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torquemeister

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  1. I finally got to work on this again today. Here's what I did: 1. wired up a push button starter from the starter solenoid to watch while turning the engine over. All 16 valves go up and down and look like what I would assume is normal. 2. removed all 8 spark plugs. #8 is completely black at the tip but does not look wet/oily. 3. compression test on all cylinders with the plugs out and with the valve covers still open. 1 = 180 2 = 210 3 = 220 4 = 170 5 = 220 6 = 180 7 = 180 8 = 0 (ZERO, never moves the needle on the gauge) The valve springs for #8 don't look broken. So this project has gone from me assuming I was doing lifters and maybe the camshaft to something entirely different. Question is, what is my next step and what is the common/likely cause or causes?? Thanks, -Chris
  2. My initial troubleshooting was based on cylinder 8 being the initial issue, but the P0300 set pretty quickly after the P0308. I bought an inexpensive scanner that gave live misfires by cylinder and it pointed to multiple cylinders. It's been a while since I did it but I remember cylinders 4,6 and perhaps 7 having the most misfires. I had pretty much convinced myself it was a collapsed lifter and parked it for about a year, so some of the details are fuzzy.
  3. 2007 suburban 5.3 with AFM. First it threw P0308, then P0300, and it goes into "limp mode" with the service stabilitrak message. It ridles/uns really rough with a lot of vibration, like it could die at any second. The clear ticking sound that gets even more obvious as RPMs increase. I was just assuming it was at least one collapsed lifter, possibly more. Last night I took both valve covers off and none of the rockers move freely. Could it still be a collapsed lifter if all 16 rockers are tight? Or is there a different most likely cause that fits these symptoms? I'm guessing the next step is to turn the engine over a few times to see if all 16 valves are moving? If so, what is the easiest way to do this? Turn the key like I'm trying to start it or will that mess something up? Thanks, -Chris
  4. Thanks, that explanation makes a lot of sense. It still runs pretty rough, even when it doesn't throw a code (while the MAF is unplugged). Makes me wonder if there is an issue that will have me taking the valve covers off as previously suggested. I'll start looking at replacement MAFs. Anybody have and experience with the cheap ones online? Or just suck it up and go with OEM?? Thanks, -Chris
  5. The only code is for the MAF being unplugged. If I plug the MAF back in, I get misfires on 7 & 8 and just a P0300 code. With MAF out, just MAF error. Compression was good on all cylinders - that was the first thing I checked when all of this started. I don't remember the actual readings now, but I believe all 8 cylinders were in the 145 - 160 range. Thanks, -Chris
  6. with engine running I had 14.4V on the power and ground. Hz readings were 2.7kHz at idle and it went up to around 4.5kHz when it was around 2500 RPM. It seemed to be responding correctly. The scanner's live data on the MAF was about 6g/s at idle and all the way up to about 33g/s at 2500 RPM. Thanks, -Chris
  7. When watching the scanner live data, I'm seeing it jump to 45-50 degrees of timing advance on #1 cylinder when RPM are in the 2500 range. It settles back down to 10-15 range at idle. Is this normal? I would never have guessed timing would be that advanced on a stock engine, so it might be a clue. The misfires go away completely if I just unplug the MAF sensor, but it still runs really rough and throws the stabilitrak disabled codes, which cause violent 1st to 2nd gear shifts. Thanks for everybody's help on this, -Chris
  8. Merry Christmas! I finally had some time to get back on this yesterday. I was really hoping to avoid pulling the valve covers. I'm not familiar with the VLOM so I'll have to read up on that. I replaced fuel injectors 7 & 8 and it idled rough but without codes. That was before I put the air hose and resonator back on. Once I put it all back together, it started throwing the P0300 code again for misfires and 7 & 8. That makes me think something like not getting enough air. I don't see any holes or cracks in the plastic from the air filter to the throttle body. Could it be a MAF issue? While running without the air hose/resonator, it went into closed loop and had no misfires. Once reconnected, it went back to open loop - fault and started misfiring. The upstream o2 sensors would go down to about .05 when I pressed the accelerator and then back up to .8 when idling. No codes for MAF, even when it wasn't hooked up to the air hose and was reading 0.00. I thought that would throw a code for sure. Thanks, -Chris
  9. I never saw the fuel pressure drop below ~53, even while hitting the gas. I didn't notice the coolant temp on the scanner; the dash gauge was reading 210 (normal) once it was warmed up. I'm not sure what you mean about incomplete monitors? Thanks, -Chris
  10. I have a 2007 5.3L that started getting P0308 misfire codes on cylinder #8 a couple of months ago. There were no issues with how it drove or idled at that time. Last week it switched to the generic P0300 code and started idling really rough; it gets a little better if you put it in park or neutral with higher RPMs. I changed plugs and wires with AC Delco for both. I found the PCV tube broken and replaced that. I checked fuel pressure at the rail, it's 58-60 at idle and running, and 60 with key on engine off. I bought a scanner tool that gives misfire counts and live o2 voltages. cylinders 7 & 8 both have hundreds of misfires over the course of a 10 minute idle in the driveway. All 4 o2 sensors read around .85V with very little fluctuation. The fuel status is listed as Open Loop FAULT. The only code I've seen recently was the P0455 which I assume came from opening the gas cap when depressurizing the fuel system to connect the pressure gauge. What should my next step be? Thanks, -Chris
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