My 4 wheelin buddy and I were driving down the road and the check engine light came on in his 94 yj 4.0. We went to Oreilleys and borrowed their scan tool and the code was 52 rich condition detected at O2 sensor. We turned on the key (without starting the engine) and fuel pressure was right on spec at 32 pounds. Went to all of Jeep trouble shooting forums and went down the list. Pressure regulator, no help. Air filter, new. Fuel injectors, no help. New O2 sensor, still turned on light after 2-3 minutes of driving. I hooked up my fuel pressure gage and found that after starting the engine it had 95psi of fuel pressure!!! Figured out to check bypass line for restriction. Unhooked line at fuel rail and hooked up hose to drain bypassed fuel into a bucket. Pressure went to spec (32 psi with vacuum line hooked to regulator and 42 with vacuum unhooked). OK maybe a pinched return fuel line. Followed line to rear of Jeep and checked at rubber line coming out of tank. Fuel flows fine out of line. Dropped the tank could not blow through return line. Pulled fuel pump assembly see no real problems. Reassemble and reinstall tank. Check pressure everything ok. Run Jeep 5 minutes and light comes on again. Repeat fuel bypass test. Same results. Time to pull the tank again. Dropped tank and removed fuel pump assembly. This time I happened to look down into tank and see where return line has rubbed a shiny spot on plastic box fuel pump sets in. Either box is warped or tank guard has rubbed on something and bent bottom of tank up against return. Cut off return line 3/4 of inch above where it sets.
Put tank back together and reinstall. Everything is great. Even hard start problem is now gone. Jeep will start up on first or second revolution every time. I have a 95 YJ 4.0 Checked my fuel pressure same problem. Dropped tank cut off return line now getting 18.5 mpg on mine with 3.55s and 32" tires. I hope this helps other Jeep owners out there. We were about to pull our hair out over this.
Put tank back together and reinstall. Everything is great. Even hard start problem is now gone. Jeep will start up on first or second revolution every time. I have a 95 YJ 4.0 Checked my fuel pressure same problem. Dropped tank cut off return line now getting 18.5 mpg on mine with 3.55s and 32" tires. I hope this helps other Jeep owners out there. We were about to pull our hair out over this.
