Engine on 1990 Jeep Wrangler

Why is engine sputtering at high speeds? Oxygen censor has been replaced, tune-up has been done. Thank you if can help
me out.

Asked by for the 1990 Jeep Wrangler
You should have the fuel pump (pressure and volume) checked and the ignition system. Either of these could be your problem. Also have them check for a plugged exhaust system.
1 more answer
Check spark plugs and lines. I had a similar problem and this solved it on my 2000 Wrangler.