Thread: Random Misfire and P0171

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  1. #1 Random Misfire and P0171 
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    Hello everyone, I need a little help with a random misfire and what you guys think it might be.

    Okay, I have already changed the plugs to NGK Iridium gapped at .060, new plug wires, new fuel filter, new air filter and I am pretty sure I have fixed all the vacuum leaks it had. I have a problem with the engine setting off a P0300 code which is for a random misfire. It only misfires though when it is on boost. When it is off boost it runs good. I checked the fuel pressure and it seemed good if i remember correctly it was around 55PSI. I put some injector cleaner thinking it was a clogged injector but that still didn't help at all.

    Also I'm thinking that maybe the P0171 would set off the random misfire? I hear a ticking noise in the engine bay that flutters or gets louder when you give it gas, so I am guessing the lean condition is happening from that exhaust leak.

    The car is completely stock, so is it being gapped at .060 bad? That was how it came out of the box. And also, what could cause the misfire only under boost, if off boost it runs good? I fixed almost everything but now this misfire is just getting too me....
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  2. #2 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    first thing is did this happen to start after you were hard on it? Second, do you use 91-93 octane? Third, do you have a scanner to check KR?
    I've had first hand experience with this same problem but the odds of having the luck I did are miniscule..
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  3. #3 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    second question answered BTW, I just read your other post
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  4. #4 Re: Random Misfire and P0171 
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    Subd as I have what sounds to be the same problem. 91 octane used, less than blips of 1* knock exist. I don't think I've been hard on it, just tuning but I do get into boost slowly.

    TIA,
    Slim
    2003 Chevy Inpala LS 3.8 l36, Stattama Turbo kit, P&P LIM, P&P heads, lS7 lifters, Intense Xtreme 7.05 oil restricted pushrods, ZZP 1.9 modded rockers, 3" no cat down pipe, poly mount all around, fuel rewire, alt volt booster, and still working on it...
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  5. #5 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    Whats your LTFTs look like both of you?
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  6. #6 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    if the exhaust leak is before the O2 then yes that would cause all of the symptoms you posted. -ie misfire and lean scenarios. I just replaced my exhaust and mine went away. Before I found my 2 piece front manifold I never could find the reason for the problem. so essentially I'm saying fix the exhaust leak and come back and report in as for "Slimguns" you can post in my thread linked here> READ THROUGH MY STUPIDITY AND see if you think this helps http://www.grandprixforums.net/threa...ll-be-THAT-guy
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  7. #7 Re: Random Misfire and P0171 
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    Fix your exhaust leak first, then diagnose from there

    Are NGKs recommended for your car? In my experience it is always best to run what your car was designed to work with (plug type, gap etc.). I never trust the gap that comes out of the box. You say it only happens when your car is making boost, so it's a high rpm miss. Try misting your plug wires with water at night while the engine is running and see if you are getting any arcing from them, try this at different engine speeds
    97 GTP stock
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  8. #8 Re: Random Misfire and P0171 
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    I really don't know how to check the knock retard on it but it is not throwing any codes for that or I don't hear any pinging. I really don't drive it hard at all, and well I have not been driving it that much cause of the misfire. I bought NGK's since I read that the car needs iridium plugs to run smoothly. And sorry for sounding like a noob with the terminology but what are LTFTs? Ill look for the exhaust leak a bit more closer this morning and try to pin-point it. Hopefully fixing that exhaust leak will cure this misfire because I just want to drive the car already lol.
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  9. #9 Re: Random Misfire and P0171 
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    you need a scanner that reads live data to see all that kr and ltft's

    iirc the torque app does all that for about 20 bucks. if you have a droid phone. some of the blue tooth obd2 scanners things also come with a disk to hook up to a pc.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  10. #10 Re: Random Misfire and P0171 
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    Yes I do have a droid phone. Ill check out that app, thank you. So I have to have the scanner and the app then? By the way, going back to the exhaust leak I think i discovered where it is at. Its the pipe that is directly below the throttle body. It is leaking exhaust at about a foot wide crack in the pipe I am guessing. Going to take that pipe off and take it to the exhaust shop.
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  11. #11 Re: Random Misfire and P0171 
    Killa Bee Scottydoggs's Avatar
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    Quote Originally Posted by Mbueno19 View Post
    Yes I do have a droid phone. Ill check out that app, thank you. So I have to have the scanner and the app then? By the way, going back to the exhaust leak I think i discovered where it is at. Its the pipe that is directly below the throttle body. It is leaking exhaust at about a foot wide crack in the pipe I am guessing. Going to take that pipe off and take it to the exhaust shop.
    you need your droid phone with the app installed to it, then a bluetooth obd2 port thing. http://www.ebay.com/bhp/bluetooth-obd2-adapter-android

    a you tube review, i have not watched the whole vid, but it should give you some sort of over view http://www.youtube.com/watch?v=vQSsUPrGLHs

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  12. #12 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    go to the Junk yard and get one there cheap. no reason to pay the shop +$100 to fix something that is easily replaced
    LTFTs = long term fuel trims. its based on a percentage when you get it scanned after the exhaust is fixed post up the results.
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  13. #13 Re: Random Misfire and P0171 
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    Wow okay thank you. I never knew there was something like this in the market lol. That is pretty cool what it could do at such a good price. Ill be ordering it and then i can check what is going on with the car.
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  14. #14 Re: Random Misfire and P0171 
    Killa Bee Scottydoggs's Avatar
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    its not the "best scanner" but for what it is, its great. shows a lot of live data.

    reads cel codes, and can clear the codes as well.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  15. #15 Re: Random Misfire and P0171 
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    Can it read air to fuel ratio's? If it can, I will love this app forever lol. Just bought both of them.

    Here is the pipe that was cracked not as bad as i said it was but still really bad.
    20140207_114356.jpg
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  16. #16 Re: Random Misfire and P0171 
    Killa Bee Scottydoggs's Avatar
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    it should show all that.

    get that crack welded up, cheap repair. as long as the pipes not 1/2 rusted through. i welded 2 large holes shut on my last exhaust pipe, the hangers ripped off. big holes and thin pipe dont weld well. i finally conceded and put a new pipe in.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  17. #17 Re: Random Misfire and P0171 
    Too broken to be broke $$ ntreftz's Avatar
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    A very small crack gave me issues galore. I would figure fixng this would be a great start lol
    Poly Uppers, 3.5 snout, HAI, Can Tune, STB, Autolite 606 coppers, 2.5 cattless dp
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  18. #18 Re: Random Misfire and P0171 
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    Well with the pipe back in place and the crack sealed good, it still misfires under boost... :/ I'm thinking of doing a compression test on the cylinders. The usual gap in the plugs is for these cars is .055 to .06 isn't it?
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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  19. #19 Re: Random Misfire and P0171 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    What cylinders though, we need to know that.

    Could be as simple as a bad coil pack or maybe the ICM is bad.

    SMGPFC Member #1
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  20. #20 Re: Random Misfire and P0171 
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    It is a random misfire, code is P0300.
    2000 Millennium Yellow Corvette- LS6 intake manifold, TSP Longtubes, borla xpipe and catback, vararam intake, short shifter.
    2001 Pontiac Grand Prix GTP- Work in progress.
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