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Cylinder Misfire Code & Rough Idle... #$%&!!!

This is a discussion on Cylinder Misfire Code & Rough Idle... #$%&!!! within the Technical / Maintenance forums, part of the General Discussion category; The Blue Beast is falling apart on me! Today I was running some errands, I came out, started it up ...

  1. #1
    Thank God Ima Country Boy Z71IN''s Avatar
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    Unhappy Cylinder Misfire Code & Rough Idle... #$%&!!!


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    The Blue Beast is falling apart on me! Today I was running some errands, I came out, started it up after running into a store and it began idling rough, and the SES light came on. I pulled over and took my trusty code reader out of the glove box and it was Code 0307 - "Cylinder 7 Misfire Detected" I said "Oh $#%^ that doesn't sound good." Figuring maybe it was a bad plug wire or something I bought a new set of wires, plugs, and while I was at it a cap and rotor. $190 later still the same thing. Asked my dad and he said maybe it is an exhaust valve hanging up. It keeps putting out the code nonstop. The #7 plug was a bit browner than all the other plugs... which were predominantly grey in color. It has 163k on it so it very well could be valve problems. Engine has been maintained VERY well and not beaten on... doesn't use oil and other than this has run exceptionally. Praying it isn't serious trouble b/c timing is REALLY bad for serious engine troubles right now, but I don't know what else it could be that is a simple fix. I think I've ruled out all the simple things. So you think I'm totally screwed??? Oh, and just another thing that might help... I have true dual exhuast with NO x or h pipe and the driver's side bank (the one with the #7 cylinder) has a noticeable lump to it... where the left side comes out smooth and steady... I'm no expert on valves so I don't know if that might help diagnose valve trouble. Thanks for any comments, help, etc.
    2004 Chevy Silverado Z71 - came stock with huge payment
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    miss fire number 7

    get a vac gauge look at the needle if its seady I will bet the valves are ok I had this similar problem with my vortec motor and it was the injector its a job removing the intake but its the only way to do it and besides you can clean everything up while your in there,hope this helps....
    chutes out...

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    Testing!!!

    If you're sure you're getting fire to the plug you're going to want to do a compression test. Get a compression gauge and test the cylinders. The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 100 psi. For example, if the highest pressure in any one cylinder is 150 psi, the lowest allowable pressure for any other cylinder would be 105 psi. If those check out fine chances are it's a fuel injector.

    Check for these things in this order:
    1. Fire at plugs
    2. Compressoin Test
    3. Fuel system
    "American by birth, Southern by God's grace!"

    "Decide quickly, make your pitch, nail down the details, donít worry about the money." - Billy Durant (Founder of General Motors)

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    Thank God Ima Country Boy Z71IN''s Avatar
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    okay, I'm going to go borrow a buddy's compression tester. As far as a fuel injector being the problem, wouldn't that effect more than one cylinder? I know tuned port has one injector per cylinder, but doesn't throttle body have a more centralized fuel spray? (I could be totally off on this as I'm not very experienced with fuel injection systems). Thanks for the replies guys
    2004 Chevy Silverado Z71 - came stock with huge payment
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    Thank God Ima Country Boy Z71IN''s Avatar
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    Okay, I got a compression tester and tested #7 and #5 since 7 was the one that threw the code. #7- 160lbs, #5 - 155lbs... so that seems to be just fine. Driving around today it is running even rougher now, is way down on power(even since it first starting acting up), and now both banks of my exhuast are thumping irregularly (where yesterday it was just the driver's side bank), also, the SES light is out and it is NOT throwing any more codes.... although now it's running worse than when it was!! So you think it's fuel problems? If so I have to yank the manifold off to get to the injectors?... I can't get to them through the top without yanking the manifold? What tests can I do to narrow it down to the injectors... could it be fuel pump/filter problems?... shoot, I guess I should have gotten a new fuel filter when I was out... I hate to keep drivin it like this... parts store is about 15 miles away. Whattaya think!??! Thanks!
    2004 Chevy Silverado Z71 - came stock with huge payment
    Flowmaster & Wester's 89/93 Dual Tuned

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    If your truck is a 1997 it has one injector per cylinder. Did you check for spark? Use a spark tester and have someone turn the engine over with the key. Look to see if you have spark.

    The compression sounds good to me. This means there are no internal problems such as valves, head gasket, or rings.

    Unfortunately you can't do an injector pop test. Dealerships use their scan tools to operate each injector to test them. They take a fuel pressure gauge and pressurize the system. They then make a selected injector open and close quickly with the scan tool. If there is a large enough fuel pressure decrease it means the injector is good. If there isn't a big enough drop it means the injector is bad or clogged.

    Make sure you do every test possible before changing parts. You've already spent over $200 in parts that didn't fix the problem. I'm not sure if you can replace just one fuel injector on the early model Vortec engines. You may have to replace the entire unit.
    "American by birth, Southern by God's grace!"

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    DAMN my avitar is sexy smokerZ28's Avatar
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    Do you know if its running overly rich or overly lean? Is overly even a word?

    "Disce quasi semper victurus; vive quasi cras moriturus"
    Translation: "Learn as if you were going to live forever; Live as if you were going to die tomorrow.


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    Women are like a finely tuned engine. You spend all your money, free time, and your love on them but sooner or later they will bite you in the ***..

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    There's rich, lean, or perfect. There's no overly!
    "American by birth, Southern by God's grace!"

    "Decide quickly, make your pitch, nail down the details, donít worry about the money." - Billy Durant (Founder of General Motors)

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    Thank God Ima Country Boy Z71IN''s Avatar
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    Well, I've exhausted all my diagnostic skills (not much). Changed the fuel filter too... no change. I decided to bite the bullet and take it to a mechanic. I would've done it myself but I dont' have the tools or the knowledge to mess with it any further. I just moved 600 miles from home and barely know anyone so I don't have the resources to tackle this one!!! I'm borrowing a vehicle from one of the few people I do know for a day or two, but if it takes longer than that I'll be car rental bound!! I'm thinking on a hunch it's running lean, but I really have no way to tell for sure. Hopefully this mechanic can nail it down and fix it cheap enough... otherwise I'm up $#&$ creek without a paddle or whatever that saying is. On top of it all I'm starting my new job tommorrow... for crying out loud!!!!
    I'll keep ya'll posted on what he finds
    2004 Chevy Silverado Z71 - came stock with huge payment
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    Unhappy

    I had the same problem on my 96' C1500 V6. Had a misfire on #6 so I took it to the stealer. Turns out that there is a recall for all 96-2001 truck w/ the SCPI FI systems here in california. Seems that the poppet valves get gummed up which will cause it to misfire and run rough. California's Air Resource Board mandated the recall which extends the warranty for 200K. They are also required to replace the SCPI unit with a new "MFI" unit if GM can't correct the problem with a fuel injection cleaning. Fortunately, they went ahead and replaced mine the first time I took it in. The service manager told me that this is the number one reason for engine misfires and rough idle on these trucks and that without this mandated warranty, this replacement would have set me back a good $700 clams!!! The bad news is that this recall is only valid here in cali....

    Here's the link to the A.R.B recall: http://www.arb.ca.gov/newsrel/nr021103.htm

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    Thank God Ima Country Boy Z71IN''s Avatar
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    Okay, the mechanic said he hooked it up to a computer and checked out something with the fuel and spark (I forget exactly what he said) and said it was all over the place... and said he thought it was the injectors. As I've read on this board he said he recommends changing all the injectors, but he could try to at least just clean them. He quoted 3 hours to do the swap and if he just cleaned them it would be at least about $250 (I guess about the same amount of time). The bad part is he wants $87 per injector!!! My dad can get a GM discount with his business and get them for around $40/ea so I'm having him ship me 8 injectors and a new regulator while I'm in there (along with the gaskets and o-rings I need I suppose). Hopefully I can do the swap okay with no problems. I'm pretty mechanically inclined, but never done anything like this (I've done water pumps, brakes, and stuff like that though with no problems though). Think I can tackle this one okay??!!!??? I can't afford to pay $1000 to get it fixed at a mechanic... I guess the only risk I run is if it turns out to be something besides the injectors... then I would have just spent another $400 and spent all that time swapping them out only to STILL not have it run. Couple of questions... will the injectors have a whole new poppet valve setup on there too or are they seperate ? (I didn't talk to the GM counter... my Dad did) Also, do you guys think that this is most likely my problem?? I can stand the thought of still having it broken after doing all this!!!!! Thanks
    2004 Chevy Silverado Z71 - came stock with huge payment
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    In my previous post, right above your last post, I said that the fuel injectors are defective on most 96 thru 2001 trucks. Although you don't qualify for the recall since your not in california, they might still give you some sort of discount if you call GM customer service. That new MFI unit with the newly designed injectors really does improve the idle and mpg's too. I went from 14.5mpg to about 19+.

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    My truck did the exact same thing your is doin now.Rough idle.Well I went and had the injectors cleaned and it got even worse.I took the upper manifold off and replaced the fuel pressure regulator and that was it.If I was you I would do that first,I am 99% sure that is your truck problem also.It is common for our 350 vortecs to have the pressure regulator go bad and cause rough idles.Trust me on this and save your self some money and try the regulator.Did mine yesturday and it runs so smooth now at an idle I can not even tell it is runnin except for the exhaust.If you need any help with it I will try to guide you through it.Just PM me and let me know.It is not hard to do at all.The regulator was only 75.00,you can get them a little cheaper but I wanted the ac-delco.
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    I doubt the regulator is the problem because the code set only on #7 cylinder. If there where more cylinders missing I would consider the regulator.
    "American by birth, Southern by God's grace!"

    "Decide quickly, make your pitch, nail down the details, donít worry about the money." - Billy Durant (Founder of General Motors)

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    If he has replaced the plugs wires,plugs,dist.cap and rotor and all the cylinders are firing then I guarantee you that his what is wrong with his.Mine did the exact same thing.
    06 Crewcab 2wd 5.3 Wheatley tune using HPTuners,4.10,comp cam,Yank,longtubes,Heads and much more
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    I understand what you are saying but if it was the regulator you would probably have misses on more then one cylinder. As Z71IN' posted:

    "I pulled over and took my trusty code reader out of the glove box and it was Code 0307 - "Cylinder 7 Misfire Detected""

    If he had a P0304, P0307 and/or other misfire codes I would consider the regulator. But the case is that only one cylinder is misfiring. There is a possibility that a fuel pressure regulator could cause a misfire but in this case it's highly unlikely.
    "American by birth, Southern by God's grace!"

    "Decide quickly, make your pitch, nail down the details, donít worry about the money." - Billy Durant (Founder of General Motors)

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    Thank God Ima Country Boy Z71IN''s Avatar
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    Originally posted by Cop_Dodger
    I understand what you are saying but if it was the regulator you would probably have misses on more then one cylinder. As Z71IN' posted:

    "I pulled over and took my trusty code reader out of the glove box and it was Code 0307 - "Cylinder 7 Misfire Detected""

    If he had a P0304, P0307 and/or other misfire codes I would consider the regulator. But the case is that only one cylinder is misfiring. There is a possibility that a fuel pressure regulator could cause a misfire but in this case it's highly unlikely.
    That is kind of what I was thinking regarding the regulator as my culprit... since it seems to be isolated to one cylinder. Although the other bank seems to be running bad too (after a while it started... explained in the original post by the dual exhuast and how just the driver's side bank was rough at first and then the pass side got rough too)... which was confirmed by the mechanic and his diagnostic tool. He suggested that it could be the truck compensating for the other side running screwy... do you know if that could be possible with the computer system in this truck? In any case since I don't have time to mess with taking it apart twice if one is not the problem I have purchased 8 new injectors and a new regulator as well. I plan on driving this thing for a while still so I figure I mind as well replace these while I'm in there. I'm just praying this solves my problems and I can do the swap okay myself!!!! Any other thoughts feel free, and thanks for those who have replied!!!
    2004 Chevy Silverado Z71 - came stock with huge payment
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    have you tried the tps?

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    Thank God Ima Country Boy Z71IN''s Avatar
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    Well guys, I got the 8 new injectors, new fuel pressure regulator and went to it last night after work. My buddy helped me and we used his garage. All in all it took about an hour to pull the upper manifold and about another hour to install the new injectors and put everything back together. I guess it was about 2.5 hours all together out the door (minus the .5 hour beer break at the end to celebrate!!) Anyways now it runs and idles way better than it ever did, so I guess that was my problem. Man was that thing dirty under there. I'll tell you, air filters do a $%^^& job that is for sure if all that dirt and grime can get past them. Anyways I'm happy as a pig in $@#& that it's fixed. Thanks so much to everyone who gave me tips and helped me diagnose. You guys are a wonderful resource!!!! To anyone who might consider paying someone 800 or 900 to do this... it really is NOT that hard. I have $420 in parts I think. If you can do brakes or something like that you can surely do this. All you had to do was move some wires, unbolt some brackets, pull of the thermo housing (syphon out some antifreeze so it doesn't spill), disconnect the fuel lines (take the pressure off first), then pull the manifold off, unclip the injectors and fuel pressure regulator, replace with new, and put it back together!
    MX5.7 likes this.
    2004 Chevy Silverado Z71 - came stock with huge payment
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