I have an intermittent code 43 on my 91 Corvette (6sp). The 'Service
Engine Soon' light comes on at high speed, sometimes during
acceleration, other times, when I'm just sitting at a traffic light.
The light may stay on for 20 minutes, other times, only a minute or
two. More often than not, it comes on after about 15/20 minutes or
driving.

Associated with this light, is an uneven amount of power when
accelerating, almost a bucking feeling.

What should I look for, and in particular, where should I be looking.
I was contemplating bringing the car to the dealer, but the thought of
a $200 diagnostic charge to replace a $30 sensor or frayed wire is
alarming.

Thanx in advance....

Craig...

 

43 is a knock sensor and there are 2 i believe that year inspect the wires first before replacing. the only way you will know which one is to scan it or replace both

 

There is an entire diagnostic procedure for this error. The knock sensor is on the passenger side of the block. Do a quick check and make sure the wire isn't damaged or broken. My scanner isn't working so I can't scan in the pages. Here's some information from the diagnostic aides section:

Ceck CKT 496 (dark blue wire to knock sensor) for a potential open or short to ground.

Also check for proper installation of MEMCAL.

If the customer's complaint is the "Service Engine Soon" light comes on when in acceleration, the B portion of the code is failing. There is a possibility that the High Engergy Ignition (HEI) system was in bypass mode when the 43 test was run. An intermittent open in the EST circuit will put the HEI module in bypass which will not allow the spark to be advanced so the 43B test would fail. If the ECM also had a Code 42 stored, then the EST circuit is likely the cause of Code 43.

There are two internal ECM tests run on this CKT to determine it is operating correctly. If either of the tests fail, a Code 43 will be set.

Test 1: If CKT 496 becomes open or shorted to ground, the voltage will either go above 3.62 or bleow 1.44 volts. If either of these conditions are met for approximately 0,5 seconds, Code 43 is set.

Test 2: The system also performs a functional test to determine if the knock sensor is responding to engine detonation. To perform this test, the ECM will advance the spark under certain load conditions and look for a knock signal respone. If knock is detected before the conditions are met to run the test, then the test is bypassed. If the test is run and no knock detected, Code 43 will be set.

Conditions for test: Coolant temp over 203 degrees F
High engine load based on air flow

 

I had the exact same problem in my 1991 as you described. Car also did not want to run over 2000rpm. Sometimes the light never came on, other times it came on immediately, even others it came on while driving. Would turn itself off randomly as well. I replaced the knock sensor and checked all wires leading to it, and the problem was eliminated. IIRC, a replacement sensor was about 54 dollars at a Chevy dealer. Unfortunately, I cannot give you a long-term analysis of the problem as the car was totalled the day after it got fixed. :sad:

 

Well you lucked out, (sort of.) L-98s like your `91 have one knock sensor. LT-1s and LT-4s have two of them. They run about $36 bones apiece from your local Chevy dealer.

Don't get the cheapie ones from Kragens, PepBoyz, AutoZone, etc... as they may NOT be calibrated to your GM ECM's specs and can throw ANOTHER Code 43. Back to the proverbial square one! :U

Be sure and torque it down to the proper specs (VERY IMPORTANT) and do not use any tape or threading compound on that new sensor. The orange tape that comes on there will suffice, thank you.

Good luck! :chevy

 

I just fixed that same problem on mine as well yesterday.

Turns out the wire was chaffed where it went through the wire clamp (by the starter) and was shorting to ground. When you unplug the sensor, there should be 4-6 vdc when the ignition is turned on. If not, then there is an open/short/bad ECM.

Work it through logically, and find the problem. Check the resistance of the sensor (3300-4500 ohms). It sounds like the same issue I had though. It was intermittent, would go off if I was hard on the gas, etc. Frustrating as hell....

Good luck

 

How do I get at this sensor, wire?

 

The best way is to remove the heat shield under the engine that surrounds the sensor.

If you have an L-98, it will be located near the starter motor. LT-1 and LT-4 engines have two knock sensors on both sides of the block in identical locations.