Ford Escort - Why does "check engine" light turn on?

[Geoff Watts]

Check the o2 sensor - they deteriorate after that number of miles.  The ECU 
is trying to go into 'closed loop' mode while you're cruising, (to get 
stoich fuel/air mix) and it can't get sensible data from the sensor.

the car will still run okay without it, probably use a little more fuel and 
idle rougher and a few other things - but probably a good idea to get it 
replaced - they're expensive in Australia, but an escort one shouldn't be 
that much.

You might want to buy the service manual and try to get some codes out of 
the ECU to make sure it *IS* the o2 sensor :)

geoff

-----Original Message-----
From:	Dmitry Samsonov [SMTP:dima at dusty.physics.uiowa.edu]
Sent:	Tuesday, May 06, 1997 3:32 PM
To:	DIY_EFI at coulomb.eng.ohio-state.edu
Subject:	Ford Escort - Why does "check engine" light turn on?

Recently I bought Ford Escort 1991 with 1.9 l fuel injected engine. It runs 
fine,
but if I drive on the highway at about 60-70 mph "check engine" light comes 
on.
If I press the accelerator for a few seconds and then release it (and 
return
to cruise control) the light goes off for a few minutes and then comes on 
again.
It is never on if I drive in town. I changed the spark plugs recently
(it did not help). The car manual says that this light is controlled by ECU
and if it on for a minute or two it can be ignored and if it is always on,
the car should be check with a mechanic. It stays on almost all the time
I am on the highway. The car has high (117,000) mileage.
Does anybody know what might cause the ECU to turn "check engine" light on 
and
is it an early warning of an engine problem or just one of the sensors got 
bad?
Thanks.

Dmitry