Re: knock sensor bad?!?

[steveb@falcon.kla.com (Steven Buchholz)]

> Next problem:
> 
> OK, remember about a month ago (or more) when I was telling you that my 
> 86 5KCST wasn't developing "enough" power?  (or at least, it seemed that 
> way.)  I noticed that at highish speeds, I couldn't get the RPMs over 
> 3000 without the check engine light coming on (fault lite).  I know that 
> while driving this lite comes on when there is too much knock and timing 
> is being retarded the maximum amount, but I didn't think that it should 
> be coming on at 70 mph w/91 gas...correct?
> 
> OK well no matter HOW we feel about that stuff, I finally ran the codes 
> on the engine (two times w/two drives to verify) and I get engine code 
> 2142.  According to the bentley, this is "knock sensor wiring or knock 
> sensor defective".  That's about ALL that they tell me.  Period.  All the 
> other sensors/wiring thingies have much more troubleshooting info.  This 
> one they seem to have dropped in my lap.
> 
> OK! I say. The computer concurs that there is something wrong with the 
> knock protection.  But where do I go from here?

If the computer says that the sensor or wiring is at fault it implies that
it is detecting either a short or open circuit.  The fact that it is inter-
mittent means that it may be pretty tough to find.  I'd recommend following 
the cables around under the hood and perhaps disconnecting and reconnecting 
connectors in an attempt to clean any dirty contacts.  You might even want 
to get at the ECU and clean the connector there too.  

One other problem to keep your eyes open for is a case where there is some-
thing loosely attached to the block.  A friend of mine has a GTI and he was 
complaining about extremely poor performance.  It turned out that the A/C 
Compressor mounting bracket had broken and was banging on the block ... 
tripping the knock sensor.  The fact that your situation actually generated 
some fault codes leads me to believe that you have an intermittent ...
> 
> BTW -- as an aside, a little question in relation to my motorized antenna 
> saga:  why does that clear vacuum hose attach to the bottom of the 
> factory motorized antenna?
> 
... it's a drain for any water that gets into the mechanism ...

HTH!
Steve Buchholz
s_buchho@kla.com