EST advances or retards the timing, depending on sensor data from more than just the knock sensor. It also uses TPS, MAP/MAF, coolant temp, etc. The knock sensor data will only show "Yes" or "No" on a scanner. If the car is idling, it will show "No". The only time the knock sensor will change from "No" to "Yes" is on heavy acceleration, or part throttle cruise conditions, unless there is a distributor timing issue, such as it being out of time, or, if the engine is overheated.
The "test" for checking knock sensor and wiring is to take a small hammer, and "tap" the engine block around the sensor while watching the data on a scanner. It should change from no to yes when tapped.
An EST code can be set for any number of reasons, and a bad ECM(computer) is one, and, unfortunately, the most common.
If the wiring to/from the ECM to the dist. is good, and the ign/ module is good, there are other things that can cause the code to set. The knock sensor only informs the ECM that it needs to retard the timing.
If you have the shop manual, follow the troubleshooting tree for the code, and you'll find the culprit.
In some instances, if the ECM sees heavy knock for a long enough period of time, and it is not able to retard the timing enough to stop it, it can set the EST code. This could happen from using too low grade of fuel, or simply having too much timing. I'd suggest checking the timing first, to see that it is in spec, and go from there.
The knock sensor isn't very hard to change, and I see quite a few that have had the wiring, and the connector damaged. Check to see that it is plugged all the way in, and that the wiring isn't oil soaked/damaged.
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Joel Adams
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