Error codes 22 and 23, knock sensor and airflow sensor

[oldfart]

Well it's taken a long time but were finally on the trail, over the winter my gas mileage has been reasonable and then abysmal, so I figured coil, plugs, etc. then a couple of days ago I got check engine light, which led me to the following error codes.

Error codes 22 and 23 both relate to the amount of fuel injected and ignition timing. But the problem is have no idea what to do with this. help!!!!!

I guess I could clean the airflow sensor or check for leaks, but man I really need expert help.

oldfart

[jedz123]

22- knock sensor
23-airflow sensor
My air flow sensor went in my impreza and It got horrible gas mileage and the check engine light came on......Replaced the Air Flow Sensor and the check engine light went off..how many miles do you got?

[oldfart]

Thanks for your reply, the car is a 1993 legacy. An additional clue is that when I'm having trouble the boost gauge goes up to about five psi as opposed to normal 8 1/2.

I put that down to knock sensor pulling back the timing. But who knows?

The guys I've talked to around here seem to think that my main problem is the airflow sensor as I was in your case. I'll probably have to replace it. How much did it cost?

Oldfart

[vrg3]

The specified procedure for dealing with trouble codes is to deal with the lowest-numbered one first, then clear the codes, and if any higher-numbered ones persist you then move on to them.

In this case, that's good advice especially because of the following two facts:

1) The Hitachi airflow sensor is actually a pretty sturdy device. It can be helpful to clean it but it rarely fails. In fact, I do not know of a single instance in which reading a code 23 led to any useful results on a Legacy Turbo.

2) The factory knock sensor is a pretty fragile device. It failed so often that Subaru redesigned the sensor in 1995 (for the 96 model year) and posted a technical service bulletin recommending that the new sensor be used to replace failed sensors even in earlier models. You can read more about this in the Library on the Legacy Central main page.

Soooo... Most likely you need a new knock sensor. Since you've got the code active anyway, go ahead and pull your sensor (you can run without the sensor and it won't be any worse than it is now). Chances are pretty good you'll find at least a small crack in the sensor.

Left to its own devices, the wastegate actuator only allows the turbo to produce about 5 psi. Normally the ECU steps in and modifies the pressure signal to the actuator, increasing boost. Right now it's not because of the active knock sensor code.

[jedz123]

My Impreza is a little NA 1.8...but the part only cost 30 bucks at the local jukyard...I don't know how many part turbo legs are in your neck of the woods but if you find one I bet you could haggle for 50 bucks...I'll Check with my buddies at the parts store for you to see how much a new one would cost.

[oldfart]

Thanks guys, I really appreciate your help.