I just recently installed a set of 1.6 roller rockers on my 84 and now seem to be having an issue with what appears to be the ESC or knock sensor. I get a noticeable stumble or cut out like the system is retarding the timing real hard or just cutting it off like some plugs are not firing. (I already replaced the plugs, wires, cap and rotor, and tried a new distributor with the exact same results) I just recently read that GM had to revise their knock sensor because the old ones were too sensitive and was wondering if anyone else had a problem similar to this, and or if anyone had the part number to the revised knock sensor.

James

 

Your info is somewhat right, but also somewhat wrong. There are several different calibrations of ESC units. The customization is done via the module, not the sensor. You already have one of, if not the, least sensitive modules produced as standad equipment on your car. IIRC, the three letter broadcast code was HKR. (I'm using the stock module on my turbo 355 with no issues after the engine warms up.) I don't have a calibration listing with me a the moment (I'm visiting relatives currently), but I don't recall any modules that would easily correct your problem, without doing a lot of plug and test work (and most of these modules would be mistuned to the knock frequency). One thing you could try would be to desensitize the whole system. IIRC, our current system uses a 5.2 kHz knock sensor with an internal 100 kOhm resistor. You could obtain a later sensor of the same frequency, but with a 4 kOhm internal resistor. I believe these were put on '89 and later Corvettes (Don't quote me, I'm going by memory while I'm away from my pile of paperwork). Ths sensor will reduce the system impedance by about half, and may, I only say may, reduce the instance of false knock retard by reducing the magnitude of the noise spikes produced by the sensor.
Distilling it down, there's few easy remedies when there is mechanical noise that mimics the same frequency that knock produces. Quite often the only choices are reducing the mechanical noise, or deafening the ESC system.
Keep us updated on what you want to try, and I'll try to offer some assistance.

 

I once used the resistor method. Installing it in one of the wires which run between the ESC and the Knock Sensor itself on my 86.

This method, though, completely disabled the KS by feeding the ECM the resistance reading it looks for when it checks to see that the system is working properly.

Others have tried wrapping teflon tape on the KS threads where it screws in the block. The thinking being that would lessen the KS sensitivity. I'm not sure that method works though.

The LT4 KS Module is a common swap for later LT1 engines. It's suppose to be less sensitive that the stock LT1 module. I installed one on my 96 LT1, but I don't know what difference it made since I couldn't do back to back.

Jake

 

Thanks for the advice guys. I have a question though, when I check for knock sensors at Rockauto and Napa, I get the same part number for 84 and 96. I check for both VIN character 5 or P and get the same knock sensor part number. Do they just sell the sensor with more resistance now?

 

Your '96 uses a plug-in ESC module (internal to the ECM), which is a different module than the '84 -'88 units which are stand-alone units that mount under the hood.

 

Changes in the ESC electronics required changes to the sensor. The '96 uses the same 100 kOhm sensor that the '84 to '88 used. The '89 to '95 systems used a sensor with a 4 kOhm internal resistor.

 

okay, from what I have read in the various posts that I have searched, I can temporarily disconnect the knock sensor to test whether or not it is too sensitive without the ESC telling the ECM to throw a code? Am I correct?

 

Yes. The (disconnected sensor) diagnostic function was not implemented until the '89 model year, I believe.

 

Thanks for all your direction on this. I'll try disconnecting it this evening and see how it does. I'll let you know the results.

James

 

Well I disconnected the knock sensor last night and did some testing. The problem is still there. Cuts out under hard or constant acceleration, and at a constant cruise it stumbles just a little. But I might have caught a break this time. I ran WinALDL and checked for codes before I disconnected the knock sensor and I had an error 42 code. This code indicates an ESC module error. This was one of my suspected modules so I'm going to replace it. After I replace and test I'll let you know if the problem is corrected.

James

 

It's been my experience that a code 42 relates to some problem in the connections to and from the ESC and ECM. I really think you should do some testing before replacing your ESC. If you do a search, you should be able to find the diagnostic flowchart on the forum. If not, ask Agent86. He may be able to help you with a PDF of the manual's flowchart.