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Misfire Question

This is a discussion on Misfire Question within the General Help forums, part of the LSx Technical Help Section category; have you pulled the plugs yet, to check for spark / and or damage?...

  1. #21
    LS1 or bust b.lee's Avatar
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    have you pulled the plugs yet, to check for spark / and or damage?
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  2. #22
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    I am having the same issue with my 99 Z28. I just checked the fuel pressure according to the factory manuals and Mitchell diagnostic software after you shut down you engine the fuel pressure should stabilize between 55 and 60 PSI and not drop anymore. Mine was slowly dropping so that points to bad injectors. I have replaced just about every sensor and I am still getting DTC p0172 and p0175 rich bank 1 and 2. I have ordered all new GM injectors and will be installing them next week I will try to update you. By the way I have a friend that is a good mechanic and his advice is no injector cleaner it can do more harm than good. I had mine serviced at the Chevy dealership and it ran like crap when I got it back and now with 67000 miles they need to be replaced so I tend to agree with him.

  3. #23
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    I agree fully with the injector cleaner being BS. I am in the process of trying to get my money back from the GM service place I took it to cause they did a flush and I didnt even need it(charged 400 bucks too). I told GM service to put it on a diagnostic and they didnt they just flushed it and called me and said"its running great-perfect idle". I went and picked it up and guess what-it was exactly the same. I took it to a diff place(I finally found a good shop) and it was 3 plugs the first shop I had the car to gapped way too large. Idiots.GM service said "o its the catalytic convertors blah blah. pshhhhhhhhhhhhhht. I want my money back period or I am calling my attourney. The good shop I finally found said the same thing I did-all GM service had to do was use the tech 2 computer to find the misfire-Instead GM was like ahh fk it a fuel injection flush should do it-then gave the car back to me knowing it wasnt fixed. UNREAL I have a messed up back so I cant work on my car anymore which sucks but after 5 places I finally found a honest/good shop. Thank God.

  4. #24
    down in it 310stanger's Avatar
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    as a technician by trade as i do not know exactly whats going on with your car i can tell you some facts about misfires.
    1. yes clogged or dirty injectors can be a cause
    2. bad injectors or a computer dumping fuel can destroy cats
    3. unburnt fuel via misfire can plug cats
    4. jus because you have a tech flush you injectors and not have it cure a misfire doesnt mean it was a bad thing to do
    5. dont use bosch platinum plugs cause they are pure shit. use autolites or ngk's and nothing else
    6. weak fuel pressure can cause a misfires
    7. bad gaps on plugs can cause misfires as the spark "blows out"
    8. 400 bucks for a throttle body injector flush is a ripoff. every place i ever worked at was between 80 and 100 bucks.
    9. not all dealers have nothing but bad techs. its a lottery as to whether or not you get the good techs at any given dealer working on your car. i've seen horrible techs and unbelieveably gifted techs working in the same shop.

  5. #25
    STAY PUFT thecorrectformula's Avatar
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    Bad rings in cyl. 2 could cause it. Check your #2 plug to see if it looks like oil could be burning on it.

  6. #26
    down in it 310stanger's Avatar
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    Quote Originally Posted by thecorrectformula View Post
    Bad rings in cyl. 2 could cause it. Check your #2 plug to see if it looks like oil could be burning on it.
    good call. i'd lean towards that being a more "extreme" case but it'd definitely cause a misfire. burned valves can do it, bad coils, bad crank sensor, bad cam sensor if the ls1 has it which i'm not sure.

  7. #27
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    i'd be pulling the fuel rail and checking for water-rust dirt in the injectors...next would be a vacuum leak around the intake on those cylinders.let me guess its the back two cylinders on the pass side?

  8. #28
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    If you are speaking to me it was caused by a shop installing my plugs w/out checking the gap and the gap being way too large in those cylinders. It also caused a piston slap sound at cold startup that went completely away with new properly gapped plugs. It was kind of a weird thing cause it took some time for the car to start to run bad after getting the misgapped plugs installed. I actually didnt think it was the plugs because I just got new plugs installed 300 miles ago-which were misgapped to my surprise.

  9. #29
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    Quote Originally Posted by 310stanger View Post
    as a technician by trade as i do not know exactly whats going on with your car i can tell you some facts about misfires.
    1. yes clogged or dirty injectors can be a cause
    2. bad injectors or a computer dumping fuel can destroy cats
    3. unburnt fuel via misfire can plug cats
    4. jus because you have a tech flush you injectors and not have it cure a misfire doesnt mean it was a bad thing to do
    5. dont use bosch platinum plugs cause they are pure shit. use autolites or ngk's and nothing else
    6. weak fuel pressure can cause a misfires
    7. bad gaps on plugs can cause misfires as the spark "blows out"
    8. 400 bucks for a throttle body injector flush is a ripoff. every place i ever worked at was between 80 and 100 bucks.
    9. not all dealers have nothing but bad techs. its a lottery as to whether or not you get the good techs at any given dealer working on your car. i've seen horrible techs and unbelieveably gifted techs working in the same shop.
    I agree with what you are saying man. I completely agree that there are great GM service techs no doubt about it BUT I didnt get one(just my luck). I am not going to get into what causes what etc. The point is when a customer tells you point blank -"I want my car put on a diagnostic cpu to check for codes" and he doesnt and does a fuel inj. flush which produces NO difference in the Idle of the car -thats just plain rediculous. And $400 bucks is plain nuts! The bottom line is if I wanted to guess at the cars problem by replacing parts(what the tech suggested) I could have done that on my own.
    My car has NGKs which the tech said were shit and he also said if he put my car on a dyno my MSD 8.5mm wires would melt! hahahahahahahahha
    okkkkkkkkkkkkkkkkk

  10. #30
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    dealer techs are mostly unexperianced guys that don't know sheeet about anything really.Good techs usually start their own shops and make real cash.

  11. #31
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    Quote Originally Posted by Rivi View Post
    dealer techs are mostly unexperianced guys that don't know sheeet about anything really.Good techs usually start their own shops and make real cash.
    Funny thing is this tech was trying to BS me but I knew better. He talked about how he used to build vette motors blah blah- I think the guy BS's so many people that he BSed himself into believing it too. He also tried to tell me my idle problem was off/on because he sat in my car for 20 minutes and it ran fine. hahahahahahahah The guy was so full of it. He put 3 hours labor for an injector flush--------yeahhhhhhh right. I dont think the guy worked an honest 8 hour day in his life.

  12. #32
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    Quote Originally Posted by 310stanger View Post
    as a technician by trade as i do not know exactly whats going on with your car i can tell you some facts about misfires.
    1. yes clogged or dirty injectors can be a cause
    2. bad injectors or a computer dumping fuel can destroy cats
    3. unburnt fuel via misfire can plug cats
    4. jus because you have a tech flush you injectors and not have it cure a misfire doesnt mean it was a bad thing to do
    5. dont use bosch platinum plugs cause they are pure shit. use autolites or ngk's and nothing else
    6. weak fuel pressure can cause a misfires
    7. bad gaps on plugs can cause misfires as the spark "blows out"
    8. 400 bucks for a throttle body injector flush is a ripoff. every place i ever worked at was between 80 and 100 bucks.
    9. not all dealers have nothing but bad techs. its a lottery as to whether or not you get the good techs at any given dealer working on your car. i've seen horrible techs and unbelieveably gifted techs working in the same shop.
    Are you a GM tech? if so-does 3 hours labor seem right for an injector flush? hahhaha what is a reasonable amount of time?

  13. #33
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    i should know...i ran a gm shop a long time ago.Its much worse today because at least years ago the guys in the shop could learn by working on the cars.Today the customers get screwed because VERY few know anything usefull when it comes to finding the real trouble.Trust me even a decent mechanic today is going to have his hands full fixing todays fussy cars.Gm has a listing for each district of the top techs in the different dealerships,i suggest you ask the service manager for his best tech next time and his rating in gms system.I found a local dealer here with a number 6 rated tech this district.BUT HE STILL screwed up installing my new fuel lines.I had to go back and force them to install them properly.I'd try to stay far away from dealers AND force them to commit to the repair.Anotherwards if it doesn't fix it they pay for it.If they won't go someplace else.

  14. #34
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    Quote Originally Posted by Rivi View Post
    i should know...i ran a gm shop a long time ago.Its much worse today because at least years ago the guys in the shop could learn by working on the cars.Today the customers get screwed because VERY few know anything usefull when it comes to finding the real trouble.Trust me even a decent mechanic today is going to have his hands full fixing todays fussy cars.Gm has a listing for each district of the top techs in the different dealerships,i suggest you ask the service manager for his best tech next time and his rating in gms system.I found a local dealer here with a number 6 rated tech this district.BUT HE STILL screwed up installing my new fuel lines.I had to go back and force them to install them properly.I'd try to stay far away from dealers AND force them to commit to the repair.Anotherwards if it doesn't fix it they pay for it.If they won't go someplace else.
    There will be no next time with GM service hahahah. I first took my car to a vette/f body "specialist" or so they claimed. They didnt gap the plugs and that ultimately caused the misfire issue. I also know that same shop damaged my transmission by "test driving " my car when I specifically told them not to.
    Next I took it to a shop that I waited 3-4 days to get my car into and they let it sit all day without even looking at it. I have health issues and really was desperate to get my car fixed and took my car to GM service knowing I was going to pay alot but as long as I got it fixed I was willing to pay a bit more at this point. After all the BS and charging me 3 hours labor for a inj flush,them giving me back the car telling me its fixed,me taking it back etc etc I decided to take my car back home and started looking for another shop to fix it. I went on a website called need 2 speed and they have alot of local shops here in florida but only 1 where I live. I read some good things so I took it there and I am soooooooooooooo glad I did. They had 8-10 f bodies there getting worked on and they are Very fair and do awsome work. Took it back today to get some other things done Muffler welded on etc. and I asked the guy how much to put this billet grill on I bought and he said Ill do that for nothing it wont take me long at all. I mean what a good guy.

  15. #35
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    Quote Originally Posted by BREAKxNECKxSPEED View Post
    They had 8-10 f bodies there getting worked on and they are Very fair and do awsome work.
    i work on female bodies...FOR FREE!!!!!!

  16. #36
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