Page 2 of 2 FirstFirst 12
Results 16 to 19 of 19

Thread: ‘96 Corvette Negative Fuel Trims. Help!

  1. #16
    Fuel Injected!
    Join Date
    Jul 2019
    Location
    Orange, CA
    Posts
    757
    Quote Originally Posted by johnny_b View Post
    Update:

    new o2s seems to have made a difference in the trims.

    Now I need to resolve a code 43. I had the code turned off in the tune so I could focus on other issues the engine might have running wise.

    Brand new ‘95 knock sensors were installed when I changed the O2s. Suspect it might be a wire issue. Plan on getting the meter out and going through it.

    Does anyone have any experience or advice on resolving code 43? I’d rather not put resistors in place of the knock sensors like some people do
    Glad the new O2 sensors are doing their thing. It's an incredibly common issue.

    Speaking of common issues, so is the Code 43. I have that same code in my '95, and disabled it in the tune because it's irrelevant. The problem stems not from an actual problem with the knock sensor elements (that is, the ability for the knock sensors to do their job), but rather from the resistor GM added to them as a means to detect whether they were there or not. These resistors go bad or can be broken by rough handling, and when they do, they throw that code despite the sensors themselves continuing to work as normal. So my suggestion would just be to leave the code disabled and continue on. However, if you're concerned because the knock sensors you installed were new, you could always just test the resistance of your sensors to see if they're within spec. If they are, then yes, you have a wiring issue somewhere. If they aren't, then there's your problem, and disabling the code is all you really need to do.
    1990 Corvette (Manual)
    1994 Corvette (Automatic)
    1995 Corvette (Manual)

  2. #17
    Fuel Injected! Terminal_Crazy's Avatar
    Join Date
    Oct 2015
    Location
    Lancashire England
    Posts
    410
    [QUOTE=johnny_b;83690]Update:

    new o2s seems to have made a difference in the trims.

    Now I need to resolve a code 43. I had the code turned off in the tune so I could focus on other issues the engine might have running wise.

    Brand new '95 knock sensors were installed when I changed the O2s. Suspect it might be a wire issue. Plan on getting the meter out and going through it.

    Does anyone have any experience or advice on resolving code 43? I'd rather not put resistors in place of the knock sensors like some people do[/QUOT

    Hi
    My '95 z28 Knock sensor wires were burnt by the headers & chafing on the body, grounding out. Code would come & go so visually check the wire, a meter won't necessarily find the fault.... Pull the pcm out & test: no fault. Put it back Code 43...pull it out Test ok. put it back code 43.

    I tuned initially with the LT4 knock module. Current PCM has the LT1 knock module. No real difference once the false noise was eliminated.
    The resistor mod... inconclusive.
    I tested inputs trimmed with a Variable resistor.
    Ah found my notes:
    Made a Desensitizing circuit based on Mike Chaney's "Knock Knocker" :email mchaney@charm.net
    I used a 1K resistor and 50K Pot so I can play with the sensitivity a little and see what happens.
    connects to PCM @ D_22 (Blue Connector) - Dk Blue Wire
    could be D_21 (Blue Connector) - Lt Blue Wire
    I can't find the data i collected though i seem to remember it just ignored the quieter taps & scored the same with heavier noises.

    This might be useful:
    2017-05-23
    Just spoke with Scott Pfautsch re Knock Module

    I'm now running 97 PCM
    see http://lt1swap.com/lt1_bcc.htm
    Here you will find listed all the BCC's I've come across programming the lt1 pcm's.*
    The LT1 computers can be programmed for whatever application you have, iron head, aluminum head, 4.3L or 5.7L.*
    Where using these codes might come in handy, is if you have a 95 iron headed motor, they will have two knock sensor on the block.*
    So if you need a PCM, you should find one orignaly from an iron headed motor, so you have the correct knock sensor module.*
    The knock sensor module is located inside the pcm, under the cover with two screws.*
    This module MUST match the knock sensors you are using.

    KNOCK SENSORS: Installed in engine block

    1993 to 1997 Camaro and Firebird used 1 knock sensor.* 1993 to 1995 sensors different then 1996-97.

    1994-1995 B-Body (Caprice, Impala, Roadmaster, Fleetwood) used 2 knock sensors. 1994-95 sensors different then 1996.

    * KNOCK SENSOR MODULE: Located inside the PCM, under the cover with two screws.* 8 digit # on top of module.


    Knock sensor module 16177700 1994-1995 F-Body 5.7L
    16214661 1996-1997 F-Body 5.7L
    16214681 1996 LT4 Corvette


    SO I GOT 97 PCM with 97 LT1 Knock Module & 95 Knock Sensors ????????????????
    I think I bricked that PCM.


    DTC Codes
    43 Knock sensor Output D22 : PCM puts out 5V, sensor pulls it 2.5V DTC SET = >4.1V Open <0.78V sensor Grounded



    Hope that's some use
    Mitch
    '95 Z28 M6 -Just the odd mod.
    '80 350 A3 C3 Corvette - recent addition.

  3. #18
    Fuel Injected!
    Join Date
    Jan 2015
    Posts
    111
    Man I wish I had known it was more common to delete code 43 before I ordered new sensors. So this resistor you speak of is it inside the computer?

    this specific pcm was borrowed from my other corvette in which it never threw the 43. So I hope it’s related to the wires.
    Last edited by johnny_b; 07-24-2020 at 07:01 AM. Reason: Cant spell apparently

  4. #19
    Fuel Injected!
    Join Date
    Jul 2019
    Location
    Orange, CA
    Posts
    757
    Quote Originally Posted by johnny_b View Post
    Man I wish I had known it was more common to delete code 43 before I ordered new sensors. So this resistor you speak of is it inside the computer?

    this specific pcm was borrowed from my other corvette in which it never threw the 43. So I hope it’s related to the wires.
    The resistor is integrated into the knock sensor. This is why the part number is unique compared to previous year Corvettes. 96-97 PCMs revert to the C3-style knock sensors that have no resistors in them because the OBDII PCMs detect the presence of knock sensors by actually checking their output and doing a sanity check rather than relying on silly resistance values like the 94-95 do.
    1990 Corvette (Manual)
    1994 Corvette (Automatic)
    1995 Corvette (Manual)

Similar Threads

  1. VSS involvement with fuel trims
    By Greezmonkey in forum GM EFI Systems
    Replies: 7
    Last Post: 05-15-2020, 05:23 AM
  2. Fuel Trims Readings odd
    By Dom in forum OBDII Tuning
    Replies: 3
    Last Post: 12-29-2019, 08:40 AM
  3. Tuning Individual Cylinder Fuel Trims
    By Terminal_Crazy in forum GM EFI Systems
    Replies: 4
    Last Post: 09-03-2018, 03:30 PM
  4. negative integer in vacuum field?
    By 89S10_Project in forum GM EFI Systems
    Replies: 7
    Last Post: 10-28-2016, 09:59 PM
  5. negative vacuum readings at WOT
    By mmigacz in forum GM EFI Systems
    Replies: 7
    Last Post: 05-04-2015, 05:04 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •