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  • First, I would like to say hello to all since I am new to this forum.



The problem that I am seeking help to fix is... What will cause a drastic drop in gas milage after 32K mile servicing.



  • I was typically at 38mpg before service and I am now at 20mpg.
  • There is no visible gas leakage, nor the odor of leakage in garage.
  • New air filter was installed.
  • New spark plugs installed and gapped at 0.040-0.041.
  • Valve lashing in spec.
  • Cam chain stretch in spec.
  • Wheel bearings good.
  • No brake drag.

I disassembled the bike again to inspect for possible loose vac hose or improperly made electrical connection. All is good.



I am rather dumbfounded at this point, which is alarming because I am usually the guy that every brings their bike to for repairs.



I will be forever grateful to any that can help me solve this mystery.



Best Regards, Scooter61

 

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Welcome to the forum Scooter 61. I am sure some of the experts will arive soon with their great knowledge and suggestions.

Dennis
 

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HI SCOOTER and welcome to the forum did you repull any of the plugs to see what they are like was the air filter standard or k&n, cheque the exhaust sensor is ok any chance you put a couple of the plug leads wrong way round as the ecu might compansate for this and if no so may not be sonoticable
 

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Everything on my servicing punchlist is O.K. I didn't skip, miss, or forgot to return anythingto normal operating condition aftr servicing. I even accessed my diagnostics page on my nav system.... no errors are reported.



Rechecked spark plug gap, plug wire condition, connection integrity, spark intensity... blah, blah, blah.....



I've been servicing motorcycles for a couple of decades, but this one has spoofed me.
 

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:)Hi Scooter61,,, when you changed the air filter, did you Initialize the ECM unit on completion???,,,,,if you are unsure how,, go to Biker workshop on the right hand side of the home page and look at no. 15 or no 10,, it explains how to in these articles,,, also if this does not help,,try putting your old plugs back in for a few days,, just to see if the new ones are Duff,,good luck pp
 

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ECM init performed correctly. I don't have the old spark plugs anymore. Thanks for directing me to Workshop!! I thrive on reference material.
 

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Dash indicator light has never come on and as stated, my diagnostics page reads "no reported errors"
 

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Any chance that the air intake is partially blocked off. Did you change plug type?

Sorry! Forgot to welcome you. Best place for Wing Info!
 

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No intake blockage. As I have stated, Ive already had the top shelter off and checked everything to insure I didn't do anything wrong. Spark lugs are OEM, NGK BKR6E-11.Service spec is 0.039" to 0.043", or 1.0mm to 1.1mm.

Since I work in a facility that has a metrology lab, I relieved them of a 1.050mm class xxx gage pin for gapverification.I did pull them last night and checkedthe gap just to insure no mistakes were made. Gap is verified at 1.05mm.



After reading the reply from "pinkpork", I did the ECM reinit just to see if it makes a difference. The info to which I was directed to is typical practice on any EFI bike I work on, but you never know. I'll take the bike out this weekend burn up a couple of tanks to see what happens.
 

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That's a new one, get that all the time working on cars. No matter what was done, new tail light bulb to major service they come back complaining of bad gas mileage. But a guy doing his own work and that happening is strange. If you don't find the problem the only suggestion I have is have it checked with a scanner to see if the fuel trim is out of whack and why. I would suspect the MAP sensor not reading the manifold vacuum.
 

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Recheck the mpg, maybe over a couple tankfuls...to cut your mileage in half should show up with some type of running problem...black smoke, fouled plugs, stinky exhaust, rough idle, fouled O2 sensor....
 

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slickster wrote:
Recheck the mpg, maybe over a couple tankfuls...to cut your mileage in half should show up with some type of running problem...black smoke, fouled plugs, stinky exhaust, rough idle, fouled O2 sensor....
I agree with slickster, that big of a drop in mileagetheengine should be running noticeably different. What did the plugs look like when you pulled them? Somethings not right for it to suddenly do that. Probably something simple I hope. Good luck.
 

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It sounds very much like a bad O2 sensor. In order to troubleshoot that you need a service manual. It might be worth checking the connectors.

From what I have been told, this will not necessarily show up as a fault code, but I have no experience with it myself.
 

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Welcome to the site

To drop the amount of mpg you say, you are either using it or losing it. Now you indicate that it is not losing it so we assume you are using it. A bad plug may cause it, so I would use the simple test of when idling, remove a lead and see if it drops revs.

Failing a plug problem, I would be with Bob and suspect an O2 sensor failure or a connector dislodged or even some bad fuel.

Did you add any parts at this time or is any fuses blown.

Keep us posted :waving:
 

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I came to answer an PM and spotted your question. I think I would not panic just yet, and run the tank of fuel out that you have and then go get some more elsewhere and see what happens. Could just be bad fuel.

If it continues, as others have said it is most likely the forward O2 sensor or sensors, the ones ahead of the CATS. They do not always register a signal to the ECU or do still produce enough voltage to be sensed but not lacking enough to cause the trouble circuit to activate.

A bad plug or two can cause this but I would surely think you would notice the motor missing or running rough if that were the case.

The O2 sensors are very critical in a fuel injected engine, they tell the ECU what to do and if in fail mode very much enrich the fuel mix, so it will eat up the fuel.

I have attached a info note on O2 sensors, as the bike manuals are sadly lacking in information on them, and those on the Honda bikes are the same as those on the Honda cars, one thing about testing them, never use the ohmmeter function to test for continuity as the voltage off the meter is higher than the micro voltage of the sensor and it will short it out, use the volt meter only.

OXYGEN SENSORS

Hope this helps.

Take Care

Kit
 

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Welcome scooter

If you are a good mechanic " sounds like you are" you would know if it wasn't hitting on all six. Assuming it is read the plugs. In my opinion a slightly off gap will not kill your milage like that, hows the color? Before I pulling my hair out I would just re check the milage.

Good Luck Tom
 

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Discussion Starter #19
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Well, I invested in what "pinkpork" had suggested, that is reinitializing the ECM. Why I didn't do this previously is probably due to my own resolve that "I already did that after servicing the bike". BTW, it wasn't bad gas because I've been suffering through this for approximately 1500 miles.



So.... I did the reinit last night, fill the tank today, zero the odometer, and ride for a couple of hours. Guess what.... I travelled 116.9 miles by the time I pull up into my garage and the gas gauge needle is between the 1/2 and the 3/8 hash marks. That is about 43% of 6.6 gallons divided into 116.9 miles equals 40.5MPG... right where it should be.



Two events occurred between 32K and the present 34+K miles.



1. I had to replace the right handlebar switch module due to a broken engine cutoff switch.

2. The bike hit the rev limiter shift from first to second. It likes to slip out of second when the engine is cold:waving:
 

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Glad to hear that it was a simple fix. Next time you fill up and can do an accurate calculation of mileage let us know what you find out.
 
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