'91 Legacy stalling, need help with diagnosis

[Kenneth1948]

'91 Legacy 200k has been running well for about 12 months.

Now I have an intermittent stalling problem. 

New fuel pump, screen and filter did not solve the problem.

Not predictable, can run 10 or 15 minutes with no problem or stall every 30 seconds.

Re-starts immediately.

Sets "Check engine" light

Previous post said this could be the MAF sensor.

The car is supposed to have some diagnostics.

I can't get them to work.

Haynes manual says disconnect connector adjacent to diagnostics plug and turn on ignition.

Check engine light does not flash.

Not sure I have the right connection? I will try to post picture. Circled connector is the one I disconnected.

Any help with reading diagnostics or probable cause of stalling would be much appreciated.

John aka Kenneth

 

[idosubaru]

if the check engine light is on you need to read the code - it's telling you the problem most likely. 

 

1.  read the code

2.  check for spark

3.  check timing marks, make sure belt hasn't jumped a tooth - the side covers are easily removed in minutes - 10mm bolts, that's it.  check both cams at least, ideally crank marks too.

 

 

stalling guesses:
vacuum leak

timing belt is off

cylinder misfires - plugs, wires

burnt valves

MAF

knock sensor is cracked

converter clogged

fuel not getting to injectors

coil pack is hosed

something is disconnected

rodents chewed through wiring

[Kenneth1948]

Herin lies the problem.

I can't read the codes.

This is a '91, it's an OBD I with "morse code" codes.

When I unplug the connector, the code(s) don't flash with the CE light.

Please see my post and photograph, I'm not sure if I have the right connector.

Rodents chewing through the wiring remind's me of an A40 Austin van that belonged to a friend of mine, with a family of mice that lived in the back of the van.

Thanks, John Kenneth

[mikaleda]

proper way to check your ecu codes here 

http://www.surrealmirage.com/subaru/engine.html

[Kenneth1948]

OK, that link helped, thank you. I was able to read the codes:

1. MAF sensor

2. Knock sensor

3. Oxygen sensor

 

1. MAF sensor: I cleaned the MAF sensor, didn't make any difference, I still suspect it might be causing this problem.

2. Knock sensor: Haynes manual says it's located "under the intake runner at the left rear of the engine." and to test the connector for ground continuity.If there is continuity to ground then the knock sensor is bad. Problem is, I can't find the knock sensor or the connector? Anyone have a picture, or link?

Also, what are the symptoms of a bad knock sensor? will it cause the engine to stall intermittently?

3. My experience with oxygen sensors is the engine will run fine but with very poor gas mileage.

Can a bad oxygen sensor cause my stalling problem? 

 

any help with 2 and 3 above would be appreciated. Thanks, john aka Kenneth

[Kenneth1948]

Identifying the OBD I Connections:

The Haynes manual is no help whatsoever, it tells you to disconnect the connection, you actually have to connect it. And the description of the connection is inadequate.

The link above from Mikeleda is very helpful.

 

I ran into the problem that the wires on the 2 parts of the black connector were not long enough to allow it to be connected. 

I had to cut one of the wires, plug the connector in and jump the connection.

The attached picture shows the black connector, connected together. The white jumper is connected with one clip right next to the connector.

The other connector is connected to the cut end of the wire (you can just see the wire top right of the circle).

Hope this helps save someone some time John Kenneth 

[mikaleda]

OK, that link helped, thank you. I was able to read the codes:

1. MAF sensor

2. Knock sensor

3. Oxygen sensor

 

Replace your MAF sensor get one from a low milage car at the junk yard then reset your codes and see what comes back.

Knock sensors are easy to replace they are one wire and one bolt. Its under the intake on the drivers side rear of the block.

The oxygen sensor code is more than likely caused by the failing MAF o would replace the MAF first and reset the codes and see what happens.

[mikaleda]

Knock sensor controls timing slightly to compensate for low octane "knock" it doesn't affect running much. The only symptoms I've heard of a bad knock sensor causing is a slight decrease in fuel milage and maybe slightly less performance.

[Kenneth1948]

Problem solved, running like a champ again!

Often we forget to post the solution once the problem is solved which is so frustrating when you have a problem and search a forum.

The problem was the MAF sensor as Mikaleda suggested.

I ordered a new cheap MAF sensor on Ebay for $35

They wanted $30 at the junkyard and there's no guarantee it would work any better than the bad one.

You can buy a new Hitachi MAF sensor for $225 which doesn't make sense for  a 25 year old car with 200k

(or any car for that matter, you can do the diagnosis for $35 then put an OEM part on if you really want to)

It's worth running the old OBD Morse code diagnosis, it was right and it beats trying to guess.

(Remember the old Haynes manual is dead wrong for this process, see the links above for the right steps.)

Finally, thanks to all who replied to this post, your help is much appreciated.

John aka Kenneth

[Fairtax4me]

Is it the square top MAF? Part number ends in AA160?

Those are used on all the 95-99 legacy models that I know. The solder joints crack on the pins that run from the plug to the main PCB. If you can solder, you can cut the silicone and pop the top off and resolder the pins. It usually fixes this problem, and you can run it again or keep it as a back-up for when your replacement does it.