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Thread: Started getting a lot of KR at the track, and don't know why.

  1. #1
    Tuner in Training
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    Oct 2013
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    Started getting a lot of KR at the track, and don't know why.

    I was at Daytona this past weekend running my 3.8 Camaro.

    It ran perfect for the first three sessions on Saturday, but on the second to last session on Sunday it was way down on power at times, and the CEL light flashed. The only code in the PCm was P0300. In reviewing the logs the times when it was down on power and the CEL flashed it was maxed out KR.

    Here is a log from Saturday (Daytona5) when it was running great and Sunday(Daytona7) when the issue started. Also, the current PCM tune.
    Dayton5.hplDaytona7.hpl110114rcomps.hpt

    I checked the engine over and can't find anything mechanically wrong with it.

  2. #2
    Tuning Addict 5FDP's Avatar
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    Pull the spark plugs.

    If you see no damage, replace them anyway. Thats just one step in fixing a misfire code. If it continues, then you know that you have with a coil pack problem or the ignition control module itself has died.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Tuner in Training
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    Oct 2013
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    I checked the plugs and they all looked good.

    I'm leaning away from a coil as the PCm never nailed it down to one or two cylinders, the ICM however could be the culprit, I try swapping it out with one of my spares.

  4. #4
    Tuner in Training
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    Before starting, its always best to scan the car with an OBD-2 scanner (Autotap, Alex Peper scanner, HPTuner, etc...) so that we know what cylinders are misfiring. One could always just start visually changing parts randomly but that can get expensive fast and is a waste of time and money.

    P0300 is the general code, if scanning, it should including something like P0302 (for cylinder #2), or whatever.

    Ok, you've scanned the car and now know what cylinders are misfiring. Best way to address it is in the following order:

    1. Spark plug(s)
    2. Spark plug wire(s)
    3. Coil pack(s)
    4. Fuel injector(s)
    5. Ignition module

    - After scanning the car, remove the spark plug from the cylinder that is misfiring and examine it. Replace if needed. If you cannot remember the last time the plugs were all changed, its time to do it. Platinum plugs will last a lot longer, but I would suggest replacing them after 50,000 miles (80,000km). Copper plugs give me better performance, and I change mine once a year at the very least. Reading up on Overkill's sparkplug article is always a good thing (http://www.oqcgp.com/forum/kb.php?mode=article&k=3 ). I always put a nice coating of dielectric grease on the threads to prevent them from seizing and on the head where the wire connects. If its not the plugs, we move on up the chain a little further.

    - The stock spark plug wires are very good for 90% of us here. Only the very hard core high-end modders need even consider top quality wires. Taylors have a nasty reputation of being good, but being able to only last less than a year before the misfires start. A fast way to diagnose if its the wire is swap it with the one from the cylinder next to it and see if the misfire moves with it to the other cylinder. If it does, its best to change all wires. If one is bad, chances are good that the others are not in peak shape either. Use plenty of dielectric grease on both contact points of the wires to prevent corrosion, another way that misfires can start. Remember to place them on the right cylinders, otherwise you will get misfires of epic proportions.

    - Next up the chain are the coil packs. Since we have scanned we KNOW what cylinders are misfiring. Again, the stock parts are of excellent quality and only the very hard core high-end modders need even consider top quality aftermarket coils. A big giveaway that its the coil, is that we get misfires on TWO cylinders and the cylinders match the ones that are controlled by a single coil. Some say that if a coil becomes defective, that it is possible that one cylinder misfires. I *highly* doubt that as there is one set of circuitry in that coil for both cylinders. Before replacing the coils, remove them, clean off any corrosion and use a thin layer of dielectric grease on the wire contact points and underneath where they contact the ignition module. Test and see if the misfire has disappeared. If not, swap the coil to another position and see if the misfires have moved. If it has, replace the coil.

    - Fuel Injectors... I've placed them here because 99% of the time the misfires come from the above possibilities a lot more often than the injectors. If you have misfires even after addressing all the points above, chances are pretty good that you have a dirty or defective injector. To address this issue, we have three steps... first I like to run a couple of bottles of injector cleaner through a few tanks. If that doesn't address the issue, the next step would be a MOTOVAC (or MOTORVAC, however you spell it). This is where the fuel line is disconnected and a special strong cleaning agent is run through your injectors as the engine is run for a period of 30-45 minutes. This is a great way to clean them out and as a matter of fact, I would consider this as a regular maintenance item at least once every 1-2 years.

    - Ignition module. I've placed this one near the bottom because its so rare that these units fail. If you have done pretty much everything else above, chances are that the module is defective. The only way to verify is to replace it with another one. Before doing the actual replacing, make sure to clean off all contact points of corrosion and cover in light coat of dielectric grease. If you happen to have a friend with a GP, you could swap them out for a while, test it and find out if it addresses the issue. If yes, purchase a new module and replace it. Since I started playing with GPs in 1999 I have never seen/heard of an ignition module failing, so its pretty rare.

    There are other possibilities of where misfires could happen:

    - A vacuum leak

    - A disconnected or defective MAF sensor

    - A defective fuel pressure regulator

    - A plugged up fuel filter (high RPM stumble)

    - A severely plugged up air filter

    - A disconnected or defective IAT sensor

    - An aggressive cam (low RPM stumble is interpreted as misfires by the PCM, they disappear as soon as you step on the gas)

    - Water in the fuel or a bad batch of gas

    The chances are that if you have followed my instructions above you will have solved your misfire issues, but if not, it could be one of the above.

    We could literally write a book on this topic, but I hope that with the above information, you will have enough information to go on and resolve your misfiring issues.

    Good luck and play safe!