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Damn P0300 code again

This is a discussion on Damn P0300 code again within the General Help forums, part of the LSx Technical Help Section category; Guys I just had a headswap done on my '00 TA. Now pre swap the car was not driven and ...

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    Senior Member Hurley711's Avatar
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    Damn P0300 code again

    Guys I just had a headswap done on my '00 TA. Now pre swap the car was not driven and sat in the garage for 1 1/2 yrs. Only driven once every few weeks. Before the swap P0300 went off. No major issues driving it, but the code was there. Now fast forward, head swap is done, new plugs installed along with a new fuel filter. Wires were added pre swap before the car sat. The day I got it back and drove it there was a slight hesitation at low RPM, but after getting past 1400 or so the car drove fine, it ran right through the hiccup. I drove the car 225 miles round trip to the mountains, same thing sometimes mild hesitation, but otherwise no problems. Today took it to lunch, 1st real city driving since the swap, and it progressively got worse. By the ride home, EVERYTIME I came to a complete stop it idled ROUGH, and from idle to 1700 RPM range in every gear the car just studdered, and putted and didnt want to drive unless I put the pedal throught the damn floor. WTF??? I run 93 octane if that helps any.

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    Veteran Hi-Po's Avatar
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    Since it was doing it before the swap, all plugs have been changed, (and gapped by you), and fuel filter is new also. I say problem lies in coil packs. One or more of them. What did your old spark plugs look like? That would be a good indictator of the problem cylinder. No chance you have access to a good scanner do you? Stock fuel pump I presume? IMO, I would look at the fuel pump since you *think* its only doing it at low RPMs. This is also where a good scanner/logger would be great help. Would not hurt to get a fuel pressure reading off the rail ethier. Thinking more into it, P0300 is a random misfire, not just a singled out cylinder. Hmmm.

    Are your cats removed? 02 extensions being used?

    I would look at:

    Fuel pump
    Plug wires being completely snapped on
    Coil pack(s)
    Properly gapped plugs
    o2 extensions
    and condition of plug wires. Make sure none of them have touched a headers... or wore though.

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    Senior Member Hurley711's Avatar
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    Quote Originally Posted by Hi-Po View Post
    Since it was doing it before the swap, all plugs have been changed, (and gapped by you), and fuel filter is new also. I say problem lies in coil packs. One or more of them. What did your old spark plugs look like? That would be a good indictator of the problem cylinder. No chance you have access to a good scanner do you? Stock fuel pump I presume? IMO, I would look at the fuel pump since you *think* its only doing it at low RPMs. This is also where a good scanner/logger would be great help. Would not hurt to get a fuel pressure reading off the rail ethier. Thinking more into it, P0300 is a random misfire, not just a singled out cylinder. Hmmm.

    Are your cats removed? 02 extensions being used?

    I would look at:

    Fuel pump
    Plug wires being completely snapped on
    Coil pack(s)
    Properly gapped plugs
    o2 extensions
    and condition of plug wires. Make sure none of them have touched a headers... or wore though.
    Plugs were gapped by bro in law(GM mechanic) O2 have extensions, fuel pump is stock, other stuff I will have him check when he is here tomorrow for lunch. ORY no cats THX this is fcking pissing me off.

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    Veteran Hi-Po's Avatar
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    What I am saying about the 02 extensions is that they need to be checked. Did you make them?

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    Moderator Cutlass's Avatar
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    Quote Originally Posted by Hurley711 View Post
    Now pre swap the car was not driven and sat in the garage for 1 1/2 yrs
    .....I drove the car 225 miles round trip to the mountains,
    First thought was bad old gas but sounds like you put some miles on it and got the old gas out, correct?

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    Senior Member Hurley711's Avatar
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    Quote Originally Posted by Cutlass View Post
    First thought was bad old gas but sounds like you put some miles on it and got the old gas out, correct?
    YEs old gas is long gone, she's had 3 tanks full of 93 octane since the swap, plus I had STABIL in there while the car sat.

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    Senior Member Hurley711's Avatar
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    OK here is an update. Drove the car today with a scanner and it bogged down real bad while driving and SES was flashing. Plugged in scanner and code came up for O2 lean bank. So even after that we cleaned the MAF, and sprayed cleaner all around the intake to check for a vacuum leak, which came up negative. Tomorrow my bro in law is bringing home his scanner from work to check which cylinders are misfiring and we are going to replace the O2.

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    LS1 or bust b.lee's Avatar
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    STABIL IS SHIT
    Every time I have used it in my quads and whatnot it has F'ed my plugs.

    Might need another set of plugs, or just a few. Just a stabil guess. I never use it anymore. Used it twice and both times it F'ed me. (Banshee / Boat)
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    Moderator Cutlass's Avatar
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    I thought you didn't need to (or weren't supposed to) use Stabil with 2 stroke gas/oil. I think the banshee is a 2 stroke right? And I guessing the boat might be too?
    Anyways Stabil has been good stuff for me. Not sure its intended to last a year and a half though??

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    The car was occasionally driven in between sitting, and since the car has had 3 fulls tanks put in. Also All new plugs and wires along with a new fuel filter. I am hoping the O2 sensor code is what I was looking for, the easy way out. Bad O2 sensor could cause random misfires correct?

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    Quote Originally Posted by Hurley711 View Post
    The car was occasionally driven in between sitting, and since the car has had 3 fulls tanks put in. Also All new plugs and wires along with a new fuel filter. I am hoping the O2 sensor code is what I was looking for, the easy way out. Bad O2 sensor could cause random misfires correct?
    Clean the maf/change 02 sensors IMO

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    Make sure to check your map sensor. You said you swapped your heads etc and the MAP sensor could be easily leaking. O2's with 70k on them are about ready to be changed anyways. Also check your TPS voltage and make sure your TPS is working properly. This the map sensor can throw that could and not so much the TPS but the TPS could make the car seem like it's firing down low.

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    Cleaned MAf didnt help and O2 are not stock they were fouled before and were replaced after header install about 25k miles ago.

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    Ok did you check the MAP? Make sure it's sealed correctly on your intake?

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    Quote Originally Posted by JESSIE P View Post
    Ok did you check the MAP? Make sure it's sealed correctly on your intake?
    Yep checked all of that, pulled and checked all the injectors, cleaned the MAF and sprayed around the whole intake and everywhere imaginable with cleaner to see if it would surge from sucking it in and got nothing.

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    I think you're really at a point to where you're going to have to log the car and see what your fuel trims look like and see what cylinders are misfiring. You could have trash in an injector or something that got past the fuel filter. Logging the car will at least point you in a direction.

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    Senior Member Hurley711's Avatar
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    Quote Originally Posted by Hi-Po View Post
    What I am saying about the 02 extensions is that they need to be checked. Did you make them?
    No these were aftermarket extended O2s from TSP

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    Senior Member Hurley711's Avatar
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    update bro in law brought home his scanner form the dealer and it showed P0301 cylinder 1 misfire. So he swapped the spark plug wire from that cylinder to cylinder 3 to see if it followed and........................nothing. We drove it for over 10 miles and simulated every kind of driving condition and the car bogged only once during the initial 30 secs after he changed the wires. SO tomorrow is a new day, Im tired of driving around waiting for something bad to happen tonight. Usually the SES light came on immediately after it was cleared. Oh well, whoever thought I would want something to go wrong??

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