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Studdering under medium load
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12-15-2013, 02:13 PM | #1 |
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Studdering under medium load
Car seems to have a slight misfire or studdering when accelerating with about half throttle. Under WOT, runs smooth. Throws no codes.
Just replaced the plugs, did not improve. Any suggestions? Recently returned to stock after running Procede + Meth for awhile. |
12-15-2013, 04:11 PM | #2 |
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How about checking the coils? Make a compression test etc
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12-16-2013, 08:05 AM | #3 |
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Pull out your spark plugs, any fuel on the plugs? Also checking the coils is a smart idea.
Could be fuel injectors however it's odd you don't have any codes, probably an early warning of a bigger problem. |
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12-16-2013, 09:11 AM | #4 |
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time for an intake clean.
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12-16-2013, 11:22 AM | #5 |
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12-18-2013, 08:49 AM | #7 |
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Thanks for the replies guys. I figured coils would be the next thing to check, but the fact that it runs fine under load is throwing me off. If a coil was bad, wouldn't it be worse under heavier loads?
Does a VANOS issue make any sense? With the Procede on and running more boost than stock, I could rather frequently trigger the VANOS solenoid code. Rebooted the car and it would come out of limp mode and run fine. I've never been able to trigger the VANOS code running stock boost, though ... |
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12-18-2013, 08:55 AM | #8 | |
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12-18-2013, 10:09 AM | #9 |
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I haven't ignored them, but I was hoping for other suggestions that might make sense. I had the intake off ~5-7k miles ago while replacing a HPFP and inspected the valves then. Some build-up, but not too bad.
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12-18-2013, 11:46 AM | #12 |
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I had a bad injector and had similar symptoms, although my studdering was there all the time and very severe, but at higher RMP it got better or less noticeable. Not sure if this helps, but from the other post it sounds more like carbon build up.
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12-18-2013, 03:49 PM | #13 |
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12-18-2013, 03:51 PM | #14 |
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I'm thinking coil pack or fuel pump related as well. Although I just installed the HPFP not too long ago so I hope that's not it I'm surprised that the computer isn't throwing any codes though as I thought it was pretty sensitive around these components failing. Just rolled over 55,500 miles.
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12-18-2013, 03:53 PM | #15 |
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Thanks for the feedback. Yours does sound more severe, mine isn't noticeable at idle and I could even accelerate to 45mph with light throttle and not notice it. It's when I go about 40-60% throttle it will start studdering a bit (although RPM's still climb relatively effortlessly, just with the noticeable misses) and I don't see the issue at WOT.
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12-18-2013, 06:04 PM | #16 |
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Coil pack would throw a code,
injector will throw a lean or rich code on that entire bank. Without a tune there is no way to do logs lpfp or hpfp to see what it happening. Maybe clean vanos solenoids intake cleaning will help and eliminate that as a possible problem
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01-01-2014, 01:22 PM | #17 |
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UPDATE in case someone comes across this thread with the same symptoms:
After replacing spark plugs and bought a new coil and rotated it through all 6 cylinders, the problem was still there. Decided to give intake cleaning a shot and went with soaking the valves in a cleaner and manually scraping off all the build up. It still has a stutter at idle which the car has had since day 1 that I've had it (others report intake valve cleaning smooths out the idle, doesn't seem to be the case for me), however my misfires and hesitation to accelerate in the 2-4k RPM range under medium throttle appear to be gone! What a pain in the ass this was! If I had to do it again I think I'd invest in the walnut blasting approach. Thanks everyone for the suggestions. |
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01-02-2014, 03:39 PM | #19 |
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01-02-2014, 03:52 PM | #20 | |
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This should help others that have yet to get an intake valve cleaning. I usually recommend them at 35,000 as there is substantial build up by then. Although I can see why one would wait for a problem before getting it done too. |
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01-02-2014, 07:02 PM | #21 | |
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And for anyone looking to do this themselves, I found an o-ring pick to be the most useful for cleaning off the build up not only on the valve stem but getting behind it and near the bottom of the valves. Something like this: http://www.gearwrench.com/auto-speci...tml?feedback=1 Very time consuming process. I felt like I was a dentist for a day cleaning plaque off my car's teeth. Also, a radiator hose removal tool like this: http://www.handsontools.com/OTC-4521...l_p_48972.html was helpful to remove that damn connector holder that is attached to the bottom of the intake manifold. It allowed me to get behind it and pry up so I could slide it off. You may have to modify it a bit, as the one I have was basically a phillips screw driver with the tip ground off and to a point, and then bent similar to the angle in that picture. Not sure if that one linked will work exactly out of box for you or not. |
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01-03-2014, 05:43 PM | #22 |
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