So I think I have exhausted all the information here on the forums about this code. I dont know if it makes a difference, but my TJ is the 4 banger and all the info I've seen seems to point to the 4.0L. So here's some pretty detailed history of my TJ up to the P0301 code and what I have done so far... with questions to see if I am heading in the right direction.
Purchased a 98 2.5L TJ in May 2019 with 158K miles on the clock (I dont know how accurate that is because I have been having the issue with intermittent gauge display death). She had some problems passing California smog so I brought her in to a shop that was willing to work on her.
1. cracked exhaust manifold. replaced.
2. bolts broke off in the head when removing the manifold. pulled the head, sent to a machinist, cleared the threads, cleaned the head of all the built up carbon.
$2000 later I drove home my jeep. definitely ran MUCH better than when i bought her. and smog was passed. I have a few years to figure out the rest of this lol. An improvement, though expensive.
Threw some 31" tires on with 1.25" spacers for a little more clearance over the bald rubber that was on her and noticeable stability on cornering. Definite improvement in handing but loss of felt torque because of the bigger tires. Especially when going uphill. Like 65mph on the freeway, 3% incline comes up, have to drop to 4th gear because it sucked my speed down to 55.
Changed the gear oil in the differentials next. Easy enough. Have no idea when it was last done. Oil came out like molasses. New oil went in like olive. Still had to down shift to 4th, on same "uphill" stretch of freeway, but it took longer to get to that. 1st and 2nd gears got a small dose of steroids though.
Then 2 weeks ago I noticed that my idle wasnt as smooth. Some very slight dips on the tachometer intermittently. Didnt think much of it until 2 days later the CEL came on. Borrowed my neighbor's reader and showed P0301. No other code. Did my research, a lot of it on the posts here. Figured why not do a tune up since I dont know when the last one was done either.
1. Bosch double iridium plugs x4
2. ACDelco wires
3. Duralast Distributor cap and rotor
Battery was disconnected to reset computer during the changes. Hooked everything back up. Test drove for about 50 miles. Engine is STRONG. No more slowing on the freeway. Hills that I normally have to downshift to second, I can accelerate on in 3rd. But the idle still dips. And alas, the CEL came back on.
Loving this JEEP and I want to take care of her. Would love to get 100K miles out of her before I have to move on... to another TJ of course. She drives so well now. But that CEL is a dark cloud hanging over my head! Soooooo... here's what im thinking...
I have the 4Cyl motor. Should I still check to see if mine is a TUPY or not (not sure if that only applies to the 6cyl) or are cracks in the head not a common problem on the 4 bangers?
RPMs just barely dip at idle. A Harley is much worse (I should know lol). Should I still consider the fuel injectors? Are the 4 hole injectors recommended?
Should a compression check be my next step?
Really appreciate any help you guys can offer me at this point. I still have a few years before my next SMOG but a lot can still happen in that time too lol.
Purchased a 98 2.5L TJ in May 2019 with 158K miles on the clock (I dont know how accurate that is because I have been having the issue with intermittent gauge display death). She had some problems passing California smog so I brought her in to a shop that was willing to work on her.
1. cracked exhaust manifold. replaced.
2. bolts broke off in the head when removing the manifold. pulled the head, sent to a machinist, cleared the threads, cleaned the head of all the built up carbon.
$2000 later I drove home my jeep. definitely ran MUCH better than when i bought her. and smog was passed. I have a few years to figure out the rest of this lol. An improvement, though expensive.
Threw some 31" tires on with 1.25" spacers for a little more clearance over the bald rubber that was on her and noticeable stability on cornering. Definite improvement in handing but loss of felt torque because of the bigger tires. Especially when going uphill. Like 65mph on the freeway, 3% incline comes up, have to drop to 4th gear because it sucked my speed down to 55.
Changed the gear oil in the differentials next. Easy enough. Have no idea when it was last done. Oil came out like molasses. New oil went in like olive. Still had to down shift to 4th, on same "uphill" stretch of freeway, but it took longer to get to that. 1st and 2nd gears got a small dose of steroids though.
Then 2 weeks ago I noticed that my idle wasnt as smooth. Some very slight dips on the tachometer intermittently. Didnt think much of it until 2 days later the CEL came on. Borrowed my neighbor's reader and showed P0301. No other code. Did my research, a lot of it on the posts here. Figured why not do a tune up since I dont know when the last one was done either.
1. Bosch double iridium plugs x4
2. ACDelco wires
3. Duralast Distributor cap and rotor
Battery was disconnected to reset computer during the changes. Hooked everything back up. Test drove for about 50 miles. Engine is STRONG. No more slowing on the freeway. Hills that I normally have to downshift to second, I can accelerate on in 3rd. But the idle still dips. And alas, the CEL came back on.
Loving this JEEP and I want to take care of her. Would love to get 100K miles out of her before I have to move on... to another TJ of course. She drives so well now. But that CEL is a dark cloud hanging over my head! Soooooo... here's what im thinking...
I have the 4Cyl motor. Should I still check to see if mine is a TUPY or not (not sure if that only applies to the 6cyl) or are cracks in the head not a common problem on the 4 bangers?
RPMs just barely dip at idle. A Harley is much worse (I should know lol). Should I still consider the fuel injectors? Are the 4 hole injectors recommended?
Should a compression check be my next step?
Really appreciate any help you guys can offer me at this point. I still have a few years before my next SMOG but a lot can still happen in that time too lol.
