FI dash light at 5K RPM

Seems when I just to get on the throttle a bit the FI light comes on. If I drive the bike gently it stays off. It appear to reset once I turn the bike off. It's a 04 ST with 25K miles. Any ideas?

There's another thread where exactly this same thing was discussed recently. You may be able to find it with the search function, or read through the list of thread titles in this same ST1300 Tech section.

IIRC, several culprits were suggested (in no particular order):
1) fuel pump or filter issue
2) chewed injector or harness wires
3) ECU faulting

I honest don't recall what the outcome was and don't have time to go find that thread.

Retrieve the stored fault codes to find out what it's complaining about.

My money would be on the knock sensors, codes 25 and 26. There are several old threads about it; usually it's either improperly-routed wiring near the sensors becoming heat-damaged or a failure in the ECM.

--Mark

FL-STRIDER said:

Seems when I just to get on the throttle a bit the FI light comes on. If I drive the bike gently it stays off. It appear to reset once I turn the bike off. It's a 04 ST with 25K miles. Any ideas?

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First thing I would check would be the 5 way tee and lines for garbage, then do a TB sync.
I would also check the wires under the air box for signs of rodent damage.

See if you notice the light coming on at about 4K RPM, if so it's most likely a knock sensor error. In most cases this turns out to be a fried sub harness and not the sensor itself.

Yep you guys were dead on correct: CODE 25. I'll check the wiring. In all my reading on this issue I couldn't find any thread on anyone having a bad sensor? It's either wiring or the ECU am I correct here? I'll pull the plastic off in a week or two and find out what's going on.

FL-STRIDER said:

In all my reading on this issue I couldn't find any thread on anyone having a bad sensor? It's either wiring or the ECU am I correct here?

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Yep. I don't think I've ever heard of a sensor failing. There's not much in them to go wrong; it's just a piezoelectric element that makes a small amount of current when something like a sound wave runs into it. (It's essentially the same as the thing as what's behind the ignition button in a gas grill.)

The misrouted wiring was more common on older bikes; I think at some point Honda figured out that it was a problem and did something about it. If yours is cooked, you have the option of splicing it or replacing the engine subharness (not as expensive or intimidating as it sounds).

I don't have any insight into what on the ECU fails, but my guess would be the circuit that interfaces the sensors to everything else. I could wonder aloud if the extra pinging caused when people fill up with low-octane fuel has anything to do with it, but that's out in left field without a lot of proof.

Keep us posted on what you find.

--Mark

Finally had a weekend free to remove all the plastic and dig into this MIL Code 25 issue with the knock sensor. I should mention my 04 does have the RED/BLUE wire on the LEFT side and BLUE on the right side. I have continuity when checking back to the ECU with either wire and no shorts when checking either sensor wire to ground. So it appears there are NO harness issues. I should also mention that either wire wasn't burned in the slightest. So it sure is looking like the ECU. I also swapped the right and left knock sensor and the code is still coming up 25. I always run Premium Fuel too. So the next question is who is the lowest HONDA OEM part supplier?

FL-STRIDER said:

So the next question is who is the lowest HONDA OEM part supplier?

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If you don't want to break the bank, eBay and salvage yards. You might also post something on Wanted and see if anyone has a pre-2008 ECM they'll lend you to try out or for sale.

--Mark

A search of part number 38770-MCS-L01 (PGM-FI UNIT, 2003-2007 model years) turns up Partzilla as lowest: $681.14. Yeaowch.

Blrfl said:

If you don't want to break the bank, eBay and salvage yards. You might also post something on Wanted and see if anyone has a pre-2008 ECM they'll lend you to try out or for sale.

--Mark

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I'm wondering if this was a heat related failure as the ABS computer and ECM are mounted back to back. I was thinking of installing a small spacer between the two (.060) to allow air to get between the units. However I'm not even sure if these parts get warm when the bike is running for long periods of time? The entire ECM seems to be potted in resin too. Probably can't hurt.

BakerBoy said:

A search of part number 38770-MCS-L01 (PGM-FI UNIT, 2003-2007 model years) turns up Partzilla as lowest: $681.14. Yeaowch.

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Thank you. I'm going to check eBay and if I come up empty I'll just have to pony up the cash.....

Here's the final word on this adventure. I was able to convince an old friend to let me borrow his 06 ECU for my bike. And guess what, it was the sensor after all. I ordered one last week and installed it this past Friday and the bike is working perfectly. So the knock sensor can fail. The right side is very difficult to remove and ideally requires a 24mm offset box wrench which I did not have. A 24mm deep well socket is too large and hits the exhaust. I was able to get a standard box wrench to work but just barely. With the left side there is no issues in removing as the engine block casting has no protrusions like the right side.

I'm glad it worked out for you without having to spend big money. Thanks for the update.

FL-STRIDER said:

Here's the final word on this adventure. I was able to convince an old friend to let me borrow his 06 ECU for my bike. And guess what, it was the sensor after all. I ordered one last week and installed it this past Friday and the bike is working perfectly. So the knock sensor can fail. The right side is very difficult to remove and ideally requires a 24mm offset box wrench which I did not have. A 24mm deep well socket is too large and hits the exhaust. I was able to get a standard box wrench to work but just barely. With the left side there is no issues in removing as the engine block casting has no protrusions like the right side.

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That is good news!

Back in the thread I thought you swapped left and right knock sensors and still got the code for RH knock sensor?

You will find that a dog-leg boxed end wrench will also work and clear the exhaust.
Glad you figured out the problem.

Yep, I removed both sensor placed them under the center of the bike and I'm thinking I must have grabbed the wrong one or the same ones really. I'm going to blam the FL heat for this slip up

dduelin said:

That is good news!

Back in the thread I thought you swapped left and right knock sensors and still got the code for RH knock sensor?

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