o2 eliminator vs pair system mod

Hello. I've just got a 2007 VFR800 with 20k miles on it. It has Motad stainless downpipes (so no cat) and a very nice Staintune exhaust, which sounds great. It is otherwise fully stock. o2 sensors in place, PAIR system operational. The low speed snatchiness is severe. Backing off from part throttle is so harsh it compresses the front forks and even when being careful it's difficult to accelerate out of tight corners smoothly in low gears. I blocked the PAIR valve pipe at the airbox and it's cured a lot of the snatchiness, which is obviously a great result. Also noticed that the pops from the exhaust are gone, but they weren't loud and I'm not bothered about those anyway.

As a longer term fix I'm going to try two options but am interested to hear people's thoughts:

1. Full PAIR system delete. Given there's no cat there doesn't seem much point keeping the PAIR system so it might as well go.

2. o2 eliminators. I ordered these before I'd fully realised the downpipes have no cat, they arrive today. The concern I had about the PAIR valve mod is that it could result in rich exhaust gases damaging the cat, so I planned to re-enable the PAIR system and use the eliminators to resolve the low speed issues.

My question is - people seem to recommend the o2 eliminators on cat-less systems, even without a PC. Is that correct or will the bike run too rich? Should I just go with PAIR elimination instead and leave the o2 sensors in place? I guess a visual on the o2 sensors would be a good starting point. One thing is for certain, the bike definitely fuelled badly at low speed so it's either o2 eliminators, PAIR elimination or both!

What you're running in to is why so many have a PC III / V or a Rapid Bike on their 6th gens.  Eliminating the O2 sensors will leave the ECU with no input signal about fuel mixture.  You'll jump the wires at the connector with a 330 ohm resistor to make the ECU think it has an input signal, albeit a non-changing one.    It will have a set program for that, which could end up being way too rich vs too lean.  You might find poor fuel economy, fouled plugs or other undersireable symptoms from doing that.   The PC or RB is used to smooth out the low speed fueling to make it run more like a well tuned carb'd bike, but in the case of PC you need the eliminators so that it can make adjustments and not have them contradicted by the ECU trying to do the same.  RB is different (with the My Tuning BIke) in that it does use the stock O2 sensors along with a 3rd (added) wideband sensor to make mixture adjustments on the fly.  Either system will smooth out the low speed on/off throttle abruptness. 

FWIW, even with O2 eliminators into place, my bike still exhibited the same behavior of leaning and surging at cruise.  I think there's really an open loop direction to lean the bike at cruise RPM that comes into play regardless of inputs.

Two methods to get around the behavior:  one is Rapidbike, which makes it go away and makes the bike better, especially with exhaust.

Second option, which actually does work and was discovered by some other VFR owners, is to defeat the ECU closed loop mode entirely.  I was doing this before I got a Rapidbike and wish I'd known about it when I first bought the bike:

- Turn ignition key switch on, kill switch on

- *Before the fuel pump completes priming (whining noise) and dash is done booting, hit the starter!

- If you did it right, the bike will *not* go into closed loop, or fake closed loop mode

What I usually did last year if my bike was cold was let the pump prime, then switch the key switch off, and then start it during the second boot sequence.  Whenever I forgot to do this, I knew I forgot once I was at steady speed between 4K and 7K RPM.  

Thanks guys.

My bike doesn't have surging issues at all, it's purely the low speed snatchiness that needs sorting out. And like I say it is sorted with the PAIR mod. So perhaps I'll just end up doing a proper PAIR system delete. There's a kit on eBay that looks great - two plates and a cap for the airbox.

I think I'll try the o2 eliminators though and see how it performs. I feel that the bike is running rich anyway! If it does run rich with the eliminators, isn't it just a narrow band of the rev range that will be affected?

Am I right in saying that if I was to run with the o2 eliminators, the PAIR system mod becomes irrelevant. If there's no o2 sensors then the issue of them getting confused by the added fresh air won't matter.

2 hours ago, Dorian

My bike doesn't have surging issues at all, it's purely the low speed snatchiness that needs sorting out.

I'd be checking Starter Valve Synch before any form of modifications to sort out the snatchiness. Out of synch sv's are a known cause of low speed snatchiness.

What's funny is that these issues vary from bike to bike.  I had a 2004 and currently have a 2007 and a 2008 bike.  I had the inevitable flatspot but no surging to speak of with the 2004.  It was a very well behaved bike overall.  It did have a very slight hesitation when adding throttle while in that steady state cruising rpm, but not enough to fool with anything.

The 2008 bike had terrible surging and hesitation issues to the point of making it miserable to ride.  I'm pretty sure that's why I got a good deal on it from the previous owner.  I have 330 ohm resistors (cheap O2 eliminators) which have completely transformed it.  It still gets the same 45ish mpg when cruising that it did without the resistors.  It was well worth the $1.50 I spent on the pack of resistors!  

I haven't done anything to the 2007 bike and don't have major surging issues like the 2007 bike did.  I do have a tad more hesitation when adding throttle from steady state cruise than I did with the 2004.  It's just not enough that I've fooled with adding the resistors or trying anything else.  All three have been fairly sensitive to closing the throttle, but adjusting the slop completely out of the throttle cable and years of riding practice pretty much eliminated that issue for me.  

There is still the flat spot in the vtech transition, which was pretty massive in the 2004.  There's a little jiggle in the 2007 and 2008 and of course, a lot more noise, but not a big deal with them.  If I had tons of cash to burn, I'd try a PC or RB on my current bikes, but I'll save that for food and gas because the transition just isn't enough to upset me.  It sure would have been nice on the 2004 bike, though.  

When I got my 03, the throttle cables were loose to the point it was not ridable. The starter valve sync was also a huge help.

On my 08 VFR, I completed the PAIR delete, installed O2 elims and completed the flapper and snorkel mods and it ran pretty well at low revs on a neutral throttle, not perfect, but much better than before the mods.

I recently used ebay to obtain the PAIR delete kit from a UK supplier for my 01 VFR and it's fitted very well. I haven't finished the bike yet so can't comment on how it rides.

2 hours ago, tbzep

What's funny is that these issues vary from bike to bike.  I had a 2004 and currently have a 2007 and a 2008 bike.  I had the inevitable flatspot but no surging to speak of with the 2004.  It was a very well behaved bike overall.  It did have a very slight hesitation when adding throttle while in that steady state cruising rpm, but not enough to fool with anything.

The 2008 bike had terrible surging and hesitation issues to the point of making it miserable to ride.  I'm pretty sure that's why I got a good deal on it from the previous owner.  I have 330 ohm resistors (cheap O2 eliminators) which have completely transformed it.  It still gets the same 45ish mpg when cruising that it did without the resistors.  It was well worth the $1.50 I spent on the pack of resistors!  

I haven't done anything to the 2007 bike and don't have major surging issues like the 2007 bike did.  I do have a tad more hesitation when adding throttle from steady state cruise than I did with the 2004.  It's just not enough that I've fooled with adding the resistors or trying anything else.  All three have been fairly sensitive to closing the throttle, but adjusting the slop completely out of the throttle cable and years of riding practice pretty much eliminated that issue for me.  

There is still the flat spot in the vtech transition, which was pretty massive in the 2004.  There's a little jiggle in the 2007 and 2008 and of course, a lot more noise, but not a big deal with them.  If I had tons of cash to burn, I'd try a PC or RB on my current bikes, but I'll save that for food and gas because the transition just isn't enough to upset me.  It sure would have been nice on the 2004 bike, though.  

That's really interesting. My bike is so bad on and off the throttle that my very first thoughts were along the lines of why don't any of the review say that the VFR is terrible to ride at low speed. Well obviously it's because they're not all like that, not to the extent that my bike is anyway. There could be reasons such as o2 sensor contamination/deterioration, or certain mods that the bike doesn't adapt to without a piggyback ECU. Are all your bikes standard?

Funny you mention a lot more noise after VTEC. Mine seems the other way. It's thunderous at idle and low revs round town but when the revs pick up it's very quiet and smooth. Probably wind noise masking a lot of it. It was almost silent with that horrific blocked up air filter (see my other thread). With a new clean filter it's got a bit of bark but still pretty quiet.

So the ECU and O2 sensors don't work exactly like in a car, where the vehicle is almost always in closed loop mode.  In the VFR, it only goes into closed loop mode at steady throttle, it's otherwise open loop.  This is why there are ~20 years of topics where people say "Help, my RPMs drop at steady throttle, WTF?"  The O2 sensors aren't used outside of this and don't affect other behavior.  If you search "VFR closed loop o2 sensors" you will find something like infinity discussions on this, going back to the early days.

That being said, O2 sensor eliminators don't eliminate the problem completely (ha!) so it is clearly also a bit open loop behavior.  I think this might be to save the cats, or because Honda's green preferences.  Whichever it is, there's only two ways to go after that problem.  The Power Commander just re-maps after the ECU which is why it's never made the closed loop issues completely go away, while the Rapidbike actually uses the O2 sensors and other inputs and hijacks the FI and ignition signals.

Anyway, not 100% sure what you mean by "snatchiness" but it won't cause the specific behavior you mention, which is shutting way down when you move the throttle.  It can make the throttle feel a bit like "piece-wise linear logic," where instead of a smooth ramp, there are steps in behavior.  Like instead of going up or down a tiny bit, you are moving 100-200 RPM in a big step that you weren't expecting, and you hunt back and forth to get where you want.  If this is part of what you're seeing, the O2 eliminators can help but won't 100% cure it.  

I can see PAIR possibly affecting you, especially with a full exhaust including cat delete.  Everyone gets rid of PAIR and no one has ever had negative problems.  Starter valve sync and throttle cables are another possible culprit...the starter valves "shouldn't" affect performance in any way after the bike is warm but they have always seemed to.  My bike did somewhat better after the sync, but nothing made the lean and surge behavior go away except for the ECU defeat cheat code and later Rapidbike.

Really useful thanks. Just to clarify a few things that I've probably not explained well:

1. What I mean by snatchiness is things like going from maintenance throttle to throttle closed causing so much engine braking the front forks compress. And being unable to roll on the throttle in a tight turn smoothly in a low gear. Even being very careful with the input.

2. Also, like I said right at the top, all of this is massively improved by blocking the air feed to the PAIR valve. The throttle is now totally controllable, no issues at all.

3. I haven't picked up on any surging or open/closed loop switching at steady throttle. That all seems ok.

Like I said I bought the o2 eliminators thinking that I had a cat and they would be a better long term option than the PAIR valve mod which could affect the cat. With hindsight I think I should have just bought a PAIR delete kit instead!

But, seeing as I have them, might as well try them right? I'm going to test ride again before fitting and see if I can detect flatness in the midrange or surging, but I don't think there's any of that. It rides really sweet with the PAIR valve blocked off, so the theory about the PAIR confusing the o2 sensors seems to apply to my bike - perhaps due to the catless aftermarket system!

1 hour ago, Dorian

That's really interesting. My bike is so bad on and off the throttle that my very first thoughts were along the lines of why don't any of the review say that the VFR is terrible to ride at low speed. Well obviously it's because they're not all like that, not to the extent that my bike is anyway. There could be reasons such as o2 sensor contamination/deterioration, or certain mods that the bike doesn't adapt to without a piggyback ECU. Are all your bikes standard?

Funny you mention a lot more noise after VTEC. Mine seems the other way. It's thunderous at idle and low revs round town but when the revs pick up it's very quiet and smooth. Probably wind noise masking a lot of it. It was almost silent with that horrific blocked up air filter (see my other thread). With a new clean filter it's got a bit of bark but still pretty quiet.

2004:  I did the flapper mod and blocked off the pair valve but didn't see any real benefit so I put it back to stock.  I had Remus cans on it.  

2007:  No engine or electronics mods, different sprocket ratio, Delkevic cans, which make it a tad more snatchy than stock cans.

2008:  Resistors (O2 Elim), currently have the Remus cans on it that were on the 2004. 

The extra noise comes from the intake when all 16 valves are operating.  Whack the throttle in a tuck where your head is close to the tank and you should hear a pretty big difference when vtec kicks in.  If you have loud pipes, you may not notice with your head up in the wind. 

These are the ones I bought.

Honda VFR800Fi, VFR800VTEC, Crossrunner PAIR's removal Kit | eBay

2 hours ago, Dorian

Really useful thanks. Just to clarify a few things that I've probably not explained well:

1. What I mean by snatchiness is things like going from maintenance throttle to throttle closed causing so much engine braking the front forks compress. And being unable to roll on the throttle in a tight turn smoothly in a low gear. Even being very careful with the input.

2. Also, like I said right at the top, all of this is massively improved by blocking the air feed to the PAIR valve. The throttle is now totally controllable, no issues at all.

3. I haven't picked up on any surging or open/closed loop switching at steady throttle. That all seems ok.

Like I said I bought the o2 eliminators thinking that I had a cat and they would be a better long term option than the PAIR valve mod which could affect the cat. With hindsight I think I should have just bought a PAIR delete kit instead!

But, seeing as I have them, might as well try them right? I'm going to test ride again before fitting and see if I can detect flatness in the midrange or surging, but I don't think there's any of that. It rides really sweet with the PAIR valve blocked off, so the theory about the PAIR confusing the o2 sensors seems to apply to my bike - perhaps due to the catless aftermarket system!

O2 sensor won't play into any of this, it's only used at steady state cruising unless you install a Rapidbike or PC with autotune, which use them all of the time.  Likewise, remember the ECU controls PAIR with a solenoid, and PAIR won't be open at steady state cruising for the most part.  If you listen to your bike closely, you should be able to hear the reed valves when they are opening...half the reason some of us disabled ours TBH.  

No reason not to install the eliminators, you may or may not notice any difference.  Completely reversible too.

I think the overall reason you are seeing issues and PAIR is affecting it when it shouldn't, is you're running stock ECU with a full exhaust.  The bike runs lean, and then very lean in the midrange to meet emissions requirements, and then the stock ECU dials it back even further in midrange cruise, etc.  Normally with a stock exhaust, blocking PAIR does nothing but remove a noise and some complexity.  

I never thought my bike was missing much in mid range either even though I knew it quantitatively was.  Installed the Rapidbike before my full exhaust and it sure is missing a lot in mid range.   The exhaust opens it up quite a bit further, from 6K up.  It turned carb-smooth with the closed loop defeat hack, but overall much smoother and useable with RB filling in the fueling and ignition maps in the middle.

7 hours ago, tbzep

What's funny is that these issues vary from bike to bike.  I had a 2004 and currently have a 2007 and a 2008 bike.  I had the inevitable flatspot but no surging to speak of with the 2004.  It was a very well behaved bike overall.  It did have a very slight hesitation when adding throttle while in that steady state cruising rpm, but not enough to fool with anything.

The 2008 bike had terrible surging and hesitation issues to the point of making it miserable to ride.  I'm pretty sure that's why I got a good deal on it from the previous owner.  I have 330 ohm resistors (cheap O2 eliminators) which have completely transformed it.  It still gets the same 45ish mpg when cruising that it did without the resistors.  It was well worth the $1.50 I spent on the pack of resistors!  

I haven't done anything to the 2007 bike and don't have major surging issues like the 2007 bike did.  I do have a tad more hesitation when adding throttle from steady state cruise than I did with the 2004.  It's just not enough that I've fooled with adding the resistors or trying anything else.  All three have been fairly sensitive to closing the throttle, but adjusting the slop completely out of the throttle cable and years of riding practice pretty much eliminated that issue for me.  

There is still the flat spot in the vtech transition, which was pretty massive in the 2004.  There's a little jiggle in the 2007 and 2008 and of course, a lot more noise, but not a big deal with them.  If I had tons of cash to burn, I'd try a PC or RB on my current bikes, but I'll save that for food and gas because the transition just isn't enough to upset me.  It sure would have been nice on the 2004 bike, though.  

The bike to bike variation in symptoms is indeed a mystery.  Some swear by removing the PAIR system.  Until last year my PAIR system was in place and caused no issues whatsoever.  When the reed valves came out, they were just slightly tan from being exposed to oil over 30,000+ miles, while photos of other reed valves show them to be clogged with gunk.  I can't ever recall any common thread between the bikes that had surging / stumbling / snatchy throttle issues and the ones that don't.  Either way, a PC III and now Rapid Bike have mine running fine.

I never did try the key on / key off to fool the ECU.  Probably should have tried it. 

Note that O2-eliminators don't replace O2-sensor or its signal. It connects heater circuit in O2 circuit to trick ECU into thinking it's still connected. Signal-circuit is completely disconnected with zero signal and ECU uses default baseline maps which tend to be on rich side. Especially under WOT, even richer than already rich factory setting. Will end up around 11.0:1 AFR, richer than factory 12.0:1. Both of which are far, far richer than optimum, max-power setting of 13.5:1 AFR for NA engine.

PAIR systems are perhaps a little misunderstood... they passively let air into the exhaust ports post-combustion to help burn unburned gasses, and usually only on deceleration does the solenoid open.  Should have no effect on performance, only emissions.

11 minutes ago, raYzerman

PAIR systems are perhaps a little misunderstood... they passively let air into the exhaust ports post-combustion to help burn unburned gasses, and usually only on deceleration does the solenoid open.  Should have no effect on performance, only emissions.

Exactly.  "User experience" is hard to capture but I think the only reason he might be seeing a difference, if there is one, is because he has a full exhaust.  Should not make any observable difference, but if it is, maybe that's why.

Going back down the rabbit hole with the way back machine across the forums, I think this is relevant for @Dorian too:

https://www.bcsportbikes.com/threads/vfr-vtec-must-read-throttle-problems.48472/page-2
 

http://www.ko4bb.com/doku2015/doku.php?id=yamaha_fz1:gen_2_fuel_snatch_problem
 

Getting back on my VFR ten years later and feeling the early FI implementation that I had completely forgotten about, I remember thinking "Oh FFS, I forgot how bad this could be..."

 But the Rapidbike makes my VFR better on this problem front too.  It is waaaaaaay easier to control mid corner by throttle, including on and off clover leaf ramps where I'm leaned way over but trying to stay between merging (poorly driven) cars each day at low to lowish speed.  Could do it acceptably before but its infinitely smoother now and don't have to think about it so much.

Update time!

I did a test ride lastnight before changing anything related to the sensors. Definitely no surging at constant revs - that's one problem it doesn't have.

Today I disconnected the o2 sensors, fitted the eliminators and went for a ride. It felt fine. I'm not going to say there was a big improvement, but it certainly ran well and the idle was very smooth. I looked into removing the sensors and fitting the supplied caps but the sensors are seriously stuck in position! A common problem by the sounds of it.

With hindsight I'd probably have been better spending the money on the PAIR eliminator kit, which I might still do. Going to run the bike with the eliminators in place for a bit and see how it goes.

People always say a PC makes a really big difference, I'm still unsure whether I want the expense. If I did get one - is there a suitable map for me to use for a setup of Motad downpipes and Staintunes mufflers? And how much better can it really get than where it's at now? The PAIR block has changed the bike from feeling faulty in some way to feeling like a good bike, albeit one that still has a slightly abrupt throttle and needs to be ridden properly. I might need to give on a try to really find out...

There are PC maps for download in the downloads forum here, and Dynojet also has many available on their website.  All are free.  One here frequently used is Cozyes map.  They're easy to change so you can keep trying ones until you find one you like for your setup.  

This and some zip ties is a PAIR eliminator kit:

Dorman 02250 Coolant Bypass Caps - EPDM 5/8in, 2 Pack https://www.amazon.com/dp/B00Z7MM0IG/ref=cm_sw_r_cp_api_i_2EHKSAKTC25EFPSZAZY6?_encoding=UTF8&psc=1

Forget what size cap I shoved in the airbox side.  I repurchased this because one of mine was cracking about twenty years later.  There is also a really good how to out there that shows how to do it by shoving marbles into the PAIR lines if you really want to do very little.  
 

The metal plates are nice and better looking but not functionally necessary.

I got a decent ride in yesterday to really check the bike out. I'm now certain it runs better without the o2 sensors connected. It idles smoother, throttle is slightly less snatchy again (not that it was bad since the PAIR mod), and overall it runs lovely. It doesn't smell particularly rich to me, in fact it's possibly better than it was.

But the bike won't be staying that way for long - have got myself a Power Commander 5!!! Arriving this week some time. I couldn't cope with not knowing what difference the final piece of the puzzle will make. Gotta say though, the bike is great as it is, so the PC will have to impress me if I'm going to keep it.

Back with an update for anyone that's still following. As above I got the PC5 and tried a few downloadable maps, but they really didn't work, to a point where a fast ride had the bike misfiring and trying to throw me off. I found one map that was smooth at up to 4k RPM, with no serious issues, but it was all over the place around 4-5k rpm.

Last week I got the bike into Dynojet Preston (FW Developments) yesterday for a custom map. And it was well worth doing. There was various rich/lean areas across the rev range and a big drop in power at the VTEC point. Perhaps caused by either the ECU or the map I was running trying to smooth out the VTEC transition.

So, is the VFR throttle still snatchy when running a custom map? I'd say slightly. It's an early fuel injected bike so perhaps isn't as smooth as newer models, but as I say, it's slight. The main think is the bike is a pleasure to ride, and a night and day difference from when I got it and it was awful to ride.

Seems like people don't understand how the O2 sensor works. It has 2 circuits, #1 is a 12v supply to heat the sensor. #2 is the Narrow band Lambda circuit which flips from rich to lean. The 02 eliminator only puts a resistance over the 12v heating circuit which the ECU uses to determine if it should see Lambda circuit outputs. If there is no load on the 12v circuit the ECU throws an error code & illuminates the Fi fault light. It also throws a code for no Lambda change but does NOT  illuminate the Fi light. Because it has a default fuel map for just this situation, its a rich map as it can't see Lambda so rich is safer than lean conditions. You only need one O2 sensor circuit to have a resistance to keep the Fi light off. So you really need to get a proper fuel tune & make sure your starter valves are balanced. 
 

The snatching is caused by the Fi shutting off fuel delivery completely when you shut the throttle on the overrun. So get used to not fully closing the throttle or opening it with more care when transitioning from closed to initial opening. The Rapid Bike Racing module has a setting to keep fuelling on the over run, I've not had a snatch since, as it acts more like carbs now. 👍