine needs lots of enrichment so it won’t hesitate. Without it, the engine would fall on its face, momentarily, when the throttle was opened rapidly. My bike adds this fuel, unnecessarily, at 1700 RPMs. You can easily see it because it uses extra injection pulses that are not timed to the firing sequence of the engine. They are called Asynchronous Pulses, and are pretty commonly used in fuel injected cars for this exact purpose.

If I disconnect the TPS on my bike, and add the necessary enrichment with the PCIII Accelerator Pump tool, the bike runs perfectly under all conditions except full throttle. The bike won’t top out, and pulls poorly at high RPMs.

Yesterday I got a chance to chance another ’08 FJR. Although I didn’t ride the bike, it does run poorly between 1500-2000 RPMs, just like mine. The guy let me put my lab scope on it. The injection pulses are just like my bike. I’m satisfied that this problem is not unique to my bike now.

Here is what a normal injection pattern looks like. This is only 2 of the 4 cylinders.

Don’t try to overanalyze these scope patterns. The resolution is too low for that. Each little notch is an injector firing. Ignore whether they have the spike at the end or not.

Normal Pattern



Here are a couple of screen shots of the 1500-2000RPM range. Note the untimed pulses.





Compare these to the ones I got on my bike about a month ago.



I don’t believe that this is a problem that only affects ’08 bikes. I’ve read too many posts from other people complaining of the same symptoms. I will check other FJRs as I come across them. Maybe I’ll be able to hit a Tech Day and check a bunch of them at the same time.

While I’m glad I’ve positively identified exactly what’s causing it, the cure is not going to be too easy. I don’t believe there is any way around it. I’ve tried cleaning up the TPS signal with negative results. I don’t believe it can be fixed without reprogramming the computer. If I get a chance to scope a couple of different year FJRs and can repeat my results, I may try tracking down the local Yamaha Service Rep to see what he has to say.

For now I am living with it, and clutching through 2000 RPMs like a rookie rider.

Questions/comments/insults are welcome.

Joe

Put a set of NGK Iridiums in mine and it cleaned it up alot. Got rid of the low rpm surging too.

joebiodiesel said:

The reason my bike misfires at 1700 RPMs, whether accelerating or cruising,

Click to expand...

joebiodiesel,

Been enjoying your write-ups (way beyond my mech skills).

Just curious, though, why cruise at 1700 RPM? Despite this bike's great low-end torque, once off the line, I tend to keep the revs at at least 3200 RPM so I can accelerate crisply w/o feeling like I'm lugging the engine. Hardly spend any time at all below 3K except in 1st and 2nd gear - and in those gears am usually through the rough spot before I even notice it's there.

Anyhow, thanks for looking into and sharing your info on the fueling/fuel mapping - I'm learning some cool stuff.

RsvlFeej said:

joebiodiesel said:

The reason my bike misfires at 1700 RPMs, whether accelerating or cruising,

Click to expand...

joebiodiesel,

Been enjoying your write-ups (way beyond my mech skills).

Just curious, though, why cruise at 1700 RPM? Despite this bike's great low-end torque, once off the line, I tend to keep the revs at at least 3200 RPM so I can accelerate crisply w/o feeling like I'm lugging the engine. Hardly spend any time at all below 3K except in 1st and 2nd gear - and in those gears am usually through the rough spot before I even notice it's there.

Anyhow, thanks for looking into and sharing your info on the fueling/fuel mapping - I'm learning some cool stuff.

Click to expand...

A totally fair question. I'm not necessarily cruising there, but I do move through it very often. Usually it happens when driving in the city, and your RPMs drop going around a turn, or something similar. It is also miserable in stop/go traffic. If I can drop a gear to get out of that RPM range, I definitely do it.

Ron, Thanks for the suggestion, but I'm pretty sure that different plugs won't stop over-fueling. I wish it was that easy!

Joe

joebiodiesel said:

At the risk of posting some info for a second time, I decided to start a separate thread on the hesitation/misfire my bike does at low RPMs. Some of this info is also in the CO Adjustment thread I posted a while back. If any of the Admins think it is inappropriate, take whatever action deemed necessary. No problem.

Like a lot of guys here I have spent a fair amount of time screwing around with my bike right after getting it. I played with the CO adjustments on the bike trying to smooth the idle. Bought a PCIII and hooked up my 5 gas. I learned an awful lot since I've started messing with it, and have the fuel mapping very close to how I want it. I no longer have a surge at low cruise speeds and still get 40-44 MPG pretty reliably when running slab. The only thing still killing me is the miss/hesitation at around 1700 RPMs. I've read posts here with cures ranging from PCIIIs to throttle cams. If you followed my thread on CO adjustments you already know I have been trying to figure out what the problem is.

Here is what I know:

The reason my bike misfires at 1700 RPMs, whether accelerating or cruising, is that it is seriously over-fueling due to unwanted acceleration enrichment. The computer appears to be overreacting to a noisy TPS signal, because removing the TPS signal fixes the problem 100%. Adjusting the TPS to higher and lower voltages moves the miss to different RPMs, but doesn't make it go away.

One of the reasons we have a TPS on our bikes is to act as an accelerator pump. As the throttle opens, and engine vacuum drops, the engine needs lots of enrichment so it won't hesitate. Without it, the engine would fall on its face, momentarily, when the throttle was opened rapidly. My bike adds this fuel, unnecessarily, at 1700 RPMs. You can easily see it because it uses extra injection pulses that are not timed to the firing sequence of the engine. They are called Asynchronous Pulses, and are pretty commonly used in fuel injected cars for this exact purpose.

If I disconnect the TPS on my bike, and add the necessary enrichment with the PCIII Accelerator Pump tool, the bike runs perfectly under all conditions except full throttle. The bike won't top out, and pulls poorly at high RPMs.

Yesterday I got a chance to chance another '08 FJR. Although I didn't ride the bike, it does run poorly between 1500-2000 RPMs, just like mine. The guy let me put my lab scope on it. The injection pulses are just like my bike. I'm satisfied that this problem is not unique to my bike now.

Here is what a normal injection pattern looks like. This is only 2 of the 4 cylinders.

Don't try to overanalyze these scope patterns. The resolution is too low for that. Each little notch is an injector firing. Ignore whether they have the spike at the end or not.

Normal Pattern

Here are a couple of screen shots of the 1500-2000RPM range. Note the untimed pulses.

Compare these to the ones I got on my bike about a month ago.

I don't believe that this is a problem that only affects '08 bikes. I've read too many posts from other people complaining of the same symptoms. I will check other FJRs as I come across them. Maybe I'll be able to hit a Tech Day and check a bunch of them at the same time.

While I'm glad I've positively identified exactly what's causing it, the cure is not going to be too easy. I don't believe there is any way around it. I've tried cleaning up the TPS signal with negative results. I don't believe it can be fixed without reprogramming the computer. If I get a chance to scope a couple of different year FJRs and can repeat my results, I may try tracking down the local Yamaha Service Rep to see what he has to say.

For now I am living with it, and clutching through 2000 RPMs like a rookie rider.

Questions/comments/insults are welcome.

Joe

Click to expand...

Wow ... what a great in depth technical investigation. I am an engineer and so I love the rigger and detail of your analysis. Unfortunately, injection systems are not at all my field of competence. But I learned a lot from this ad thank you joebiodiesel for sharing your findings. You should swing by the Ferrari F1 teams technical center ... they'd appreciate the details ... and the bike!

Good luck finding a cure / workaround!

Just love these posts - keep it up JBD :clapping:

It seems to me that you have done all the hard work and just about solved the problem associated with the TPS signal. You just need some electronic/control help from one of the other gurus (Ionbeam or Useless Pickles to name just two). There must be some simple way of conditioning the TPS signal so you get a nice clean signal at the ECU. Come on guys - step this way

Don

I guess my question is why not tune that out with the PC V with the O2 sensor disconnected?

I know I am going to look at my map and see what it says in that range but wonder if you could pin down the TPS range/%?

And not anywhere your level, but when I hear the word "noise" in a electrical discussion, isolation and ground come to mind. I am wondering if isolating the TPS wiring only would change anything, but have no idea how practical that is. I know TPS works on voltage and wherever that voltage is coming from maybe could be worked with? I know you said changing voltage forced it to other RPM ranges, but is it possible to clean up the voltage from where it originates? Or is it possible to somehow filter that signal, at that rate, to make it stop?

Again talking out my butt, but with the issues we see on the FJR Gen II with grounding issues could it be that simple. Do you have any flavor of spider bite prevention on your bike?

I wish I was close I would test mule my 10 all you wanted. Great work and I have learned a great deal.

I really became involved in FI with my 05 Road Glide and a Daytona Twin Tech Fuel Controller TCFI.

I read hundreds of logs and Auto Tune suggestions they generated. I do know what kind of work you are poring over so again I appreciate your effort and work.

Thanks for the great feedback. I definitely appreciate it.

The O2 sensor is for correcting fuel mixtures during closed loop operation, and on our bikes that is only during steady cruise conditions. It also is only capable of making pretty small adjustments. Lastly it makes corrections only if a condition is present for a long while, and not while the engine is running poorly. If the computer used the O2 sensor all the time, like you think it should, it would definitely clean up a few of the performance quirks that a lot of people notice on our bikes.

So, this being the case, it would never make a correction to acceleration enrichment. It happens too quickly, and the computer won’t make a fuel change on a momentary condition.

Even if you could stand holding the engine at 1700 RPMs for an extended period of time, it still wouldn’t be able to correct it because the engine is misfiring from being over-fueled. When the engine misfires, the unburned charge, including the unburned oxygen goes down the exhaust. If we has a fast O2 sensor(which we don’t) it would actually see a momentary lean condition due to the misfire…and all the extra oxygen.

Here’s a perfect example of exactly that happening. This was a new Ford pickup that had a dead miss on one cylinder. The O2 sensor reads lean (under .5V), except for repetitive rich spikes over .5V when the other cylinders fire. This truck came from the auction, so I don’t know its repair history, but someone put an incorrect injector in it, and that injector was delivering twice the volume that it was supposed to. The O2 is reading lean, but the misfire is due to a seriously over-rich condition.

The O2 on the top left is normal. The O2 on the top right indicates a misfire, but it looks lean if you don’t know it’s missing.



The culprit. The one on the left is OEM.



The reason you can’t tune it out effectively with a PCIII is that the false throttle enrichment is not predictable. It doesn’t do it steadily.

If I substitute the TPS signal with a completely clean one from my signal generator the false enrichment is gone, so cleaning up the signal should work fine, but I am not sure how to do it. I tried various capacitors, but it only made things worse. Hopefully someone can educate me on why that might be, or offer some suggestions. I doubt relocating the harness would make any difference, because if it did, you’d think that this problem would be present all the time, and not only during a specific RPM range and TPS voltage. This is the part that stumps me, and makes me think the only way to correct this is reprogramming the computer.

I know I am going to look at my map and see what it says in that range but wonder if you could pin down the TPS range/%?

It seems anything below about 25% will still do it, but it does it worst at around .1V above closed throttle. On mine, that is .84V at the moment.

Again talking out my butt, but with the issues we see on the FJR Gen II with grounding issues could it be that simple. Do you have any flavor of spider bite prevention on your bike?

Because I bought my bike in March, when it was still snowing in Central NY, I had time to make my own harness for the grounds. Glad I learned about that problem here and fixed it before it became an issue.

I wish I was close I would test mule my 10 all you wanted. Great work and I have learned a great deal.

What's funny is that I'm on my way to Harrisburg right now. I'm teaching a couple of classes at HACC on Tuesday. I won't be in town long though. Less than 24 hours, and then off to Pittsburgh for the rest of the week.W

I really became involved in FI with my 05 Road Glide and a Daytona Twin Tech Fuel Controller TCFI.

That thing looks pretty cool. Much more high tech than a PC.

joebiodiesel said:

...Here is what I know:
The reason my bike misfires at 1700 RPMs, whether accelerating or cruising, is that it is seriously over-fueling due to unwanted acceleration enrichment. The computer appears to be overreacting to a noisy TPS signal, because removing the TPS signal fixes the problem 100%. Adjusting the TPS to higher and lower voltages moves the miss to different RPMs, but doesn’t make it go away.

...

Joe

Click to expand...

Great write up and analysis Joe. Can you provide details about the noisy TPS signal? Is it literally a bad signal coming from the TPS like voltage dropouts or spikes? Or some other anomaly with the way the ECU is interpreting it's signal?

Thanks.

Denver' the necromancer has dug up a zombie. Joe isn't a real regular on the Forum, you may want to send him a PM and see if he wants to reengage in this thread.

Eh, it's only been dead a few years! I'm gonna put a set of carbs on my 06....FI sucks!

not2shabby said:

Eh, it's only been dead a few years! I'm gonna put a set of carbs on my 06....FI sucks!

Click to expand...

Here's your "Died and Gone to Heaven" setup: Weber 45DCOE!

Denver_FJR said:

joebiodiesel said:

...Here is what I know:

The reason my bike misfires at 1700 RPMs, whether accelerating or cruising, is that it is seriously over-fueling due to unwanted acceleration enrichment. The computer appears to be overreacting to a noisy TPS signal, because removing the TPS signal fixes the problem 100%. Adjusting the TPS to higher and lower voltages moves the miss to different RPMs, but doesn’t make it go away.

...

Joe

Click to expand...

Great write up and analysis Joe. Can you provide details about the noisy TPS signal? Is it literally a bad signal coming from the TPS like voltage dropouts or spikes? Or some other anomaly with the way the ECU is interpreting it's signal?

Thanks.

Click to expand...

I don't log in regularly, but do stop by on occasion. I was very surprised to see this thread resurrected!

I doubt I still have the screen shots from the TPS signal, so I can't post them here, but there were momentary spikes above and below the signal voltage. I went to great lengths to filter them out. The only thing that worked was when I completely replaced the signal with a signal generator. When I added enough filtering to the TPS signal to stop the misfire, the bike had serious performance issues. I have stopped caring deeply about it for now. I deal with it 2 ways.

1) Avoid engine revs under 2k when starting from a stop, by clutching the bike like a rookie.

2) I have a kill switch on the left handlebar that opens the TPS circuit. I only use it when avoiding those RPMs is a nuisance, like when moving in slow traffic.

Sorry I don't have a solution for this. I sure wish I did.

Joe

I'm an electronics engineer also with 25 years experience in Jet engine electronic controls. Noise problems can be a pain and there are people out there that make a career of preventing and or solving noise issues both conducted and radiated. This is interesting indeed. I assume the TPS signal has no noise on it except in this sweet spot, which is a little strange. Is the high side of the TPS noisy as well, IIRC the high side is a 5V reference voltage sourced from the ECU. It's possible to have noise on the low side too. The other thing that is critical when looking at noise, is where your scope probe ground ref is at. This can be an issue if there is a difference in voltage between the grounds. Was the TPS position signal noise synchronus with the injector pulses, or coil firing pulses. There is a chance that the noise is getting coupled in through the wiring. It's been a while since I looked at a wiring diagram but I'm wondering if the ECU has separate digital and analog grounds that come to the outside world, but I kinda doubt it. I'd like to have a weekend with a scope smuggled out of work to play with this.