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Knock Sensor LED Mod
Troubleshooting Info

"Normal" LED Behavior:
Normal operation of the Knock Sensor LED seems pretty consistent among most 1G owners I've heard from (as well as my own experiences).

If the LED is wired correctly, it will:

• light solid when you turn the ignition key to the "ON" position (one click before it starts)
• flicker for a few seconds when the car starts, then will turn off
• flash rapidly when the knock sensor "hears" detonation (it may appear to be lit solid when the knock sensor is "REALLY" detecting detonation)
• remain on solid for approximately 5 seconds after turning the ignition key off (it will turn off when you hear the click from behind the center console)

Feedback from quite a few others seems to indicate that their LED frequently flashes as described below:

• Flashes rapidly beginning at 6000 RPM in 1st and 2nd gear
• Flashes rapidly or nearly solid at 5000-5500 RPM in higher gears (especially common if driver has accelerated rapidly through 1st and 2nd, - typically caused by increased intake temperatures as a result of intercooler heat soak)

Troubleshooting and Common Questions:
While there have not been a LOT of problems with this modification, there are several "themes" to the problems I've heard about.

• LED is lit Solid while the engine is running:
  The Knock LED lights solid when the key is turned on, and flashes when the car starts, but never turns off until 5 seconds after the engine has been shut off

  To the best of my knowledge, this problem has ALWAYS been traced back to the fuel being used. Responses indicate that once a higher octane or different brand of fuel is installed, this LED behavior disappears after 30 to 60 miles of normal driving. Pulling the ECU Backup fuse in the lower right corner of the interior fuse panel will temporarily clear the "solid-on" state, but it WILL reappear in a few miles if there is no change in the fuel. (Thanks Todd Day for your help on this issue!)

• LED does not light when the ignition is turned ON:
  I know of a couple of conditions that have been known to cause this problem.
  
  • Error in wiring the circuit - Probably the most common wiring error I've seen is a poor connection on either the ground wire to the LED or in the slice into the Orange Wire at the ECU
  • Faulty Boost Solenoid - I was directly involved in one install where everything proved to be wired correctly, but the LED did not light with the ignition ON. This problem was resolved by testing the Boost Solenoid and finding NO resistance across it. Normal resistance for the BS is 36-40 Ohms. The faulty BS was also the cause of a performance problem with this car. My GTech Pro showed 1st gear, 3K roll-ons to be .61g with the new BS, vs .55g with the faulty unit (definately noticable!).

• Confusion caused by my directions:
  There have been several questions sent to me as a result of confusion over where to place the resistor (based upon whether the BS is in use or not). I have changed the wording in a couple of spots on the HowTo page to attempt to remove the confusion.

• I tried this mod on my 2G DSM, and it seems to be behaving really strangely:
  Sorry, but this mod only works on 1G DSMs and Galants. There has been some discussion on the Talon Digest regarding this subject and to the best of my knowledge, noone has been successful at building a similar mod for the 2G cars. If you are up to the challenge and build a functional 2G Knock Sensor LED, I'd be happy to document that mod here (or link to your site if you build your own page).

Please send your suggestions and comments to Damian_Sigman@homemail.com
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Page created April 20, 1997 - Damian Sigman