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6Th Gen Getting ~30Mpg...?


PorradaVFR

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What's a warm-up signal from the TPS? Kinda sounds like muffler bearings and headlight fluid... :s

^^^ Agreed - sounds like they're blowing a smoke screen. The only time I saw a bad TPS was in very high mileage units or where lots of moisture was present. Not that it can't happen . . . just seems unusual. $2,000 bucks seems ridiculously high for this job and it would be worth testing the TPS yourself if you can. The FSM shows plugging in a special harness to test it, but some 14 ga solid wire can be used to backprobe the connections to do the same thing. Maybe just clean up the tape issue in the PAIR system and see what happens. Any money that would go to new O2 sensors would be better put toward a PC and eliminate them.

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Man, so many typos in my post...frustration?

So I shopped around and found the throttle assembly for far less. I agree on the O2 sensors, I'll quite likely just opt for eliminators instead of replacing those, leave the PAIR back to factory (open) and given that I got a smoking deal on the bike to begin with I'll absorb the ~$1k bill as belated cost. $4k for an ABS with 300 miles was too good to be true after all, I guess.

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OK guys we need a little sanity here. I've pulled this model bike apart too many times to count and done a lot of diagnosis. Here's what I can tell you FOR CERTAIN:

  • The VFR ECU has no "long term fuel trim". The O2 sensors ONLY kick in when the bike is cruising.
  • Fitting O2 eliminators will completely STOP closed loop mode. This means that the ECU will not "adjust" fuel. Ever.
  • Any bike running with O2 eliminators will stay in Open Loop mode permanently
  • The PAIR valves are open by default and ONLY close in circumstances where the O2 sensors would normally kick in

So, what does all this mean? It means if you fit O2 eliminators, your fuelling issues have ZERO to do with the O2 sensors.

Now, about the TPS sensor being faulty. I cannot speak with certainty on this topic, but the VFR ECU is a mix of Speed-Density and Alpha-N fuelling. What this means is that at low-mid throttle positions, the ECU uses the Manifold Absolute Pressure (MAP) sensor to control the fuel mixture. At larger throttle openings, the ECU switches to "Alpha-N" which means the fuelling is based on only the Throttle Position (alpha) and the engine rpm (N).

What kind of things can go wrong here?

  • Air leaks in the MAP hoses would probably make the bike run lean, not rich
  • The TPS *could* be out of alignment. This could be checked by looking at the TPS screws to see if they have been disturbed, because they are glued and set in place once adjusted at the factory.

The reason the "TPS fix" is so expensive is that Honda won't sell you a TPS, you have to buy the whole throttle body assembly. I had a zillion spare parts for this bike, including an entire assembly. I sold it all to member MVinOZ so if you want to contact him to see if he has a throttle body handy, you could pick one up for very little.

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I thought the solenoid for the pair valves is normally closed except when the throttle is closed ie decelerating and idle? Also maybe its the coolant temp sensor sending out the wrong voltage telling the ecu to give it more fuel because its supposedly not up to temp?? Not a expert just throwing out ideas

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  • 2 weeks later...
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Argh. Just heard back from the shop and the good news is I have information, the bad news is that's it's...bad news.

  1. Someone (NOT me) duct taped over the PAIR ports...based on the condition of the tape it was "years ago"...but the hose was not blocked and it was slopped, leaving some of the rubber ducts pinched. The PO did not strike me at ALL like a fiddler, so I have no idea what the hell that's about.
  2. The O2 sensors are not fully heating up so they're not performing 100%...not sure how that affects their signal, but it's not right.
  3. The TPS is bad...it's sending a warm-up signal all the time, meaning even a Power Commander would not be able to compensate for it..and the price quoted for a new one is nearly half what I paid for the bike to begin with. Ouch. They further note that the factor assembly uses safety screws so it cannot reliably be disassembled and even if it was there's no adjustment to make.
  4. Bottom line - all told with parts it's looking like $2,000 to replace the whole deal. Nuts.

Does anyone have a 2002-2005 TPS/throttle assembly they don't need?

*sigh*

Ok gang, picked up the bike yesterday and did a long way home ride. I'm VERY pleased with the result. While not cheap (but not the $2k I feared either) the new throttle bodies, O2 eliminators and removing the duct-tape "fixes" have made a very significant difference and improvement to the bike. Off-idle throttle is butter smooth, the VTEC changeover is all but invisible and while I do not yet have any idea what the fuel mileage will be I can say with certainty that she's no longer exhibiting the snatchiness that I was noticing after picking her up from the first shop.

The dealer also noticed (and SHOWED me) that the bike was giving a #8, #23 and #24 code - (TPS and O2 sensor heaters). The mechanic also showed me how to read the codes and cleared the repaired ones from the system.

** Sidenote - I have the service manual but cannot find where the codes are listed, does someone have that?

So basically the O2 sensors were not heating to spec so they were sending a bad signal, the PO had messed with the air box so it was not flowing as it should and the TPS was sending a bad signal that a Power Commander would not have corrected for. So while I'm in for more than I wish, I got a smoking deal on the bike to begin with so basically I've now paid a fair price for it. I'm very pleased how she's running now and may well go back to shop #1 to replicate the dyno run and see how she's behaving now.

Thanks everyone for the input. I have the removed throttle bodies, fuel pressure regulator (was fine, but was included with the new throttle bodies) for sale in classifieds if anyone wants to mess with it, or needs to scavenge parts from one.

Finally the saga ends well!

:goofy:

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  • 2 weeks later...
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I've just run down what remained of the tank when was in the shop and added around 60 miles on the new tank. Very vague, but the first "block" on the fuel gauge took about 18-20 miles which is at least a visual improvement.

I'll post up on the next fill since the last included the shop test-riding it and I would not know how much time idling might have affected the mileage seen. She's running great, still pleased with the results.

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  • 2 weeks later...
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So filled up yesterday. 107 miles, 3.5 gallons. Yeah, 30.5 mpg by my math. I still note her running much smoother but that's not what I expected. May well re-dyno her to see if the FAR is improved as expected. If the numbers are better I'll live with the mileage I suppose. Hmmm

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Nuts.

You ain't kidding. She definitely running smoother as I had clearly become accustomed to the snatchy off-idle throttle so the improvement there was notable...but not $1700 better. :goofy:

Like I said, I'll likely end up back at the original shop to run her on the same dyno. If the numbers are better I'll likely take the side cases off for a tank's worth and see if the mileage comes up to where I'd expect. If not and the dyno shows a better FAR I'll just call it a day and accept she's thirsty.

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Looks like there are 2 marinas on a lake just northwest of Paso Robles that sell real gas...buyrealgas.com or pure-gasoline.com ... I would not hesitate to see how it ran on real gas.

I am not saying that will magically restore the 25% you are down on power and up on fuel consumption but I know the blends that they require in your area are quite troublesome for the refineries. I would run a tank of pure gas just to see, and your panniers are taking a 3-5% hit on he fuel economy as well but they wouldn't impact your hp numbers.

I sure seems from your dyno chart that you are running on 3 cylinders...I guess you have already confirmed that it is not the case but wow, 75 hp or so is pretty disappointing.


Call a few marinas in your area and see if they have pure gas or real gas available.

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Looks like there are 2 marinas on a lake just northwest of Paso Robles that sell real gas...buyrealgas.com or pure-gasoline.com ... I would not hesitate to see how it ran on real gas.

I am not saying that will magically restore the 25% you are down on power and up on fuel consumption but I know the blends that they require in your area are quite troublesome for the refineries. I would run a tank of pure gas just to see, and your panniers are taking a 3-5% hit on he fuel economy as well but they wouldn't impact your hp numbers.

I sure seems from your dyno chart that you are running on 3 cylinders...I guess you have already confirmed that it is not the case but wow, 75 hp or so is pretty disappointing.

Call a few marinas in your area and see if they have pure gas or real gas available.

The dyno chart I posted was before the repairs were made and as I noted, they were substantial. I do need to re-run it, hopefully to reveal the bike is as it should be from a HP/torque/fuel-air ratio. If those are now better aligned to expectations I'll tolerate the fuel mileage. If not...well hell, I dunno. Not going to keep spending money on it when she's not at all unpleasant to ride.

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That makes sense Porrada, we took our 3rd Gen to have it dyno tuned after rebuilding the carbs...it was 76 hp before and 93 hp after installing a jet kit and tuning the carbs a bit.

But that bike is 23 years old and I would question the sealing of the valves and rings on that bike.

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Maybe the bike isnt going into closed loop mode? Im no expert but I know one my bike warms up you can hear the pair valve solonoid click off when revved to 1500rpm from idle. I know the pair has to shut itself off when the bike is running from the o2 sensor to avoid any misreadings.

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These suggestions are out in left field, so feel free to ignore them.

First, you're still reporting low mileage for the amount of gas that the bike is consuming. We assume that the # of gallons that you are pumping is accurate (that the gas pumps are correct), but what about the distance you are traveling? Some bikes have relatively-accurate odometers from the factory, but that's not a given. And a lot of people will change out sprockets to increase acceleration - but at the cost of higher engine speed at any given road speed (and also affecting the odometer accuracy, if that is driven off the rear wheel / drivetrain). You may want to run 100+ miles on the highway, using the highway mileage markers (or using a GPS), and then see how much gas you used. You may find that your odometer is off, and that your mileage is decent.

Second, are there things that could be affecting your rolling resistance? I assume you're not riding around on 15 psi in your tires, but it would be a good idea to double-check your tire pressure. Also, check that your drive chain is properly lubricated & not adjusted too tight. And check that you don't have any issues with one of your brake calipers dragging. (If you put the bike up on the centerstand, with the rear wheel of the ground, and you leave the bike in neutral with the engine turned off, how freely can you spin the rear wheel by hand? How much resistance do you feel?) While I'm thinking of it, it couldn't hurt to check front wheel bearings & rear axle bearings, too - although that's not as easy to do.

Again, these are out in left field, but I didn't see any mention of these, so I thought I'd suggest them.

Good luck!

Ron


Looks like there are 2 marinas on a lake just northwest of Paso Robles that sell real gas...buyrealgas.com or pure-gasoline.com ... I would not hesitate to see how it ran on real gas.

I am not saying that will magically restore the 25% you are down on power and up on fuel consumption but I know the blends that they require in your area are quite troublesome for the refineries. I would run a tank of pure gas just to see, and your panniers are taking a 3-5% hit on he fuel economy as well but they wouldn't impact your hp numbers.

<snip>

Call a few marinas in your area and see if they have pure gas or real gas available.

+1 to that suggestion. Try running an entire tank of ethanol-free gas if you can find it anywhere, and see what sort of mileage you get from that.

Also, in addition to the sites above, I find http://www.pure-gas.org/ to be very useful.

Good luck!

Ron

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  • 3 weeks later...
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<Darth Vader voice> The cycle is now complete....(hey, just realized there's a pun there too). :goofy:

So - took the VFR back to the original shop to have her re-run on the same dyno to hopefully quantify the impact of the repair work done by the dealer. Sure enough, the FAR is much improved, with slight improvement to the power/torque lines but I must note the prior chart did not hit the top of the rev range. At this point with a few tanks through with 30-31mpg I'm going to put this dog to rest and accept that mileage and be happy with the better fuel/air mix that is as closer to as it should be.

post-2418-0-40151000-1399912812.jpg

My current tank is not from Costco which has switched to a blended fuel over here. Maybe that will have an impact, but I'm not holding my breath. I'm just gonna ride Dusty as she is. :comp13:

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