why a ground mod?

I'd say you have it figured out pretty well.

-rick-

Well this old keeps popping it head up,The reason for doing it is that Subarus have a bad earthing system and as all of the sensors mounted on the engine send back a pulse or a varible volt to the ECU if the sensor does not see a true 12-14 volt then the ecu sees a lesser value as well and does not set its parameters correctly.. My '90 Legacy GT(this is a Jap import modeel in New Zealand so has the EJ20T engine) made huge improvements just by earthing the engine I used my own earthing points mind you mainly on the intake manifold

DILLIGAF DJ

okay, this is the part i'm trying to understand.

what is a "bad earthing system"? was the wire undersized, or was there a corrosion problem? is this a design "feature" (poor engineering), or a maintenance issue (clean contacts periodically)?

specifically, what problems did you have that were fixed?

also, why use "your own earthing points"? is there something wrong with the ones that subaru designed? (i.e. were they in corrosion-prone areas, or were there disconnected areas that you were trying to reach?)

i know it's a lot of questions, but all the previous discussions seem to be full of WHAT and HOW, with very little WHY.

....... tom kle> Well this old keeps popping it head up,The reason for doing it is that

ok it fixed a hesitation that I had at full boost(15 psi) as well as it idled alot smoother,I used my own earthing points because I decided that the engine needed definate earthing to the intake manifold and to the block of the engine also decided that the sensors on the RHS front fender could do with an earth as well,So I went from LHS strut tower to Battery - terminal to LHS of the intake manifold to rear of the alternator to RHS of intake manifold to sensors on RHS inner front fender to RHS strut tower.You can just clean exisiting earth point and do regular maintenance as well and that should be alright for most,my Legacy is no longer stock and hasnt been so for 150,000 Km and I swear that the earthing system has helped with the longevity of the engine

All the above.

Multiple 12 Ga hot leads running to single 20 ground line (see headlamp assy); grounding ring terminals mounted over intact paint with

Saying the existing system is fine---goes well with insisting that the only way to disconnect the battery is by disconnecting the negative terminal ;-)

I don't know if this is the reason in the Subies, but for computers and high end electronics the problem is due to multiple grounding points.

If the grounds are not at identical potential, there will be electrical leakage between the grounds. Even in a home stereo a misplaced ground wire or a reversed mains plug can lead to easily audible hum. Since many (most?) sensors in a car operate on a voltage difference, any change to the 0v point would mess up the value the coputer uses for its adjustments.

If it were just a matter of ground resistance, say from poor contact, I'd expect the performance inprovent from the kits to be temporary. Corrosion under-hood is inevitable.

The few reviews of star ground systems I've read (none specifically for Subies) have said that they are a tweakers delight. You have to experiment like crazy and may or may not see any improvement. Unless you have a dyno in your garage, those are worse odds than installing a CAI kit.

Philip

Subies have multiple ground points from the factory. Take a look at a wiring diagram.

I've looked at my Outback's wiring diagram and all of the critical sensors use a separate return wire. As a result, their output is not referenced to chassis ground. Reducing ground strap resistance will not affect them.

The hum on your stereo is because the signal has to return on the ground wire. On pro audio equipment, as on the subaru sensors, there is a separate return line for the signal and a ground that is *only* a ground and is not connected to the signal. That's the correct way to do it.

I maintain that they won't hurt anything and may help. Some people have seen a noticeable improvement without resorting to a dyno.