Codes

41 - Oxygen sensor circuit indicates system always lean.

Here is a listing of the Ford fault codes:

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

This can be caused by a vacuum leak or a cylinder misfire. A more elusive cause is a leak in the fresh air tube between the mass air flow sensor and the throttle body. If any air sneaks in without going through the mass air flow sensor, the engine computer will not know about it and will not command enough fuel to go with it. That will result in a lean condition.

A potential clue to a misfire is you may smell the unburned fuel at the tail pipe. Oxygen sensors only detect unburned oxygen, not unburned fuel, so while a misfire will send unburned fuel and oxygen into the exhaust, it is only the oxygen that gets detected.