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P0300 code random misfire...

This is a discussion on P0300 code random misfire... within the General Help forums, part of the LSx Technical Help Section category; I'm going to change the crank sensor tonite. It will go in for new exhaust Friday, so I will see ...

  1. #61
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    red
    02 trans am ws6

    I'm going to change the crank sensor tonite. It will go in for new exhaust Friday, so I will see what that does. Thanks for everyones help so far...

  2. #62
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    red
    02 trans am ws6

    Got the crank sensor replaced also I dropped a plug so I put a different one in. no code yet just not as ballsy... dynoed at 349 before thenew tune, long tubes and y. but its awfly hard to here any misses with the exhaust I'll keep everyone posted

  3. #63
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    00 LS1, WS6, V8 Gremlin
    96 & 98 GTPs, 64 'Cuda

    Don't forget, if you change the crank sensor you need to do a CASE learn as soon as possible.

  4. #64
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    02 trans am ws6

    How do you case learn? Is it leaving the ingnition on and pulling the fuses?

  5. #65
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    00 LS1, WS6, V8 Gremlin
    96 & 98 GTPs, 64 'Cuda

    No, you need a Tech II, Snap-On or equivalent scanner that has the capability to perform one. Any time you disturb the crank sensor (or change it) it usually ends up being just a bit off in timing, the CASE learn procedure reflashes the key areas of the PCM that depend on an accurate reading.

    Here it is with the GM Tech II, it's similar with a Snap-On MT2500.
    http://www.regalgs.org/caselearn.htm

    I realize you've eliminated almost everything else but I can't recall that I've ever seen a CPS only go out enough to cause random misfires. Most of the time I see them fail the car will run fine for a while then die unexpectedly but will usually start right back up as if nothing ever happened.

  6. #66
    gen3performance
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    2000 corvette

    missfies

    the pluged convertor could or may not set a different code.same for the crank sensor.i don't know where you are sending your injectors to be serviced but you can pick up a brand new,matched flow set from summit pretty cheap.i bought 42lb svo green injectors for i think 300 or 350.i would compare the cost of servicing to the cost of new.the service may clean them but there still could be a problem in the winding.the broken wires i have found are any where from where it enters the connector to 8" from the connector.all you have to do is pull the wire to stretch it.not to hard ofcourse but if it is broken in the insulation it will stretch at the break and you will see it.the insulation will kinda turn a lighter color from being stretched.the copper wire inside will be broken but the rubber insulation will be fine.as far as the exhaust i'm guessing that you did run the car with the exhaust still disconnected to see how it reacted.a convertor can appear fine and still be melted in the center.the rotten egg smell still makes me think the cats are your problem even though i know it is due to incorrect air fuel mixture it just seems worse when the cats are no good.the cats will set a code for ineffiecency if the post o2 picks up a rich exhaust stream.if it were plugged it would not pick up a rich condition due to no flow or very little flow at all.crank sensors due stupid things and very rarely set codes unless there is a hard failure.the relearn the other guy talked about is the crankshaft variation relearn procedure.hope this helps a little

  7. #67
    Member Phlash_riot's Avatar
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    Midnight Blue
    1999 T/A

    I can't say that this is has anything todo with it but I think after I installed my SLP lid and K&N filter it might have started then with me...but not REALLY sure. If it did start for me then could this issue have somethign todo with the MAF not being set or computer not being set for the high amounts of air that is flowing now adversed to before the install?

    Also I talked to the GM dealership out here in San Diego where they also sell high performance crate engines he commented on the injectors as many have already said but he also commented on the TB and too much air getting by due to the wearing down of the TB plate over time... any comments on that?
    As far as the injectors he said aht I should bring them in off of the car and have them machine cleaned. He quoted my 100 bucks for the job or I could buy a injector & TB cleaning 3 part kit that sells for about 45 but not nearly as good as the machin cleaner/tester? But at $100 i might as well look into a small upgrade in injectors aa it would be only about 2 times the price of the cleaning and then i could go further on them as far as upgrade in the future are concerned

    So if i do get injectors i would say that I should go with 32lbs-ers? we have 28lbs stock if i remeber rightly and 32s shouldn't need a tune to run OK after install but I am not sure about that though.

  8. #68
    Member Phlash_riot's Avatar
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    Midnight Blue
    1999 T/A

    Any update on this from anyone? I still have the same issue but as I have moved to CT recently, I have not had the time todo work on her nor the garage area todo it. I just got my new house last week and hope to delve into it in the near future.

  9. #69
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    2002 Camaro Z28 35th

    OK let me add my story to the mix:

    '02 Camaro Z28 has been running super since I bought it. Has K&N FIPK and Corsa Cat Back exhaust. On the way to the shop for yearly inspection (can you believe it), SES light starts blinking, engine runs rough, exhaust smell. Code shows #7 lots of misfires, #2 half as much. Mechanic has now gone through most of the diagnostics - replace gas filter, clean all injectors, swap injectors, replace #2 injector with reman, swap plugs, swap coils, replace Crank Position Sensor and did two relearns. He hasn't done a smoke test for intake leaks or a compression test because two cylinders started acting up at the same time. Searching Archives on different forums has turned up both Vacuum leak behind intake manifold (although I don't think this would be specific to two cylinders) and weak/broken valve springs. Does anybody have a clue as to what might be going on? It seems I would have a better chance of winning the lottery than to have a cylinder specific item like valve springs, coil, etc. on both cylinders fail at exactly the same time. Is it possible that a sensor (O2 or MAF) could cause multiple cylinder specific problems on two cylinders at the same time?

  10. #70
    Just another Joe Eagle's Avatar
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    2002 WS6

    REMOVE your PCM connectors and check them for water and/or corrosion. I had all sorts of misfires, p0300, p0301, p0306, p1416, p0128, as well as p0420 (drivers cat malfunction). Turns out my PCM took on some water and corroded the connection. When I found it I was sure I had ECT issues. Was going to get in there and ohm out wires... but instead I found water in the PCM connections.

    I also had a few times where the SES light would blink (multiple codes registering at the same time or P0300 DTC being thrown).

    BTW, plugged cats should throw p0420 or p0430 codes.

    -Eagle
    Last edited by Eagle; 06-20-2007 at 07:09 PM.

  11. #71
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    2001 ws6 trans am ramair

    ok here i go got my 2001 ws6 aboyt 2weeks ago it was running super good about 6 days ago the ses light come on so i took it to mti here in houston and the p300 code comes up so the there tells me lets put new plugs and wires i say ok he say it will go away it did for like 2 days but now its back and its running bad it will die out if i dont let it get warmed up any one know what can it be help thanks

  12. #72
    Retired NOT tired SteveC's Avatar
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    2001 Z28 (Sara)

    Thumbs up

    Quote Originally Posted by 2001NBMZ28 View Post
    Try resetting the PCM, think I read somewhere that'll reset the crank position sensor - easy to do and won't hurt to try, just grumpy idle for a few minutes until it relearns. Just in case you need it:

    PCM Reset
    Turn key on, don't start car
    Pull PCM BATT aand PCM IGN fuses in engine compartment
    Wait 5-10 min
    Turn ignition off
    Replace fuses
    You are correct, the P0300 will also trigger P1336 (Crankshaft Position System Variation not learned), which the PCM will then fire left bank, right bank instead of the normal cylinder firing sequence.

    If this is the case, you will need a tech 2 device (dealer) or I believe EFI live to perform the Crankshaft Position System Variation Learning Proceedure.

    Good luck to you

  13. #73
    Member Phlash_riot's Avatar
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    Midnight Blue
    1999 T/A

    In case anyone is keeping updated on this:

    Replaced the EGR since i never got it deleted from the computer and still had the "sputtering"
    reset the PCM engine runs a little btter but sputtering is now a stutter. it actually got worse. I'll drive it around more tomarrow and see if it gets any better after more driving and the computer relearns everything.

    Next thing I am goin g to try is replacing all of the injectors

    Have alrady replaced:
    fuel filter
    spark plug wires : MSD
    Spark Plugs: Bosh platniums
    Air Filter
    New heads: replaced for other reasons but problem was there before and after
    push rods
    vavles and valve spings checked by ROB
    rockers are ok visually and moved freely when out
    no noticle damge on cam shaft
    O2 senser visual check appears fine
    Also I am NOT throwing any codes

    Also going to check MAF - Clean it
    Clean other sensors that cna get gotten to

    Well hopefully someone out there has some new info. I will be keeping a close eye on this thread or you can email me
    Phlash_riot@yahoo.com

    EDIT: The weather is mid to upper 70s and LOW humidity

    EDIT 2: Just found this
    "TSB #990604005A -- SOME OWNERS MAY COMMENT ON DRIVEABILITY SYMPTONS OF LONG OR HARD STARTS, CHUGGLE, ROUGH IDLE AND LIGHT OR INTERMITTENT MISFIRE DUE TO CLOGGED FUEL INJECTORS. *TT (NHTSA ID #619360, APRIL 01 2001)"

    What is the "NHTSA"?
    makes me go Hrmmmmm.... .... .... .. .
    Last edited by Phlash_riot; 07-02-2007 at 07:43 PM.

  14. #74
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    Quote Originally Posted by Phlash_riot View Post
    In case anyone is keeping updated on this:

    Replaced the EGR since i never got it deleted from the computer and still had the "sputtering"
    reset the PCM engine runs a little btter but sputtering is now a stutter. it actually got worse. I'll drive it around more tomarrow and see if it gets any better after more driving and the computer relearns everything.

    Next thing I am goin g to try is replacing all of the injectors

    Have alrady replaced:
    fuel filter
    spark plug wires : MSD
    Spark Plugs: Bosh platniums
    Air Filter
    New heads: replaced for other reasons but problem was there before and after
    push rods
    vavles and valve spings checked by ROB
    rockers are ok visually and moved freely when out
    no noticle damge on cam shaft
    O2 senser visual check appears fine
    Also I am NOT throwing any codes

    Also going to check MAF - Clean it
    Clean other sensors that cna get gotten to

    Well hopefully someone out there has some new info. I will be keeping a close eye on this thread or you can email me
    Phlash_riot@yahoo.com

    EDIT: The weather is mid to upper 70s and LOW humidity

    EDIT 2: Just found this
    "TSB #990604005A -- SOME OWNERS MAY COMMENT ON DRIVEABILITY SYMPTONS OF LONG OR HARD STARTS, CHUGGLE, ROUGH IDLE AND LIGHT OR INTERMITTENT MISFIRE DUE TO CLOGGED FUEL INJECTORS. *TT (NHTSA ID #619360, APRIL 01 2001)"

    What is the "NHTSA"?
    makes me go Hrmmmmm.... .... .... .. .
    NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION or big government for short.

  15. #75
    Senior Member Too Fast's Avatar
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    Quote Originally Posted by Phlash_riot View Post
    I can't say that this is has anything todo with it but I think after I installed my SLP lid and K&N filter it might have started then with me...but not REALLY sure. If it did start for me then could this issue have somethign todo with the MAF not being set or computer not being set for the high amounts of air that is flowing now adversed to before the install?

    Also I talked to the GM dealership out here in San Diego where they also sell high performance crate engines he commented on the injectors as many have already said but he also commented on the TB and too much air getting by due to the wearing down of the TB plate over time... any comments on that?
    As far as the injectors he said aht I should bring them in off of the car and have them machine cleaned. He quoted my 100 bucks for the job or I could buy a injector & TB cleaning 3 part kit that sells for about 45 but not nearly as good as the machin cleaner/tester? But at $100 i might as well look into a small upgrade in injectors aa it would be only about 2 times the price of the cleaning and then i could go further on them as far as upgrade in the future are concerned

    So if i do get injectors i would say that I should go with 32lbs-ers? we have 28lbs stock if i remeber rightly and 32s shouldn't need a tune to run OK after install but I am not sure about that though.
    Well, the light bulb went off over my head! You say this may have started after the K&N install, I have heard many times that excess oil from the K&N will get your MAF dirty. That could be the whole problem. Clean it and go from their. There is some specific MAF cleaner available, but at work I use some carb cleaner than finish it with brake clean.

  16. #76
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    Quote Originally Posted by Too Fast View Post
    Well, the light bulb went off over my head! You say this may have started after the K&N install, I have heard many times that excess oil from the K&N will get your MAF dirty. That could be the whole problem. Clean it and go from their. There is some specific MAF cleaner available, but at work I use some carb cleaner than finish it with brake clean.

    Good idea. I will get some cleaner today. mabye tonight i will have a nice running car again.

    mabye that's why it wasn't thowing a code then
    Last edited by Phlash_riot; 07-03-2007 at 07:23 AM.

  17. #77
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    Midnight Blue
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    ok cleaned out the MAF and even the TB and new STP filter. well still symptomatic.... not as much...but still there. have to drive it around some more since i reset the PCM again after it threw a bunch of codes from the TB cleaner i dumped down it. running out of things that it could be so that it kinda nice and the only expesive one it the injectors.

    So if using a K&N filter is no good for our cars what is the best one out there?

  18. #78
    SS#430 1 of 74 7camaro7's Avatar
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    I got this damn PO300 code too! I've done plugs, wires, and 4 coil packs. It got better and tomorrow I'll do the other 4 cp's. I think I'll be back in the game fellas. I've been missing my SS for over a month for the pressure plate going out and all this other bs. I pray nothing else bad happens to me, my car, or my family. For me life's been sucking lately. I'm in college and I quit my job about 2days before my code kicked in and as I'm on my way to fill out like 10 applications that's when everything goes bad. Thank God for grannies! Mine has been there to help me countless times. I'll let you guys know how the new coil packs work on my ride.

  19. #79
    Just another Joe Eagle's Avatar
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    Quote Originally Posted by Phlash_riot View Post
    ok cleaned out the MAF and even the TB and new STP filter. well still symptomatic.... not as much...but still there. have to drive it around some more since i reset the PCM again after it threw a bunch of codes from the TB cleaner i dumped down it. running out of things that it could be so that it kinda nice and the only expesive one it the injectors.

    So if using a K&N filter is no good for our cars what is the best one out there?
    Did you pull the two large ECM connections and check for any thing wrong there? I had wierd issues with P0300 and others too... ended up I had water in one of the two connections which was slightly shorting some of the connections in there...

    -Eagle

  20. #80
    Member Phlash_riot's Avatar
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    Quote Originally Posted by Eagle View Post
    Did you pull the two large ECM connections and check for any thing wrong there? I had wierd issues with P0300 and others too... ended up I had water in one of the two connections which was slightly shorting some of the connections in there...

    -Eagle
    Not sure what ECM connections you are talking about but I will go look under my hood and see if I can figure out what it is you are trying to point me to.

    Engine is running a little bit smother... little bit. but now it seems to Lag until i hit about 3500RPM at WOT then it take off. mabye the computer is learning a bit more see how it goes since i have only put 3-5 miles in it since resetting PCM.

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