Let me start by saying I am not trying to gain max HP, just trying to have a nice, smooth ride.
Made a couple observations while enjoying a very nice southern Arizona Saturday ride of approximately 250 miles.
First, I got approx. 32 MPG - have read other posts where people are talking about 40+ MPG.
Second, while cruising at about 65 MPH, at barely any throttle, the engine rpm would drop down - and if I held the same throttle position it would come back and run smooth for a few seconds and then drop down again. Kind of seemed like the computer was reading rich, adjusting, reading lean, adjusting, etc. Am I correct to believe the computer reads and adjusts like that?
I would say the bike also doesn't have a great throttle response - doesn't really snap when I goose the throttle from idle.
The bike in question is a 2002 VFR800 with a Leo Vince carbon fiber exhaust and K&N filter. Otherwise, engine setup is stock.
I was wondering if I should be getting better than 32 MPG? It wasn't a slow ride, but wasn't racetrack conditions either.
Also wondering if a power commander would clean-up these conditions for me, or if I really wouldn't get much bang for the buck.
No on the PCIII, before trying a few other(cheaper) fixes like 02 eliminators, or higher pressure fuel pressure reg.
Off the top of my head I would say you have a bad T-stat or it's the Winter blend fuel causing the poor mileage. How many miles on this thing, every had the plugs changes??
What rpm is it at at 65mph? There's also a flapper valve that can effect the 3500-4500 rpm range.
Search through our Mods threads or 6th gen threads as most everything has already been covered 10 times by now. :rolleyes:
Drop 1 tooth on the front sprocket and acceleration feels so much better. :fing02:
Adjust most of the slack out of the throttle cable too while your at it.
Tucson; As far as the Power Commander,yes /no decision. Depends on what your about as a rider /enthusist and what if any plans you have to modify your machine. I currently have a power commander and oxygen sensors
blocked or removed. Later this season I am probably getting a higher pressure fuel regulator. Theoricitally then, I should have all my bases covered with reguard to fuel delivery and adjustability. I have not tried just blocking my oxygen sensors ,but initially I dont like the idea, eddie
32 mpg is low, regardless of other factors IMO. Cold weather can affect mileage but not usually by 20%. A stuck thermostat could be the culprit tho.
How many miles are on the bike and are you running the original spark plugs? Have you checked your fuel line or screen? Could they be blocked?
I had to replace the fuel cutoff and engine stop relays in my '04 last year. The first symptom that they were bad were loss of power during steady throttle on the freeway. But they never affected fuel economy or liveliness of the engine in general, so I'm guessing that's not the issue with your bike.
As for the PCIII, I installed mine (and O2 sensor eliminators) last year and it did improve smoothness, plus I think added a little power to the midrange. My bike was OK before but I'm glad I bought and installed that mod. It was worth it for me.
I'm in the early stages of owning a PCIII. I found it for 130$ on ebay so it was sort of a steal. Fuel mileage dropped to 30mpg at first, this was before I used common sense and checked the map. The seller said that it was stock but it wasn't. I'm still on the 1st tank using CozyE's map. So far mileage is back up but not back to 42mpg. With the fuel response that I am getting it is worth it. Once we get out ot the winter gas, I'll look for better results on mileage. I'm not too worried about it though, the truck gets 13.5mpg and the RV gets 7....
[image: View Post]Baileyrock, on Mar 2 2009, 09:11 AM, said:
No on the PCIII, before trying a few other(cheaper) fixes like 02 eliminators, or higher pressure fuel pressure reg.
:+1: I've done both of these mods and don't plan on getting a PCIII. I'd recommend starting with the O2 eliminators. I went with the $0.99 O2 eliminator described in the mods section.
The bike has 18,000 miles. I just bought it and have a receipt showing the plugs were changed at 16,000.
The rpm was probably somewhere around 4,000 when the power was coming and going cruising at 60-65 in 6th gear. Can you tell me more about this flapper valve?
The bike runs well otherwise - nice power, and the acceleration from 60ish to 100ish in 5th or 6th gear passing cars was nice.
I will take a few more tanks of gas to confirm the mileage.
Does anyone know what happens to the ECU/ fuel regulation when you unplug or debilitate the oxygen sensors. Does the fuel mixture go into a non adjustable closed loop
or by disconnecting them does the ECU think the engine is cold thus giving the engine more fuel? I think we need to know these details before we suggest to someone
to just unplug or remove their oxygen sensors. eddie
[image: View Post]onedowneaster, on Mar 2 2009, 03:37 PM, said:
Does anyone know what happens to the ECU/ fuel regulation when you unplug or debilitate the oxygen sensors. Does the fuel mixture go into a non adjustable closed loop
or by disconnecting them does the ECU think the engine is cold thus giving the engine more fuel? I think we need to know these details before we suggest to someone
to just unplug or remove their oxygen sensors. eddie
The bike operates in a open loop, following a predetermined (and very lean) map. If the RPMS are between 4K-5K and the throttle is held steady the bike will go close loop and try adjust the mixture. Any change in throttle position will send control back to the map. Removing the O2 sensors and replacing with 330ohm resistors only prevents the bike from ever going close loop, thus helping prevent the "hunting" that you may notice. The resistors are across the heater terminals. As long as there is a load (330 ohms) across the terminals, the controller believes the O2 sensor is there. Because the signal from the "O2 sensor" is zero volts, it doesn't act on it and stays open loop.
End of thread · 10 posts recoveredWayback Machine snapshot 8 Apr 2011