VTEC Fuelling Issue - Part Two: after Japan's answer about the o2 sensor-swap

[Jason Creasey]

Greetings, fellow Vifferians....

After the long & rocky road of our last three months' discussion about the o2-sensor swap, we finally have word from Honda Japan whether the original o2-sensor wiring was correct... or not. (Anyone not 'getting' what I'm rambling on about may want to make a large cuppa (actually, make that an intravenous caffeine-drip) & read this 43-page epic kicked off by our most excellent 'test-pilot' Calimori. (To additionally clarify for anyone new mucking in on this, I'm the chap that's been 'liaising' ( ) with Honda UK to find out "What's going on?!")

To summarise:

Over the last three months, we've been discussing about (& experimenting with) the way the o2 sensors on the VFR VTEC have been wired up. Honda UK thought they'd found an anomaly in the VTEC's wiring diagrams & suspected that the two o2 sensors had been wired up 'the wrong way around' at the factory. (You may want to read this RiDE article published earlier this year if you haven't already.)

Many VTEC owners around the globe - not just the UK - have tried the swap since we published the information here in January (special thanks to Calimori for finding this out in the first place! ) As a consequence, the large majority of riders have experienced significantly-improved 'behaviour' of their machine in the rev-range where the o2-sensors are 'payed attention to' by the bike's electronic control unit (approx 2500 to 5000 rev's) for the purposes of 'improving' the engine's emissions. Whereas many people used to experience strange backing off/surging problems whilst holding a constant throttle in this rev' range, the symptoms disappeared for most riders, many of them saying that the VTEC was finally the superb bike they always imagined it would be....

Cue one happy Honda UK, who were pretty convinced that they'd finally found the reason (& the fix!) behind the 'problems' that so many VTEC owners had complained about since Day One of the machine's existence. Honda UK were so convinced this o2 sensor wiring problem was the cause that they've been willing to reimburse Honda dealers (as a UK-only 'goodwill gesture' rather than an official [read Japan] 'warranty claim') the labour-time to carry out the o2-sensor wiring-swap & starter valve synchronisation for VTEC owners, irrespective of whether the bike was inside or outside of the initial two-year manufacturer's warranty.

And the missing key to an official confirmation of this 'wiring problem'? An answer from Honda Japan......


Fast forward to 8th April 2005:

1) Honda Japan has told Honda UK that the original wiring of the o2 sensors IS correct.

2) When the sensors' connectors are swapped over as we've been doing, the ECU thinks it's getting 'rubbish' back from the o2 sensors. As a consequence, the ECU ignores the o2 sensors (i.e. goes into 'open loop' mode) & is simply reading a preset fuel map in its memory without making any emissions-related fuelling adjustments. THIS is why the VTEC runs more smoothly, & NOT because the new way of wiring the o2 sensors is the 'correct' way.

3) However! : Honda UK do recognise that most of us have experienced improved behaviour of the bike with the o2 sensors wired up incorrectly. As a consequence [but I expect this will only stand until Honda Japan tell them to stop.... JC] Honda UK will STILL cover the dealer's labour-costs of the wiring-swap if you are sure you still want the swap to be made... Whether your dealer will willingly do it for you though (knowing that they'd be wiring the bike up 'incorrectly') is another matter.

4) Dave Hancock (Manager of Aftersales and Technical Development at Honda UK) has contacted Japan again, this time asking them - based on the fact the bike runs better with the o2 sensors being 'ignored' - what they plan to do about it...


---


So... we're back to square one in some ways, EXCEPT of course there is a temporary fix to your 'jerky throttle-response' (or 'leaning-off at a constant throttle' - whatever we want to call it) IF you're happy to wire the o2 sensors up around the wrong way.

A few further points to keep in mind are:

Yes, it might be right that the fuelling's a bit richer than it was prior to the wiring swap, BUT, most people have reported very little difference in change of mpg (such as Calimori, who's now clocked up 1200 or so miles since the swap) so we can fairly safely guess there's isn't over-fuelling happening on any grand scale as some people thought might happen. (Don't forget that the ECU only 'listens' to the o2 sensors in a small-ish area of the rev-range anyway, so it's not as if your fuelling will be richer right the way across your rev-range, even if cutting the o2 sensors 'out of the loop' does cause some increase in richness.)

The threat of catalyser damage seems unlikely from this slightly-richer running. Symon in Honda-Technical told me that, yes, a richer mixture will make the engine run cooler for sure, BUT will also make the exhaust run hotter because of the increased unburnt fuel vaporising in the exhaust (or words along those lines). However, the VFR's catalytic converter is made of metal (rather than ceramics as in most car exhausts, which have been known to melt when they get 'too hot' apparently), & Symon isn't quite sure what would happen to this metal converter if it gets 'too hot' (or even what that 'too hot' temperature may be....)

Three people have had o2 sensors fail within a few 100 miles since doing the wiring swap. However, all three folk did have Power Commanders & o2-eliminators fitted in the past, & it's NOT currently possible to establish if the sensor wiring-swap was the cause OR if having the o2 sensors disconnected for a while (while the PC/elim's were fitted) was the problem. However, Calimori was one of those three people, & he's done approx' 1000 miles to date since having new o2 sensors fitted; his wiring's still around the 'new' (i.e. wrong) way, & the sensors are still working fine. So..... although this is just theory, logic suggests that the sensor-failure might have been more related to the use of a Power Commander (or even just o2-eliminators) rather than the wiring swap.


So, here we are, 10th April 2005, armed with what's really happening with our VTECs when we swap over the o2-sensors' connectors, & now awaiting another answer (if any) from Japan, this time to the question: WHAT, if anything, are they going to do about the fact that their 'technological flagship' runs better wired up incorrectly?!

As soon as I hear anything, you will - of course - be the first to know. In the meantime, let's keep the discussion going

All the very best,

Jason

[Si Click]

The plot thickens.
This adds some weight to Wiz's theory [here... JC] regarding the starter valves. It always struck me as very unHonda-like for them to have made such a fundamental error when they they normally seem to go to a great deal of trouble to get everything as perfect as they can. OTOH UK dealers misunderstanding the brief and mis-sync'ing the valves does seem entirely feasible.

Great work Jason, without you and Calimori doing some serious hard work hundreds of VTEC owners would just be having to put up with their bikes' faults. "Oh they all do that Sir."
Now there is real hope that that Honda may be forced to provide a full diagnosis and cure.

[Lone Ranger]

Jason,

at the risk of adding to what could become another epic thread, I must congratulate you on your excellent summary of the previous thread. If only Honda Japan could be so efficient!


Kevin

[Excalibur]

Jason ...

[bakerman]

I have done several 000 miles since doing the swop and even now with sensors still swopped the standard bike is better

BUT

last week the FI light came on and my dealer has had a look and says that the bike reckons one of the O2 sensors was having a problem. Having reset the bike the FI light has stayed off since, I have done around 1000 miles in the last week. My dealer has tried talking to D Hancock but not managed it yet.

02 VTEC, 52k miles (some of which were quite hard :t )

[Lone Ranger]

See this post in the "new hope" thread.


Kevin

[kakugo]

Don't know if this can help, but here's what happened AFTER I swapped the O2 sensors.
After feeling very, very happy about the engine, I began to notice that my fuel consumption was quickly worsening. First I put the blame on inferior fuel, but then I began to suspect the "built in" map was to blame. Since I cover a lot of miles each week, I was very worried by this novelty (even if I knew that the VFR's a thirsty beast). Anyway, I went back to the old O2 solution (ie the "right" way around) and immediately began to notice a marked improvement in fuel mileage, although I have to admit that the engine now feels gutless and nowhere near as good as before. Despite having tasted the fruit, I decided to keep my O2 sensors as they were out of the crate... out of sheer fuel economy! I don't want to win the "Friend of OPEC" award, sorry sir!
PS: thanks for your wonderful job, I am pretty sure you are nearer the truth than you think...

[jabberwocky]

Originally Posted by kakugo

Don't know if this can help, but here's what happened AFTER I swapped the O2 sensors.
After feeling very, very happy about the engine, I began to notice that my fuel consumption was quickly worsening. First I put the blame on inferior fuel, but then I began to suspect the "built in" map was to blame. Since I cover a lot of miles each week, I was very worried by this novelty (even if I knew that the VFR's a thirsty beast). Anyway, I went back to the old O2 solution (ie the "right" way around) and immediately began to notice a marked improvement in fuel mileage, although I have to admit that the engine now feels gutless and nowhere near as good as before. Despite having tasted the fruit, I decided to keep my O2 sensors as they were out of the crate... out of sheer fuel economy! I don't want to win the "Friend of OPEC" award, sorry sir!
PS: thanks for your wonderful job, I am pretty sure you are nearer the truth than you think...

I would have to concur with kakugo, I did the sensor swop and yes noticed the smother vtec transition, but at the cost of fuel cosumption, to such an extent that I had swopped the sensors back again. I have been following Wiz's thread on the starter valves and will make this my next plan of attack.

Martyn

[kakugo]

Glad to hear I was not the only one scared by fuel consumption...
Anyway, I finally managed to get my warranty claim on the thermostat approved (after FOUR months... no comment), so I'll probably have the starter valves checked using Wiz's suggestions when the bike will be taken to pieces.

[vfr980002]

Jason,
Glad I finally found you, I'm from the Yahoo VTEC list and some of the members sent me your post. I like to think of myself as the nerd because I'm pretty hyper-sensative to the VTEC's needs.
Getting back on subject, I reversed my O2 sensors as your e-mail suggested and in fact the flat spot seemed gone. I rode 2500 miles with them reversed and it seemed as the mapping was inverted from stock. I get outstanding MPG between 46-56 but with the O2's reversed I was lucky to get 47 MPG most of the time I did 42. I did switch them back before a 2000 mile trip 2 weeks ago and the flat spot did appear from time to time but I prefered MPG over performance when I'm on the road. I'm unsure how my conclusion will be thought by other VTEC riders but I'm convinced that the O2 sensors are correct from the factory. A tech at Marysvile, Ohio said to me that the engine was designed to starve the engine for fuel at 4500 RPM in order to meet CARB 2008 and If I wanted to get rid of the flat spot go buy a power Commander. I hope this helps from one riders point of view.
Robert
66,771 miles
PS I never had any negative problems with the O2 sensors reversed, in fact the bike ran pretty dam good it's just I'd prefer MPG on 2,000 mile trips.
Rob

[Jason Creasey]

Hi Rob,

Thanks for your feedback, & welcome to the club

JC

[Clooney]

It's been interesting to note the kind of fuel consumption figures being quoted with regard to this issue over the past few weeks/months. Since my o2 sensor swap in January, which dramatically improved the bike, I have not noticed any real change in the fuel economy - however, what this means is that I'm only getting, at most, about 30 mpg which seems to be a lot less than the average. I'm doing close on 200 miles a week which is almost all urban riding. Is anyone else getting this low level of mileage?

[vfrsutton]

just worked mine out and I'm getting 45-48 mpg on 180 miles per week consistently over the last year and 8000 miles.

all urban in London.

also it's been generally accepted that the o2 sensors are not the isssue but the starter valves in the throttle bodies? FYI my sensors are set as per factory gate.

[MarkJHarris]

As to fuel economy, mine is often mid 30s too. Generally because I ride like a loony and live on the Isle of Man which is all point and squit (it would be squirt but for the state of most roads here) and the lack of roundabouts and other motion friendly junctions.

I've noticed the poor initial throttle action get progressively worse (totally O.E. setup right now) as the weather and humidity get hotter and damper as well. Having said that, it only ever gets to 70' on the Island EVER.

I am off to Donington next month so will get the throttle bodies re-balanced and if that doesn't fix it the Power Commander will go back on.

What I can't figure out is why Dynojet didn't make the O2 elims as a jumper plug to enable the heating wires to still function and make the O2 sensor think it was working as well?

My answer may well be to actually remove the O2 sensors and fit short bolts in the holes and re-fit the elims as well as the PC3. This done the zero map in the PC3 is a marked improvement on standard let alone the changes to soften the VTEC transition that are in the stock map Dynojet supply.

I'll be interested to see how my VTEC behaves with full GIVI hard luggage and Baglux tank bag on hte Day of Champions ride-in and a couple of laps of Donington GP circuit fully loaded.

[bethanysgrandad]

I have copied, and edited, the account below from my original post because I think it is relevant that there seems to be a trend emerging. I should also mention that I swapped my connectors in the very early days and reported then that I saw an improvement. Never have checked the consumption though.

It all started as I was making good progress along the M8 North-ish of Edinburgh with a bunch of IAM guys about a month ago on our way to Fort William, when suddenly the FI light came on nice and bright. Didn't have much choice but to carry on, and the bike appeared to be running OK anyway.

Turned off the motorway, pulled over and parked the bike. FI light started to flash. Dickhead here didn't know that the flashing was the ECU outputing a fault code. Stopped the engine, left it for a couple of minutes and restarted. No light and everything seemed fine so continued to Fort William.

Question....is the bike likely to let me down in the middle of the Highlands of Scotland. Haven't a clue, but I know of a man who does.

I called Dave (GreenVFR) and described the situation. He didn't think that the bike would let me down and went to great lengths to explain the ins and outs of the multiple sensor set up that controls the fuel injection system.

He then offered to take a look at the bike and check things out if I could get it across to him. An offer that I couldn't refuse.

I then asked him what his thoughts were on the fact that I had swopped the O2 sensor connectors over. Well I don't think he was very impressed, and I did hear the word muppet in there somewhere.

I managed to get the sensor connectors switched back in time to get a couple of hundred miles on the clock so that the mapping system could re-establish.

As arranged I took the bike over to him at the end of a great week of rubber laying even though it seriously pissed down for most of the time. No problem with 020s in the wet IMHO.

Dave took the bike out for a spin and came back with the comment that it was running nice and smoothly. To be honest it always has.

He then started to give it a thorough visual once over. In no time at all, and a couple of cups of tea later, my bike was in bits and the ECU was being interrogated to establish why the FI light had come on.

Surprise, surprise (well not to Dave) the fault code shown was for an O2 sensor failure. He thought due to the connectors being previously swopped over, althought that had been done months before. It was however a mystery as to why it had taken all this time to show itself, so maybe it wasn't that. Can't tell.

Anyway, ECU store cleared and bike put back together.

"If you've got half an hour I'll check the starter valve settings" say's Dave. "Fine by me" I said. I'm only five hundred miles from home and could do with another cup of tea.

So up comes the tank and other bits and pieces start to accumulate on his workbench.

After much chat, work by Dave and me getting in the way, Dave shows me on the Carbtune that he has got the starter valves absolutely stone blind.

So with the bike back together Dave goes for another test ride and returns with a satisfied grin.

Time for me to head-for-the-hills as it's Harrogate or bust cos' that's where the hotel was.

After a full five minutes, or less, I realised that my previously smooth Vtec was now transformed into a slinky smooth Vtec. It was brilliant. It just purred for me. Low revs, high revs, mid revs, any revs. Smooth, smooth and smooth.

I then had a brilliant run down to Harrogate on a bike that was just flying. Well I thought so.

Those starter valves seem to make a huge difference.

All I can say is that if it weren't so bloody far I would be begging Dave to service my bike. I believe he knows what he's taking about and is passionately interested in what he does.

And he's a nice bloke........and makes a pretty good cup of tea.