Re: fault codes

[Steve Manning <stephenm@ix.netcom.com>]

At 12:04 AM 7/26/96 -0700, you wrote:
>My 90 is periodically giving me the "check engine" light.  It only seems to
come on 
>during periods of extend idling AND only when the engine is fairly warm;
gauge reads 
>slightly over halfway to "H".  When the light comes on, it will go away
after a  
>minute or two of normal driving; i.e., once I get out of traffic.  
>
>When I try to dump the codes, the engine dies; that is, I insert a fuse
into the top 
>of the fuel pump relay, remove it after 4 seconds and the engine slightly
revs up a 
>bit and then dies.  I can't read the codes if the engine dies.  I was able to 
>replicate this every time I tried to read the fault codes.
>
>Anyone else ever seen this?  Engine runs great; there is sometimes a slight
miss at 
>idle however.  
>
>Chris
>1988 90 with fresh plugs, wires, cap, rotor, air filter, O2 sensor, clean
ISV, 	
>	crankcase breather update, all vacuum leaks fixed, and a sump 
>	full of fresh Mobil 1.  Soon to replace: fuel pressure regulator and 
>	filter...and (sigh) more than likely the fuel pump as it is starting
>	to make some strange buzzing sounds every once in a while...
>
>

Check the full throttle switch.  I had this problem and it took me forever
to trace it to this.  What happens is the full throttle switch can go bad
and be constantly engaged, which can cause it to get confused with whether
or not it should pay attention to the O2 sensor, among other things.  It
also screws up other sensor readings.  You can check the Bentley for the
diagnostic procedure, or an easy test is to put it in diagnostic output mode
and see whether or not it works properly as a switch for the different checks.

Contrary to a previous note, IMHE (in my humble experience) there are only a
couple of reasons why the 'check engine' light will come on in an '88 90Q -
knock sensor at full retard, and no signal from O2 sensor.  I might have
missed one, but there aren't many.

As far as it dying while you try to run diagnostics, make sure the a/c is
off.  It will NOT run diagnostics with the a/c on; the engine will die as
you described.

E-mail if you want more help...................SLM

Steve Manning:	stephenm@ix.netcom.com (Metro D.C. area, USA)
	Mopar:	'67 & '68 Plymouth Furys (big blocks)
		'70 Barracuda convertible (small block)
		'87 GLHS (tiny block)
	Audi:	Two '88 90Q's (built on the same day)
	Misc:	'73 Ford Country Squire wagon (daily driver!); other stuff...