Hesitates on accelleration, spark retarded

[nelstomlinson]

2002 legacy outback, automatic transmission.  It hesitates when I step on the gas, sometimes for several seconds.  When the engine is cold, it may not move at all for up to a minute.  When I look at live data, I notice that spark advance is negative 8 to negative 15 when it's hesitating, maybe +15 at idle, +30 to +40 when accellerating normally.  The throttle position sensor is reading normally, even when the spark is retarded.  Manifold pressure runs around 5ish psi at idle, rises when I open the throttle.

What in the world could cause the spark advance to go the wrong way intermittantly?  What other data should I look at?

[Rampage]

Knock Sensor?

It shut the engine off 3 times on our 95 while driving. No CEL. That was before I had a scan tool to look at live data, but I know it adjusts timing.

[nelstomlinson]

Rampage, knock sensor wouldn't cause timing to go to -10 degrees on acceleration, would it?  Anyway, the engine has never once died, it just makes no power at all, until suddenly the spark advance jumps into positive territory and away we go.

I had a spare aft oxy sensor on the shelf, so I threw that in last night.  Zero change, so that wasn't it.  The front oxy sensor was changed out a couple months ago by a mechanic who solved an earlier proble.

What controls spark advance on this machine?

[Rampage]

The ECU uses a map to adjust timing under different engine situations and uses knock signals from the knock sensor to retard the timing in order to stop the knocking. When a faulty knock sensor keeps sending signals to the ECU, the ECU will keep retarding the timing because it thinks the engine is knocking. To make our engine shut down, it must retard it quite a bit. I don't know if a retard limit was added on later models on not, but a new knock sensor fixed our 95.

[nelstomlinson]

Took this to the mechanic.  He found that the bolt that secures the timing belt pulley on the crank had come loose and the pulley had wallered out the keyway, so the pulley was drifting 20 or 30 degrees.  He was able to get the pulley back to the correct position and tightened the bolt.  It's running great, so far so good. 

I talked with the machine shop I usually use, and he's telling me that the crank can't be repaired, and he recommends getting a short block from the dealer if the mechanic's fix doesn't hold.

 

Thanks for the info on the ECU, Rampage.

[Rampage]

Good to hear it is running great.

You said timing belt pully. That is a toothed sprocket. Did you mean the serpentine belt pully (harmonic balancer)?

For that, normally, the crank is not harmed, just the inside of the pully. The key chews away the inside of the pully.

I replace our harmonic balancer with Dorman and they work good.

The bolt requires lock-tight put on the threads and be torqued to specs or it may loosen up. I made a tool to hold the pully and get the proper torque.