Code 9 Problems

Thanks to The Dan for a simple header.

For the past two years, I would get an occasional code 9 (blinking FI indicator), with no discernible change in performance, usually the code 9 would be gone the next day.

Recently I've started getting a code 9 daily, accompanied with:

• Poorly running engine (symptoms suggest fuel starvation).
• Surging at speed (steady throttle).
• Idling at 1500 rpm (was 1000 rpm).
• Fuel economy has dropped off to180 miles per tank (was 280 miles per tank).

Occasionally the code 9 would disappear whilst driving, more often it would remain until the following day. The malfunction that is causing the code 9 message is intermittent, with no repeatable pattern of behavior or usage (that I've noticed) that may be initiating the code.

The Honda shop manual states that a code 9, indicates a malfunction of the IAT (intake air temperature) sensor, however a number of posts here on ST-Owners suggest checking the vacuum hoses, and plastic tee's nestled within the throttle body assembly.

Here's what I've done to date, with no consistent improvement:

• Replace spark-plugs. No change in engine performance.
• Adjusted valves. No change in engine performance.
• Run Sea-Foam through the system. Initially, better engine performance, then back to poor performance, and a code 9.
• Replace IAT sensor. No change in engine performance.
• Complete diagnostic check (Honda manual pages 5-24 & 5-25). Resistance, supply voltage, and signal voltage are all in spec.
• Replace ignition coils, spark-plug wires, spark-plug caps (broke an insulator during spark-plug replacement). No change in engine performance.
• Replaced fuel-pump assembly. Initially, better engine performance, then back to poor performance, and a code 9.
• Inspected all vacuum lines, and tees. All are clean as a whistle.
• Inspected fuel pressure regulator. It appears okay, diaphragm holds a vacuum (need to get a replacement, and swap out).
• Inspected fuel line (pressure side). It appears okay, and flows fuel easily

Here's what I've learned:

• The spark-plugs at 80,000 miles were probably fine, though due for replacement.
• The valves can go for a long time before requiring adjustment.
• Sea-Foam may or may not be useful.
• The original IAT sensor is probably fine.
• The original ignition coils, and wires are probably fine.
• A torn rubber spark-plug cap does leak voltage.
• The original fuel-pump assembly is probably fine.
• That I'm amassing quite the inventory of spare parts.

Yet the engine still runs poorly. I'm open to suggestions.

Any chance you could borrow an ECU from someone?

Anna'sDad said:

The Honda shop manual states that a code 9, indicates a malfunction of the IAT (intake air temperature) sensor, however a number of posts here on ST-Owners suggest checking the vacuum hoses, and plastic tee's nestled within the throttle body assembly.

Click to expand...

I've seen that suggested as a remedy for a flat tire, too. But seriously...

Here's what I've done to date, with no consistent improvement:

Click to expand...

Whee, that's a long list, and only one of the things on it has any connection to the IAT sensor. (BTW, I'm convinced that Sea Foam burns better than the gas you put it in, so the temporary good performance isn't surprising.)

Most of your symptoms sound like the engine isn't being fueled properly for conditions, which could well happen if the ECM is getting bogus-but-plausible temperature data or if it's had to punt and use the fall-back values. The transition from occasional to full-time code 9 says the sensor, ECM or the wiring between them has failed. It's probably not the sensor since you replaced it, but I'd treat it as suspect anyway.

If you haven't been through the diagnostic procedure in the manual, do that before anything else. If you get to the end of the procedure and need to swap ECMs, the same part was used from 2003-2007; someone may have one for loan. Also check the cleanliness and health of the connections at the ECM, the sensor itself and where the engine subharness plugs into the main harness. If you installed any farkles that involved running wires around there or just did any work, make sure the cable didn't get overstretched when the tank was put back down.


--Mark

Blrfl said:

If you haven't been through the diagnostic procedure in the manual, do that before anything else.

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Oops, yes I've completed that procedure, and unfortunately (or not) the three areas to test are all within specification. Guess I'm just stalling on purchasing a replacement ECM.

I edited my original post to include diagnostic testing.

Anna'sDad said:

Guess I'm just stalling on purchasing a replacement ECM.

Click to expand...

How's the wiring? (Not just voltages, but do you get consistent continuity between the sensor and the ECM, even when giving each joint a jiggle?)

--Mark

Blrfl said:

even when giving each joint a jiggle?

Click to expand...

Now, that's going to take some time!

Yesterday while checking the fuel pressure regulator, I pulled, and inspected the fuel rail components, as well as the injectors, and injector harness. All items looked good, and went back together without a hitch. I did start the engine at various times during the re-assembly, and at all times the code 9 indication was present. Not too surprising, as the engine was not completely closed up during these brief start-ups.

This afternoon when I headed out to work, the code 9 was not present at start-up. Indeed, the code 9 did not make a reappearance, until moments before I parked, this after about 45 minutes of 35-45 MPH driving, a 45 minute stop, then 30 minutes of 75-85 MPH, and finally 15 minutes of stop & go city driving. At all times the engine ran much better than it has in a while, not sure if this is attributable to something I did yesterday, or the Sea-Foam I added to the tank at fill up this afternoon.

During the tear-apart of the fuel rail, I also freed up the stuck remote idle stop adjuster, so the engine now idles back at a more sedate 900-1000 RPM. However I did notice that the engine is not as smooth as it once was at idle, I suppose it's time to look at synchronizing the start circuit (though I'm unsure if this will have any discernible effect on the overall engine performance). Regardless, it will all have to wait for the next available Monday.

Firstpeke said:

Any chance you could borrow an ECU from someone?

Click to expand...

Now that Mr. Firstpeke, would be an ideal situation.

Anna'sDad said:

This afternoon when I headed out to work, the code 9 was not present at start-up. Indeed, the code 9 did not make a reappearance, until moments before I parked, this after about 45 minutes of 35-45 MPH driving, a 45 minute stop, then 30 minutes of 75-85 MPH, and finally 15 minutes of stop & go city driving. At all times the engine ran much better than it has in a while, not sure if this is attributable to something I did yesterday, or the Sea-Foam I added to the tank at fill up this afternoon.

Click to expand...

You're changing too many things at once, none of which are related to the fault. First on your list should be making the ECM happy, because that's the elephant in the room. The only things involved in a code 9 are the ECM, the sensor and the wiring between them.

What you've got going on sounds like an electrical connection that's building up resistance or breaking entirely as it warms up. It's not likely that the wire inside the harness has gone south, but I'd check the ends where they meet the pins in the connectors and the connectors themselves. (There are five: one at the ECM, two where the main harness meets the engine subharness and one at the sensor.) Some contact cleaner would probably be a good idea, too.

--Mark

Blrfl said:

You're changing too many things at once

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Agreed.


I apologize for the delay in responding, an accident out at Burning Man has demanded my attention this past week. Fortunately my daughter (the Anna in Anna'sDad) will make a full recovery. Good news!

Yesterday was my day off, and I got down to business. Here's what I discovered:

• A quick inspection of the connectors that are involved with the IAT circuit, one just aft of the engine on the left side, and the other at the ECM, came up clean (got to love those weather tight connectors).
• A detailed inspection of the wiring harness, has yielded the proverbial smoking gun! Two chaffed conductors, the Gray/Blue, and the Yellow/Red, to be specific. Amazingly enough, the Gray/Blue conductor provides IAT temperature changes to the ECM, and the Yellow/Red conductor provides MAP changes to the ECM. No wonder the engine wasn't running well.

The area where the chaffing occurred is in the tail section where the main wiring harness runs alongside the right side frame member, approximately 3 inches forward of the Red service connector (the one with the cap).



Honda thought to provide an inner wrapping of sheet plastic to the wiring harness in this area, probably to prevent just this type of abrasion, unfortunately the wrapping is short by fractions of an inch.



The Gray/Blue conductor is missing the most insulation, however the copper looks to be intact, I think a bit of tape on each conductor, then re-wrap the bundle, and I'll add some plastic (from a drink bottle) as an abrasion protector, and I think, I'm good to go.



It's a bit ironic how I stumbled upon the abraded wires; this morning after examining the two connectors mentioned earlier, I found myself resigned to replacing the ECM. I removed the ECM to confirm part numbers, and purchased an used ECM on eBay (can you see where this is heading?). Whilst tiding up the wiring harness, I noticed torn black electric tape, and closer inspection led me to discover the chaffed conductors. Now I have a spare ECM on my parts shelf, not sure when I'll need it, but when I do, I've got it!

Good find!

[making a mental note]

And this is why I hate intermittent electrical issues.

Good sleuthing. That's worth an inspection next time I'm doing major work under the seat.

Don't be surprised if the problem resurfaces. If it was a result of the wires finding ground, you're golden. If the wires are damaged and breaking contact, that's going to be a problem.

--Mark

Blrfl said:

That's worth an inspection next time I'm doing major work under the seat.

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+1. Good idea. Preventing electrical shorts is well worth the time spent because they are so difficult to run down sometime.

Anna'sDad said:

Whilst tiding up the wiring harness, I noticed torn black electric tape, and closer inspection led me to discover the chaffed conductors.

Click to expand...

Nice find. I know all to well how electrical problems go and noticing some chaffing is a huge BZ. Well done.

Oh, and awesome job with that fix.

Blrfl said:

That's worth an inspection next time I'm doing major work under the seat.

Click to expand...

+100
I will be doing the same thing. I really haven't had my 04 torn down, only oil changes, head light, tires, blown fuse, relocating added fuse block, added powerlet, fixed wind screen cable/worm gear slipping, and that's pretty much it. To date I haven't had all the tuperware off or done any major work on it... it is a Honda.

Make sure the repair is water tight. Water turns copper into a blue dust like substance. A substance like silicone sealer should do the trick. Water can get past electrical tape eventually.

If you're going to use silicone get the alcohol cure not the common vinegar curing stuff.