Cadillac STS Forum - 2005 through 2012 Discussion, 2005 STS 4.6L Northstar Misfire in Past Cadillac Vehicle Discussion; Hello guys I am having a hard time figuring out what is wrong with my STS. I have a 2005 ...
Hello guys I am having a hard time figuring out what is wrong with my STS. I have a 2005 STS 4.6L Northstar....Let me start by saying I first bought car with 89,xxx miles on it. Have done regular fluid changes and thats about it....Fast forward to now about 137,xxx miles. Driving and then all of a sudden check engine light comes on. I hook scanner up says cylinder 5 misfire...At this time I realize I have never done plugs or coil packs for this car...I then change all 8 plugs and Move the coil pack from 5 to cylinder 1. after driving for about 3 days check engine light pops back up...BUT NOW cylinder 7 misfire !! as you can see its been frustrating trying to pinpoint the actually cause for the misfire code cause now it has changed cylinders. I then change cylinder 7 coil pack with cylinder 1 (Remember this is originally Cylinder 5s pack)...Its been about a week and nothing since I noticed bolts on intake manifold were loose so I torqued those down back to spec and wonder what I should do about my misfire????
I was just questioning from experience. I've spent as much time working on the wrong cylinder as anybody. My system for finding the problem cylinder is to get the engine running as bad as it will run and then spray water on the exhaust manifolds with a spray bottle looking for the cylinder with cold exhaust.
i was thinking this could be the problem as well...I really dont want to just dump money into things thats not the problem...next step i think is to change all the coil packs see how that runs then move on to the injectors.
Fixed it!! Bought new coil packs, dropped them in, turned her on, vrooom vrooom back to normal!!! Acdelco !!!!!!!!!
I regret to admit I bought the cheap, made in china coils off of Amazon for $25 ea. and was I ever disappointed! 3 out of 8 were DOA, and after getting replacements the car just does not idle as smooth as it did before. It's not really missing, it's just not smooth. Also, my MPG is not what it was.
Before, I seriously couldn't tell if it was running. Now I can definitely tell it's running by subtle, frequent stumbles. I just don't believe the new coils are putting out the voltage required or specified or necessary for this engine.
I also believe that there were probably short-cuts taken during manufacturing such as fewer copper windings to save money or to just make it so it barely works.
I am so disgusted. Now I need to bite the bullet and buy some AC Delco's so I can get that smoothness again.
I had posted before about my engine doing what I called "soft" missing so I took it into a local shop for analysis and they found the spark plug ports were taking on oil... and lots of it. #7 was totally full, others not as much.
I replaced the valve cover and spark plug port gaskets, spark plugs, coils and did an oil and filter change. The DIC was indicating 92% but the oil was very dark, probably due to the misfires. I guess it was blowing past the rings and polluted the oil. Also, I was getting warnings of speed limited to 142 MPH and it was throwing codes for the cat on the right bank but did not ever throw a misfire code, which I thought was strange.
After my repairs, no more codes or warnings for over 2 months... thank goodness.