Getting a reading of infinite resistance on my knock sensor ("84 Vette). Anyone know for sure if this is an indication of a bad knock sensor? Research is unclear on whether or not the 84's should have resistance. Thanks.

 

that is normal to have infinite resistance with the knock sensor-just a
piezo chrystal in there

 

I'm sure Rbob would know You might ask on the http://www.crossfireinjection.net forum if you don't have a factory service manual.

 

Makes sense - thanks for the reply.

 

Thanks for reply, have FSM no indication of a resistance test. FSM test chart requires disconnect of KS while at 1500 rpms and noting timing delta. Super hot LT headers in the way on my beast so I was looking for an alternative test.

 

They want the ESC module disconnected while the engine is running at 1500 RPM. This should cause runaway knock, which will cause the RPM to drop from the knock retard and code 43 to be set. This checks the ECM input for knock counts.

To check the sensor, disconnect the ESC module and with a DVM on the A/C scale, between terminals E & D of the connector (not the module), engine running at 2K RPM, measure the voltage. It should be at least 60 milli-volts

Pin D is ground, with Pin E being the sensor.

Most (all?) knock sensors that use an external module measure 100K ohms.

RBob.

 

Good stuff, thanks Bob. Will do.

Just for laughs thought I'd let you guys know that the last shop that worked on my car had the fan connected to the KS and KS lead to the ESC connected to the fan sensor. So I joined the stooges act by tapping the KS lead and wiring it to the fan switch. Well, the fan worked just fine - yep, just found this while I was performing the KS & ESC tests.

 

Quote:

Originally Posted by RBob

This should cause runaway knock, which will cause the RPM to drop from the knock retard and code 43 to be set. This checks the ECM input for knock counts.

Interesting - as noted the ESC was inadvertently connected to the fan switch and I tapped it to get the fan running thinking I had a short. No code 43. Wondering why the ECM didn't pick this up.

 

Swapping those two connections won't cause code 43. If the ESC module is unplugged, or the wire between it and the ECM is open, or the +12 volts to the module is open, that will cause code 43.

The ECM pulls the knock count signal down, with the ESC module pulling it high. When the ESC module thinks there is knock it pulls the signal to the ECM low. If the ESC module isn't pulling the signal tot eh ECM high, the ECM sees continuous knock.

RBob.

 

New Knock Sensor hit today - for the record it reads 100k ohms resistance. Old one must be hosed it read ∞ .

Thanks for your comments - all. Always appreciated.