I don't know what's out there for the Cherokee, but intake systems, exhaust systems, and sometimes chips can increase your mileage. Not sure what kind of injectors are out there for the cherokee, but different injectors could help to...kind of a fine line though.
I've heard some chipped/programmed diesels do better and I've heard/seen some do worse, so that would be something to look into with the Cherokee.
Basically anything that lets it breath better will definitely increase your mileage. Everything else has variables.
'94 ZR580
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