What retards spark?

So I've still yet to get my tuning stuff as money has been too tight, so I haven't ventured into tuning my rich fuel levels. One problem I am still having with my truck is a retarding of my spark. I'm pretty sure the knock/esc is not the problem. Reason is, the knock sensor needs replaced, as it's not picking up knock. Therefore, it throws code 43, and from what I've read, automatically pulls timing.
Even when this happens and the timing is retarded there is still a further pulling of my timing happening. What I am trying to determine is whether it's something computer related, or something mechanical. Is there anything else in the computer that could pull timing even when timing has already been pulled due to the code 43?
In case it matters....I am getting this extra retard at idle as well as above idle.
Also, this additional timing retard is intermittent.


Info just as a reminder:
Suburban: 350 TBI '7747 $42
stock engine, with all new sensors except TPS which is in spec.

Knock sensors rarely go bad without human interference. ESC is the main controller of spark retard. Take a look at code 43 in the PDF doc below on how to test the entire circut. You can get some retard and advance on old engines with worn timing chains but can usually see this with timing light and marks jump back and forth a little.
http://www.gearhead-efi.com/gearhead...c/TBIcodes.pdf

Will take a look at the pdf. I'm pretty sure I "broke" the knock sensor. Had to replace my intake manifold because of a thermostat bolt problem. When I replaced it, I pulled the knock sensor out to drain the block of coolant, and it hasn't worked since. Don't think it's the chain. With or without the bypass wire connected, I get a very steady timing mark.

By unplugging the bypass wire, what kind of timing will it run? I know the distributor has some advance built in, but how much? Basically still trying to rule out a dist problem vs computer problem.

Distributor has no advance. But the ECM does, how much it pulls depends on the chip/bin temp and RPM.

When you disconnect the wire timing should be set to 0 TDC. Lock down distributor, check, turn off motor, connect wire, clear codes.

You didn't put terminal tape on the sensor when you re-installed it did you?

Quote:

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Originally Posted by PJG1173

You didn't put terminal tape on the sensor when you re-installed it did you?

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Nope. Read beforehand not to put anything on it.

you can hook up a multimeter to check operation when you "tap" on the block w a hammer you will see the frequency of the output change.

Yea,I tried the tap on the block method. Didn't however try it with a multimeter. Tried it with the laptop connected and got no knock. I'll give the multimeter way a try.

Purpose:
The Knock Sensor (KS ) is used to detect engine detonation (ping).

Operation
A 5 volt reference is applied to the knock sensor which has an internal resistance of about 3900 ohms. This resistance will lower the applied voltage to about half or 2.5 volts. When a knock is present, a small AC voltage is produced by the knock sensor and transmitted to the control module riding on top of the already existing 2.5 volts. An AC voltage monitor inside the control module will detect the knock and trigger the control module to start retarding the spark incrementally

Circuit Description:
The Knock Sensor (KS) system consist of a knock sensor with one wire that goes directly to the PCM. There is a check performed by the PCM. The check consist of monitoring CKT 496 for a voltage that is more than .04 volt and less than 4.6 volts.

If the voltage is either too high or too low for 16 or more seconds, DTC 43 will set.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. The first test is to determine if the system is functioning at the present time.
2. Test two determines the state of the 5 volt reference voltage applied to the knock sensor circuit.

Diagnostic Aids: The PCM applies 5 volts to CKT 496. A 3900 ohm resistor in the knock sensor reduces the voltage to about 2.5 volts. When knock occurs, the knock sensor produces a small AC voltage that rides on top of the 2.5 volts already applied. An AC voltage monitor, in the PCM, is able to read this signal as knock and incrementally retard spark.

If the KS system checks OK, but detonation is the complaint, refer to DIAGNOSIS BY SYMPTOM/ DETONATION/SPARK KNOCK/PINGS See: Testing and Inspection\Symptom Related Diagnostic Procedures\Detonation/ Spark Knock.