Gas Mileage dropping - no reason I can see

[Denver_FJR]

... And sometimes it would just suddenly slow down suddenly, then catch back. Sometimes. Once an hour? Once in 30 minutes? Does anyone else also understand, as I do, that trying to figure out something that happens on a mechanical device sometimes is just about the most maddening, frustrating and time consuming thing to do?

Problem sounds a bit like a bad spot on the TPS.

Anyone else understand frustration troubleshooting intermittent problems? Uh, yeah! The lack of OBD interface really frustrates me, guess I've become spoiled having it on other vehicles.

Still curious about the check-engine light. Dealer ever check history?

 

[birkdale10]

Another update. The mechanic found something.

This is way beyond my tech expertise, so I did some searching and browsing other posts for 'ambient air pressure sensor'. The other posts seem to agree that it is something that is important, controls something that needs controlling and could cause very similar problems to what I have been describing if it isn't working properly.

The shop lifted the gas tank and tested the sensor and it is non-functional. I was told that it is reading '99% ambient air pressure' at all times. They said there are a number of short, medium and extremely tiny hoses that are all connected to this sensor and they have pinholes in them. A new sensor is ordered, and has arrived, and a whole bunch of hoses are ordered and the box they are in is on the invoice but the box is missing and a trace has been started.

I am told that my bike has 1st priority as soon as all the parts are there. All I can do is wait.

 

[RadioHowie]

 

[Constant Mesh]

The ambient air pressure sensor is under the seat. It has no hose connections. They are replacing the intake pressure sensor and its hose network.

The sensor may be OK. One of the hoses in the network may be disconnected or the one going to the sensor may be plugged with crud.

That same network of hoses is also connected to the fuel pressure regulator at the right end of the fuel rail. If the hoses are leaky the regulator would be adversely affected too.

 

[Big Sky]

This is an interesting thread and I don't mean to hijack it but the scenarios are closely related, it seems. I sold my brother-in-law my '03 in spring of '12. I then purchased an '05. We rode together in '12 and '13 and the bikes, under similar loading conditions, got nearly identical mileage. However, I just finished a 2,750-mile tour with him, again under very similar loading conditions, and his '03 was now delivering 5 to 10 percent less fuel economy. But here's the kicker: when I rode behind him I could distinctly smell unburned fuel. Okay, so the bike may be developing a rich condition (bad sensor somewhere as with the OP?) but why is the catalytic not cleaning up the exhaust? Will a faulty or failing sensor not always throw a code? Yes, I'm putting my ineptitude on display...

 

[RichDoyle]

The catalytic converter can't deal with excess fuel. It's there to deal with other undesirable gases in the exhaust. In fact excess fuel compromises its efficacy in this area.

 

[Fred W]

@Big Sky - most sensor problems are supposed to cause a check engine light. I would be suspicious of a faulty fuel pressure regulator. That will result in rich condition with no CEL

 

[carlson_mn]

The air pressure sensor defaults to a very standard pressure reading if it fails. The only time you'd notice it causing an issue is if you were riding up into unusual elevation.

 

[FatNakedGuy]

I'm still trying to figure out why my 04 randomly smells like burning leafs on start-up. It's pleasant and all but WTF?!

 

[RichDoyle]

The air pressure sensor defaults to a very standard pressure reading if it fails. The only time you'd notice it causing an issue is if you were riding up into unusual elevation.

The air pressure in the manifold MUST be reasonably accurate or you can expect to get a too-rich mixture. The reason is, at partial throttle, this pressure is well below atmospheric and the injectors should be getting adjusted to deliver a lower fuel flow to adjust for the reduced airflow. This is a control loop I'm right in the middle of in my airplane all the time.

 

[RichDoyle]

I'm still trying to figure out why my 04 randomly smells like burning leafs on start-up. It's pleasant and all but WTF?!

I notice that often, as well. But it isn't just the FJR. My other bikes have done the same thing, though, so I figure it's a benign thing.

 

[Just Krusen]

Catalytic converters burning off start up fuel?????????????????

 

[birkdale10]

I got my bike back today. I need to find time to go for a long enough ride to use up a tank of gas, and check if the mileage is better.

Total cost: $907. 4 hours labor. The expensive parts were 'sensor, pressure', 2 of them at $208 each. I was shown the hoses that were also replaced - and two of them had holes in them. Not pinholes - 1/4 inch holes. These hoses are supposed to carry air and don't do that very well.

I looked at the exploded diagram at the Yamaha site, and it shows that the parts were 5JW-82380-00-00 and the list price on them if I had bought them directly would have been $133 each. I'm not too happy about the difference betwixt 208 and 133.

4 weeks, 3 days in the shop.

It seems to run fine. None of the hesitation the I had been feeling. Just need to put some miles on it.

 

[RossKean]

I hope they respect you in the morning!

 

[Fred W]

List price on 5JW-82380-00-00 is $231.99, so they did not even charge you full list for those parts. Yes, you can buy these parts greatly discounted on-line, but when you go to a shop you should expect to get charged list price (or close to it) on parts. And don't expect to be able to buy your own parts, most will not allow it. It's part of their profit line.

That part number is used as the Intake Air Pressure sensor (i.e. manifold vacuum) under the tank, and also as the Ambient Air (atmospheric) Pressure sensor under the seat. The intake sensor is connected to a bunch of small vacuum tubes that tee out to go to each of the 4 throttle bores and also to the fuel pressure regulator on the end of the fuel rail.

My bet is that the entire problem was just those holes in the vacuum tubing, and that both of the sensors are probably fine. (Did you get the used parts?) I'd be curious to see where the holes in the tubing were, if they were near some restraints or something else under the tank that chafed those rubber hoses. This may be something for the rest of us to keep an eye out for.

You probably could have just replaced all of the vacuum tubing (just buy a long piece of vacuum hose and cut all the pieces to the right lengths) and have fixed it for less than $20. Once they ordered those parts they probably just wanted to just stick them all in and charge you for them. This sounds like pretty standard service at a dealership. It's why many of us refuse to bring our bikes to one for service.