Ok, Here It Is. I Will Start My 2001 XJ With No Problem. I Start Driving And Everything Is Good. I Approach My First Red Light So I Come To A Stop. Then The Oil Pressure Gauge Slowly Drops To Below 10. Then I Press The Gas And Start Driving And The Oil Pressure Gauge Will Rise Again But Stays Below 30. Then I Stop Again And It Completely Drops To 0 And The Check Gauges Light Comes On. Then Again As I Drive, It Rises But Never Passes 30 And Will Drop To 0 Everytime I Stop. Then I Turn Off The XJ. If I Wait For 30 Minutes Before Starting It Again, It Will Start Normally, If I Start It To Soon It Will Struggle To Start. Sometimes It Just Doesn't Start At All. If It Does Start, I Will Put It In Drive And Press The Gas Only To Have It Completly Turn Off On Me Again. Took It To Firestone For A Engine Computer Check ( The Check Engine Light Was On Too) They Pulled Out Codes P0455 And P0463. They Also Told Me The Fuel Level Sending Unit Voltage Was To High And That There Is A Leak.

 

P0455 is a gross(large Evap leak) look under the hood for cracked or broken vacuum lines on the evap purge valve. The P0463 can be caused by alot of different factors, reset the codes (clear them) and see if p0463 returns. If it does more than likely your sending unit is failing and you will need to replace the fuel pump module.



P.S. From New Jersey

 

Do These Codes Relate To My Jeep Having Start-Up Issues And The Oil Pressure Gauge Dropping To Zero And Struggling To Rise?

 

Those are the symptoms of low oil. Might have a non-original dipstick, might just be low on oil. It might be electrical leakage in the wiring from the oil pressure sensor, might be a bad sensor. And, if the engine is not coming up to operating speeds/RPMs, it might just be fuel starvation is just keeping the engine in the doldrums.

Drain the oil, install a new oil filter, put in the correct amount of oil specified in the owner's manual (six quarts, if memory serves), run the engine until the oil pressure guage pops up, shut it down, wait two minutes and check the dipstick. Remember that reading.

I've seen cars with the wrong dipstick. Don't depend on it until you're sure it is right.

Turn the key on and listen for the fuel pump to kick on for two seconds, then stop. If you don't hear it, it isn't running.

Remove the schrader valve cap from the fuel rail and check to see if fuel squirts out, not dribbles, when you turn on the fuel pump.

Could be a plugged fuel filter, build-up of crud in the intake, bad injectors, lots of other things. Go after the problem by eliminating one thing at a time. You'll find the problem.

I think you have TWO problems, not one, and they are not related.

 

Yes, the vacuum leak can effect your fuel pressure. And yes, a failing fuel pump will most certainly cause it to run poorly and start hard.