I started getting code 43 on my '95 LT1 383 (forged crank & pistons, H-beam rods, Hot cam, Mac headers, 52mm TB, LT4 intake & heads & knock module, PCM4less tuning). Additionally, there is a bad stumble/surge right around 2K rpm that goes partially away as soon as the motor heats up.

I performed the knock sensor test as mentioned elsewhere in this section & got 4.8V at the wire (this varied a good bit depending on how well the meter probe was grounded), so I am close to the 5V spec. The sensor itself is another thing. I put the ohm meter on it, and the readings vary from 300 to 1700 (spec is 4.5K). The reading comes as soon as the meter probe touches the pin, then it goes back to "1" (meter default). I pulled the sensor & got the same readings.

From all indications, this is a bad knock sensor. I tested the one on my old LT1 motor and it does the same thing. I really don't remember if I replaced this when I had the motor out, but from the looks of it, it is a new part so I think I did.

I'm looking for any knock sensor experience here.

 

I've had nothing but trouble from my knock sensor, so I just defeated it. I replaced it once because the original one had an intermittent open in it, and then a few months later I was looking at the data stream and noticed tons of false knock. I screwed around forever trying to find a solution, but in the end I just did the resistor mod and the car runs much better now. I always run 93 octane anyways, so I see no use for it as long as you have a good tune, which I'm sure you do.

 

i just had PCM4less turn mine off.

 

You tested two sensors and they both tested the same? Are you sure you are doing it correctly?

 

The numbers were different, but neither was 4500 ohms (or near it). I put the black lead on a ground, and the red lead on the connector inside the sensor. I did it also with the sensor off the car with the black probe on the threaded part & got the same variable results. I'm going to test a new one @ the parts store tomorrow & see what I get.

 

Bought a new sensor @ NAPA today, it tested at 98 ohms steady. I put it in, and the car seemed to idle better,but after a few minutes, I got code 43 again. The SES light comes on for a few seconds and then goes out. I have to think this is a PCM programming issue, since I have checked the wire for voltage and have a new sensor in place.

Even with the SES light on, the scan software shows the car is in closed loop.

The car runs great, except for the surging around 2K RPM.

 

It couldn't be a programming issue. If you did a PCM exchange, the PCM MAY be faulty, but it's not very common to happen. I've also never seen a knock sensor fail. They can get pretty rusty but they will still work.

Did you check your knock module? Try swapping that too.

 

I'm not sure how often they actually fail since it isn't talked about much here. But mine did go bad at about 90k.

 

98 ohms for sensor resistance is not right.

 

Try it with a different ohm meter.... something is screwed up and I doubt its three sensors.

 

Good advice- bought a new meter today & the sensor on the old motor & the one I pulled off are 3.8K ohms. I was unable to test the one on the car since I had to use the car to buy the meter . I'll test it later & update once this is done, but I suspect it will be the same since I'm still getting the SES light.

Still getting an intermittent SES light, and a related code 43. Next step is to desensitize the sensor with the two resistor trick unless there are further words of wisdom here.

 

Why do you think "desensitizing" the knock sensor will cure your problem? The code is set when the PCM doesn't see the correct voltage in the cirucit. Either the wire isn't supplying a reliable 5V to the circuit, the sensor is not the correct resistance, or the sensor is not getting a good ground. The sensor output is a variable frequency that rides on the resulting 2.5V circuit value. The PCM could care less whether it sees a knock signal... all it is looking for it the correct circuit voltage.

 

My situation seems similar to izzyz28's above, and the resistor trick worked for him. I'm not a wiz with PCMs, but I know adding resistance in a wire will reduce the voltage. As I understand it, the PCM output is supposed to be 5 volts when the wire is disconnected, and 2.5 volts connected. Does the SES light come on when the 2.5 volts goes out of range (what is the range if so?) or drops out entirely? My SES light comes on & then goes out, indicating an intermittent problem. If I'm getting false knock (I haven't checked the knock count yet), it appears this modification could help.

EDIT-
I visited Shoebox's site & saw this wiring diagram and it says the voltage at the PCM from the KS should be 1.6 volts with the key on & 1.5 volts with the motor running.

Also, the LT4 KM was new in box when I installed it, but I will double check this as well as I have two motors & two PCMs.

Based on the additonal words of wisdom, before I do the resistor mod, I'm going to try a few more checks (sensor ground, installed resistance) and see if there is something else wrong.

EDIT
I checked the sensor wire & it was fried by a header tube. I cut out the bad part & soldered in another 12" of wire and re-routed it away from the tube, so this should fix the problem.

Thanks for all the help!

EDIT #2
The surging is greatly reduced, but I'm still getting a code 43! I used PCM software to reset the light & it comes back on within 10 seconds. To top that off, the car is now eating fanbelts, so I'm going to check all my pulleys.

EDIT #3
Found a power steering pump bolt was stripped out, hence the fanbelt issue. A couple of Heli-Coils will fix that.

 

Update-
I've been doing some other things & had to neglect the TA for a while . I got back under it a few days ago to first check pulleys- seem OK. Put on an old belt for testing & so far so good.

Now for the KS- with my new meter, I'm getting no connection between the sensor tip and ground. I tested the old sensor & got the same reading (no change on the meter). When I touch the meter tips together, the reading changes, so I know the meter is working.

Thinking logically, both sensors were at one time connected to the wire when it was fried. Is it possible for the sensor to be damaged if the feed wire goes to ground? I know this can't be a good thing since it is supplying + voltage. After the wire repair I got 4.87 volts at the sensor wire end with the wire off the sensor & the key on BTW. The wire has been re-routed & sleeved for protection to prevent the prior problem.

Tested the wire @ the PCM as per the Shoebox wiring diagram & got 4.88 unplugged & 4.69 plugged in (should be 1.6), so there is definitely a problem on the KS end.

Using PCMCOMM, I'm getting a large amount of knock at idle. The timing seems too aggresive as well- up to 41 degrees at 3K RPM. I adjusted the retard settings on the LTCC from no retard to 3 degrees per 1K RPM with no effect. The LTCC LEDs light up showing proper operation.

I found a local place to do a dynotune, but at $400 a pop, I want to get my turbo install done first & do it all at once. If the Code 43/KS/surge issue can be fixed by me, that would be great.

EDIT
I got this fixed on 2-22-05- I replaced the NAPA sensor w/ my old one & this seems to have worked. No more code, but the stumble is still there around 2K RPM. I have not road tested it yet.