Seriously Bad Fuel Economy

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Slappy

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Over the last couple of months my fuel economy has gone seriously down hill. Ive gone from 240 a tank to 150 a tank. I have had the valves checked, all within spec, I have new plugs, less than 1,000 miles on them. I use the same oil/weight and filter. I drive the same roads every day commuting at the same speeds both ways. Same tires at 42/40 pressure. I generally use the same gas from the same station. The air filter is less than a year old and seems to be in fair condition.

Could it be a bad or going bad O2 sensor or mass airflow sensor? What else can cause fuel economy to go this far south that quickly?

 

ionbeam

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How are you measuring your gas mileage? Old fashion miles divided by gallons or are you using the dash readout? Do you always fill on the side stand or center stand, or do you mix it up? Do you always fill the tank up to some consistent visual reference point like the bottom of the filler strainer?

Any shop that does emissions testing can give you a reading for short bucks. A probe inserted at the end of the exhaust, with a fully warmed up engine should show 1.5% CO or less. While this isn't a root cause diagnosis, it is a way to confirm that there actually is a problem.

I really doubt that the O2 or air flow sensor are responsible, if they were that far out of range you should have a diAG code set and possibly a check engine light. Codes set?

Assure us that you haven't added something like a Power Commander or adjusted the CO levels...

High on the list of suspects would be one or more fuel injectors not fully closing. A few tanks with Sea Foam or Techron may clean the injectors. The injectors can be pulled out and flow tested, but before doing any of that pull the plugs and see how they look. Soft fluffy black deposits are a sure clue to rich operation. Since you just changed your plugs they should be pretty clean. Do you have the old plugs to look at?

Possibly the ECU thinks that the engine is cold and is staying in the cold enrichment mode. Again, check the diAG readouts for temperature readouts. A quick, but not conclusive test -- when the engine is fully up to operating temperature, in first gear accelerate briskly then chop the throttle off. If you hear pop, pop, pop in the exhaust the ECU thinks the engine is cold and has the Air Injection System active. The AIS isn't the cause of the mileage problem, that fact that the ECU has the AIS active may imply that the ECU is running the cold enrichment FI map. This would also cause the perception that the engine is running quite smoothly and may have slight bogging on acceleration. In fact, any excessive richness, regardless of root cause will cause these two symptoms.

One other silly thing you can check is to see if you have a fuel leak/drip. The root cause of this could be an excessively hot gas tank or a tank venting problem causing dribbles at the overflow tube. Do you smell gas when parked in an enclosed space like a garage?

 
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BobMercer

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Slappy,

Has the gasoline formulation been changed in your area from winter to spring/summer? Significant temperature change in your area? Have you checked your brake discs for galling or scoring from a dragging caliper? Is your engine running less smoothly, likely from an improperly positioned plug wire? Just guessing at remote possibilities, nothing scientific. Keep us posted if you find a problem. Good luck.

Bob

 

ionbeam

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No mention of throttle body sync. Has this been done?
I can't see any way that a TBS could cause a drop of 90 miles per tank. Even if the adjuster screws fell out. There was no mention of driveability problems.

 

Slappy

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To answer ION's questions

153 miles 5.2 gallons last fill up. Never trust electronics when an abbicus will do.

Always fill on the center stand and I always top off to where the gas touches the bottom of the filler strainer.

I removed the power commander because the mileage was going down using that. Been on the bike a year. So I thought maybe I had an issue but alas no. Last tank I got 180 out of it this tank I got 153.

I have not touched the CO settings because the power commander will not let you go into DIAG mode. At least not on my 07.

I have run two bottles of Yamalube ring free and one gallon, 6oz at a time, of sea foam. That fuel system is clean.

This is a strange thing. Once I took the power commander off. I let the bike warm to the point where it goes from 1500 to 1100. I very slowly roll the throttle. When it hits 1500 it acts like it wants to backfire. This only happens before any bars show. Once one bar shows it goes away. Also, if I am goofing off in traffic and let the bike lug in 2-4 gears, and I wack the throttle there is a burp, then a pause then the bike accelerates. This has been going on since day one. ECU was replace back in 08 under the recall.

I went into diag and checked the Throttle Position Sensor. Starts at 16 and ends at 102. Hits every number in between.

Did a throttle body sync after they did my valves. All cylendars dead nuts on.

Absolutely no leaks from anyplace on the bike. I actually slightly over fill the gas every couple of months to be sure the over flow tube is clear and working properly.

So other than taking it in and putting it on a machine it sounds like I am SOL.

 

Constant Mesh

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I wouldn't expect the high idle to drop down to 1100 before you saw coolant temp bars. Don't suppose the fuel pressure regulator is acting up and operating at a higher pressure pushing more fuel through the injectors.

 

Slappy

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To Answer Bob.

I live just outside San Diego. The gas here has been iffy since I have lived here. Whether it has gone from winter to summer blend I dont know. It looks and smells like the same gas and there are no signs saying they have switched over to summer blend.

Temps have been in the 60's to 70's all winter long. I ride to work every day accept when its a torential rain storm.

Just changed the rear pads. They are working perfectly. I need to check my front pads. I am getting a squeak from the front left outside pad.

Engine runs better when I add seafoam vs just running gas. I run 91 octane. I have put 91 in since the day it was born and will till the day it dies.

I will check the plug wires tonight after the engine cools. The fuel economy was going south with the old plugs so I doubt its that but I will definitely check.

 

LAF

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Are you going to the same station for 91 octane every time? In this day and age I am betting that with a few exceptions 91 has been sitting. I then question why you use 91? Mine runs fine on 87 but I have run 89 don't think I noticed a difference.

Other then old 91 gas, with no performance issues other then the cold hesitation you mentioned that clears, I got nothing for you.

Hope you find the issue.

 

FJRBluesman

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I knew you cruising the COstco parking lits and calling it a ride would take its toll on the poor ole FeeJ.

I'm stumped brother. Let the wiz-bang-gurus help, like ionbeam, Fred W's, et al.

Good luck.

 
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BobMercer

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When you removed the Power Commander did you reconnect the O2 sensor? That is, if it was disconnected when the PC was installed.

Regional fuel formulations are not something that is widely discussed, but it happens in certain parts of the country and Kalifornia is a likely suspect. Not to be critical, but you are wasting a lot of money running the FJR on 91 octane. My '05 and current '07 run perfectly at 45mpg with 87 octane. With fuel costs being what they are, go for the 87.

Bob

 

escapefjrtist

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When you removed the Power Commander did you reconnect the O2 sensor? That is, if it was disconnected when the PC was installed.
Exactly! Great minds think alike Bob! ;)

Running premium fuel will give you a mileage penalty. Add Ethanol and premium and you could be looking at 15% reduction verses plain'o regular. You mention that you're filling up at the same gas station. Any chance that they're starting to push more Ethanol in the fuel? Buy a few tanks of top tier fuel at a different station and see if the mileage changes.

Have fun!

--G

 

dcarver

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When you removed the Power Commander did you reconnect the O2 sensor? That is, if it was disconnected when the PC was installed.
Exactly! Great minds think alike Bob! ;)

Running premium fuel will give you a mileage penalty. Add Ethanol and premium and you could be looking at 15% reduction verses plain'o regular. You mention that you're filling up at the same gas station. Any chance that they're starting to push more Ethanol in the fuel? Buy a few tanks of top tier fuel at a different station and see if the mileage changes.

Have fun!

--G
Wow - my experience has been opposite, sorry. Premium Calil fuel has always returned slightly higher MPG. 3 - 5. And if I leave the state to where the gas is real, and get some elevation, like in Colorado, I've seen high 40's otherwise, in Kali, in my hood, running sporty, 28 - 35 is normal.

 

escapefjrtist

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When you removed the Power Commander did you reconnect the O2 sensor? That is, if it was disconnected when the PC was installed.
Exactly! Great minds think alike Bob! ;)

Running premium fuel will give you a mileage penalty. Add Ethanol and premium and you could be looking at 15% reduction verses plain'o regular. You mention that you're filling up at the same gas station. Any chance that they're starting to push more Ethanol in the fuel? Buy a few tanks of top tier fuel at a different station and see if the mileage changes.

Have fun!

--G
Wow - my experience has been opposite, sorry. Premium Calil fuel has always returned slightly higher MPG. 3 - 5. And if I leave the state to where the gas is real, and get some elevation, like in Colorado, I've seen high 40's otherwise, in Kali, in my hood, running sporty, 28 - 35 is normal.
The million $$$ question Don, is how much Ethanol is in the fuel. You might find that premium Cali fuel has less Ethanol than plain'o. If so, that's your difference...and it's worth the extra $$$.

At elevation and without a PC, we've consistently had mileage in the low 50's. Of course, you know I ride pretty slow compared to the forum speedsters! ;)

--G

 

dcarver

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The million $$$ question Don, is how much Ethanol is in the fuel. You might find that premium Cali fuel has less Ethanol than plain'o. If so, that's your difference...and it's worth the extra $$$.

At elevation and without a PC, we've consistently had mileage in the low 50's. Of course, you know I ride pretty slow compared to the forum speedsters! ;)

--G
--G, for a million USD I will provide you the answer!

..and as far as riding slow? Me don't think so...

 

Queensland Ken

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Ethanol ????

Here down under they are supposed to advertise the fact that the petrol contains Ethanol.

I've had to fill up at a Ethanol only servo once and the MPG went way way down.

On some tours, I've had the "sudden drop" after a fill up, then "somehow" it all gets better.

Suss bloody petrol stations selling Ethanol and charging for normal unleaded. !!

 

C&C

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You mentioned (then apparently ignored) the squeaking front brake; I would investigate this symptom. Personally, I would switch to regular fuel (as others have offered opinion). And make sure that your O2 sensor is functioning. Again, check that brake.

 

Constant Mesh

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What you've described is an almost 40% drop in mileage. Using 10% ethanol fuel will reduce mileage by 3% or so.

I mentioned elevated fuel pressure but that's a remote possibility. In the service manual a special fuel pressure testing hose is described and how it's used. I doubt a typical dealer would have this hose.

It's hard to imagine what could make the mileage drop this much.

 

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