PO300 after replacing passenger side lifters

[Scott Stitham]

2002 Yukon XL 1500 5.3. At start of shutdown began eventually rebuilding engine with foster son- learning as we went. When finally got on road, had a period of terrible issue with oil control, PCV sucking oil, bad lifter noise. Came to suspect bad lifters bought off Amazon, so three weeks ago replaced drivers side with Sealed Power lifters, and cleaned a lot of oil out of intake manifold. This solved the oil issue, raised oil pressure, and finally made it run like it had been rebuilt. No pinging, knocking, fouling, sucking oil- just this awesome truck for a few weeks and around 1500 miles.

However, the crappy lifters were still on the passenger side, and especially at start up we got lifter noise until they pumped up, but then eventually the lifter noise grew more consistent. So this weekend we replaced the lifters in that side as well, which solved the lifter noise.

But less than a minute after starting, it began to run rough and shake. The interior lights began to surge with the engine. Threw code for PO300, then warning it was severe and would cause damage to drive. Subsequent starting was rough, then would start but in less than a minute would run rough and throw code.

We have replaced the intake manifold gasket and smoke tested, but can find no leak. Replaced MAP sensor. Checked for spark, replaced plug wires (we had extras around), and then plugs on passenger side- all with no change. The plugs were only a few weeks old, but the center ones- 2 and 4- were noticeably dirtier with more black and a stronger gas smell. Our thinking has been to look for things in that side we just worked on, as it was running great before we changed out those lifters. There is also a strong gas smell from exhaust.

Looking at live data at idle, notice LIFT B1 is -16%, while LIFT B2 is 18%.

So stuck with this rough idle and random misfire, with no idea where to look next. Any ideas?

 

[Scott Stitham]

So we isolated the problem, finally testing for compression. We also pulled the valve cover to see if there were any problems, but the rocker arms all seemed to be working normally.

However, we did compression test on that head and found C2 at 0, C4 at 145, C6 at 10, and C8 at 30. This is a rebuilt head that was not having problems prior to this, and is still u dear warranty. Rings were replaced. Engine was running great except for the lifter noise, and we replaced with Sealed Bearing lifters identical to what we installed in other head three weeks ago.

I guess the next step is a leak down test?

 

[exp500]

Low compression in more than one cyl makes me think valves open. recheck. Pressure check coolant sys. for head gasket issue. Post full vehicle details. We are here to help.