slight misfire/stutter in o.d. while lightly accelerating - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-26-2010, 01:41 PM   #11
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I think I may have found the problem....a small vacuum leak in the intake manifold...when I rev the engine while under the hood I can hear a light hissing sound in the intake when the rpms are dropping back down...does this seem reasonable to anyone?
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Old 10-26-2010, 10:18 PM   #12
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Take some MAF cleaner and spray it around where you think the leak is. The RPMs will change if there'* a leak.
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Old 10-27-2010, 11:34 AM   #13
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Yes it does. Vacuum leaks can cause all manner of havoc on modern PCM controlled engines. I even went as far as to order the assortment kit of vacuum fittings from NAPA because I've had more than my share of vacuum leaks. One of the leaks I've repaired two or three times is the tee coming off the fuel pressure regulator.

Use the MAF cleaner as was suggested to find the location. I've used WD-40 also, but since it'* not a solvent, it won't evaporate like MAF cleaner so it will have to burn off of the hot engine surfaces.
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Old 10-28-2010, 03:06 PM   #14
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Well I used the maf cleaner to try and find any vacuum leaks and no success. I sprayed everywhere on the intake and throttle body and on top of injectors with no change. But now today after looking through everything in the motor I found something terrible I think the car is done...when I took the oil fill tube off of the valve cover there were dark flakes at the bottom of the tube and some of them were orange ish in color...I have no idea what this is but I'm sure its not good. Is it from a piston or bearing? When I revved it up with the tube off I saw the flakes were shooting up near the lifters not too many but they were....is it over?...what could this be
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Old 10-28-2010, 03:30 PM   #15
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O yea I forgot to say I recntly sprayed the throttle body with some cleaner could it be that the compression is bad and all that crud from the tb came through the valves or is it something else
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Old 10-28-2010, 10:46 PM   #16
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Sounds like dried moisture foam. I would check the oil. If a bearing is gone you may see metal flakes in the oil. If a piston has chipped you would have a smashed spark plug.
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Old 10-29-2010, 01:50 AM   #17
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Problem solved! Wow I think I was just getting really worried and overeacted...I went over everything again and I realized those flakes were from the o ring gasket on the fill tube breaking down....the car was driving me crazy so I kept driving around really trying to tune in to what it was...it had to be electrical I kept telling myself...so I wanted to change the plugs one more time to see what it would do so I got some autolite coppers and stayed away from bosch platinums (that they wanted to sell me) haha I've read some threads about not using them in theses engines....so I test drove after I changed them...damn still hesitating,rough idle and missing in overdrive...lol so I got pissed off and floored it redline through all gears from a stop and my ses light finally started to go off...it was blinking...I knew this meant a misfire I actually was happy because I knew I could finally get a code now....so while driving I connected my code reader (i had it on passenger seat)....bam right there....misfire cylinder number 2 glad it wasn't random. So right there I drove to oreillys and bought a coil pack...change the 2/5 coil pack....started it up and smoooooth. Got all power back and perfect idle....I was happy as hell...my car was driving me crazy. I didn't think the coil pack would give those symptoms so lightly. Thank you guys for helping me troubleshoot with what you could though
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Old 10-29-2010, 01:54 AM   #18
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That would make sense. Getting the misfire finally caused the problem to come to the surface. Easy fix. Funny no one asked you to test your coils, including me.
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Old 10-29-2010, 01:55 AM   #19
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And it took that wot to throw the code even though I could feel it from normal driving?
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Old 10-29-2010, 01:57 AM   #20
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You may have been getting a weak spark causing a bad fuel burn. Under WOT the misfire was complete, and there for set off a code.
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