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P0300 on Highway cruise

This is a discussion on P0300 on Highway cruise within the General Help forums, part of the LSx Technical Help Section category; Hi guys having an odd issue I just got my ls6 swap finished and tuned by frost (who did a ...

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    Senior Member redbird555's Avatar
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    2002 Camaro Z/28 Pewter

    P0300 on Highway cruise

    Hi guys having an odd issue I just got my ls6 swap finished and tuned by frost (who did a great job) and I'm getting a p0300 code on the hwy only. If i drive around town everything is fine but the minute I get on the hwy I will start getting a flashing ses light but it isnt detectable in the car the engine seems to be running fine in fact after I get off the hwy the light will go off and not come back on until next time. The first things I'm going to check are plugs and wires but being it isnt set off in town I'm not sure if it can be that? I'm going to try and do a iac relearn tomorrow per the instructions frost sent me just in case it didnt work well the first time and I'm going to be borrowing a buddies scanner tomorrow to look at the long term fuel trims just wondering if anyone here had something to add. The car does have a small exhaust leak that I'm working on getting fixed but its at the collector and I'm not throwing any o2 codes so I think its ok there.

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    Moderator Cutlass's Avatar
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    1999 Formula WS6 M6-sold
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    I've had this exact thing happen before on a car I was working on. I couldn't understand why I couldn't feel the misfires the computer was detecting. Turns out it was false misfire detection and the solution was to perform the Crankshaft Position Sensor Relearn procedure on the Tech2.
    Apparently someone replaced either the crank sensor or the engine on that vehicle and the old CKP Learn calibration was different enough to trick the computer.
    May or may not be the same thing you are experiencing. Just a thought.

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    Senior Member redbird555's Avatar
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    2002 Camaro Z/28 Pewter

    yup I've been reading up on that did hp tuners or other scan tool show signs of one side running lean or show individual cylinders misfiring? also can hp tuners do a case relearn and will it erase my ls6 tune in the computer now? the ls1 was swapped for a crate ls6 but was tuned for it however maybe that needs a case relearn

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    O U 8 1 2 Spaz's Avatar
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    Quote Originally Posted by redbird555 View Post
    Hi guys having an odd issue I just got my ls6 swap finished and tuned by frost (who did a great job) and I'm getting a p0300 code on the hwy only. If i drive around town everything is fine but the minute I get on the hwy I will start getting a flashing ses light but it isnt detectable in the car the engine seems to be running fine in fact after I get off the hwy the light will go off and not come back on until next time. The first things I'm going to check are plugs and wires but being it isnt set off in town I'm not sure if it can be that? I'm going to try and do a iac relearn tomorrow per the instructions frost sent me just in case it didnt work well the first time and I'm going to be borrowing a buddies scanner tomorrow to look at the long term fuel trims just wondering if anyone here had something to add. The car does have a small exhaust leak that I'm working on getting fixed but its at the collector and I'm not throwing any o2 codes so I think its ok there.

    mihgt be setting off the knock sensor with the leak...

    what rpms are you hitting on the highway??? what are the differences between your highway and city driving???

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    Senior Member redbird555's Avatar
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    2002 Camaro Z/28 Pewter

    I never got a knock sensor code so I dont think the exhaust leak was causing it but the good news is that I 'm pretty sure I know what did. I narrowed it down to more of an rpm thing than speed under 1500 I was fine anything over would trigger the light.I borrowed hp tuners from a friend and ran a couple tests thanks to cutlass' feedback on here I noticed when revving in park I would get 15-30 misfires on cylinders 1,3,5, and 6 so I performed a case relearn on the whole system and immediately the values went down to maybe 1-2 misfires on a couple cylinders took it for a cruise and replicated the condition under where it would do it and nothing. In fact the ses light even went off on the laptop I didnt notice barely anything when cruising so fingers crossed i think I may have got it nailed.

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