[Supras] Factory shielding of knock sensors

[berniek at technicaldevelop.com]

Brian and list:

I'll check and see that the shield is grounded. I disconnected the 
harnessing in the '91 and pulled it back to the fender when I removed 
the cylinder head. The knock sensor connectors are now easy to get to. 
When I cut back the protective tubing by about 2" for examination, I saw 
tape tightly wound over the end of the shield and outer jacket of the 
coaxial cable, so getting to the shield and checking continuity is easy. 
The '90 and '91 manuals show the sensor wiring as shielded ("sealed") 
and grounded near the AFM ground.

You are correct. The AFM and knock sensors are on opposite sides of the 
engine. However, they are not that far apart because of the harness 
crossover which runs right in back of the upper timing cover.

Bernie

Walker, Brian (Rich. Dist) wrote:
>
> Bernie, I never noticed the factory shielding being grounded at all 
> (88T) which is why, when replaced, we grounded it near the ecu. It 
> doesn’t make a lot of sense to run the ground so far either, aren't 
> the KS's on the intake side, opposite the AFM? That's a lot of extra 
> wiring to run and like mentioned, I didn't noticed them being grounded 
> when removed. One sensor fell apart when disconnecting the wire, never 
> showed codes though (I'm thinking it and the wiring was the source of 
> the wildly varying power)
>
> Perhaps Toyota realized at some point shielding works much better when 
> grounded?
> Brian
>
> Date: Mon, 23 Jul 2007 00:16:14 -0400
> From: "berniek at technicaldevelop.com" <berniek at technicaldevelop.com>
> Subject: [Supras] Factory shielding of knock sensors
> To: "Supras at supras.com" <Supras at supras.com>, berniek
> <berniek at technicaldevelop.com>
> Message-ID: <46A42B8E.1050405 at technicaldevelop.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> The '91-up manual set I have here shows the knock sensor cabling to be
> shielded in much the same manner as mods which have been posted on this
> same group. I inspected the forward most sensor wire and found it to be
> shielded about 2" back from where the overall protective tubing starts
> at the sensor. According the the wiring schematic, the shields are
> grounded to a common point near the AFM ground. However, I have seen
> mods involving shield grounding at both the block and the ECU case (with
> soldering to the ECU case whch can be done to aluminum with SAL-Met flux
> with difficulty). So the factory shield grounding point does not seem
> that outrageous. Yet I had instances with my '90 where knock sensor
> codes were set. I have a brand new '90 harness in the original plastic
> bag (which will be for sale) which shows the same shielding. Maybe it
> was an upgrade from the original. since I did have knock codes set a
> couple of times on the '90 before the BHG. There were no codes set on
> the '90 when it was received from the dealer.
>
> Were the list modification comments intended for older harnesses only?
> Both the 91 and '90 manuals show the shielding (referred to as
> sealing"). Any comments would be appreciated. Thanks.
>
> BernieK
>
>
>