weird compression readings!!!

Okay, so here goes;

As I was preparing to depart in my 2000 SW2, I sat down and fired her up.
She ran for about a half second, then died. When I hit the starter again,
the engine spun quite fast, as if there was no longer any compression in the
cylinders. And of course, it didn't run. Just spun. First thought; broken
timing chain, but at 90k, seemed a little early. So,...

I removed the spark plugs and did a compression check - and Oh my gosh, 50
lbs? all 4 cylinders, 50 to 75 psi. Dang, that's not good! No wonder it
won't run. Next thing, pulled the valve cover. Guess what, the timing
chain was fine, tight, and oiled. Camshafts turned, valves opened and
closed. Hmmmm.....

Put it all back together and noticed the engine sounded like it had some
compression, maybe not as much as it should, but more. Held open the
throttle and it started to fire off. After a little sputtering and rough
running, (about 2-3 seconds), it smoothed out. Engine seemed to run fine,
and on a test drive, it operated normally. Plenty of power and smooth.
When I did another compression check the following day, I got 175 psi across
the board! No wonder it runs now!
The engine did pick up a miss, but a new set of plugs seemed to solve that.
But the plugs didn't look that bad. But the number 4 hole was getting a
little darker since the first compression check. I thought maybe the
injector had plugged, but the new plugs and some injector cleaner in the
tank seemed to clear that up.

So my primary question is, what on earth could have caused the loss of
compression and then the (just as sudden) return of compression? Do SW2's
have an emissions device that could have hung open and prevented compression
from building? Could the throttle body have slammed so tightly shut as to
have cut off the air supply sufficiently to prevent compression?

It was the same compression tester, and done in the same manner each time.

Any thoughts or ideas? the car runs again, just want to know what happened
and what to look for as a possible future failure coming down the line...

Thanks!

 

Thats the only plausible thing I can imagine. Have you ever cleaned it?

 

I am not sure about the loss of compression, but it sounds like your
engine flooded out. My '92 has flooded out about 3 times in its life of
120,000 miles. When it floods, the eng spins so easy while cranking,
your would think it has no compression.

Yes fuel injected cars can be flooded the same a carburated ones.
Computer glitch?
If you press the accelerator pedal to the floor before turning on the
key, it gives a signal to the PCM to NOT fire the injectors. Just like
unloading a "choke" on a carb.

After several small series of cranks without letting up on the pedal,
it will start, run rough, smoke, etc... and then clear out.

If the throttle body was stuck shut, you would feel that in the pedal
unless you stretched the cable out.

James