nvu
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nvu last won the day on July 14 2023
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I don't know if there's a definitive procedure for creaking bolts. I could tell the if a creaking bolt has gone beyond it's yield, it just feels springy when you tighten. A good bolt can creak too, it's sometimes due to the threads in the block not matching the threads on the bolt. Good bolts that creak still feel as stiff as ones the didnt creak. I run them in and out a couple times lightly with a drill and clean/relube the threads. then try again. Be aware MLS gaskets deform as part of sealing, and then bite a bit into the aluminum at final torque. You shouldn't loosen the bolts all the way once you started, if you need to work on a problem bolt, back off the other bolts as little as you need to and always leave them in tension. At the torque wrench stage, try and keep everything creak free. Keep cleaning and relubing if needed. After that is the 1st 90 degree stage, some likely creak, you need to remember the feel of the good bolts and decide. It's the last chance to back off and redo. The second and final 90 deg stage, if it's a bad bolt you will definitely feel it. Never go more than 180deg total for those two stages, if it felt loose after the two stages... it's overstretched already.
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It's not recommended to reuse headbolts, but I've reused headbolts before. You'll know you have a bad one when you do the final torque and it squeaks too much or just doesn't feel tight. I have a bunch of used ones laying around so it's not a big deal. It might be a show stopper if you don't have spares on hand.
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did you go from nonturbo to turbo? the p0420 is pretty tricky to catch even on the original car. even throwing on a different exhaust system could trigger it. don't try and chase the problem itself, but get other things dialed in and worry about p0420 last. the car will run fine with p0420 code and no other codes, at least anything before 2007. it just won't pass smog. with that, some things to check if you haven't done so already: your mass air flow sensor is probably okay. make sure the car runs strong in closed loop, no misfires or rough idling. part throttle should be smooth, put it in 1st and see if it can creep along smoothly in idle. creep along smoothly 1000-1500rpm. try 2nd gear if it's bucking or missing, then check your maf sensor, intake, vacuum leaks... on the exhaust side of things, make sure the entire path from engine to the rear cat has no leaks. the flex joint and gaskets just before and after the cat are usual suspects. test with whatever way you think will help, i don't know of any surefire way for me, i had one car that would pop a p0420 every couple months, even did pressure smoke testing and never found the anything. only by chance one year i decided to sand a rusty looking flange only to find that it was slightly bent, the other mating flange was bent in the same direction so everything mated up and sealed fine, but was C shaped ever so slightly, you can't even tell by eye. after getting everything flat again, the problem went away for good. still on original cat from 2002