legacycentral bbs

Hi,
I'm new to LegacyCentral. I have a 91 Legacy - non turbo - that has a steady miss, poor performance and the cat. converter gets too hot.
The car acts like the ECU has gone to baseline as if a pimary sensor has failed, but there have been no error codes recorded. I have tried to perform the D-check but all I get is a steady flash of the CEL.

I have replaced the plugs and wires, checked for good fuel pressure, checked connections and wires at all sensors, checked vacuum lines ...

This is a good running Soob that is well maintained with 230,000 miles. Any suggestions or ideas?

Welcome to the BBS.

How did the plugs look when you replaced them? Were they black, white, gray, etc?

The coolant temp sensor controls the AFR and has a lot of impact on how the engine runs. It notoriously does not throw a code if it's not running correctly. You mention the cat running hot is why I suggest it. Usually running rich will cause the cat to run hot, also if they are plugged could cause them to run hot. Only other thought as to why there would be more fuel would be the injectors...

Thank you for the reply.

Good point - sadly I replaced the coolant temp sensor less than 10k miles ago. But maybe the new sensor has failed.

The car has performed like this before when there has been a failed sensor, but there has always been some kind of a code, even if it was the wrong code. This no code thing has me stumped. I know that when a sensors fails the ECU goes to default configuration and the timing is retarded. At our altitude it makes the car run very rich, as a result the CAT gets saturated with fuel.

Injectors are a possibilty - But I don't know if that explains why the ECU would go into default mode.

The spark plugs looked gray, not wet, not over heated. They looked like they were firing poperly. They did have the electrode (center post) rounded on the edges. I replaced them with new platmium plugs.

Was the coolant temp sensor you put in an OEM Subaru sensor? They don't normally go bad that quickly, but I suppose you could check it's resistance and compare it to the chart in the factory manual to see if it's reading about right.

Where do you live?

I live in Colorado. I think I will test the coolant temp sensor to see if I get the right ohm readings.

OK, I fixed it.

It turned out cylinder #1 had a bad fuel injector.

Checking the ohm reading is a simple and quick thing to do. Had I done that earlier I would have quickly found the problem.

Moral to the story - If there is no error code do an ohms reading on the injectors, it's a quick fix.

Thanks for all of the ideas and support.

What was the resistance you measured? That's good to know an injector can be bad in a way that you can diagnose electrically without the ECU throwing a code.

vrg3 wrote:What was the resistance you measured? That's good to know an injector can be bad in a way that you can diagnose electrically without the ECU throwing a code.

The three good injectors read 11 to 14 ohms. The bad injector read over 7,000 ohms.
The specs says the ohms should read between 10 to 12 ohms.

Wow. That surprises me that the ECU wasn't throwing a code.

It's amazing how well these motors run on just 3 cylinders, isn't it?

Glad you figured it out. That is weird the ECU didn't throw a code for that injector.