This may be a dumb and completely unrelated point but I had a similar "miss" at WOT above 4k and it turned out my fuel pump was going bad and so I wasn't getting enough when I really needed it.

New pump no more miss.

 

The O2 sensor will only tell you if the things are rich or lean for a brief moment in time, it won't tell you by how much (similar to pulse-width modulation). And the accuracy of the sensor drops pretty dramatically the further you get away from a stoichiometric air–fuel mixture (ex. WOT). That was one of the reasons Bosch "ignored" the O2 sensor in the pre-torque based ECUs at high load levels. The long term fuel trim level in the MY96 ECU might point to something but...

 

It might be a few weeks till I get to this - lots of stuff happening and its hard to cram some diagnostics in the middle.

I will post when I chase again.

Cheers,

Mike

 

Ok, the issue appears to be solved - and it was pretty subtle (and a bit disturbing).

It appears the primary and secondary rotors on the distributor were not aligned, the secondary was out by a tooth or two. I am not sure how many because a local shop found the problem -> but they took apart the distributor, reset the alignment, and the car has been running very strong with no misses for over the last week.

I may phone the mechanic to find out exactly what he did so I know about it.

I had rebuild the distributor with a new belt about 20,000 miles ago and it had no issues, so the belt somehow slipped in the last 6 months or so. The belt looks new, it could be some wear on the notched pulleys, its hard to tell.

Anyways, the owner is estatic - this car really goes (no kidding here), and is now running strong right to redline in every gear.

We will keep our eyes on it to see if it reoccurs, and if so, we may have to replace some of the parts in the distributor.

Cheers,

Mike

 

Congrats, Mike. Must be a relief to have this one figured out, and here's to hoping there are no more issues with the distributor.