Fltmedic12

Hello fellow Jeepers, here is todays problem.


1998 4.0 5spd AX-15


loss of power is noticed at low RPM, mainly immediately after shifting. It will last anywhere from a brief moment (<1sec) to about 2-3sec. I would best describe it as a dead spot in the throttle. After shifting I can feel power, then what feels like complete loss of power and the Jeep will stutter, then complete power again. Sometimes this will happen at the end of gear change causing the Jeep to buck. I have reduced the occurrence of this by preloading the throttle slightly more during shifting (about 1500rpm). This "dead spot" can be reproduced when in neutral and throttling up to about 1000-1200rpm, it will come up, cut out, then come back up to about 1500rpm. In the last month or so it has become more problematic with the dead spot lasting longer or not going away at all without letting off the throttle completely and reapplying power.


What I've done (not in order or all at once)


Ignition (from coil to plugs)
cleaned the TB and IAC
checked and repaired all vacuum lines
replaced exhaust manifold (crack at the collector)
replaced TPS x2 (1st replacement was bad, held idle rpm at around 2000)
replaced #1 O2 sensor


Last oil change was approx. 500 miles ago
Idles smooth at around 700-750rpm
15ish mpg city
Exhaust is slightly rich smelling with a faint sound of a miss
No CEL illumination


Researched showed majority of folks experiencing a similar issue resolved it with TPS replacement, complete tune up, or TB/IAC cleaning. None of which was my case. One case I found claimed an exhaust leak was causing issues with the #1 O2 sensor, also not in my case. This has been an ongoing issue since I took ownership of the Jeep and is one of the last issues I need to work out. Any and all input will be greatly appreciated. Thanks

Ranger_Dan

My guess would be to look for a vacuum leak...It would explain the lagging in acceleration under power. Does it return to a good idle during the lag if you let off the gas?
I also mean to ask, does it studder regardless of you being in gear our out of gear, or is it just easier to get it to lag on in gear acceleration.
That's my guess...Could also be the computer but I doubt it personally.

RTorrez1

Start by checking for any codes. You can still have stored code even without a CEL.

Fltmedic12

Ranger Dan - no vacuum leaks, checked and double checked. Condition is reproducible in and out of gear. I guess I should have mentioned ECU was replaced as part of initial repairs back in 2012. ECU came direct from Chrysler.


RTorrez1 - no stored codes, I guess I should have specified that.


Just something else I should mention, condition presents with cold and op temp engine (open and closed fuel system)

Ranger_Dan

How about the throttle body, Throttle position sensor, could be that to...They can go without a quietly without a code like yours...It works, just not right.

Fltmedic12

Please refer to my initial post

sycoglitch

You have not stated what brand TPS etc you used in your initial post

travis99xj

Have you checked cam and crank sensor signals

travis99xj

Or even your distributer

Fltmedic12

I haven't checked the CPS but the cam sensor was as part of the complete tune up. will look up the numbers and check the CPS tonight after work.


And to clarify I ONLY replace with OEM parts, so both TPS's were OEM

salad

Try testing the ECT, IAT, and MAP sensors. Also see if you can watch fuel pressure while this happens.

Have you actually tested the TPS?