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2002 wrangler 4.0 low power

10K views 55 replies 10 participants last post by  Tkeltgen 
#1 ·
I've got a 02 TJ 4.0-3 speed auto and 3.73's with what appears to be low power, just bought the jeep a week ago. Changed all maintenance stuff so that I could think of to have a good starting point. Haven't checked to see if it has thrown any codes. It's got 265/70/18's on it. Low ends not bad but mid range is kinda poor and top end is really slow in recovering interstate speeds if I have to slow down. It's running just over 210 deg.

Just wondering if it's the tire-gear combo or a cat issue? Seams a little warm to me.
Going to check manifold and pre and post cat temps tomorrow to see if anything jumps out at me.

Any thoughts anyone?
 
#7 ·
How fast are you calling highway speed
What rpm at that speed and how much grade on the road

A TJ ain't a sports car and while that non overdrive three speed auto is robust and trail worthy you cannot run too low gears and have reasonable highway rpm as it has no overdrive


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#10 ·
Unless you've owned a tj before you can't gauge what's normal or not in a weeks worth of ownership.Tj's in a class of their own, slow bricks and horrible HWY vehicles.
But very fun to drive once you understand them.
210 is the normal operating temp for the 4L.
 
#11 ·
Might have found part of my problem, yesterday on the way to work it thru p0300 and p303 codes. Then on the way home (have way) it appears to have a dead miss. Going to get a reader today to see if it's the same cylinder. I'm leaning towards the coil rail, we'll see after some testing. She gets to stay home today, don't want to burn up a cat.
 
#12 ·
The #3 cylinder is in the middle where it gets really hot. Check the exhaust manifold for cracks there and that the heat shield is still in place top of the intake runners for 3 & 4 cylinders in the center. Also look for the 3 & 4 Injector heat shields that protect the injectors for heat soak after engine shut down. There is a TSB (18-031-03) out on this. Inspect the injector wires for 3 & 4 also for heat damage.
 
#15 · (Edited)
Those tires are almost 33" in diameter and are going to need some lower gears to get anywhere near the power you're looking for. According to the charts...looks like you need 4.88's.
 
#16 ·
4.88 with 33 inch tires and a three speed non overdrive auto no way I would recommend that

Even with a 4.0 with an overdrive 5 SPd most recommend only 4.56 and they run nice on highway with 4.11

I have a98 sport with 4.56 and 33 and my wife has a 04 Rubi on metric 32.5 ish with 4.11 and on the road I prefer the 4.11. Both are 5 spds


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#17 ·
If you look at the numbers...the three speed with 4.88's will perform very similiar to 5 speed with 4:56...which is a great combo and what I run with my 5spd.
 
#20 ·
I run 33" with a 4.10 with my 3 speed. Its definitely not a highway driver, but the rpms even at 65 mph should not really hurt the I6 by any means.

I also had misfires for awhile, partially was dirty injectors.It eventually led to me replacing the crankshaft and cam shaft sensors. Those misfires led to me not being to start my jeep at all; luckily I was in town.
 
#22 ·
I found this when looking what was recommended for gears with 32" tires:

Also, when making altering your factory gear ratio or wheel size your speedometer and odometer may read incorrect. Make the necessary changes to your speedo by replacing your Jeep Speedometer Gear .
A basic method to calculate is to mutiply .12 by your tire diameter. (.12 X 38" = 4.56)

Yesterday it thru two different codes:
P0300, P0303, P0305
How would I know if the the two sensors are malfunctioning ( Crankshaft and camshaft)?
 
#23 ·
Not sure how you check the sensors, I found out the hard way;it didnt start. But those sensors may intermittently cause issues. My camshaft sensor completely failed, but decided to replace both; cheap insurance. Cost me close to 1000 to fix those.
Maybe run it by the dealer to check them. ???
 
#25 ·
Ok, replaced the cam sensor Sunday along with clearing codes. It thru codes today but not sure yet which ones. I'll read them tomorrow to see if the same ones. Wasn't thinking it would be the crank sensor that could cause randoms??
The next two thing I'll verify will be compression and then fuel rail pressure.
 
#26 ·
Still confused: the codes it thru were 300, 303 and 305. But it ran fine, yesterday coming home. 45 min into an hour drive the CEL started flashing on a decel, then within a few minutes it started with a heavy miss. Picked up a code reader and read it when I got home. It thru misfire codes in each cylinder except 306. It was running fine until then and the once it cooled down it runs fine again. In the last week and a half we've replaced plugs, coil rail camshaft sensor. During the issue yesterday it felt like either fuel delivery issue or a coil breakdown, with a heavy throttle response it would fall on its face with bad pulsating buck ( kind of like a rev limiter would do). It runs fine now, so I think it's a heat up related issue?? I have only recieved misfire codes up this point. I was thinking about checking fuel pressure at warmup. Any help would be appreciated, Thanks
 
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