My friend recently purchased this 94 and it seems to run rich and performance is lacking. I scanned with dm and pulled these three dtc 13,43,65. 13 is left 02 fail, 43 is knock sensor or ESC Fail, 65 Right 02 rich. Now a little background, the engine has alot of go fast goodies, L T headers, lt4 intake, Heads, Am throttle body, under drive crank, high lift cam, lt4 knock sensor. I know this is all pretty vague, but what I saw and told. Ok, we jacked up the car and checked wiring 02 sensers, knock, pm ground, all looked good. unpluged KS rerun on dm. both 02 sensor dtc's gone leaving KS alone. This probably normal. Now is the temptation to throw parts at it. Friend replaced engine KS, with no performance gains, He lives 15 miles away. I think we should replace left O2 senser, Verify PCM origins by VIN. I have already verified lt4 knock module in PCM. Friend also purchased DM and Tunercat. Question finally: How should we continue with repair?

 

DTC 43 indicates there is a problem with the knock sensor circuit. If you simply unplug the sensor harness connector, the trouble code should not go away. When the code it set, the PCM used calculations based on engine operating conditions, to retard ignition timing almost all the time. No way that won't hurt performance.

To check the knock sensor problem, key on, harness connector off the sensor, you should get 5V when measured from the single wire in the connector to the block. With harness still off, measure the resistance from the single pin on the knock sensor to the block. Should be around 4,000 ohms. Reconnect the harness to the sensor. Measure voltage from the wire to the block. Should be in the range of 1.5 - 3.5V. Anything outside those limits sets DTC 43.

DTC 13 can be caused by on open circuit due to a sensor failure, or a harness wire failure. Swap the O2 sensors side-to-side. If the code stays on Bank 1, its a wiring problem. If the code follows the sensor to Bank 2 (DTC 63) its a sensor problem.

DTC 65 can be caused by a short in the wiring harness, dropping the voltage close to 0 mV. The side-to-sdie swap may uncover more info. If you cleared the codes, they are not going to reset until the PCM tries to go into closed loop.

 

Thank you Injuneer,
Sounds like a great start, will post with results.

 

Great news, We did all of your suggested testing, fixed a questionable O2 connector, the knock sensor tests all fell within limits, swapped the O2's back to originial positions. We then took the car on a test run, with DM hooked up, closed loop and all dtc's gone and the car is running GREAT. His Gas Mileage was down under 10 mpg and Idleing 1400. Everthing is now in normal specs. Now, baby steps through TunerCat.
Thank you Injuneer! and Z28.com!

 

In searching my DTC 43 problem.. I found this post.

Injuneer...

I tested the connector disconnected from the knock sensor and it read : 4.85 pretty consistently.

I test the connector connected to the sensor and it tested: 4.69 pretty consistently.

I was not exactly sure how to use my test meter to test the resistance...but it appeared that best I could get from the knock sensor to the block was 1200, but I am not sure I was testing it correctly.

With the information I have given...Does this appear to be just a bad knock sensor?

Thanks,

James

 

I may have found my problem.

I have a 93....and I think I installed a 95 knock sensor. I didn't realize they were different over the years.

 

They should be the same. 96-97s are different.

 

It sounds like your sensor resistance is too high, or its not well grounded to the block through the threads. I suspect you measured something much higher than 1,200 ohms.... maybe it was more like 120,000 ohms. The 96/97 knock sensor has a resistance of about 100,000 ohms.

 

I just took the sensor from a spare engine I purchased. I was told it was from a 95, but I am now thinking it is a 96-97.

I had another spare block from a 95, so I tried that one and this fixed the problem.

Thanks for the help,

James