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Mysterious lean run engine destruction
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Question
Mrlees
Hi all. Purchased a 98 Sierra 1500 with the 5.7 with 100k miles to tow my race car last year please bear with me this is a long intensive troubleshooting process with little luck.
Soon after buying notice major power drop at WOT when I exceeded 3500 rpm.
I also noticed coolant consumption, took it to a friends shop and sure enough, the intake manifold gaskets were cracked and leaking coolant into the intakes.
Repaired that, but the low power at high rpm problem continued. Started logging data during driving and noticed severe lean issue (~.030 v on both O2 banks) when loaded at high rpm. MAF, MAP numbers were good,assumed low fuel pressure, went ahead and replace pump because on testing it was about 55 psi, not super low but out of spec so I did it.
No joy, replaced MAF and MAP and CATs (one after the other as each failed to resolve the issue) no solution yet.
Took it to a shop and had tech observe data during lean conditions while I drove pulling a trailer (loading it helps bring on the symptoms) held it lean to long, broke an exhaust valve Arghhhhh! Otherwise during driving conditions live data showed no faults or unusual data. Btw, cats had gotten white hot during last lean run, confirming lean readings were accurate
Buy new long block, installed with all top end components of old engine, of course the problem follows the electronics. WTF is next? I'm tired of throwing money at it and I'm out of money.
Summary:
Lean over 3500 RPM specially on WOT
New longblock
New fuel pump
New fuel filter
New MAF, Map, coil, O2 sensors, rotor, wires,
Confirmed 65psi fuel at WOT when lean
WOT MAF ~120
WOT MAP 80 not sure what units the system is logging
Also, runs great cruising, good O2 numbers just high RPM is when it happens. Love the truck but can't use it if I can't tow with it.
And no fault codes with the new engine (I could hold it lean long enough to get low O2 voltage codes on all sensors, but found out the hard way that is a horrible idea)
I really need help here, can't figure it out and 2 separate shops say everything looks good, no idea.
Any ideas? Thanks!
Lee, newly broke guy
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