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4.3 emission problem

Discussion in 'Chevy Trucks' started by Snoworks, Feb 5, 2003.

  1. Snoworks

    Snoworks Senior Member
    Messages: 466

    I have a 1994 Jimmy 4.3L. It will not pass emissions. I have done the following work to the truck:

    1) Rebuilt entire motor
    2) New plugs, cap, rotor & wires
    3) New egr valve
    4) Fuel injectors have been cleaned
    5) New O2 sensor
    6) New exhaust

    I am still picking up the following codes:

    #13 - O2 sensor circuit
    #43 - Knok senser circuit
    #44 - Lean exhaust

    Any suggestions! After reading a post regarding knok sensors, maybe I should replace this as well. Does anyone know where the knok sensor is on my truck. GM says its in the back of the block, but I don't know what to look for.

    Chuck B
  2. wyldman

    wyldman Member
    Messages: 3,265

    The knock sensor is usually in the side of the block (pass side),in the hole where the block drain plug would normally be located,just above the starter.The code 43 is could be the knock sensor,wiring,est module,or ecm.Most likely it's a knock sensor,or wiring to it.

    Judging by the two other codes,I would say you have an oxygen sensor circuit problem.A code 13 is set when the O2 sensor voltage does not change after 2 min from engine start.I would say,if you have replaced th O2,then you may have a connection problem between the O2,and the ECM.Is the wire touching the exh manifold anywhere ?.

    The O2 must also have a ground path,so if you have really rusty manifolds,it may not be grounding correctly.There is also a tan colored ground return wire for the O2 attached to the engine ground somewhere,just can't remember off the top of my head.Back of one of the heads maybe ?

    Both O2 codes will throw the system into open loop,which will cause your e-test failure.I assume it failed on HC's ? and possibly CO ?
  3. Snoworks

    Snoworks Senior Member
    Messages: 466

    Wyldman - Emission readings= HC's need 1.60 or less; reading 2.58. CO's need 40.0 or less; reading 41.

    So the knok sensor has nothing to due with emissions, is this correct. I will check for proper ground on the O2 sensor!

    Chuck B.
  4. wyldman

    wyldman Member
    Messages: 3,265

    Well the O2 problem is probably causing most of it.When a 43 is set i'm not sure if it locks the timing or not.If you have a scan tool you can see what effect it has on the timing advance.If it does not allow the timing advance when the 43 is set,then it will raise you HC and CO's,but lower NOx.

    The knock sensor may not be grounding properly either.Check it the same way as the O2,and there is a brown wire off the ESC module that should be grounded as well.Maybe they have the same connection point and it's loose or corroded ?

    CARDOCTOR PlowSite.com Addict
    Messages: 1,312

    check ground wire for o2 circuit at ecm. have had several gm with o2 ground problems usaually with a scan tool attached .the o2 will read over 1 volt if theres a ground problem

  6. Snoworks

    Snoworks Senior Member
    Messages: 466

    I tried to check the wiring/ground wires at the O2 sensor and the knock sensor. The knok sensor only has one wire(Green), that goes directly into a wiring harness. The O2 sensor has 3 wires (one black, two white), that runs up over the transmision and into the main wiring harnes.

    Cardoctor - Were is the ECM on this truck? How do I find the ground wire for the O2 sensor at the ECM? How do I go about testing for voltages, as you described.

    I used to be a auto mechanic in the early-mid 80's, since then things have got way more complicated. Can I use an old multimeter to check the voltage requirements?

    Chuck B.
  7. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    You need a scanner on that truck,see if the 02 sensor is working,it should be very active jumping above and below the .45 volt mark.The range is .1-.9 volts.You may have a problem here.I have seen trucks with good o2 sensors fail the test,those trucks have a lot of trouble with the central port injector,they dribble fuel,and idle is rough,runs rich,will not pass an emissions test with a real bad one.You have other issues here,but that injector is a very common item on the 4.3W (8th digit)code engine,Which i think you have .I
  8. wyldman

    wyldman Member
    Messages: 3,265

    The O2 sensor grounds through it's body,to the exhaust system.If the exhaust isn't grounded,then you will have problems.The knock sensor grounds as well through itself,to the engine block.The three wires on the O2 are O2 signal,and two wires for the heater circuit.

    Using an ohmmeter,touch one probe to the body of the O2 sensor,and the other to the battery negative post.You should have 5 ohms or less.Do the same for the knock sensor.You should also have 5 ohms or less.

    The O2 ground return to the ECM is on pin D6.You should be able to measure from D6 (key off,connector unplugged) to the battery negative and have less than 5 ohms.

    ECM is located behind glove box area in the truck.Big silver box.
  9. Alan

    Alan PlowSite.com Addict
    Messages: 1,393

    From the dark recesses of my failing memory I think the knock sensor on the 4.3 (at least in the S trucks with automatics) is located in the skirt that the bellhousing mates to. Or possibly in the block just above that skirt. Haven't seen one out in the open in a couple years so I'm a little rusty on that.
  10. wyldman

    wyldman Member
    Messages: 3,265

    Alan,you are correct.I just double checked on a few of our newer S10's,and they both have them on the back of the block above the bellhousing,right beside the oil pressure sending unit.Both the auto and manual trans are the same.

    CARDOCTOR PlowSite.com Addict
    Messages: 1,312

    sometime you have to pay the man

    at this point maybe its time to send it to the shop

  12. Snoworks

    Snoworks Senior Member
    Messages: 466

    Truck has two knock sensors, one between the 1 & 3 spark plugs, and one at rear of motor next to the sending unit. I think John D. on the right track. The truck has had a rough idle for a long time, even after the rebuild. Truck also has run very rich, since new!! If you plow with it for a long time, you get sick from the exhaust fumes. I priced out a new injector for $450.00, ouch!!! I will be checking the O2 and Knock sensor info. before purchasing.

    Cardoctor - I did pull the codes myself previously, and then brought the truck in to have them diagnose the problem. Turn out, I spent $145.00 to find out what the codes were again. A big waste of money. While talking to the technician, who had no clue about anything. I asked, what needed to be done to correct the problem, and he said the EGR Valve needed to be replaced. I told him that the EGR Valve was brand new. He said oh, yes the front one is new, but the rear EGR Valve is bad. There is no rear EGR Valve!

    They did tell me to replace the O2 sensor, which I did. I still have the same problems! Most mechanics, nowadays, just replace parts until the project is fixed. Vary rare to find a mechanic to trouble shoot for the problem, IMO.

    Thanks for the help!!!!
  13. wyldman

    wyldman Member
    Messages: 3,265

    John may be right on with the injector.I wasn't thinking it was the newer style vortec,with the central port style injection.I've been helping another member here with a 4.3L problem too,and got you confused.

    The truck should still only have one knock sensor,usually with a dark blue wire,by the oil psi sender.The green wire is usually the temp sender,which is probably what your seeing in the head between the #1 & #3 plugs.

    I will also second car doctor and John's recommendation about paying someone to put a scanner on that truck and see what's going on.Find somewhere else to take it where they know what they are doing.

    Good luck,if you need anymore help let me know.
  14. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    Snoworks, Autozone here has the injector for thr CPI for 256 bucks,I do not know how long it will last,I put one on my brother in laws 2 yrs ago,its still perfect.Its not a bad job to do,well under an hr.This is very common onm the S trucks,along with EGR problems.I put Delco injector in my 95 Blazer when the injector went bad,i got a good deal on it(it helps to have connections;).Mine started to go at 135K,rough idle,long crank times hot or cold,loading up when hot starting are all signs of it leaking.Also expect to replace the catylitic convertor next if you were running with the bad injector for any lenth of time.It gets overheated with all that raw fuel.
  15. Snoworks

    Snoworks Senior Member
    Messages: 466

    John, thanks for the tip. Autozone has it for $299.00, so you saved me $104.00 off Napa's price.

    Chuck B.
  16. Snoworks

    Snoworks Senior Member
    Messages: 466

  17. BigRedBarn

    BigRedBarn Senior Member
    Messages: 133

    It's probably just snake oil, but has anyone ever tried that stuff in a bottle that's supposed to help (guarantee, maybe?) your vehicle pass an emissions test? I don't remember seeing it lately, but seem to remember seeing it on TV 2 years ago or so.

    Maybe tham thar "Revenuers" took it off the market.
  18. CHPL

    CHPL Member
    Messages: 82

    IF you do take the plenum off to change the injector assembly be sure to look at the 2 plastic fuel lines that connect to it. I have seen one or both crack and leak fuel into the engine also. They are cheaper then the injector is to replace. I have run into a few of them .