jdmintegra

I keep getting a knock sensor light on my 98 teg car runs and pulls great nothing out of the normal..i did notice when letting idel i thouched the throttle like just burbed it and it had a minor knock then whent away does fine at high rpms just when u burb it has a minor knock for no even a sec..i do have timing advanced so im wondering is it a spark knock

ILLEGAL

whats your question?

jdmintegra

oh just wondering if the advanced timing was doing it or what could be the cause

Fabrik8

Did you advance the timing mechanically or using the ECU?

How long has it been doing this, and does it seem to have anything to do with when you advanced the timing?

Given the need for higher advance at higher RPM, I'm guessing there aren't any problems at high RPM if you're using a stock (non-tuned) ECU. At slower engine speeds, you may be running into knock sensor problems because of the advance.

So follow me here:

The ignition coil takes a certain (somewhat-fixed) time to charge up, and then it fires. The higher you go in the RPM range, the shorter each cycle is, and the more the somewhat-fixed time gets out of sync with where it needs to be in order to fire at the right time. Think of the coil as not having fast enough reflexes at high RPM, so you need to give the coil more of a head start as the RPM goes higher. That's why you need ignition advance maps and stuff like that in the ECU that change with RPM. Part of needing maps instead of just a scalar (that changes with RPM) is to get optimum power at different loads, but ignore that part for simplicity because it doesn't matter in this discussion.

So if you've mechanically changed the advance by turning the distributor, you've physically changed when the coil starts to charge across the entire RPM range. There is already some leeway for more advance in the ECU tuning usually, so that shouldn't be affected at decently high RPM.

At lower RPM, everything happens slower, and having the mechanical advance means that you're just firing the spark plug too early, possibly before the piston is where it should be on its downward path. This can cause the pressure to rise at the wrong time, and could be making the piston rattle or something like that. The knock sensor could be picking that up, probably because whatever is happening might be in the right frequency range that the knock sensor is tuned to. Could be valvetrain noise too, but either way if it just started when the advance was changed then the advance is still the culprit.

SO I don't think you're getting detonation or pre-ignition because of the low RPM where it is happening. That doesn't mean that your knock sensor isn't hearing something else instead.

jdmintegra

thanks that makes sense

Fabrik8

You still didn't answer my two questions at the beginning.

Fabrik8

Set the distributor back to stock position..

Private Messages work well too by the way, visitor messages are public..