trey3

I installed everything last night and there is a big improvement in engine idle and power. The computer isn't reporting any misfires. I am still hearing a bit of what sounds like a light backfire or knock under load. That may be because the cats are currently removed for testing and it is louder and put together with cheap clamps. I am going to have the cats welded back on. That should quite things down. Like I said before, the mystery tapping at startup is now no longer. I suspect that rod or lifter is stuck. I did a compression test and it was bouncing around 130psi on most cylinders. It would bleed off to about 90 pretty quick. I have since learned a fluctuating needle is an indication of misfire or a sticking valve. It is likely gummed up with something. I forgot to mention I replaced the head gasket about 15 years ago due to coolant leaking into the oil. A few years after, I had to pull the oil pan and clean out the sludge and change the pickup. I also forgot to mention I had a minor mystery coolant leak start up again last summer and I suspect it was doing the same thing. I added some Bars Leak liquid aluminum and that stopped the consumption. But I bet that coolant contamination didn't help. I also found the camshaft position sensor was seriously baked. I am sure any moisture was shorting out the wires. My new plan is to run a bottle of Techron before I have the cats welded back on. The next oil change I may run a bottle of motor flush. I know that could very well make things worse. At this point it might be worth the gamble. I am not too worried since I could likely pay for a new engine with about 8 months of payments on a new Suburban. Don't get me started on what happened to the truck part of the new ones... This project wasn't without other drama (not just the heat index of 110). First, I am pretty sure I got fake AC Delco coils from an Amazon seller. I should have known at half the price. The box looked better than any AC Delco box I had ever seen or I would have likely fallen for it. It was a nice gloss. What is odd is the Amazon coils themselves look more legit than the actual one I got form O'reilly. The coil on the right is the real one. Does everyone agree, or am I being paranoid? It wasn't worth the extra $250 for the doubt, especially since they will likely take up residence on a new engine at some point.

I forgot to mention it is about to hit 340,000 miles. So it very well could be something valve related or other internal issue. The past few months I have noticed the valve tap, or whatever it is, that has been happening for the past 200,000 miles at startup isn't as loud as it once was. I guess it could be stuck. I replaced the plugs and wires. I also learned about the 2008 TSB about the AC Delco spark plug gap change from .060 to .040. Still had the misfire. Since they are all original and I plan to keep the truck, I have ordered new OEM colis, knock sensors, camshaft position sensor, and fuel pressure regulator. I am going to clean and test all of the injectors off the vehicle and clean the intake. It is soaking now. I did notice today while doing some pressure washing the little hose to the fuel pressure regulator was split at the boot on the intake. It might have been that. Ordered a new one of those too. Since I am in so deep, I am going to replace the valve cover gasket, mainly to take a look inside. If that doesn't cure it, it might be time for a long block. Then I will be making post to discuss a 6.0 swap. Thanks again Chem_man.

Ahh, so basically this vintage isn't able to tell the exact location of a random misfire. If it is bad enough it will be detected on a specific cylinder, thus a P0301 through P0308 code. Correct?

Thanks again chem_man for the info. I finally found a combination of Android and scan tool that would work with Torque Pro. It tells me: TID: $0c CID:$20 Max 172 Current 53,727 TID: $0c CID:$30 Max 381 Current 53,675 So obviously a misfire. I added in each cylinder and 0 was displayed for all of them. I would assume it has to track that somehow to throw a specific cylinder code. Do those numbers above correspond to a cylinder?

That is great to know. Now I just need to round up an Android device. Thanks for the info.

I see this is a pretty common issue, and I am trying to narrow it down. Thanks to a previous post, I know it is not my Catalytic converter. It idles fine and cruises down the highway fine, but even a slight hill, it is a pretty obvious miss. No MIL or stored code. My question is regarding the $06 data. I have purchased TOAD and OBD Auto Doctor but can't figure out how to display the cylinder misfire data count. Other $06 data displays fine. Is it safe to assume a 2000 is capable of outputting such data? I want to make sure I am not trying to get data that isn't there. It should be since it is OBDII, or is GM hiding it? I know it is a long shot, but if anyone is familiar with either program and how (if?) it works with a 2000 pcm, I would be very thankful to hear from you.