FI light indicator at 75-90, loses power, gas mileage help

Please don't blow me away for not checking codes but not yet near bike. I have read up how to read the codes and will follow up with that. My problem is as follows.

My bike is 2003 ST1300 42k miles. A couple of people on this site have helped me before with a U joint and bearing issues.

Ok, I put over 1500 miles on my bike during Daytona Bike week a week or so ago. By mistake, I put 87 Octane in the tank, only about half the tank. On the way home, when I hit 75-80, the FI light would come on, stay on, I would lose a bit of power, like maybe one cylinder was not firing or maybe all were suffering a bit, don't know, but it still would go, but not as powerful as normal. I later made sure I used only high octane gas and also put in injector cleaner. However, no mater what I have done, at about 75-80, the FI light comes on. I can feel the bike is a bit sluggish and the gas miles goes to crap. Almost drops a 1/3 less. Light stays on solid until you turn it off..

I know I need to go ride it and make it set the FI light and then come home and read the code by putting it on the Center Stand. Other than that, I do not have a connector to check or short out for the indicator.

Has anyone had a similar problem and what was it.

Thank you again,

Rory

Yup. Knock sensor. Pull the codes per the procedure in the shop manual and then clear the codes. If you're lucky the code won't return. If it does you'll need to investigate. If it is indeed a knock sensor error, the most common cause seems to be a fried / melted sub harness between the sensor and the bike's main harness.

wjbertrand,

Have not yet been able to ride bike to get codes, but funny you say something about fried or melted sub harness. I thought I had smelled something burning like rubber. I didn't think it was coming from my bike. I will check codes, but maybe I have a wire against something hot. Something to investigate. If knock sensor, where is the best place to buy one from.

The only strange thing, I can ride it all day long, it seems not to have anything to do with RPM but speed. I rode A1A from Daytona to St Augustine and back, it never set off light. As soon as I get on interstate and hit 75-80, it pops on. It may have been doing this for a while, as I noticed my fuel mileage had dropped and always felt I was riding into the wind. But, I now know, when it feels like I am riding into the wind, the light is on. I will try to make the light come on on center stand but it hasn't come on until I reach a speed on the road above 75....

Thanks, love this forum.

Rory

If the source of the problem is one of the knock sensors (or associated wiring) you don't need to ride it to set the FI indicator. Just start the bike, warm it up a minute or two, then rev it up to 4k and hold it there for 10 seconds to see if the FI indicator lights up. If it does, close the throttle, leave the key on, and lower the side stand with the bike in gear to kill the engine (don't turn the ignition off yet, or you'll have to start all over again). The FI light will then flash on and off to give you the error code. There are numerous threads on this site that describe how to decipher the codes, some that guide you what to do next. If you have a service manual, it will help a lot with your troubleshooting.

You say it is ground speed related but not RPM but I would doubt that.

IF it is throwing the knock sensor code the engine will have to be above 3900 RPM for at least 10 seconds. If I remember right 3900 RPM will get you around 70mph indicated. Once the FI light comes on it will retard the timing in order to prevent the "knock". This will reduce power and increase fuel consumption.

Follow the instructions from Don B in post #6 above, that will give you the code. Put the bike on the centerstand, rev it to 4k RPM for 10 seconds or so until you see the FI light come on and then drop the sidestand. I would expect you to see 2 long blinks and 6 short blinks. That would be code 26 for a right knock sensor error. The left side is code 25 (I think).

Chances are good that there is no problem with the knock sensor. It will either be the wiring/plug at the sensor or the ECU. For me it was a bad ECU.

Ok, I warmed up bike on Center Stand, then I ran the RPM up to 4000, held it there for 30 seconds, nothing. Then went to 5000, 6000, 7000, 8000 and held at each for at least 30 seconds and no indicator light.

This may just muck the issue up, buy I had my bike detailed yesterday and it got really wet. After the wash, it didn't want to run for a bit, and I could see and smell water steaming off the hot parts. Now today, when I put it up on Center, more water dripped out of the bike. Anyway, the reason I bring this up, it sounds a little bit like I am having a miss or maybe timing issue or bad plug, or it could be just that I still have water in some electrical place at this time until it dries out. I don't recall it having the exhaust sounding like a bit of a miss at times. I think we ignore this symptom until the bike dries out completely. It is not a bad miss, very intermittent but you can tell it seems to be missing, but I think the bike needs to dry out.

I will ride later today to set the code. So some reason, it is load related at 75-80.

Rory

Try pulling the codes manually if you get nothing with the side stand down technique. The computer should remember the error codes for some period of time but I'm not sure if you can read them without doing it manually. The manual method involves a jumper wire between two terminals in the red diagnostic connector under the right side of the passenger seat. I can't remember the exact sequence but it was fairly simple and it is described in the service manual.

I have the manual but it does require a special adapter and a 03 is different from an 07 or later. It poured rain here tonight in Florida, so I was not able to run the bike,but I am taking it to a HOG meeting tomorrow in Daytona. LOL So I will set code, or should set it on my way up there. I bet it says 26 from everything I read..... but not sure that is going to be any help because I hear, knock sensor, cables, or ECM..... I have the service manual but not the adapter for an 03...

I just wanted you to know it was not RPM related but speed related.

Thanks,
Rory

troykahack said:

I have the service manual but not the adapter for an 03...

I just wanted you to know it was not RPM related but speed related.

Thanks,
Rory

Click to expand...

In that case I am baffled and once again completely useless. Don't worry, I am used to being useless.

I never did the jumper wire technique but my bike was an '04 and I am pretty sure it had the red connector. Of course I could be wrong again. I am wrong a lot.

Good luck.

Redfish,

According to my service manual, Honda made a harness change for model year 07, so your 04 would be the same for me. Riding today if it warms up a bit, will read code today, hopefully.

I'm not familiar with the adapter you mentioned in post 10, but I don't think it would have anything to do with the diagnostic connector. The service manual describes how to get the error codes, as well as how to reset them. If your problem truly is speed related, you can easily take it up to 75mph for 10-15 seconds in your garage with it on the CS. Just put it in 5th, let out the clutch and gradually bring it up to 75. Just do it carefully and be sure the front wheel stays planted on the floor and the rear wheel well away from it. If that sets a code, it would be logical to assume the problem is speed related, something I've never heard of before. If it doesn't set the FI light, apparently the engine needs to be under load to set it. That would call for a test ride.

Ok... got the code... 26 but a bit perplexed by the whole thing....

This was a VERY consistent, at one time easy to duplicate problem. However yesterday, it was very cold here in Florida. I put 150 interstate miles and drove it hard, and didn't set a code. However, during this time, my water temp gauge never went over two bars. As soon as I was able to get the water temp to three bars, the indicator came on. When I tested on Center Stand, do not recall the water temp on display. I will try it later after being fully warmed up on center stand. Don't know if motor temp/water temp has anything to do with the problem or not, but during bike week, the first few days were much cooler than the last of the week, a difference of more than 20 degrees. I don't know if temp has anything to do with the problem or not, but we now know that it is setting the Right Knock Sensor fault.

So, what is the general thought moving forward? I have heard change knock sensor, check wiring harness, ECM? Start with a look at wiring and replace knock sensor?

Although I agree that you can get the bike to run 80 on center stand, it requires a bit of safety precautions to insure the rear tire doesn't rock back accidentally and create more problems to deal with. Also, I am not sure it really creates the load the bike would have in actual riding conditions?

Again, this forum is awesome. For the time being I am just going to proceed on the code fault and not worry about temperature or load being a part of this problem but do hope this weekend was the last cold front for Florida.

Where should I purchase a knock sensor? ECM?

Thanks....
Rory

Your t stat is stuck, I live in CT and get three bars in the twenties. Beyond that as far as the error codes are concerned, these guys have a much better idea about what's going on.

Rory-
You do not need an adapter for any model year ... they all have red 'service connectors' under the passenger seat near the right grab rail, and you can short the correct pins in it per the service manual.

When you wash the bike, it can take hours or days for some water puddles to evaporate ... moving it and seeing some water drain out the next day after a wash is not unusual, especially in a humid environment.

From your descriptions above of how the bike runs and behaves, I'm with the others that mention two issues: 1) stuck open thermostat, 2) knock sensor or wiring issue maybe.

You generally won't load the engine long enough above 4000 rpm, except at highway speeds after the engine has thoroughly warmed up, to cause the ECU to set error codes 25 or 26.

At lower elevations, a low octane fuel is more likely to pre-detonate (high octane is more 'necessary' at lowest elevations), so your tank of 87 octane in Florida is more likely to have led to predetonation, especially with a stuck open thermostat. With a stuck open thermostat, the engine temperature and fuel mixture (by ECU, while monitoring oxygen sensor and coolant temperature) is not correct yet. My guess is you're getting 30's mpg on the dash indicator?

First things first: replace the stuck open thermostat. While the Tupperware is off, also trace the knock sensor wiring for scorched wires and check the knock sensor per the service manual (likely a resistance reading, but the manual should prescribe how to check it).

troykahack said:

Ok... got the code... 26 ...

This was a VERY consistent, at one time easy to duplicate problem.

Click to expand...

Before you go any further, make sure the problem is actually on the right side. There was a time early on when the bike's behavior didn't agree with the service manual and it would throw a 25 for the right side and a 26 for the left. There was a minor revision to the ECM firmware in 2004 that may have fixed it. Since you have a 2003, force a failure of the left knock sensor by unplugging it, then do the the 4,000 RPM test and see which code you get.

The right-side knock sensor wire has to be routed a certain way or parts of it end up melting from exposure to heat from the exhaust system. I think Honda figured this out at some point, because it seems to be more of a problem on earlier bikes than later ones. A few people have had melted connectors. The wiring is part of the engine subharness, which costs about $45 and isn't difficult to replace with the plastic and air box removed.

If the wiring doesn't appear to be heat damaged, do the short and open circuit inspections described in the manual.

Your bike is old enough and has probably been in a humid clime long enough it might be worth cleaning the connections at the sensor, where the subharness joins the main harness and where the main harness connects to the ECM.

I don't recall that the sensors are prone to failure, but since the left and right sides are the same part, you could swap them and see if the problem migrates to the left side (code 25). Do this swap after you've ruled out the wiring, because disconnecting and moving things around could make the problem get worse or go away entirely.

There have been some ECM failures, but I'd hold that for last since it's an expensive part to replace (cheaper if you find a used one). A few members here have spares they might be willing to lend you for testing; just make sure you get one from 2007 or earlier, as they made a major change in 2008.

--Mark

Every time I look at the What's New? forum, and see the title of this thread, my brain short circuits and I see Flight indicator. Do you really not know when you are airborne?

Hope you have this problem licked by now.

Wow, all awesome thoughts to think about...

Didn't even consider the thermostat as possible part of my issue. But does make some sense. The first few days of bike week were very humid and cold. When it warmed up, I did have the problem.

Having said that, is was the day I accidentally put in 87 octane, the problem first presented itself. I this even part of my problem or misleading me?

You are correct, I am only getting about 31 mpg, when i used to get well over 40, sometimes 50. Is this because of the thermostat problem or another problem. Wire, ECM, Knock Sensor (Right or Left)? Swapping is good idea.

On the center stand, I can hear that the motor is not running properly, I can hear a miss. But it shouldn't miss just because the temperature is not warm enough. I would think it would correct for this in the ECM? I have let it run in garage until it had 3 bars which I would think is normal, between 3-4 bars.

BakerBoy, are you saying my mileage has dropped into the 30's because of what, the thermostat, ECM, wiring, knock sensor? You hit the nail on the head with the mileage drop off, but even with low mileage, it doesn't set a code????? However, when the code does set, you can feel it... it doesn't stop, it feels like you are running into the wind. However, you can turn the motor off and then back on, then it smooths out again until the code sets. Once I finally got the code to set last night, it was pretty consistent again.

Where is a good place to buy parts. I bought some before when I had a u joint (drive shaft) and some special tools. I guess I can Google and find the place again unless someone can recommend one. I don't mind buying a few parts and a harness, then keep it around in case somebody needs one.

Just don't want to pull the plastic until I have my parts in hand. Thank everyone for their thoughts. So awesome.

Rory

I have bought parts from Partzilla with good success. I know there are many other vendors.

Rory, a stuck thermostat results in mpg being lower than usual...30s is reported by others here. As that appears to be a clear issue, I suspect the knock sensor issue maybe a symptom (but trace the wires and check the knock sensors while Tupperware is off--the bike may have both problems)..

BakerBoy said:

Rory, a stuck thermostat results in mpg being lower than usual...30s is reported by others here. As that appears to be a clear issue, I suspect the knock sensor issue maybe a symptom (but trace the wires and check the knock sensors while Tupperware is off--the bike may have both problems)..

Click to expand...

I agree with this.

First, the thermostat is a common issue, it is a known problem, it is stuck. Replace it. Period, end of discussion. The ECU will try to get the engine to the correct operating temperature and this drops fuel economy.

Second, the knock sensor is there to prevent knock or pre-detonation. The bike will run on low octane fuel but has a better chance of pre-detonation. Since the bike is not throwing the code simply based on RPM I am inclined to believe you are getting a real code. The knock sensor may be doing its job.

Very rarely is the knock sensor bad. It is no fun to change, you will need a very deep well socket but you will have trouble getting that between the header tubes and the sensor anyway. While I agree with "swapping" the sensors as a good troubleshooting method, that is very difficult to do. It is far easier to just unplug each sensor wire, add a wire extension in each one, and connect them to the opposite sensor.

It sounds to me like you need to change the thermostat, get the right fuel, and then see what happens.