Might be chasing a non-issue - not sure. It has been this way since I got it - the jeep feels very sluggish. I had a 2.5 years ago and was always told to get the 4.0 as it was "fast for a jeep" .I tried some 0-60 times to test against *normal* stock times of 9-10 seconds. The jeep is fully stock at this point and the BEST i could manage was 12.64 and that was starting off in 2nd. So about 25% slower vs expected. 3.73 gears 30x9.5 stock tires. Now I know its "not built for speed", but I do think it indicates something off. Now could it be the 200K miles? Maybe. But with all the work that was done before and after I got it (last 10K miles - oil pump, timing chain, cam, lifters, push rods, plugs, etc) it really is in exceptional mechanical condition. It doesn't smoke, leak oil, etc. It runs 60 PSI oil pressure down the road, and 30-40 idle.
I suspected a cracked exhaust manifold because I could hear it. I tested with soap water and shop vac in reverse and found leaks on the gasket, as well as above the back mini cat. I tore it down to replace the gasket and inspect the manifolds closer. No cracks! New gasket and the mini cat connections are nice and tight - all verified by soap water and reverse vac. I thought this might help, but I didn't notice anything. Its quieter for sure, but performance wise feels like I'm dragging something.
Online said could be exhaust restriction. I checked back pressure in the exhaust system at both pre-cat O2 sensors. In both cases, there is almost no back pressure. it stays right at 0 at idle. And I might get .1 -.2 PSI with engine at 2900 RPM. So very low based on specs. I read this can actually be too low and might cause the sluggish feel as well since it prevents the exhaust from "scavenging" properly. I tested the gauge best i could - and a human and blow about 2 psi into a bottle (google) and that is what I can blow as well - so I suppose I am human after all.
There are no check engine lights.
Next steps, in my mind:
1. Inspect the main cat and muffler to see if there is anything in there. The mini cats looked OK - all ceramic was intact and present. But its possible the PO didnt realize the main one came apart.
2. Cylinder compression test. I did check the cooling system for combustion byproducts (CO2) and it was clear (head gasket check). Antifreeze is clear with no oil residue. Oil is good - no foam or water.
3. I just cleaned the Throttle body and idle air sensor. But during the back pressure test noticed the two O2 sensors are different - probably not an issue unless one is bad, but bad O2 sensors can cause it to be sluggish as well.
4. PO had timing chain replaced when the cam was replaced - possible timing issue - maybe a tooth or 2... I am not sure how detectable that would be. There have been no indications that this could be it.
5. Fuel rail pressure check
6. Swap injectors?
Watching videos online of stock acceleration in 4.0 wranglers makes me think I am not barking up the wrong tree... thoughts ideas or suggestions?
I suspected a cracked exhaust manifold because I could hear it. I tested with soap water and shop vac in reverse and found leaks on the gasket, as well as above the back mini cat. I tore it down to replace the gasket and inspect the manifolds closer. No cracks! New gasket and the mini cat connections are nice and tight - all verified by soap water and reverse vac. I thought this might help, but I didn't notice anything. Its quieter for sure, but performance wise feels like I'm dragging something.
Online said could be exhaust restriction. I checked back pressure in the exhaust system at both pre-cat O2 sensors. In both cases, there is almost no back pressure. it stays right at 0 at idle. And I might get .1 -.2 PSI with engine at 2900 RPM. So very low based on specs. I read this can actually be too low and might cause the sluggish feel as well since it prevents the exhaust from "scavenging" properly. I tested the gauge best i could - and a human and blow about 2 psi into a bottle (google) and that is what I can blow as well - so I suppose I am human after all.
There are no check engine lights.
Next steps, in my mind:
1. Inspect the main cat and muffler to see if there is anything in there. The mini cats looked OK - all ceramic was intact and present. But its possible the PO didnt realize the main one came apart.
2. Cylinder compression test. I did check the cooling system for combustion byproducts (CO2) and it was clear (head gasket check). Antifreeze is clear with no oil residue. Oil is good - no foam or water.
3. I just cleaned the Throttle body and idle air sensor. But during the back pressure test noticed the two O2 sensors are different - probably not an issue unless one is bad, but bad O2 sensors can cause it to be sluggish as well.
4. PO had timing chain replaced when the cam was replaced - possible timing issue - maybe a tooth or 2... I am not sure how detectable that would be. There have been no indications that this could be it.
5. Fuel rail pressure check
6. Swap injectors?
Watching videos online of stock acceleration in 4.0 wranglers makes me think I am not barking up the wrong tree... thoughts ideas or suggestions?
