[V8] power drop outs

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Fri Apr 6 17:43:27 EDT 2007


... this is exactly what I was talking about when I said it can do more harm than good ... 

When the manufacturer designs the control electronics for a vehicle one of the main goals is to try to keep the grounding for small signal inputs (like the OXS) separate from the ground for big power and noise sources ... alternator, headlights, starter, etc.  Of course all the grounds need to be connected together, but the technique that is typically used is to provide one single common point between the "noisy" ground and the ground for the sensitive signals.  One of the other things the engineers do is to make sure as little current as possible flows in the sensitive circuit paths.  The rationale behind this is simply Ohm's Law ... every ground has some resistance to it, and the more current running through that ground means that more voltage is dropped across the ground.  

On the V8 that common ground point is at the back of the engine block under the distributor on the driver's side (US).  If you connect that sensitive ground wire for the OXS signal to a strut tower it means that the OXS signal voltage seen by the ECU is going to be influenced by the amount of current flowing via the ground for the alternator to battery ... which means it will be greater when the headlights are on ... 

I'm sure there are folks out there thinking "So what ... I've got my car with a 4-wire OXS grounded to the body of the car and it works."  Do what you want, its your car ... but I can guarantee you that your car will run better and more predictably if you would just use a 3-wire sensor and depend on the ground connection through the rusty exhaust with very little current flowing through it than if you get a 4-wire and ground it somewhere that will have a variable voltage inserted due to ground currents.  There's no question, when done right the 4-wire will be better than the factory 3-wire, but you need to have that OXS ground wire connected to the block of the engine ... preferably near the lug that the ECU gets its ground from.

Steve B
San José, CA (USA)
> 
>  Ok I have yet to install the 4wire 02 sensor I got
> from Bruce..thanx Bruce!!..but,
> I've read listers putting the extra ground wire on the
> shock tower. But can I use the ground point on the rad
> fan ground found on the driver side shock tower area?/
> or there's 2 ground points at the back of the d-side
> engine block..so were can one get the best signal
> from?


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