Spark Plug Wire Resistance

[ZeroHour]

I'm trying to troubleshoot my brother's Subaru Wagon's absurd issue with a P0420 Code.

Needless to say Subaru people seem to lack responsive or knowledge on their forums, So I'd figured I would give it a shot over here on CEG! We seem to have much more reliable car nuts here :laugh:

The Subaru has a Catalytic converter loss of efficiency code. Although it has a new catalytic converter on the car. had been replaced previously by a shop. I have a feeling the previous owner got hosed in this situation, and since my brother now has the car and its getting the same code again, I'm trying to track down all the other issues.

Somewhere along the line, the shop changed the plug wires over to an "STI" set of wires. Except this STI is for Spark Transfer International, a small company that produces "HP adding wires". Needless to say the wires measure in at 1/4 of there factory spec. I'm concerned that these things are causing either poor spark, bad spark, or RF interference.

Does anyone here on CEG have experience with this? I've changed enough spark plug wires in my time, but never bothered to chance down "performance" plug wires.

Factory spec are 5.6 Kohm to 12.x Kohm
His wires are 1.4 Kohm to 2.0 Kohm

Any suggestions appreciated!

 

[BAD SVT]

i dont think spark plug wires are related to the CAT. i'm sure u know that as well. but in my research, i havnt seen any physical proof of "power adding" wires. if anything, it allows the engine to run close to stock figures. if u're sure the spark plug wires are not right, how about changing them? i'd imagine that shouldnt cost u much. or if the shop put in the wrong ones, take it back to them so they can correct it.

 

[ZeroHour]

A new set of wires is $50...but its not my bill to float. It's my brother's car. He's a working student and has already put out the money for both the o2 sensors this month.

My concern is that the low resistance wires are actually cause a higher voltage spark -> causes a change in the fuel burn -> causing a A/F ration different than ECU can manage -> Poor Cat Performance -> CEL.

 

[BAD SVT]

quite possible... but still seems a tad of a stretch to me.

 

[ZeroHour]

Lol Oh I know, but its almost to the point where you have to start guessing if the wire is bad, the ECU has gone bad, etc. Its pretty hard narrow it down to anything else that could be causing a Catalytic inefficient code.

This is actually a common issue for Legacy, Outback, and Forester Models built from 2000-2004/2005 with the 2.5L engine. Most people start ignoring the light, get a MIL eliminator, or get an anti-fouler and space the 02 out from the cat.

Between the P0420 issues, spongy brakes, bad Head Gaskets, terrible understeer, and twitch ABS/VDC system I don't know why people rave about Subaru's. I never hated them until I owned one. And now both myself and my brother have one. :facepalm: