Posted by Brad Gyde on April 16, 2011 at 11:21:31 from (70.8.190.240):
Hey guys,
We have a mechanical issue we can't seem to solve..
Working on a 2007 GMC w/ 4.3 V6
Idles fine when cold, once warm, will not idle a majority of the time.
Has major miss on cylinders 2, 3, and 4 between 1200-2000 RPM. Have not checked it at higher rpms, at idle (when cold) none seem to show miss.
The other 3 cylinders show occasional miss in that rpm range (our scanner "resets" the miss counter every 30 seconds or so, cyl 4 will show anywhere from say 40 up, 2 and 3 will usually be about half of that number, and the others ma show 1 or 2, if any)
What has been done:
Few months ago, we put a cap and rotor on it.. Has ran fine since until about a week ago (but has only been 2k miles since changing) and has ran fine until about a week ago..
Checked fuel pressure.. Shows 60 key on, truck off.. 60-65 truck running at various rpm's. Slowly drops after key is turned off.
We swapped plugs around (took #4 plug and put it in #1 cylinder) the miss did not change.. stayed at #4
Checked for vac. leaks (ether trick) Nothing there.
Checked for wire arcing.. Nothing we can see.
We removed cap and rotor, just to have a look.. Looks good there.
Cleand the MAF sensor (with MAF cleaner, per directions on cleaner can)
Today, we took the coil/ICM to a parts store, and they tested both, said the ICM was bad.. $75 later, no change so to speak.
We have changed the temp sensor as well (at a previous date) and the argument between my father and I is that the temp sensor likely has nothing to do with it
Previously dad changed the temp sensor, as it showed a "code" about low temperature- which I can see a logical problem with a half stuck open thermostat, which we also changed previously.. I don't believe the sensor was bad when he changed it, and I can't say one way or another, since we changed both at the same time. I say it's not the problem now because A) it shows accurate temperature from gauge to what our scanner says, and B) NO temp code this time.
Anyone have any ideas what to look for at this point?? Our scanner will tell us different outputs of different sensors, but I don't know what "spec" would be on most of them to know if there is a problem there or not.
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