SOLVED: 98 K1500 5.7L Vortec random misfire P0300 P030x

Discussion in '96+ Vortec Performance + Computer Swaps' started by THerm, Oct 10, 2020.

  1. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    Stabbed back in, all reassembled and purrs like a kitten. I'll be back with some data logs for a follow up, but I'm very pleased with the results. No CEL after 3 startups.

    Timing advance for #1 still seems high, about 20-25 usually while underway. Anyone know what this is about? Normal?
     
  2. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    Quick update for anyone in the future that cares to know this:

    Only check engine light I got today was P0158 for a known faulty post-cat O2 sensor (no big deal but I want to fix that, too). Everything else looks to be on the up and up, and truck runs beautifully. Calculated about 17mpg on a 20 minute drive around town and into the country. NOT BAD.

    Average fuel trims:

    STFT B1- 1.02%
    STFT B2- 0.44%
    LTFT B1- 4.57%
    LTFT B2- 3.03%

    upload_2020-10-17_15-18-23.png

    This is a far cry from the thousands of misfires on cylinder 4 I was having before.

    upload_2020-10-17_15-21-53.png

    I don't know what's normal or acceptable but this is much better and truck is running much smoother now. This was a ~30 minute drive.

    Average ignition timing advance cylinder #1 was about 25°. Again, not sure if this is meaningful but the truck is running acceptably for me now.

    The only other PID I have that may be meaningful is the Knock retard (degrees), but I never saw it change from 0. I am not sure if this is the same as CMP retard or not.

    Anyways, if you're having a misfire at idle, P0300, P030x, definitely suspect the manifold gasket. As you can see in the pictures above, even some aftermarket parts were just plastic and silicone. They can sag in the middle and allow air into the intake. In my case, there was no coolant in the oil, or vice versa. Just extra air getting to a couple of cylinders, only one cylinder bad enough to throw the code.

    The aftermarket Fel Pro gasket set with the metal gasket will hopefully hold out longer than the rest of the truck. While it was a PITA getting this job done, it's totally doable without any special tools. Make sure you study up, watch all the videos you can and follow the torque specifications on the valve covers and manifold (upper manifold if you do that, too). FYI the 1A auto video for replacing the lower manifold gaskets calls for complete removal of the power steering pump pulley and bracket, and alternator bracket. Neither was necessary, and I only had to remove 1 valve cover.

    upload_2020-10-17_15-18-14.png
     
    HotWheelsBurban likes this.
  3. east302

    east302 I'm Awesome

    Messages:
    2,262
    Likes Received:
    1,134
    Joined:
    Oct 4, 2013
    Location:
    Jackson, MS
    That’s relating to spark knock and how much the timing is being retarded, so it wouldn’t be the same thing. Zero is ideal on that.

    I think the DTC P1345 for the CMP/CKP correlation doesn’t come on until it’s 14-degrees out of spec or something like that.
     
  4. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    I think that one is -2 to +2 degrees, but again I am no expert and I’m hoping I don’t need to be. From the looks of it, it doesn’t take a rocket scientist to put a distributor back in after all.
     
  5. east302

    east302 I'm Awesome

    Messages:
    2,262
    Likes Received:
    1,134
    Joined:
    Oct 4, 2013
    Location:
    Jackson, MS
    Yeah, spec for the CMP retard is zero degrees (plus or minus two) at 1,000-rpm. I think it can be off by as much as 14 or so before it trips the code. Meaning, it can be out of spec and not trip the code.

    I’d keep it on the list of things to eventually take care of, but it sounds like you got it reasonably close.
     
    THerm likes this.
  6. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    Good to know, thank you for your input. May be worth the effort to shop around mechanics in the area for one that knows about timing these engines.
     
  7. 98 Nitro

    98 Nitro I'm Awesome

    Messages:
    248
    Likes Received:
    80
    Joined:
    Apr 10, 2017
    Location:
    Indiana
    X2 on Dash Command for setting the distributor.
     
  8. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    Can you point me in the right direction on that? I cannot find a PID for this.
     
  9. east302

    east302 I'm Awesome

    Messages:
    2,262
    Likes Received:
    1,134
    Joined:
    Oct 4, 2013
    Location:
    Jackson, MS
    Did you buy the extended PID option for it? The regular version is free but doesn’t include the CMP retard.
     
  10. THerm

    THerm Newbie

    Messages:
    15
    Likes Received:
    8
    Joined:
    Oct 10, 2020
    Location:
    Missouri
    I looked again. Dashcommand for iOS is $10, then extended parameters are $10. The problem was dark mode. When I clicked on GM it was just blank, or so I thought. Just had to click through the lines to see what they are.
     
    HotWheelsBurban likes this.

Share This Page