OK, here's the deal. My 1998 Tahoe has a Vortec 5.7 liter, 4L60E, and is a 4x4. I just recently put in a brand new GM crate longblock (old motor spun a rod bearing). These Vortec's have a fuel injection setup that is not your "run-of-the-mill" sequential FI. They have what is called a Central Sequential Multiport Fuel Injection system (CSFI)...some refer to it as CPI. Anyway, it uses a central fuel control metering body that houses 8 individual injector packs. Then you have 8 poppet valves for each cylinder leading off of the fuel metering body. The FP regulator is housed inside of the upper plenum of the intake and does not depend on ported vaccum, but it is prone to leak.
Anyway, these CSFI metering assemblies are prone to problems especially with the poppet valves. The PV's are spring loaded so they depend directly on fuel pressure to open correctly.
Well enough rambling...we determined that my #1 and #2 poppet valves were not functioning properly, however there are no cylinder misfires or anything else abnormal on the scanner for that matter. Oil pressure is good. We can audibly hear "lean popping" and upon inspection of the 1 and 2 plugs, they show extremely lean.
The problem is, the 1 and 2 cylinders were apparently burning significant oil due to the white/blue smoke. We chalked this up to the extremely lean condition causing a lack of upper cylinder lubrication and the rings getting roasted. The valve seals are brand new and still good. The upper guides look fine(new heads).
Funny thing is we just ran some very strong cleaner through the poppet valves in an attempt to "free" the 1 and 2 poppet valve and although it did run much better after this, it is obvious that the 1 and 2 are still not getting "full" fuel delivery (plugs still show lean and a infrared thermo test shows the 1 and 2 primary much colder than the rest). But now the white/blue smoke has dissappeared??
Anyone care to take a stab?
I'm still working on this, but I'm open to ideas!
BTW I bought a full warranty, so I'm pretty darn close to just swapping out longblocks AGAIN!
Anyway, these CSFI metering assemblies are prone to problems especially with the poppet valves. The PV's are spring loaded so they depend directly on fuel pressure to open correctly.
Well enough rambling...we determined that my #1 and #2 poppet valves were not functioning properly, however there are no cylinder misfires or anything else abnormal on the scanner for that matter. Oil pressure is good. We can audibly hear "lean popping" and upon inspection of the 1 and 2 plugs, they show extremely lean.
The problem is, the 1 and 2 cylinders were apparently burning significant oil due to the white/blue smoke. We chalked this up to the extremely lean condition causing a lack of upper cylinder lubrication and the rings getting roasted. The valve seals are brand new and still good. The upper guides look fine(new heads).
Funny thing is we just ran some very strong cleaner through the poppet valves in an attempt to "free" the 1 and 2 poppet valve and although it did run much better after this, it is obvious that the 1 and 2 are still not getting "full" fuel delivery (plugs still show lean and a infrared thermo test shows the 1 and 2 primary much colder than the rest). But now the white/blue smoke has dissappeared??
Anyone care to take a stab?
I'm still working on this, but I'm open to ideas!BTW I bought a full warranty, so I'm pretty darn close to just swapping out longblocks AGAIN!
I am going to probably get everything fixed on it this weekend and put her up for sale for a reasonable price. It's time for a new tow vehicle. Do you want a Hoe! 
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