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Thread: p0300 Tried almost everything....

  1. #1

    p0300 Tried almost everything....

    2002 5.3L LS in a 1998 tahoe.

    I have had a bad misfire from day one.... took my plugs off the ecm and checked continuity on all of the injector and coil wires... turned out 2 of my injectors were plugged into the wrong place. luckily they were pins not used... Inj 3 was plugged into the inj 2 pin and inj 2 was plugged into a dead pin. So I got that fixed and it ran ALOT smoother... Cleared the codes and drove it down the street and back... still hesitating and it died on me in my driveway.. Pulled the new codes... p0300 random misfire....

    So here is what i did.

    Checked each injector to make sure it was in the correct pin on the ecm.

    #1 C1 - 36
    #2 C1 - 4
    #3 C1 - 3
    #4 C1 - 44
    #5 C1 - 76
    #6 C1 - 37
    #7 C1 - 43
    #8 C1 - 77

    checked 12V to each injector.
    checked resistance of each injector 12.9 - 13.0 across the board..
    checked signal wire for each coil to ecm. All are correct.

    #1 C2 - 26
    #2 C2 - 67
    #3 C2 - 69
    #4 C2 - 27
    #5 C2 - 68
    #6 C2 - 28
    #7 C2 - 29
    #8 C2 - 66

    Checked 12V to each coil.
    Checked ground to each coil
    Then I found something interesting... Cylinders 7 and 4 seem to be the problem..
    My headers are new and I let it run through a small heat cycle and the tubes off of those cylinders are still glossy paint where as all the other cylinders are turning colors due to heat...

    So I checked resistance of those two coils from the output to the ground terminal...
    I got 5400ohms for both which I hear is a normal reading..

    So I tested my fuel pump.. Hooked up a gauge and got 52 psi at idle and no drop in psi at all during revving...

    Fuel filter is new..
    Plug wires are new...
    I checked the plugs the other day and found 1 wet plug on the cylinder with the mis wired injector.. Replaced it..


    Update... I also replaced all 8 plugs and no improvement. Moved plug wires around to see if the dead cylinders followed but nope still the same.. I even swapped coils for a good cylinder and the problem didnt follow..
    Any ideas on what to do now?
    Last edited by 2drhoe; 04-07-2014 at 06:54 PM.
    98 Tahoe 4WD. 2002 5.3L LS swap.. Lowered on shackles and keys. 22" Escalade rims with custom SS centercaps, 2 tone red and gunmetal paint with silver pinstripe.SS front bumper cover.Rear roll pan. Street scene mesh grille inserts.debadged and demoulded.6K HIDs and hidden yellow fogs.Billet bowtie.K&N intake system. Flexalite Efans.Dual optima batteries. Pacesetter shorties High Flow cats. Flowmaster muffler with single exit exhaust. Escalade Seats and console. SS headrests. Remote Twin turbo build in progress!!!

  2. #2
    Join Date
    Feb 2013
    Location
    Henderson, NC
    Posts
    12
    I know it sounds far fetched and beyond but I had the same problem and by accident found out the distributor was the problem ...there was a crack in the shaft letting out vacuum so a misfire happened .....I replaced the plastic shaft distributor with an aluminum shaft aftermarket distributor ans those problems were solved

  3. #3
    thanks for the suggestion but that would be super far fetched considering the fact that my 5.3 doesnt have a distributor... I guess I should have cleared that up... issues are with the 2002 5.3L LS engine.
    98 Tahoe 4WD. 2002 5.3L LS swap.. Lowered on shackles and keys. 22" Escalade rims with custom SS centercaps, 2 tone red and gunmetal paint with silver pinstripe.SS front bumper cover.Rear roll pan. Street scene mesh grille inserts.debadged and demoulded.6K HIDs and hidden yellow fogs.Billet bowtie.K&N intake system. Flexalite Efans.Dual optima batteries. Pacesetter shorties High Flow cats. Flowmaster muffler with single exit exhaust. Escalade Seats and console. SS headrests. Remote Twin turbo build in progress!!!

  4. #4
    Join Date
    Jan 2012
    Location
    DFW, TEXAS
    Posts
    594
    distributor? put the pipe down or pick it back up! then step away from the computer.
    OP have you done a compression test? Any top end noise(if possible)?
    Have you moved injectors and coils to another cylinders to see if it(misfire) moves? Do you have a noid light? and/or pull that cyl plug and verify a spark.

  5. #5
    Join Date
    Jun 2011
    Location
    Rogers, Ar
    Posts
    51
    Might want to hook up a noid light and verify the injectors in question are being controlled properly

  6. #6
    i think that is my next test....
    98 Tahoe 4WD. 2002 5.3L LS swap.. Lowered on shackles and keys. 22" Escalade rims with custom SS centercaps, 2 tone red and gunmetal paint with silver pinstripe.SS front bumper cover.Rear roll pan. Street scene mesh grille inserts.debadged and demoulded.6K HIDs and hidden yellow fogs.Billet bowtie.K&N intake system. Flexalite Efans.Dual optima batteries. Pacesetter shorties High Flow cats. Flowmaster muffler with single exit exhaust. Escalade Seats and console. SS headrests. Remote Twin turbo build in progress!!!

  7. #7
    Join Date
    Feb 2011
    Location
    Barnwell, SC
    Posts
    471
    I had the same problem. My injectors were clogged.
    99 Silverado 4.8l : Soon to be 80E swapped, then 6.0 swapped, ......
    05 Yukon Denali 6.0l : Nelson Performance Tune, ......
    8X S10 Blazer on a 8X 3/4 ton frame : 5.3l swapped, Nelson Performance tune, Schoenfeld LT's, 226/226 .598/.598 112, TH350, planetary doubler, NP 205, locker, spool, 38's, ......
    Quote Originally Posted by blacksss46 View Post
    couldn't agree more. its like boobs you'll get a C and end up wanting a D...just get the bigger one and be happy

  8. #8
    hadnt thought about that.... makes sense seeing that this engine has probably been sitting for a year almost..
    98 Tahoe 4WD. 2002 5.3L LS swap.. Lowered on shackles and keys. 22" Escalade rims with custom SS centercaps, 2 tone red and gunmetal paint with silver pinstripe.SS front bumper cover.Rear roll pan. Street scene mesh grille inserts.debadged and demoulded.6K HIDs and hidden yellow fogs.Billet bowtie.K&N intake system. Flexalite Efans.Dual optima batteries. Pacesetter shorties High Flow cats. Flowmaster muffler with single exit exhaust. Escalade Seats and console. SS headrests. Remote Twin turbo build in progress!!!

  9. #9
    getting close to the end of my rope.... Still no combustion on cylinders 4 and 7. I have checked all of my pins.. moved and cleaned both of the injectors and both of the coils... still nothing in those 2 cylinders.... I dont get it.... What should I see if i probe he injector outputs on the ECM for those 2? any specific voltage or pulse? What about the coils?
    98 Tahoe 4WD. 2002 5.3L LS swap.. Lowered on shackles and keys. 22" Escalade rims with custom SS centercaps, 2 tone red and gunmetal paint with silver pinstripe.SS front bumper cover.Rear roll pan. Street scene mesh grille inserts.debadged and demoulded.6K HIDs and hidden yellow fogs.Billet bowtie.K&N intake system. Flexalite Efans.Dual optima batteries. Pacesetter shorties High Flow cats. Flowmaster muffler with single exit exhaust. Escalade Seats and console. SS headrests. Remote Twin turbo build in progress!!!

  10. #10
    Join Date
    Jan 2012
    Location
    DFW, TEXAS
    Posts
    594
    don't give up, there is an open circuit in the wiring or bad pcm
    Last edited by blacstar; 04-13-2014 at 07:48 PM. Reason: punctuation

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