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Thread: Tuning out Knock Sensors to get rid of code 43 in my 95 LT1

  1. #1
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    Tuning out Knock Sensors to get rid of code 43 in my 95 LT1

    I have had a code 43 in my 1995 Caprice 9C1 (LT1) and have put in new sensors, sensor connectors and bypassed the harnessed and wired the KS to the computer, bought a new ECM. I started putting ground straps everywhere and it STILL wont turn off. Its been going on for months now and I cant think of anything else except add more straps. Everythings torqued to spec and wires are right. Is it possible for me to use tunerpro RT and disable the KS so my light will be off? Sure i risk detonation but I have been for the past 6 months at least becuase nothing i have done has worked. Getting 9 mpg in something that can get up to 20 if i behave like i did before is not good for the wallet and with it not working anyway it cant be good for the car

    leadfoot from impalassforum.com said this:

    "My race 409 was blowing them all the time. Code 43 pulls 5 degrees of timing, mine would run at the track, just fine, plus my tune has KR disabled at WOT, anyway.

    Too much effort to chase issues, I just had my tuner disable code 43 in the PCM. I've never had detonation issues, but I do run an additive, just for safety's sake.

    Might not work for you, but I don't get the CEL any more."




    what do you guys think and how can i do it if i can do it? Iv thrown a new ECM, Knock sensor, wires, connectors, knock modules (stock and LT4) and it wont go away. To tune it out or not to tune it out?
    Last edited by CapriceLT1; 06-08-2012 at 11:14 AM.

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    EFI GearHead ! EagleMark's Avatar
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    Have you cleared codes either by scan tool, TP or removing power from PCM? I don't remember where you were and don't want to confuse you with someone else...

    Sure, look under flags for "Knock Sensor Diagnostic, Error 43 " and uncheck. This will disable the code 43 CEL light only and not the knock system.

    If you go further to disable Knock System Retard for timing I would look at data logs first to see how much and where knock is and how much spark is being retarded!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    Your not, I am the same person on impalassforum lol. Just trying to get as mush info as possible since I haven't gotten anywhere in the past few months. I have cleared the codes with my friends MAC tools scanner at his shop, disconnected the battery for a few hours while working on the car and it still comes back no matter what. The only thing that I have come up with is to keep adding grounds. But thats it. Next post will have a 45 min log (long i know but i watched most of it since im still learning and curious) and it with NEW ecm, wires, KS connector, old/new KS and wiring. I have new KS to install and I am just going to defect the ones I have now. Maybe I got bad sensors? I changed one and got nothing, code still there.

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    I dont think it was 45 minutes but this is with the new ECM (computer) and moving the ground that is comes off the negative battery terminal (the ninja star ground)
    Attached Files Attached Files

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    EFI GearHead ! EagleMark's Avatar
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    Looking at data does not show any ground issue, but you do have issues! That code 43c active seems to be messing up everything! Looks like a limp home situation as your closed loop, right and left O2 ready but BLM is not enabled so it's 128 BLM always, open loop. Also spark retard is pulling spark whenever you accelerate although there are no (once) knock counts. Both fans always on and never TCC lockup. So big issues!

    To check knock wires there should be 5 volts on wire key on wire disconnected from knock sensor and about 2.5 volts connected, each side. The code sets if the voltage is outside the range of 1.5-3.5V.

    To check knock sensors use an ohm meter and pretty sure they should be 4900 ohms to ground.

    This is what data log is showing, same code has three MALF flags 43a, 43c and 43d... so turning off CEL is not going to help anything except the CEL off when it's really telling you something is really wrong and making the car run really bad.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    It is running really bad. 02 sensors are new. I know turning the CEL off wont fix the problems lol. So fix the knock sensors and everything else should be ok? But thats what iv been trying to do. Not many people have stepped up. I will check all the connections and give you the readings tomorrow and we can go from there i guess. I just want her to be back to normal again :'(
    Last edited by CapriceLT1; 06-08-2012 at 07:57 PM.

  7. #7
    EFI GearHead ! EagleMark's Avatar
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    To check knock wires there should be 5 volts on wire key on wire disconnected from knock sensor and about 2.5 volts connected, each side. The code sets if the voltage is outside the range of 1.5-3.5V.

    To check knock sensors use an ohm meter and pretty sure they should be 4900 ohms to ground.
    That's the procedure for that circut, you've already done the advanced part which was replace PCM, knock module or Knock sensors. I know you said you checked wiring, but do the voltages and ohms. Being you have replaced the wires, plugs and PCM, probably check ohms on knock sensors first. Even though IIRC new they could be faulty or wrong units!

    Has that LT4 knock module you put in there ever worked? Does the LT4 module swap require LT4 knock sensors? Remember I said to pull it and look at pins in PCM and pull white cover off module to see sockets in module? Or just slip the origanal back in too?

    EDIT: Conflicting info? LT4 is OBDII which requires differant knock sensor, but everone is using OBDI knock sensor with LT4 module. So the differance must be in PCM.

    But! Tests for knock sensor ohms is differant from OBDI to II... and part numbers differant?

    OBD-I (1993-1995) knock sensor GM PART # 10456126 ACDelco #213-96OBD-II (1996-1997) knock sensor GM PART # 10456287 ACDelco #213-325

    so conflicting to me as test is:
    Key OFF. Connector off at the knock sensor. Measure the resistance between the KS terminal and ground. Resistance should be between 3300-4500 ohms (OBD-I) or 93k-107k ohms (OBD-II). If it is not, the sensor is faulty or the sensor is not making good contact with the block. Try another resistance reading from the sensor terminal to the outside metal of the sensor body
    In reading this it may be a ground issue with sensor to block as well.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    LT4 module swap DOES NOT require LT4 knock sensor. The pins are the same. what did you mean in the first quote? how do i test the sensor for 2.5 if both are connected?

    "To check knock wires there should be 5 volts on wire key on wire disconnected from knock sensor and about 2.5 volts connected, each side. The code sets if the voltage is outside the range of 1.5-3.5V."


    I am going to have my dad help me with the electrical tomorrow since its not my best area in the automotive field, add some grounds, test the circuits and wiring etc

  9. #9
    EFI GearHead ! EagleMark's Avatar
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    Just probe the knock sensor wire or plug while connected for about 2.5 volts and 5 volts disconnected. Just print that stuff for your dad, if he has been around a Digital Volt Meter it will all make sense.

    I understand the LT4 knock module plugs in and is less sensative for that aluminum head roller rocker design. I just don't understand why it also has differant KS part numbers and test procedure. But it's been done for so long I just took it for granted it worked untill I looked into it? Since it has worked for so many I don't think it's your issue, just have a hard time understanding how with the facts...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    I will let the old man look at the forum lol. Well, I lost the negative battery ground cable (baby cable that bolts to side fender) i started the car and it zapped right through it so I'm getting new negative cables since a small fire occured. Too much power went through the cable because the car has so much cancerous rust that it burned through the cable. I was in a parking lot at work put the fire out and was able to start it up and after i left the lot i lost my brakes. Got home and a newer line had a hole rubbed through it. Im going to keep this one alive as long as i can and buy a RUST FREE 9C1 or SS (so if your in NY and reading this and know someone whos getting rid of one let me know!) Shes in the driveway right now but as the week goes on I will be adding a few cables here and there.

    I was thinking a good spot would be where the negative battery cable bolts to the middle of the block, to put a cable from there to the frame. Would that be a good spot or would it "cancel" it out, do you know what i mean. Like its a bad spot, it would negatively affect the point of having the battery cable being there by adding a cable from there to the frame. Let me know what you think, and thanks! I really appreciate everything!

  11. #11
    EFI GearHead ! EagleMark's Avatar
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    Ground from block to frame is a good thing anywhere.

    I have a rust free Roadmaster for sale, but was hit in driver door... and a rust free Caprice wagon for sale, needs motor... both white woodgrain... all B bodys here are rust free, no salt.

    With any luck may have a 1996 Z28 next week with 55k, garage kept!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    More grounds never hurts. I like to run a ground from the alternator bracket directly to the battery in addition to the frame.
    I'm in your area BTW. I live out in derby but I'm downtown every day for work. I have a 94 F-Body LT1 in my wagoneer but I'm running the one year 93 ECU.

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    Man I wish you were closer I would take that RM

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    Quote Originally Posted by cmaje72 View Post
    More grounds never hurts. I like to run a ground from the alternator bracket directly to the battery in addition to the frame.
    I'm in your area BTW. I live out in derby but I'm downtown every day for work. I have a 94 F-Body LT1 in my wagoneer but I'm running the one year 93 ECU.
    I had to part out the 9C1, still on the road but the trans is going and it has WNY rust so with that plus the electrical problems, i bought an s10. Its really what i need since i use the caprice AS a truck as it is lol. I would like to have a 95 T/A With the LT1 one day so im saving the engine and some performance parts i have and parting the rest out. I will be tuning the "sten" though!! Hopefully soon.

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    Quote Originally Posted by EagleMark View Post
    Ground from block to frame is a good thing anywhere.

    I have a rust free Roadmaster for sale, but was hit in driver door... and a rust free Caprice wagon for sale, needs motor... both white woodgrain... all B bodys here are rust free, no salt.

    With any luck may have a 1996 Z28 next week with 55k, garage kept!

    NICE!!!! The "sten" has surface rust but for 120k and basically solid body for 2000, i couldnt beat it. Im going to paint it, cold air intake, maybe e-fan next summer and that it. Not bad for a 96. They are really pricey with trucks around here

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