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Old 07-17-2011, 12:58 AM   #1
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Default 2004 gxp misfires

guys my 04 feels like its just falling apart...

three weeks ago I replaced the front engine mount because I had engine movement and we were pretty sure that was the cause... oh and the mount was toast..torn rubber at the stud.
after the mount was replaced it was still bouncing, and started running a little hard at idle....

coded maf sensor, multiple misfires, front o2 sensor, and two fuel codes that I forget...oh and a cruise control code.... no body codes....

oh and numerous times cruise control has been on at 75 mph, the SSS pops up and then low traction and cruise shuts off...

cleaned the maf, and cleared the history, oh and replaced rear engine mount too...

still have the misfires, maf code is gone, fuel codes gone, o2 code still there.

thoughts? coil? injector? best trouble shoot option?

thanks,
Rich
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Old 07-17-2011, 09:24 AM   #2
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is it the lean o2 code? specific codes would help. i think i remember someone having issues with the gxps running too lean, maybe a search on here for the specific code
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Old 07-17-2011, 12:51 PM   #3
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Are the plugs and wires new or original? My Ranger had a real bad misfire once..it turned out to be a bad plug.
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Old 07-17-2011, 03:58 PM   #4
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If you have a way to get a scan tool hooked up to it. Or take it to your local Auto Zone and they can at least hook up a code reader. Try to determine exactly what cylinder is being affected if indeed it is a misfire. It'* possible it could be something else causing the root of your problem. If you are capable of diagnosing with a flow chart I might can help and send you some info. just let me know
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Old 07-18-2011, 04:21 AM   #5
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yes o2 lean code....

please limit replies to knowledge of the LD8 engine..(it has no spark plug wires)

as to getting it coded, its only reading misc misfire codes, not telling us which one

plugs new 20,000 miles ago, unlikely to be plug....most likely a coil or injector,,,

anyone know of a scanner that can give me the definate misfire cylinger? We have the big obdII but it isnt isolating it....

checked plugs for being loose, and they are all in and snug, god I hate the back half of doing that......
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Old 07-18-2011, 07:23 AM   #6
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there are separate codes for random misfire and individual cyl. misfire. if your getting the random then its all of them.

so that being said it may be your fuel pressure may be starting to decline do you have a gauge?
here is the other thread with some more possibilities; https://www.gmforum.com/bonneville-gxp-northstar-powered-cars-107/p0171-p0174-04-gxp-299148/page2/
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Old 07-18-2011, 09:23 AM   #7
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This engine has coil overs, so no plug wires. The P0300 code is of little use, I hate that code. You may have to have it scanned a few times over several days and you should get a P030x code, like P0303. Once you have that code you can replace that coil. However, if you have a good eye, you can pull the plugs and inspect them real close. You may see a slight difference in one plug, should be a bit darker then the rest. That one will be your weak spark. The lean code could be a dirty O2 sensor. Running with a misfire will run rich and plug up the O2 sensor causing it to read lean.
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Old 07-18-2011, 10:41 AM   #8
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thanks jw, and dan...

yeah its a mess.... we've scanned it as many as 5 days in a row and no isolation code to tell em which cylinder... driving us nuts...

I cant replace the two O2 sensors until I fix this issue...

it'* also causing an engine bounce,(not mounts just replaced those)

could the fuel pressure regulator cause any of this? it'* inexpensive and in a suprisingly easy to get to location to change???

no vaccuum issues, but how bout PCV? can that cause any of this?
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Old 07-18-2011, 11:13 AM   #9
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Pull the vacuum line and sniff it, if you smell gas, the FPR is bad. You can check the PCV, if bad it'* a vacuum leak.
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Old 07-18-2011, 12:46 PM   #10
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in that thread i posted venom says no pcv just fixed orifice on a northstar
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