Catalytic Conveter Failure?

[A26B]

I had a great day yesterday with a ZR-1 owner from Switzerland who came to visit. He is in Tulsa, on work, for a few days, happened to find me on Google & emailed to see if he could come to my "shop" to get some LT5 parts.

Background: 1990 ZR-1, with about 40,000 miles. he has owned the Z for about 6 years & does his own work.

Background: He has installed an EMS, stand-alone engine management system with A/F monitoring on each bank. This was done as a last resort to solve a chronic, inoperative secondary system.

Background: The engine began to smoke & use oil. On disassembly, he found the oil control ring lands , to be worn completely down to the same level as the center groove, on the RH bank only. The engine was repaired using NOS liners & Total Seal rings on the RH bank. Oil consumption was improved and compression was even on all 8 cylinders.

Tuning required about 10% less fuel on the RH bank. Endiscopic examination showed cylinder scoring on the RH bank & some flaking of the nikasil coating. The RH bank was again disassembled. There is no visible damage to the piston top or cylinder heads.

Endiscopic inspection of the catalytic converters showed the RH cat to have the catalyst "all pushed towards the rear", "blackened" and "somewhat melted but not seriously."

There is no miss, engine makes good power and virtually all sensors have been replaced before #1, including the ECM.

The questions are:
1. What could have caused the incredible wear to the original oil rings on the RH bank only?
2. What could have next caused nikasil flaking to the NOS sleeve/liners on only the RH bank cylinders?
3. Why would the RH bank need about 10% LESS fuel than the LH bank to achieve balanced A/F ratios?

I can think of no engine internal that could caused #1 & #2, with the possible exception of secondary throttle valves not opening on the RH bank causing #3.

I have heard of 90 model problems with cat failure and catalyst reversion into the engine, but there is no visible damage indicating that. The cat would seem to be bad but not to the extent of complete blockage. Could exhaust restriction/backpressure cause these problems?

What say you experts out there? Who has experienced Catalytic Conveter failure & what were the symptoms?

PS: I have invited him to the forum and to become a Registry member to take advantage of the fellowship & great help available here.