99 XJ drop in mileage and top end power.

[Geonovast]

99 XJ 4.0/AW4/231.

 

I've had the truck for almost 3 years, and up until recently it was pulling 21-22 on the highway consistently. I was ok with this.

 

About 2 months ago or so, my mileage tanked to about 14-15. Wasn't any effect on power.

 

The last few days however, I've noticed that once I get above 50 mph, the thing just doesn't want to really go. I can get it up to 75, but it takes much longer than usual and requires more pedal to keep it there.

 

Also, every once in awhile, it will have a massive loss in power right when I'm starting to drive. I'll start it up, put it in drive, give it some gas, and it just falls flat on its face as if I'm suddenly trying to get 10,000 lbs moving behind me. It'll do that for 2-3 seconds, has backfired on me, and then it'll be fine for the rest of the drive.

 

I'm leaning toward some kind of fuel delivery problem, but not really sure where to start. Unfortunately my fuel pressure tester is inaccessible.

[87Chief]

Check your O2 sensor, and check your exhaust manifold for any cracks