I'm being told now I need a engine control unit. Subaru wants $850. Do I have any other options?

 

1995 Legacy L Wagon

80000 Miles

2.2L

I'd suggest trying to find a used one. You should be able to pick up a used one for around 100-200 bucks.

 

I'd try these guys

http://www.4subarusuzukikiaparts.com/

http://www.superrupair.com/

http://www.boxer4racing.com/

http://car-part.com/

I pulled the ECU from my 1990L before I got rid of the car, anybody know if it will work in a 95? Could he use it long enough to see if that realy is the problem before he spends big bucks?

nope....won't work....95 the computers went OBD2.....95 actually is different from 96 even.....

Yeah, in this case you do need one from a 95 Legacy. If it helps, you can use one from either an automatic or a manual...

 

Why are you being told you need a new ECU? They don't go bad often.

The mechanic thought that my cel code p0170 fuel trim problem was the o2 sensor. I changed that. Cel came back. I took it back to him and he now says that after it runs for a while all inputs from the different sensors that determine fuel mixture are going crazy on the second cycle. He thinks that the ECU is the only thing that could cause that other than a bad ground. He knows I'm not going to pay him to change it.

Hm. Have you tried cleaning and/or swapping out the MAF sensor? That sensor -- or its wiring -- is usually responsible for a fuel trim trouble code.

 

I would assume your mechanic checked the oxygen sensor's wiring when he changed the sensor.

 

It could be the ECU's fault, but it likely isn't in my opinion.

 

Can you find out from your mechanic what kind of behavior the fuel trims seem to show? What exactle does "going crazy" mean?

 

Does the car idle okay? If not, maybe you have a vacuum leak.

 

Other potential causes include (roughly in order of likelihood) are fuel injectors and fuel filter, the EGR system, canister purge, and the PCV valve.

The first time it was in the shop he said it was running rich. He said he was sure it was the front o2 sensor. I changed the o2 sensor. He wanted $300 to put a NAPA sensor in. I got a Bosch Universal sensor for $55. Soldered the OEM plug on, 60 miles later the cel came back. Same fault code but this time he said it's too lean. He said everything looks good on the first cycle but on the second cycle all the sensors (MAF and o2) had erratic outputs. He cleared the cel, it ran good for another day or so and the cel came back. I disconnected the ECU plug, cleaned the contacts, cleared the cel and 10 miles later, it's back. Idles rough after the battery is reconnected, even after sitting and running for 20 minutes in the driveway. Drive it for 10 miles or so and it idles nice. Runs good. I just hate to see that cel. I checked the voltage to the MAF sensor and it's there. The Haynes manual says to check the output with a scan tool. I don't have one. I would think the mechanic I took it to would have done that. So far I have paid him $79 to steer me in the wrong direction. I guess I can take it to the Subaru dealer.

Are you sure you did a good job with the oxygen sensor connector? The stock wires are made of some kind of alloy that's really hard to solder and/or crimp properly. I'm pretty experienced with electrical work and mechanical soldering, and I actually ended up just putting new wires in the connector instead of trying to solder to the stock oxygen sensor wires.

 

You might want to just try cleaning out your MAF sensor. Remove it from the car (pull the snorkel off and then undo the 4 10mm-head bolts holding it to the airbox), and spray it gently and liberally with brake cleaner. Make sure as much of the brake cleaner (and the dirt and grease dissolved in it) as possible runs out, and make sure the remainder evaporates. It's very volatile so it shouldn't take long. Then see if anything improves. It'll only take a few minutes and a buck or two, and can't hurt.

 

A steadily lean or steadily rich reading at the ECU, especially if it switched after an attempted repair, in my opinion, is very unlikely to be the ECU's fault.

I would run a ground jumper to areas that you suspect may have a bad ground to see if that helps. For ECM help here is a link you could try http://www.python-injection.com/nf/html/prodtoc.htmThey may have what you need.

I'm going to redo the wiring on the o2 sensor and clean the MAF sensor. I changed the fuel filter about a week ago. I'll let you know what happens. I'll use the connector Bosch sent with the universal sensor. It was hard to solder to.

Good luck!

Well, changed the connections on the o2 sensor and cleaned the MAF sensor. CEL comes back. Still runs ok. What should I do next?

Even if the problem's solved, it could take a few trips before the ECU turns the CEL off.

 

Or did you have the CEL cleared after cleaning the MAF sensor and rewiring the oxygen sensor?

I had the battery disconnected while I did these things. I was told this clears the codes out. When I started it back up the CEL was off. It returned about 10 miles later.

It may or may not clear the codes... I'm not sure.

 

But I wouldn't think a fuel trim malfunction code could appear after only 10 miles. Maybe, though.

 

D'oh.

 

It could still be the ECU but I still doubt it... :|

Does the rear o2 sensor have an influence on fuel trim?

Don't believe so. It's used just to gauge catalytic converter efficiency.

 

You might need to start checking out the EGR system and stuff like that...

 

But maybe first you should have the codes cleared just to make sure it's not actually already solved.