Odd FI problem on 90 Legacy

A

Anthony

My 90 Legacy wagon is having what seems to me to be a very odd set of
symptoms. At low RPM and throttle it stutters like it has a plugged fuel
filter. I figure it was over due for one so I replace the fuel filter but
there was not change.

Now for the odd part, it has a wondering idle when cold but doesn't stutter
until it warms up. Also it seems to run fine above 3500 RPM. This makes
5th gear all but unusable. My mileage hasn't gone down and I don't see any
signs if it running rich. The check engine light has never come on either.

These symptoms don't add up to me. If it were consistent across the RPM
range, I'd think the fuel pump is getting weak. The car has 172k miles on
it and I guess it's about time for things to start failing.

Tony
 
Check the obvious first: plugs, wires etc. Sturtter is more evident at low
speed since less fuel/air is going into the engine. Check for an air leak,
this really throws off low speeed running, with often little effect on
higher speed running. Also add some injector cleaner and moisture absorber
(dry gas) before getting it looked at.
Ed B
 
If that doesn't work try unplugging your O2 sensor, it'll run rich (like
when the engine is cold) if the shudder stops then it may be fuel mixture
problems. Another problem could be hot carbon deposits in your cyclinder
igniting the fuel before the spark plugs do. This can be relieved somewhat
by using higher octane fuel.(this won't fix the problem of carbon build up
but may prevent the carbon igniting the higher octane fuel).

Mike
 
I found 2 air hoses off but strangely enough, it didn't help. It's probably
time for spark plugs so I bought a set and if I can get some help, I'll run
a compression test at the same time. It doesn't make and strange noises but
now feels like it's running on 3 cylinders at low rpm (no power and it
shakes.)

I already ran 2 bottles of injector cleaner (and at least a full tank of
gas) through it with no success. I'm not supposed to work on cars where I
live but I manage to sneak in a little here and there. For any major work I
have to take it to a friend place then wait for it to cool so I can before I
can get anything done.

Tony
 
I'll look for the O2 sensor and try that. This car has 172k miles on it and
I'm the second owner. Who knows if the O2 sensor has ever been replaced.

Tony
 
A note of caution on checking the coil

I have 2 '90 Legacy's. Last summer, one was running, one was not, so I
checked the coil in the not running one. By the 'specs' in my Chiltons book,
the coil was bad. So I took the coil out of the running one just to verify
if this was it before plunking down $100+. It did not help. Not only did
both coils not pass the resistance test, they both ran fine in the running
car. The problem turned out to be something else. Beware of Chiltons ! The
edition I have for '90 Legacy is full of inaccuracies.
 
Thanx, but I had a run in with Chilton 20+ years ago on a VW Dasher. I had
just replaced the transmission and filled it with gear oil. Later I read in
the manual that I had only put in half as much gear oil as it was supposed
to have. It cost me $10 to have it put on a rack an to be told the gear oil
level was fine. Normally I would have done it myself but the monsoon season
had started here in the Pacific Northwet and I didn't want to crawl under it
in the rain. I bought a factory manual and burnt the Chilton.

The problem sounds fuel related. I know this sounds dumb but as a former
motorcycle mechanic I have a feeling for these things but I don't know squat
about fuel injection. I guess it's about time I learnt. I'm going to check
the resistance on all the fuel injectors when I get to it next. I've been
riding my bike so the my Subie has been a low priority.

Tony
 

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