Here's the background: I've got a 2008 Honda BF150. I rebuilt this engine around 18 months ago because there was a hole in cylinder head (number 1 cylinder) that was allowing water to mix with the oil as well as oil/water to spray onto the air-fuel (AF) sensor. [Note: The hole was caused by not properly flushing the saltwater out of the engine by the previous owner.] I bought a used cylinder head, made sure it wasn't warped, and then reworked it. All last year everything ran great. It ran fine on dozens of 50+ mile a day trips. Then, at the end of last year, I started getting intermittent AF sensor warnings. Then they became constant.
I tested all of the wiring as best I could without having a Honda Diagnostic Harness. But testing the AF sensor, I've learned, is not that simple. The shop manual say it needs to be within 2-3 ohms across the black wires. That's not really an accurate test. But I did check the continuity in all of the wiring and put a load on the wiring to the AF heater to test it. I didn't find anything definitively wrong with it. Trying to just eliminate the problem, I replaced the AF sensor (~$200) and the AF heater relay (~$40). That wasn't it.
Still trying to follow the shop manual, the next possible culprit was the ECM.
I bit the bullet and bought the Dr. H software and USB diagnostic kit. When I hooked it up, it showed that the "AF sensor FB" signal value coming out of the ECU was always 0. It's supposed to be 1, plus or minus some calculated value to adjust the air fuel ratio up or down. The point is, 0 isn't an acceptable value. So I bought a used (known to be good) ECM and installed it. That fixed the problem, but only for 1 fishing trip. On that trip, the motor literally ran for about 6 hours solid with no issues. Then I went to take it out again the following weekend, and the AF sensor alarm went off again as soon as I got out of the no wake zone where I hit the throttle. It would run for 60 seconds, and then the alarm would go off.
Had the new AF sensor gone bad, and if so what might have caused that?
Here's what I thought:
Option 1: Was is possible that the exhaust manifold, since it was the original one on that motor, could have also been damaged by the saltwater left in it by the previous owner -- maybe allowing water to mess up the new AF sensor?
Option 2: I knew there was some corrosion in the wiring harness by the main connector. I bypassed one connection on one of the wires and ran new wire segments with a simple waterproof M/F connector. But still, was there a bad connection?
So, I acted on option 1 and bought a brand new exhaust manifold (and all the gaskets/seals) and a brand new AF sensor. I installed the exhaust manifold and the new AF sensor. I t had the same problem, except that sometime that engine buzzer wouldn't take 60 seconds to go off. Sometimes it would take less than 10 seconds to go off. Needless to say, that wasn't it.
So I decided that to address option 2 and I bought a used wiring harness. I finished installing it this morning, with the same results. I'm still getting an error code.
On the MIL, it shows 41 (4 long and 1 short blink).
On the Dr. H software, it shows 41-3 and 41-4.
It's not the AF sensor.
It's not the AF heater relay.
It's not the ECU.
It's not the wiring in the outboard's wiring harness.
When the motor is idling or running wide open, it runs great. Until the MIL light comes on.
Is there something "external" the outboard that could cause the MIL to come on and it just report whatever it last saw as a problem?
David
I tested all of the wiring as best I could without having a Honda Diagnostic Harness. But testing the AF sensor, I've learned, is not that simple. The shop manual say it needs to be within 2-3 ohms across the black wires. That's not really an accurate test. But I did check the continuity in all of the wiring and put a load on the wiring to the AF heater to test it. I didn't find anything definitively wrong with it. Trying to just eliminate the problem, I replaced the AF sensor (~$200) and the AF heater relay (~$40). That wasn't it.
Still trying to follow the shop manual, the next possible culprit was the ECM.
I bit the bullet and bought the Dr. H software and USB diagnostic kit. When I hooked it up, it showed that the "AF sensor FB" signal value coming out of the ECU was always 0. It's supposed to be 1, plus or minus some calculated value to adjust the air fuel ratio up or down. The point is, 0 isn't an acceptable value. So I bought a used (known to be good) ECM and installed it. That fixed the problem, but only for 1 fishing trip. On that trip, the motor literally ran for about 6 hours solid with no issues. Then I went to take it out again the following weekend, and the AF sensor alarm went off again as soon as I got out of the no wake zone where I hit the throttle. It would run for 60 seconds, and then the alarm would go off.
Had the new AF sensor gone bad, and if so what might have caused that?
Here's what I thought:
Option 1: Was is possible that the exhaust manifold, since it was the original one on that motor, could have also been damaged by the saltwater left in it by the previous owner -- maybe allowing water to mess up the new AF sensor?
Option 2: I knew there was some corrosion in the wiring harness by the main connector. I bypassed one connection on one of the wires and ran new wire segments with a simple waterproof M/F connector. But still, was there a bad connection?
So, I acted on option 1 and bought a brand new exhaust manifold (and all the gaskets/seals) and a brand new AF sensor. I installed the exhaust manifold and the new AF sensor. I t had the same problem, except that sometime that engine buzzer wouldn't take 60 seconds to go off. Sometimes it would take less than 10 seconds to go off. Needless to say, that wasn't it.
So I decided that to address option 2 and I bought a used wiring harness. I finished installing it this morning, with the same results. I'm still getting an error code.
On the MIL, it shows 41 (4 long and 1 short blink).
On the Dr. H software, it shows 41-3 and 41-4.
It's not the AF sensor.
It's not the AF heater relay.
It's not the ECU.
It's not the wiring in the outboard's wiring harness.
When the motor is idling or running wide open, it runs great. Until the MIL light comes on.
Is there something "external" the outboard that could cause the MIL to come on and it just report whatever it last saw as a problem?
David