EJ25 Liberty RX (Legacy) hiccups at cruise

[Clifford Heath]

Folk,

This has been a problem on and off for a while now. It came on
again a couple of Km after a refill at a station we don't normally
go to.

The engine behaves fine under acceleration, but within a few seconds
of cruise, will start to hiccup, losing power totally for half a
second, and repeat that irregularly *every few seconds*. It's quite
jerky - annoying almost to the point of being undriveable, and I'm
also worried that it might be doing damage - pinking? If you
alternate between slight acceleration and lifting the foot, it
doesn't seem to happen - until you stop changing speed for ~2 secs.
The acceleration response is fine, so I don't think it's the fuel
filter.

I suspect that the ECU has detected cruise, and is experimenting to
find how much it can lean out the mix... but is going too far. I
suspect the O2 sensor. Given that this is expensive to replace, is
it possible/easy to expect to *try* a replacement before committing
to paying for it? Apart from just replacing it anyhow, is there any
other option?

Has anyone else had this symptom or can suggest an alternate cause?

Clifford Heath.

 

[bigjimpack]

Bad gas? Finish the tank fill with gas you know is good and add a gas
line antifreeze to remove water and see what hapens

 

[noyb]

Bad gas? Finish the tank fill with gas you know is good and add a gas
line antifreeze to remove water and see what hapens

Don't think so - we've been through 5-10 tanks of gas
from our regular sources since it started happening
again recently. Also used injector cleaner, which does
seem to help a bit, maybe. We only ever buy premium
gas in any case. Dirty gas will foul the filter and
cause problems on acceleration, but this is at cruise.

Clifford Heath.

 

[Todd H.]

Folk,

This has been a problem on and off for a while now. It came on
again a couple of Km after a refill at a station we don't normally
go to.

The engine behaves fine under acceleration, but within a few seconds
of cruise, will start to hiccup, losing power totally for half a
second, and repeat that irregularly *every few seconds*. It's quite
jerky - annoying almost to the point of being undriveable, and I'm
also worried that it might be doing damage - pinking? If you
alternate between slight acceleration and lifting the foot, it
doesn't seem to happen - until you stop changing speed for ~2 secs.
The acceleration response is fine, so I don't think it's the fuel
filter.

I suspect that the ECU has detected cruise, and is experimenting to
find how much it can lean out the mix... but is going too far. I
suspect the O2 sensor. Given that this is expensive to replace, is
it possible/easy to expect to *try* a replacement before committing
to paying for it? Apart from just replacing it anyhow, is there any
other option?

Has anyone else had this symptom or can suggest an alternate cause?

Clifford Heath.

o2 sensor is a frequently mentioned item that explains all sorts of
strange driveability problems.

My own experience, however, was that a timing belt replacement caused
me hell like you're experiencing. Not exactly the same, though. My
stumbles and bucks were intermittent and on accelleration (reliably at
4k rpm when it happened--and maintaining 4k rpm as a cruise speed
would exhibit bucking that was annoying, but not undriveable) and on
deceleration around 1250 rpm. Turns out a bad timing belt tensioner
led to a flattened a tooth on a new timing belt when was slipping
periodically by one tooth, causing my woes.

 

[Clifford Heath]

My own experience, however, was that a timing belt replacement caused
... Turns out a bad timing belt tensioner
led to a flattened a tooth on a new timing belt when was slipping
periodically by one tooth, causing my woes.

That's good info Todd. I'm trying to understand exactly what the
effect was caused by. Surely if the timing belt slips the timing
will be off permanently? Or was it just sending a spasm down the
belt by jumping on the tensioner only?

Clifford Heath.

 

[Todd H.]

That's good info Todd. I'm trying to understand exactly what the
effect was caused by. Surely if the timing belt slips the timing
will be off permanently? Or was it just sending a spasm down the
belt by jumping on the tensioner only?

It seemed like it was slipping back and forth, and the ECU was able to
adjust to compensate...but only to a point.

Took nearly all of 2007 to get to the bottom of it.

 

[Fred Boer]

Hi:

I had driveability issues recently caused by a bad O2 sensor. It was more
prevelant at startup when cold than at cruising speed, but it did sometimes
happen at cruising speed with a warm engine. Usually it happened when I
lifed up off of the gas. It was as you describe, though, bucking and
surging. And it was intermittent. And the Check Engine Light wasn't
triggered as you might expect.

Initially it was diagnosed as an ignition coil - later, correctly identified
as a bad O2 sensor. FWIW... Good luck!

 

[Clifford Heath]

It seemed like it was slipping back and forth, and the ECU was able to
adjust to compensate...but only to a point.

Sounds like it might have been climbing up on top of the tension
idler, then dropping back into the notch, and causing tension
changes that advance both cams (or retard - is it on the trailing
or leading side?). I guess a tight/failed idler bearing will do that.

I need to do the cam cover gaskets anyhow, maybe the idler is easy
to do at the same time. Tackle the O2 sensor only if that doesn't
cure it.

Clifford Heath.

 

[Todd H.]

Sounds like it might have been climbing up on top of the tension
idler, then dropping back into the notch, and causing tension
changes that advance both cams (or retard - is it on the trailing
or leading side?). I guess a tight/failed idler bearing will do
that.

My situation was caused by a defective (brand new, OEM, Subaru) timing
belt tensioner not pumping up to tension on a brand new belt after the
engine had been hand turns the designated 3 or whatever times
(specified in a TSB on the issue) when a new belt was isntalled. A
tooth on the belt was flattened in this initial startup sequence and
wasn't found until months later.