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Red spark plugs


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4 replies to this topic

#1 subaru_dadeo

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Posted 03 October 2003 - 11:52 PM

My daughter pulled two one-month-old spark plugs from her '92 Legacy sport sedan, and the tip and ground electrodes were rust red. Coating doesn't rub off. I've never seen this before. Any ideas why this has happened? Plugs are Bosch Plus 4's. Engine idles fine, but she's noted some loss of performance.

Also, I put a timing light on the engine, and the timing was about 29 degrees BTC. She thinks the knock sensor is bad & has another coming tomorrow. Could this be the cause of the (1) spark plug color, (2) performance loss, and (3) really advanced timing?

Thanks!

#2 Cougar

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Posted 04 October 2003 - 12:58 PM

I would guess that the coating is due from the particular fuel that is being used in the car.

As far as the timing goes I think you have to may have to connect some electrical connections together first before you can check your timing with a light. I would check a service manual about the proceedure.

If the knock sensor is bad you will get a code stored in the ECU and I think the CEL light will turn on. This sensor is monitored by the ECU so it would know if there is a problem with it. They are not cheap to replace needlessly.

#3 Legacy777

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Posted 04 October 2003 - 11:58 PM

I would tend to agree about the reddish plugs and it being a certain type of fuel or additive.

The timing, you really can't adjust the timing, the computer sets it based on varioius sensors, including crank & cam.

knock sensor, if it's never been replaced it's probably the old style which are known to crack and become oversensitive. There is a new style out that is supposed to alleviate these problems.

#4 subaru_dadeo

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Posted 05 October 2003 - 10:16 PM

Thanks for the responses. I discovered in an old Readers Digest car repair book that the red color can come from manganese additives in unleaded fuel. Regarding the knock sensor, we changed that yesterday with a "white" wire model, as we've heard the same story about the older knock sensors. Timing at idle is at 19 deg BTC now which is within spec.

#5 Cougar

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Posted 05 October 2003 - 11:17 PM

Glad you got things straightened out. Thanks for the feedback.




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