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Stumbling and Misfires?

This is a discussion on Stumbling and Misfires? within the Technical / Maintenance forums, part of the General Discussion category; I have a 96 GMC C1500 with a 4.3L V6 and a 5 speed with 240K miles. The truck started ...

  1. #1
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    Stumbling and Misfires?


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    I have a 96 GMC C1500 with a 4.3L V6 and a 5 speed with 240K miles. The truck started stumbling and through a P0300 random misfire code. I cleared the code and check the fuel pressure that was about 58 static and holds with 58 to 64 running and revving to 2 K RPM’s. After searching on the forum I saw several post where the EGR valve could be the problem. I disconnected the EGR and the problem went away (drove it several days.).

    I installed a new EGR yesterday and it ran fine. This morning the stumbling is back again.
    The problem appears to go away after the truck warms up.

    My routine (morning) is stop and go to the interstate (~1.5 miles) travel down the interstate (~ 1 mile) and then the problem seems to diminish or go away. In the afternoon I do not have the problem after being parked all day.

    It seems to run like crap in the morning until it warms up. Is this the difference between open and closed loop?


    I have replaced the following in the last couple of years.
    TPS 2 years
    Idle air control valve 1 year
    Plug wires cap and rotor 5K miles
    Fuel pressure regulator 5K miles
    O2 sensors 20K
    Had the Cat checked buy a local Muffler shop before changing the EGR.
    Cleaned and checked the Spider (central sequential fuel injection), and did a non scientific flow test with a jar and marked cup. 5K miles

    Any ideas? I do have an Auto tap to look at computer.

    I have seen other problems:
    Distributor gear
    Distributor shaft
    Position Sensor in the distributor

    Thanks,

  2. #2
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    Re: Stumbling and Misfires?

    Do you have headers or anything on it? In my Camaro my plug wires were barely touching the header tubes and once it got warm it fell on it's face all the time. I threw on some shorter plugs and new wires and it was all good.

  3. #3
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    Re: Stumbling and Misfires?

    i have a similar problem right now, i did notice once i took off that hose that leads to the pvc valve that it calmed down tremendously and no shaking watsoever! only problem remains is that if i put it in any gear it still stutters and wants to die but never does! ne ideas?

  4. #4
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    Re: Stumbling and Misfires?

    The Truck is 100% stock. No headers to deal with.

    I did try spraying the plugs, wires, coil and distributor. No difference in the idle.

    I am starting to suspect an air leak post MAF. I accidentally left off the breather tube from the Passenger valve cover to the air intake (not PCV) and the truck stumbled very badly.

    I am going to try to put the MAF at the Throttle body and eliminate the entire intake path.

    Any suggestions on the best way to find a intake leak?

    I do vary the speed of the truck while it stumbles, appears to make it better, but when it wars up everything is fine.

  5. #5
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    Re: Stumbling and Misfires?

    I did a test today for fuel delivery issues.

    I mounted a Fuel pressure gauge to the windshield wiper and monitored the fuel pressure during my drive.

    The fuel pressure was at 60PSI during the drive @ 70MPH and 2100 RPM. The truck still started surging and the fuel pressure was solid. At WOT the pressure max out at 64 PSI.

    I am suspecting an intake leak. After the truck warms up or heat soaks it does not have the surging problem. Given the upper intake is plastic this would make since. I do not suspect a sensor usually electronics sensors degrade with heat.


    Any suggestions?

  6. #6
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    Re: Stumbling and Misfires?

    I did a test today for fuel delivery issues.

    I mounted a Fuel pressure gauge to the windshield wiper and monitored the fuel pressure during my drive.

    The fuel pressure was at 60PSI during the drive @ 70MPH and 2100 RPM. The truck still started surging and the fuel pressure was solid. At WOT the pressure max out at 64 PSI.

    I am suspecting an intake leak. After the truck warms up or heat soaks it does not have the surging problem. Given the upper intake is plastic this would make since. I do not suspect a sensor usually electronics sensors degrade with heat.


    Any suggestions?

  7. #7
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    Re: Stumbling and Misfires?

    i've had the same problem for the last year. usually mine does it when the air is saturated with moisture. we got a 1/2 inch of rain last night but the air was very dry. on the other hand yesterday morning it was very humid but we had no rain and my truck was a pain to get started and stumbled badly. mine has gotten so bad it is hard to start in the morning or won't start at all. my gas mileage went south after it started having problems starting.
    i'm now considering that it maybe an air flow issue. when driving it feels like the the engine is being choked when i start to give it gas.
    i've been browsing this site and others for the last year and no one has an explanation as to why the 96' v6 5speeds have the random misfire.

  8. #8
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    Re: Stumbling and Misfires?

    Kidd,

    Mine is bad enough that it happens everyday. Did you replace the fuel injection assembly?

    I ran without the MAF today and the problem is still there.

    Any suggestions?

  9. #9
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    Re: Stumbling and Misfires?

    i've only checked the fuel pressure and it was fine. i did use a can of that sea foam last summer to clean it out. i put it in the tank when it was less than 1/4 full. it did a good enough job i had to change the spark plugs.
    we're supposed to get more rain this weekend i'm going to look down the throttle body and make sure the butterflies are opening.

  10. #10
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    Re: Stumbling and Misfires?

    Well I tested the truck this morning.

    O2 sensors appear to start @ ~ .8V and transition down to .3V and oscillates back a forth. The two preCat O2's were replaced previously.

    The engine temperature allows for 3 selections one selection stays @ 10 deg F and never changes the other two warm up with the truck. One of the two started very low 10 deg F and the other started at 100 deg F with an outside temperature of 75 F. The air intake temp measured 73 deg F.

    I do not know if this truck has one temp sensor for the computer and one for the gauge.

    I sprayed around the intake and all entry points with intake cleaner no change in engine speed.

    I did notice the long term fuel trim bank 1 was –880 % and the bank 2 value was 2%. I do not were this value comes from or how it is calculated.

    The MAF appeared to increase with additional throttle.

    Questions:

    Are there multiple coolent temperature sensors on the 96 4.3L vortex V6?

    How is the long term fuel trim calculated and detected?

  11. #11
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    Re: Stumbling and Misfires?

    Same problem on my 99 silverado 4.3 vortec. I am convinced my problem is with a sticking valve. It only happens in hot weather when I really get on it. (usually around 80-90 in 5th gear). I had one of those BG engine flushes done, and it helped but hasn't completely fixed the problem. Its probably time for a valve job, but I have heard horror stories of the bottom end going out of these motors after major repairs.

  12. #12
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    Re: Stumbling and Misfires?

    Well it rained the other day and the truck barely made it home. It was so bad @ 60 MPH I thought it would break something.

    Do the distributors on the 4.3 have any type of seal to prevent moisture form getting on the distributor cap?

    It has to be ignition or electrical related.

  13. #13
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    Re: Stumbling and Misfires?

    i had this same problem and ended up replacing the entire ignition. start with the coil, then move to ignition module. my trucks entire ignition was almost 8 years old by that time though. i would say replace the plugs but it looks like you already did. but at least check for fouling and if the gap is set properly and if you have the right plugs. it should tell you the gap on the emissions sticker on the fan shroud. check your manifold gaskets too, they will cause a misfiring or stumbling if they are bad as well. only if you keep the pedal at the same position and the revs the same though. if it's alright at a steady pace than it's not a gasket problem.


    1983 Jimmy Sierra Classic-Future LSX Swap Recipient
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  14. #14
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    Re: Stumbling and Misfires?

    found this on www.OBDII.com.

    Many 1996-1997 GM engines have a problem with false codes and misfires, blown coils and alike.
    The problem with the dealer is the data they get or don't get is WRONG because the scanner only shows some codes. When when the engines reach 80,000 or so miles the "Knock" sensor will retard the timing due to increased engine noise up to 20 deg thus causing cross firing inside the dist cap and a slew of other issues. There is a GM Tech Bulletin #76-65-04 regarding a software update. http://calid.gm.com/vci/bulletins/766504.htm
    Condition: Read carefully, the MIL light and DTC codes may or may not show, and sometimes show with NO faults.
    See notes #5 and #7


    Service Information
    MALFUNCTION INDICATOR LIGHT (MIL) ON, POOR DRIVEABILITY
    Bull #76-65-04
    SUBJECT: MALFUNCTION INDICATOR LIGHT (MIL) ON, POOR DRIVEABILITY CONDITIONS
    (PERFORM FLASH CALIBRATION)
    MODELS: 1996-97 CHEVROLET AND GMC LIGHT DUTY TRUCKS
    1996-97 CHEVROLET TILTMASTER AND GMC FORWARD
    W4 MODELS
    1996-97 OLDSMOBILE BRAVADA
    WITH 4.3L, 5.0L, 5.7L ENGINES (VINS X, W, M, R - RPOS LF6,
    L35, L30, L31)CONDITION:
    AN OWNER MAY REPORT THAT THE MALFUNCTION INDICATOR LIGHT (MIL) IS ON AND/OR THE
    VEHICLE HAS ONE OR MORE OF THE FOLLOWING DRIVEABILITY CONDITIONS.
    1. 5.7L (L31) ONLY: SURGE OR CHUGGLE AT SPEEDS OF 42 TO 65 MPH WHILE AT STEADY
    SPEED OR UNDER LIGHT TO MODERATE ACCELERATION WITH THE TCC APPLIED.
    2. MIL ON WITH DTC P0172 OR P0175 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS.
    3. MIL ON WITH DTC P1406 STORED AND ROUGH ENGINE OR POOR DRIVEABILITY SYMPTOMS.
    4. WHEN OPERATING AT ALTITUDES ABOVE 5,000 FEET, AN AUDIBLE SPARK KNOCK NOISE IS
    HEARD.
    5. HESITATION AND/OR MISFIRE DURING LIGHT CRUISE CONDITIONS DUE TO IGNITION
    CROSS-FIRE WITH NO DTC STORED. THIS WILL ONLY OCCUR ON V-6 ENGINES WITH CAM
    RETARD OFFSET IN EXCESS OF 26 DEGREES AND V-8'S WITH CAM RETARD OFFSET IN EXCESS
    OF 15 DEGREES.
    6. THE MIL MAY BE ON AND A DTC STORED FOR AN ENGINE MISFIRE BUT NO MISFIRE
    OCCURRED.
    7. ENGINE EXHIBITS AN IDLE SPEED SURGE OR ROLL.
    1996 MODELS ONLY
    8. MIL ON WITH DTC P0102 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS.
    9. 5.0L (L30) + 5.7L (L31) ONLY: DIFFICULT STARTING IN EXTREME COLD (BELOW 0
    DEGREES F) CONDITIONS.
    10. 5.7L (L31) ONLY: POORER THAN EXPECTED FUEL ECONOMY WHEN HEAVILY LOADED.
    1997 MODELS ONLY
    11. MIL ON WITH DTC P0121 STORED BUT NO REPORTED DRIVEABILITY SYMPTOMS.
    12. C/K + S/T MODELS WITH EITHER V-6 ENGINE AND MANUAL TRANSMISSION: AN EXHAUST
    BACKFIRE MAY OCCUR WHILE SHIFTING WITH MODERATE THROTTLE AT ENGINE SPEEDS ABOVE
    3500 RPM.
    13. EITHER V-6 ENGINE AND MANUAL TRANSMISSION: AN ENGINE FLARE BETWEEN SHIFTS
    MAY BE NOTED WHEN THE ENGINE IS COLD.
    14. C/K, S/T AND M/L MODELS EQUIPPED WITH L35 V-6 ENGINE, AN IMPROVEMENT TO THE
    VAPOR CANISTER PURGE DIAGNOSTICS IS INCORPORATED INTO THE NEW CALIBRATIONS SO
    THAT THE TECH II CAN TURN ON CANISTER PURGE AT IDLE SPEED.
    CORRECTION:
    FOLLOW THE STRATEGY BASED DIAGNOSTIC STEPS FOR THE CUSTOMER'S REPORTED SYMPTOMS.
    IF DIAGNOSIS DOES NOT REVEAL A CAUSE, REFER TO THE TABLES BELOW FOR THE
    APPLICABLE CALIBRATION CHANGE. PERFORM PROGRAMMING PER THE LATEST TECHLINE
    INFORMATION FOR PROGRAMMING PROCEDURES.
    IMPORTANT: THE CALIBRATIONS LISTED ARE FLASH CALIBRATIONS AND ARE NOT AVAILABLE
    FROM GMSPO. THEY ARE AVAILABLE ON 1997 TECHLINE CD DISC 5 AND LATER.
    WARRANTY INFORMATION:
    FOR VEHICLES REPAIRED UNDER WARRANTY, USE:
    LABOR OPERATION LABOR TIME J-6355 USE PUBLISHED LABOR OPERATION TIME
    1996 MODEL YEAR
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL STYLE
    T-UTILITY 4.3L L35 AUTO NF2/NB6 -Z49 16232320 16235814
    T-UTILITY 4.3L L35 AUTO NF2/NB6 +Z49 16232321 16235815
    T-UTILITY 4.3L L35 AUTO NN8 -NA7/NA3 16232322 16235816
    T-UTILITY 4.3L L35 AUTO NN8 + NA7/NA3 16232323 16235817
    S/T-ALL 4.3L L35 MANUAL NF2/NB6 -Z49 16232324 16235818
    S/T-ALL 4.3L L35 MANUAL NF2/NB6 +Z49 16232325 16235819
    S/T-ALL 4.3L L35 MANUAL NN8 16232326 16235820
    S/T-PICKUP 4.3L L35 AUTO NF2/NB6 -Z49 16232327 16235821
    AND, S-UTILITY
    S/T-PICKUP 4.3L L35 AUTO NF2/NB6 +Z49 16232328 16235822
    AND, S-UTILITY
    S/T-PICKUP 4.3L L35 AUTO NN8 -NA7/NA3 16232329 16235823
    AND, S-UTILITY
    S-PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16232330 16235824
    S-PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16232331 16235825
    T-PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16232332 16235826
    T-PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16232333 16235827
    S-PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16232334 16235828
    S-PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16232335 16235829
    T-PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16232336 16235830
    T-PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16232337 16235831
    S/T-ALL 4.3L L35 AUTO NM8 16232424 16232426
    S/T-ALL 4.3L L35 MANUAL NM8 16232425 16232427
    M-VAN 4.3L L35 AUTO NF2/NB6 -Z49 16232385 16235846
    M-VAN 4.3L L35 AUTO NF2/NB6 +Z49 16232386 16235847
    M-VAN 4.3L L35 AUTO NN8 16232387 16235848
    L-VAN 4.3L L35 AUTO NF2/NB6 -Z49 16232388 16235849
    L-VAN 4.3L L35 AUTO NF2/NB6 +Z49 16232389 16235850
    L-VAN 4.3L L35 AUTO NN8 16232390 16235851
    M-VAN 4.3L L35 AUTO NM8 16232391 16232428
    L-VAN 4.3L L35 AUTO NM8 16232392 16232429
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    C/K-10/20 TRUCK 4.3L L35 MANUAL NA5/NB6 -Z49 16232310 16235832
    C/K-10/20 TRUCK 4.3L L35 MANUAL NA5/NB6 +Z49 16232311 16235833
    C/K-10/20 TRUCK 4.3L L35 MANUAL NN8 16232312 16235834
    C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 -Z49 16232313 16235835
    EXCEPT EXT.
    CAB STEP SIDE
    C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 +Z49 16232314 16235836
    EXCEPT EXT.
    CAB STEP SIDE
    C/K-10/20 TRUCK 4.3L L35 AUTO NN8 16232315 16235837
    EXCEPT EXT.
    CAB STEP SIDE
    C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 -Z49 16232342 16235843
    WITH EXT. CAB
    STEP SIDE
    C/K-10/20 TRUCK 4.3L L35 AUTO NA5/NB6 +Z49 16232343 16235844
    WITH EXT. CAB
    STEP SIDE
    C/K-10/20 TRUCK 4.3L L35 AUTO NN8 16232344 16235845
    WITH EXT. CAB
    STEP SIDE
    C/K-10/20 TRUCK 5.0L L30 AUTO NA5 -Z49 16232345 16235853
    C/K-10/20 TRUCK 5.0L L30 AUTO NA5 +Z49 16232346 16235854
    C/K-10/20 TRUCK 5.0L L30 AUTO NN8 16232347 16235855
    C/K-10/20 TRUCK 5.0L L30 AUTO NF2/NB6 -Z49 16232348 16235856
    C/K-10/20 TRUCK 5.0L L30 MANUAL NA5 -Z49 16232349 16235857
    C/K-10/20 TRUCK 5.0L L30 MANUAL NA5 +Z49 16232350 16235858
    C/K-10/20 TRUCK 5.0L L30 MANUAL NN8 16232351 16235859
    C/K-20/30 TRUCK 5.7L L31 MANUAL NA4/NA5/NM8 16232422 16256096
    C/K-20/30 TRUCK 5.7L L31 MANUAL NA4/NA5 16232355 16235864
    -NM8/Z49
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    C/K-ALL 20/30 5.7L L31 AUTO NA4/NB6 -Z49 16232356 16235865
    C/K-ALL 20/30 5.7L L31 AUTO NA4/NA5 16232357 16235866
    -NM8/Z49
    C/K-ALL 20/30 5.7L L31 AUTO NA4/NA5/NM8 16232423 16256097
    C-10 TRUCK 5.7L L31 MANUAL NA1/NA5 16232362 16235872
    -NM8/Z49
    C-10 TRUCK 5.7L L31 MANUAL NA1/NA5/Z49 16232363 16235873
    C-10 TRUCK 5.7L L31 MANUAL NN8 16232364 16235874
    C-10 TRUCK 5.7L L31 AUTO NA1/NA5/NB6/NF2 16232365 16235875
    -NM8/Z49
    C-10 TRUCK 5.7L L31 AUTO NA1/NA5/Z49 16232366 16235876
    C-10 TRUCK 5.7L L31 AUTO NN8 16232367 16235877
    C-10 TRUCK 5.7L L31 MANUAL NA1/NB6 16232368 16235878
    -NM8/Z49
    K-10 TRUCK 5.7L L31 AUTO NA1/NA5/NB6/NF2 16232369 16235879
    C/K-20 TRUCK -NM8/Z49
    K-10 TRUCK 5.7L L31 AUTO NA1/NA5/Z49 16232370 16235880
    C/K-20 TRUCK
    K-10 TRUCK 5.7L L31 AUTO NN8 16232371 16235881
    C/K-20 TRUCK
    C/K-10 UTILITY 5.7L L31 AUTO NA5/NB6/NF2 16232372 16235882
    -NM8/Z49
    C/K-10 UTILITY 5.7L L31 AUTO NA5/Z49 16232373 16235883
    C/K-10 UTILITY 5.7L L31 AUTO NN8 16232374 16235884
    K-10 TRUCK 5.7L L31 MANUAL NA1/NA5 16232375 16235885
    C/K-20 TRUCK -NM8/Z49
    K-10 TRUCK 5.7L L31 MANUAL NA1/NA5/Z49 16232376 16235886
    C/K-20 TRUCK
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    K 10/20 TRUCK 5.7L L31 MANUAL NA1/NB6 16232378 16235888
    C/K 20 TRUCK -NM8/Z49
    K-10 TRUCK 5.7L L31 MANUAL NN8 16232377 16235887
    C/K-20 TRUCK
    C/K 10/20 ALL 5.7L L31 AUTO NM8 16232383 16256102
    C/K 10/20 TRUCK 5.7L L31 MANUAL NM8 16232384 16256103
    G-VAN 10/20 4.3L L35 AUTO NB6 -Z49 16232316 16235838
    G-VAN 10/20 4.3L L35 AUTO NA5 +Z49 16232317 16235839
    G-VAN 10 4.3L L35 AUTO CV4/NN8 16232318 16235840
    G-VAN 10/20 4.3L L35 AUTO NA5 -Z49-EXP 16232319 16235841
    G-VAN 20 4.3L L35 AUTO NA5 16232338 16235842
    G-VAN ALL 5.0L L30 AUTO NA5 -Z49 16232352 16235860
    G-VAN ALL 5.0L L30 AUTO NA5 +Z49 16232353 16235861
    G-VAN ALL 5.0L L30 AUTO NF2/NB6 -Z49 16232354 16235862
    G-VAN 10/20 5.7L L31 AUTO NA5 -Z49 16232379 16235889
    G-VAN 10/20 5.7L L31 AUTO NA5/Z49 16232380 16235890
    G-VAN 10/20 5.7L L31 AUTO NA5/NM8 16232301 16256101
    G-VAN 10/20 5.7L L31 AUTO NA5/NN8 16232381 16235891
    G-VAN 10/20 5.7L L31 AUTO NB6 -Z49 16232382 16235892
    G-VAN 20/30 5.7L L31 AUTO NB6 -Z49 16232358 16235867
    G-VAN 20 5.7L L31 AUTO NA5/NM8 16227552 16256098
    G-VAN 20 5.7L L31 AUTO NA5 -NM8/Z49 16232359 16235868
    G-VAN 30 5.7L L31 AUTO NB6 -Z49 16232360 16235869
    G-VAN 30 5.7L L31 AUTO NA5/Z49 16232361 16235870
    P-CHASSIS 4.3L L35 AUTO NA5 16227523 16235852
    P-CHASSIS 5.7L L31 AUTO NA5/NM8 16235811 16256099
    P-CHASSIS 5.7L L31 MANUAL NA5/NM8 16235812 16256100
    P-CHASSIS 5.7L L31 AUTO NB6 -Z49 16187756 16235871
    P-CHASSIS 5.7L L31 MANUAL NA5 -NM8/Z49 16187887 16235895
    P-CHASSIS 5.7L L31 AUTO NA5/NB2-NM8/Z49 16187888 16235896
    W4 5.7L L31 AUTO NB6 -Z49 16235809 16235893
    W4 5.7L L31 AUTO NA5/Z49 16235808 16235894
    1997 MODEL YEAR
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    T-UTILITY FOUR 4.3L L35 AUTO NF2/NA3/NB6 -Z49 16243498 16256222
    DOOR
    T-UTILITY FOUR 4.3L L35 AUTO NF2/NB6/Z49 16243499 16256223
    DOOR
    T-UTILITY FOUR 4.3L L35 AUTO NN8 -NA7 16243532 16256224
    DOOR
    T-UTILITY FOUR 4.3L L35 AUTO NN8/NA7 16243533 16256225
    DOOR
    S-UTILITY FOUR 4.3L L35 AUTO NF2/NB6 -Z49 16243502 16256230
    DOOR
    S-UTILITY FOUR 4.3L L35 AUTO NF2/NB6/Z49 16243503 16256231
    DOOR
    S-UTILITY FOUR 4.3L L35 AUTO NN8 -NA7 16243536 16256232
    DOOR
    S-UTILITY TWO 4.3L L35 AUTO NF2/NB6 -Z49 16243504 16256233
    DOOR
    S-UTILITY TWO 4.3L L35 AUTO NF2/NB6/Z49 16243505 16256234
    DOOR
    S-UTILITY TWO 4.3L L35 AUTO NN8 -NA7 16243537 16256235
    DOOR
    T-UTILITY TWO 4.3L L35 AUTO NF2/NB6 -Z49 16243500 16256226
    DOOR
    T-UTILITY TWO 4.3L L35 AUTO NF2/NB6 +Z49 16243501 16256227
    DOOR
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STLYE
    T-UTILITY TWO 4.3L L35 AUTO NN8 16243534 16256228
    DOOR
    T-UTILITY TWO 4.3L L35 AUTO NN8/NA3/NA7 16243535 16256229
    DOOR
    S/T UTILITY TWO 4.3L L35 MANUAL NF2/NB6 -Z49 16243510 16256243
    DOOR
    S/T UTILITY TWO 4.3L L35 MANUAL NF2/NB6 +Z49 16243511 16256244
    DOOR
    S/T PICKUP 4.3L L35 AUTO NF2/NB6 -Z49 16243506 16256236
    S/T PICKUP 4.3L L35 AUTO NF2/NB6 +Z49 16243507 16256237
    S/T PICKUP 4.3L L35 AUTO NN8 16243538 16256238
    S/T PICKUP 4.3L L35 MANUAL NF2/NB6/NA3 -Z49 16243508 16256239
    S/T PICKUP 4.3L L35 MANUAL NF2/NB6 +Z49 16243509 16256240
    S/T PICKUP 4.3L L35 MANUAL NN8 -NA7 16243539 16256241
    S/T PICKUP 4.3L L35 MANUAL NN8/NA7 16243580 16256242
    S/T PICKUP 4.3L LF6 AUTO NF2/NB6 -Z49 16243512 16256245
    S/T PICKUP 4.3L LF6 AUTO NF2/NB6 +Z49 16243513 16256246
    S/T PICKUP 4.3L LF6 MANUAL NF2/NB6 -Z49 16243514 16256247
    S/T PICKUP 4.3L LF6 MANUAL NF2/NB6 +Z49 16243515 16256248
    S/T ALL 4.3L L35 AUTO NM8 16251340 16256249
    S/T ALL 4.3L L35 MANUAL NM8 16251341 16256250
    M-VAN 4.3L L35 AUTO NF2/NA3 16243516 16256251
    -Z49/NN8/NM8
    M-VAN 4.3L L35 AUTO NB7/NC1 16243517 16256252
    M-VAN 4.3L L35 AUTO NF2/Z49 16243518 16256253
    M-VAN 4.3L L35 AUTO NN8/NA7 16243581 16256254
    M-VAN 4.3L L35 AUTO NM8 16251342 16256259
    L-VAN 4.3L L35 AUTO NF2/NA3 16243519 16256255
    -Z49/NN8/NM8
    L-VAN 4.3L L35 AUTO NB7/NC1 16243520 16256256
    L-VAN 4.3L L35 AUTO NF2/Z49 16243521 16256257
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    L-VAN 4.3L L35 AUTO NN8/NA7 16243582 16256258
    L-VAN 4.3L L35 AUTO NM8 16251343 16256260
    C/K TRUCK REG 4.3L L35 AUTO -Z49 16243522 16256261
    CAB STEP SIDE
    C/K TRUCK REG 4.3L L35 AUTO Z49 16243523 16256262
    CAB STEP SIDE
    C/K TRUCK REG 4.3L L35 AUTO NN8 16243583 16256263
    CAB STEP SIDE
    C/K TRUCK 10/20 4.3L L35 AUTO -Z49/NN8 16243524 16256264
    C/K TRUCK 10/20 4.3L L35 AUTO Z49 16243525 16256265
    C/K TRUCK 10/20 4.3L L35 AUTO NN8 16243584 16256266
    C/K TRUCK 10/20 4.3L L35 AUTO -Z49/NN8 16243526 16256267
    C/K TRUCK 10/20 4.3L L35 AUTO Z49 16243527 16256268
    C/K TRUCK 10/20 4.3L L35 AUTO NN8 16243585 16256269
    C/K TRUCK 10/20 4.3L L35 MANUAL -Z49/NN8 16243528 16256270
    C/K TRUCK 10/20 4.3L L35 MANUAL Z49 16243529 16256271
    C/K TRUCK 10/20 4.3L L35 MANUAL NN8 16243586 16256272
    C/K TRUCK 10/20 4.3L L35 MANUAL -Z49/NN8 16243530 16256273
    C/K TRUCK 10/20 4.3L L35 MANUAL Z49 16243531 16256274
    C/K TRUCK 10/20 4.3L L35 MANUAL NN8 16243587 16256275
    C-TRUCK 10/20 5.0L L30 AUTO NB6 16243419 16256281
    K-TRUCK 10
    C-TRUCK 10/20 5.0L L30 AUTO NF2/NN8 16243420 16256282
    K-TRUCK 10
    C-TRUCK 10/20 K 5.0L L30 AUTO NF2/Z49 16204232 16256283
    K-TRUCK 10
    C-TRUCK 10/20 K 5.0L L30 MANUAL NF2 -Z49/NN8 16251347 16256284
    K-TRUCK 10
    C-TRUCK 10/20 K 5.0L L30 MANUAL NF2/Z49 16251348 16256285
    K-TRUCK 10
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    C-TRUCK 10/20 K 5.0L L30 AUTO NF2 -NN8/Z49 16243422 162562866
    K-TRUCK 10
    C-TRUCK 10/20 K 5.0L L30 MANUAL NF2/NN8 16251349 16256287
    K-TRUCK 10
    C/K TRUCK 20/30 5.7L L31 MANUAL NA4/NA5/NM8 16204188 16256291
    C/K TRUCK 20/30 5.7L L31 MANUAL NA4/NA5 -NM8 16243425 16256292
    C/K 20/30 ALL 5.7L L31 AUTO NA4/NB6 -KL6 16243426 16256293
    C/K 20/30 ALL 5.7L L31 AUTO NA4/NA5 16243427 16256294
    -NM8/KL6
    C/K 20/30 ALL 5.7L L31 AUTO NA4/NA5/NM8 -KL6 16204191 16256295
    C-TRUCK 20/30 5.7L L31 AUTO ZW9 16232516 16256296
    C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NB6/NF2 16243431 16256304
    -NM8/NN8
    C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NF2/Z49 16204196 16256305
    C/K TRUCK 10/20 5.7L L31 MANUAL NA1/NF2/NN8 16232484 16256306
    C/K 10/20 ALL 5.7L L31 AUTO NA1 -NM8/Z49 16243432 16256307
    C/K 10/20 ALL 5.7L L31 AUTO NA1/Z49 16204197 16256308
    C/K 10/20 ALL 5.7L L31 AUTO NA1/NN8 16232487 16256309
    C 10/20 ALL 5.7L L31 AUTO NM8 16251344 16256310
    K 10 ALL
    C 10/20 TRUCK 5.7L L31 MANUAL NM8 16251345 16256311
    K 20 TRUCK
    G-VAN 10/20 4.3L L35 AUTO NF2/NB6 16243417 16256276
    -Z49/EXP
    G-VAN 10/20 4.3L L35 AUTO NF2/Z49 16204133 16256277
    G-VAN 10 4.3L L35 AUTO CV4/NN8 16204134 16256278
    G-VAN 20 4.3L L35 AUTO NA5 16243418 16256279
    G-VAN 10/20 5.0L L30 AUTO NB6 -Z49 16243423 16256288
    MODEL-BODY ENGINE TRANS EMISSION/USAGE OLD CAL NEW CAL
    STYLE
    G-VAN 10/20 5.0L L30 AUTO NA5 -Z49 16243424 16256289
    G-VAN 10/20 5.0L L30 AUTO NA5/Z49 16204135 16256290
    G-VAN 20/30 5.7L L31 AUTO NB6 -NM8/Z49 16243428 16256297
    G-VAN 20 5.7L L31 AUTO NA5/NM8 16204143 16256298
    G-VAN 20/30 5.7L L31 AUTO NA5/Z49 -NM8 16243429 16256299
    G-VAN 30 5.7L L31 AUTO NB6 -Z49 16243430 16256300
    G-VAN 10/20 5.7L L31 AUTO NA1/NF2/NB6 16243433 16256312
    -NM8/Z49
    G-VAN 10/20 5.7L L31 AUTO NA5/Z49 16204136 16256313
    G-VAN 10/20 5.7L L31 AUTO NA5/NM8 16204130 16256314
    G-VAN 10/20 5.7L L31 AUTO NA5/NN8 16243434 16256315
    P-CHASSIS 4.3L L35 AUTO NA5 16226705 16256280
    P-CHASSIS 5.7L L31 AUTO NA5/NM8 16204158 16256301
    P-CHASSIS 5.7L L31 MANUAL NA5/NM8 16204157 16256302
    P-CHASSIS 5.7L L31 AUTO NB6 16243457 16256303
    P-CHASSIS 5.7L L31 MANUAL NA5 -NM8/Z49 16204162 16256318
    P-CHASSIS 5.7L L31 AUTO NA5/NB2 16204163 16256319
    -NM8/Z49
    W4 5.7L L31 AUTO NB6/-Z49 16235809 16235893
    W4 5.7L L31 AUTO NA5/Z49 16235808 16235894FIGURES: 0
    GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A
    "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS
    THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN
    THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE
    EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND
    SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO
    YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL
    MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON
    WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.

    May be the Knock sensor or the distributor gear.

  15. #15
    loose nut behind da wheel JeremyB's Avatar
    Join Date
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    Re: Stumbling and Misfires?

    I think the person that posted that on the other site had an Astro with a 4.3 and ended up fixing the problem with a distributor cap that has brass contacts. For some reason I don't think the distributor base has a vent hole in it for the 4.3.

    The number 5 in that TSB still makes me mad. There should be a note that says fix this problem first, they would just let someone drive around with the cam retard being way out of spec and charge them for a calibration that would do no good

    I am pretty sure there are 2 temp sensors, one at the thermostat housing for the pcm and one between cylinder 1 and 3 for the gauge
    Last edited by JeremyB; 04-02-2007 at 02:15 AM.

  16. #16
    I Hate You All, Equally.
    Join Date
    Aug 2006
    Location
    Hell, Frozen Over.
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    Re: Stumbling and Misfires?

    so this is absolutely only for the 96-97's? has there has been any accounts of this for the 98's?


    1983 Jimmy Sierra Classic-Future LSX Swap Recipient
    2002 Silverado 2500HD CCSB LT-Daily Driver
    1995 Corsica-Super-Sleeper in Progress

  17. #17
    loose nut behind da wheel JeremyB's Avatar
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    Re: Stumbling and Misfires?

    It probably does happen with 98's, I know of no major changes that could prevent anything

  18. #18
    I Hate You All, Equally.
    Join Date
    Aug 2006
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    6,071

    Re: Stumbling and Misfires?

    General motors will feel my wrath! their service department anyway


    1983 Jimmy Sierra Classic-Future LSX Swap Recipient
    2002 Silverado 2500HD CCSB LT-Daily Driver
    1995 Corsica-Super-Sleeper in Progress

  19. #19
    I Hate You All, Equally.
    Join Date
    Aug 2006
    Location
    Hell, Frozen Over.
    Posts
    6,071

    Re: Stumbling and Misfires?

    im a technician so i can weasel all the answers out of them. they think everybody is so stupid.i've called them on a few occasions. where they gave me the wrong answer or part and i just cant believe they have a job. some of them are genius' but some are so stupid it hurts


    1983 Jimmy Sierra Classic-Future LSX Swap Recipient
    2002 Silverado 2500HD CCSB LT-Daily Driver
    1995 Corsica-Super-Sleeper in Progress

  20. #20
    Registered User
    Join Date
    Jul 2004
    Location
    Texas
    Posts
    90

    Re: Stumbling and Misfires?

    I will try a new Knock sensor. My timing shows -22 deg at Idle.

    How do you set the timing on a 4.3. What parameter needs to be monitored?

    Any test for the knock sensor? I tapped on the exhaust maiafold with a wrench and did not see any difference in knock retard.
    Any other suggestions.

    Pulled out the Knock sensor tonight. Measures 102,000 ohms another post suggested 3900 ohms. My Chilton does not state a value. Anyone have an estimate?

    The sensor did not appear to respond to metal tapping on the motor. It my be dead.
    Last edited by Fast4drss; 04-02-2007 at 09:09 PM. Reason: addition to message

 

 
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