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Paul Workman · 09-30-2011

It definitely sounds like a fuel related issue; similar to O2 issues and injector issues. For what it is worth, I've had a fuel pump fail right out of the box!

Note: While studying failure rate as part of a paper I was doing on MTBF, I came across several statistical analyses showing two high risk periods in the life of (both animate and inanimate) objects: Failures are low until the object reaches a certain point in it's life. At some point, the rate of failure begins to climb; gradually at first, and then the failure rate begins rising ever more quickly - don't we all know it! But, by far the most failures in a very short time occur at the onset of the object's life - resulting in the phrase, "infant mortality". It seems to defy logic: "It can't be the (so and so), it's brand new..." (And, so it was too with a new fuel pump I installed...Bad out of the box!)). Bottom line? Completely forget about age of an object...Verification is the only way to be sure it is working!

Read the plugs and compare each bank. And, if you could data log (scan) it while driving, you could gather a plethora of information about what's going on in REAL time, e.g., O2 cross counts, right and left BLMs (and injector dwell).

Injectors: Haven't seen where you've measured resistance across each injector (after the engine is good and warmed up). If they are the stock injectors, they need to be replaced. (Mine were replaced, at my request, the day before I took delivery from the dealer. Problem was, as I found out later, the were replaced with NOS and the problem with alcohol showed up again when I gave the car to Marc H for tuning. I was chagrined

to say the least! But, I digress...) They need to be of uniform resistance (usually within a spread of an ohm), around 12.5 to 13.5, by most accounts.

All of this to say that you'll want to get to the bottom of the lean condition right away. Otherwise, you might be looking at burning a valve (or worse) and if $300 is hard to come by, try overhauling the head on an LT5! Its hard to say what could happen for sure if one side is less restricted than the other; it would depend on circumstances. The LT5 is not cheap to fix, so I would not be wanting to stress it until the known issue was resolved.

FWIW,

P.

09-30-2011	#14
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: 1990 exhaust manifold issue... It definitely sounds like a fuel related issue; similar to O2 issues and injector issues. For what it is worth, I've had a fuel pump fail right out of the box! Note: While studying failure rate as part of a paper I was doing on MTBF, I came across several statistical analyses showing two high risk periods in the life of (both animate and inanimate) objects: Failures are low until the object reaches a certain point in it's life. At some point, the rate of failure begins to climb; gradually at first, and then the failure rate begins rising ever more quickly - don't we all know it! But, by far the most failures in a very short time occur at the onset of the object's life - resulting in the phrase, "infant mortality". It seems to defy logic: "It can't be the (so and so), it's brand new..." (And, so it was too with a new fuel pump I installed...Bad out of the box!)). Bottom line? Completely forget about age of an object...Verification is the only way to be sure it is working! Read the plugs and compare each bank. And, if you could data log (scan) it while driving, you could gather a plethora of information about what's going on in REAL time, e.g., O2 cross counts, right and left BLMs (and injector dwell). Injectors: Haven't seen where you've measured resistance across each injector (after the engine is good and warmed up). If they are the stock injectors, they need to be replaced. (Mine were replaced, at my request, the day before I took delivery from the dealer. Problem was, as I found out later, the were replaced with NOS and the problem with alcohol showed up again when I gave the car to Marc H for tuning. I was chagrined to say the least! But, I digress...) They need to be of uniform resistance (usually within a spread of an ohm), around 12.5 to 13.5, by most accounts. All of this to say that you'll want to get to the bottom of the lean condition right away. Otherwise, you might be looking at burning a valve (or worse) and if $300 is hard to come by, try overhauling the head on an LT5! Its hard to say what could happen for sure if one side is less restricted than the other; it would depend on circumstances. The LT5 is not cheap to fix, so I would not be wanting to stress it until the known issue was resolved. FWIW, P.