Help diagnosing P0307 misfire...
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Cadillac Escalade, EXT and ESV Forum - 1999 - 2006 Discussion, Help diagnosing P0307 misfire... in Cadillac Escalade Forums; Hey all...got the dreaded flashing CEL light on the way to work yesterday and am trying to chase down the ...
  1. #1
    Golfhack5 is offline Cadillac Owners Member
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    Help diagnosing P0307 misfire...

    Hey all...got the dreaded flashing CEL light on the way to work yesterday and am trying to chase down the cause.

    Little background...over the last few weeks I have noticed the mpg's drop by 2-3mpg and the truck exhibited some hesitation and "jerkiness" when going downhill with the cruise set at 70.

    I put it on a scanner and pulled P0307 (cylinder 7 misfire). So last night I put in a new plug in cylinder 7 (I will also be replacing the rest but didn't have time) but that did not fix the problem. Swapped 7 coil with 5 and still got a misfire but code changed to P0300 (random misfire). Does this mean the coil is bad?

    If it's not the coil I figure I will swap injectors next. Any other suggestions?

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    the cadillac man's Avatar
    the cadillac man is offline Cadillac Owners Master
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    It is possible that its the coil pack

    I wonder though if it is the injector though

  4. #3
    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    I agree the injector could be the culprit but with the misfire code coming up different after swapping coils it leads to believe that the coil is more likely. I am not a mechanic so my thought process could be way off...

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    the cadillac man's Avatar
    the cadillac man is offline Cadillac Owners Master
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    Quote Originally Posted by Golfhack5
    I agree the injector could be the culprit but with the misfire code coming up different after swapping coils it leads to believe that the coil is more likely. I am not a mechanic so my thought process could be way off...
    It can be a bad coil I have seen that before

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    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    Was not the coil. I replaced 7 coil with a known good one and still got P0307. This is after all new plugs and wires. On to check the injector next....

  7. #6
    the cadillac man's Avatar
    the cadillac man is offline Cadillac Owners Master
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    Ouch
    At least its only one

    Let's hope it fixs the issue

  8. #7
    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    Turned out to be the injector and coil! Replaced the injector this morning with the original coil and still misfiring. Replaced the oe coil with the new one I bought and presto....runs perfect! Sort of odd that both would go out but oh well it's fixed.

    I'm somewhat glad I went through this because I ended up taking the engine covers off and during that finally discovered the coolant leak I've been chasing for months. The heater core hoses are secured to the passenger side engine cover and when I removed them from their retaining clips the one on the left started dumping coolant at the quick connect fitting! It's been hard to find the leak because it has been random. Way worse when I park on an incline which now makes sense since I know where the leak is coming from.

    The previous owner of the truck did zero maintenance but I will slowly get it back to perfect....

  9. #8
    the cadillac man's Avatar
    the cadillac man is offline Cadillac Owners Master
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    Wow glad you found out the coolant leak

    I'd say the coil was close to failing also and the injector failing just done it in

    Sucks that the previous owner didn't take care of it

  10. #9
    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    Hmmm the misfire is back in cylinder 7...the worst part is that I'm an hour + from home on vacation. This time was a little different. The misfire started around 40mph cel light flashed for about 10 seconds and went off. It did this three separate time all at speeds between 40-55mph. Anything under 40 and it seemed ok. I naturally don't have any tools with me but I will plan on replacing the fuel filter and checking everything to make sure nothing came loose if I can make it home. Does this sound it could be a bad fuel pump even though it's only missing on one cylinder??

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    wesyder's Avatar
    wesyder is offline Cadillac Owners Enthusiast
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    The is no conventional fuel filter, there is a screen in the tank on the fuel pump assembly

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    the cadillac man's Avatar
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    I second that no filter on the fuel pump 03+ just a screen on the pump

    It could be bad injectors

  13. #12
    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    Thanks for the info guys...I learned something new! I would be pretty ticked if it's a fuel injector considering I just replaced it...

  14. #13
    the cadillac man's Avatar
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    If its not a ac delco unit then it may be defective

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    Golfhack5 is offline Cadillac Owners Member
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    Re: Help diagnosing P0307 misfire...

    Made it home and checked compression and fuel pressure...both good. I never really looked at the old injector but upon closer inspection I noticed it was completely clogged. Almost looked like coffee grounds packed inside. So I start thinking maybe the new one I installed is clogged already too? Take everything apart and sure enough it's clogged. Not completely like the oem one but was headed that direction. So I cleaned the oem injector as best I could and put everything back together....wala! It's fixed and no more misfire.

    So now the question becomes why is 7 cylinder injector clogging so quickly? I know it's the last injector on the rail so how could all these "coffee grounds" be getting past all the other injectors? Bad gas? Bad screen on the fuel pump? If it's the screen is that serviceable or does the entire pump need to be replaced?

    I am hoping bad gas...any other thoughts?

  16. #15
    the cadillac man's Avatar
    the cadillac man is offline Cadillac Owners Master
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    It could be bad gas but I am leaning more towards bad(aging) fuel pump

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