kcore

I have a 92 Silverado 305 engine TBI. I recently gave it a tune up like i have done in the past (plugs,wires,cap,rotor,airfilter,pcv valve,fuel filter and ignition module) but know when i bypass the EST to time it it runs fine but when i plug the EST back together and clear the codes the idle goes up to 1,000 rpms and back down to 100 rpms back up then back down and keeps doing that. PLEASE HELP i ran out of options of what to do or what could be wrong.

Blue Bowtie

Try disconnecting the knock sensor, plugging a 3900 ohm resistor in it's place, enable the EST, and see what happens at idle.

kcore

Thank you for replying i will try that. But i have to say the computer was not giving any codes is that normal.

Blue Bowtie

If the KS detects a detonation event, and signals the ESC, the ESC will retard timing. That is normal system operation, and will not set an error code.

If the KS is reading false knocks, or the ESC wiring is subjected to EMI, RFI from ignition wires, or poor connections, the system can interpret that as a regular detonation and act accordingly. It would still not set a code. You'll get an error code (42) is the ESC loses communication with the ECM oe HEI switching module in the distributor, or if the KS provides no signal to it. The 3.9K resistor will "fool" the ESC into thinking that a KS is connected, but is quiet and recieving no knock signals.

The ESC retards timing in steps, then recovers in steps. The attack and recovery rates are fairly fast. If the KS is presenting random signals at lower RPMs, the timing at lower RPMs may be all over the place. You can confirm this with a timing light. Usually, once the ESC is active the timing at idle will jump to around 20° BTC and remain fairly stable. If it is jumping all over, the ESC could be acting upon a failing KS or electrical noise in the system.

kcore

Thank you for the info i know what you are talking about now because i did at first get the (42) code and did replace the starter which is right above it so i will try to do that and see what happens. Thank you so much.

kcore

How do i connect the resister to it.

kcore

What it did was make it at a very low idle is that what it was suppose to do.