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rough idle, then smooth, runs rough with any touch of the gas

831_xj

NAXJA Forum User
Location
Santa Cruz
96 4.0 auto

Just swapped a 91 block and head over to this 96 and swapped the appropriate sensors for obd2 engine harness as well. Been driving fine for 2 weeks. Was driving and came to a stop light. When I went to take off I had a crazy rough running jeep and couldnt get past idle speeds
Will start up and idle rough as hell, eventually the idle smooths out and is around the 750 rpm mark. ANY touch of the gas it with sputter and run like absolute crap.

I do have a scanner with live data

TPS voltage - 5.17 FEED 3.98 at WOT and .8 at closed.. smooth transition throughout
49 psi at idle fuel pressure and when attempting to gas
MAP "hg" 4.5 at idle
Swapped map with a known working one from another jeep
Swapped TPS from another jeep
changed the coil
changed IAC
changed plug wires and inspected spark plugs
changed cap
removed distributor and verified timing
changed fuel injectors
Tried unplugging o2, coolant temp sensor

Can't really think of anything else
 
Just a thought how are the o2 sensors and wires ?

What does the fuel pressure read when it's doing this? Fuel filter ?


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Mine would do something similar when my front O2 sensor was going bad. Never did throw a code.

I was kind of at a troubleshooting dead end and started throwing parts at it. Swapped the TPS, didn't help. Swapped the front O2 sensor and the issue disappeared.

I also had something similar when my CPS was oil soaked. Replaced the valve cover gasket and cleaned the CPS with brake cleaner. I really thought I was going to need to replace the CPS, been working fine for years. I have a new spare in my toolbox.

Another instance I can think of was when I had a wiring issue and my ASD relay would chatter. Redid a splice and all was well.

When I tore the wires loose from my rear O2 sensor and they melted on the exhaust I had all sorts of weirdness. I found that quick (couple of hours) doing a thorough visual inspection of all the harnesses with a high lum flashlight.

Found the orifice for my MAP mostly plugged with gunk, never caused any issues I was aware of, but seems like a probable trouble point sometime if ignored too long.

Out of ideas for the moment.

One thing I forgot, when my front O2 sensor went, the Jeep would run fine cold for a couple of minutes ( or about a block) first thing in the morning, then it would get cranky.
 
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Cris-crossed plug wires and or fuel injector connections?

My best bet is a poor vacuum seal from the throttle body to the MAP sensor.

Or a high voltage leak or bad wiring in the harness (damaged from the engine swap.)

Have you tried swapping the ICM yet or the CPS?
 
Run well or run poorly?

"It would run off factory settings with the o2s disconnected"
 
CPS has been swapped.. It runs the same with o2 disconnected.. poorly.

It ran fine for 2 weeks since the swap so no way wires couldve been mis matched. I've looked that over though.

TB was removed and MAP was swapped with a known functioning one. My old map is on the ZJ and is currently working as normal.
 
I'm leaning towards the Cam sensor crapping out..?

Could a shot torque converter be giving the CPS wonky readings?

This was an all of a sudden incident. Driving normal one second.. Take off from the streetlight and runs like dookie.
 
Cam sensor tested just fine with feed being 5.17. The other side reading 5v to 0v while turning over engine by hand. And fluctuating 2.3-2.8v while running

Checked the codes again and I am not so sure if these were thrown because I cleaned a connector by the driver side head light that was badly corroded with a wire brush while the key was on.. or if they're related

P0113 - Intake Air Temperature Circuit High Input
P0138 02 Sensor Circuit High Voltage (Bank I Sensor 2)
P1492 Battery Temperature Sensor Voltage Too High
P1391 Intermittent loss of CMP or CPK
 
Like I said before it sounds like some damaged wiring in the harness.
 
Have you checked closely for wiring damage where the O2 sensor/CPS sensors wires get close to the front drive shaft, exhaust manifold areas. A 12-14 volt power line to the Or sensor heater could have melted in the harness near those sensors wires and causing the high voltage codes on the sensors.
 
Is the throttle body dirty? Is the IAC stuck? Have you looked at the butterfly or is the throttle body gasket leaking?

You keep checking sensors and not finding anything wrong. You need to start troubleshooting the basics.

You need to read post 13 I think.
 
Found a tranny bolt had worked its way out.. Guess I forgot to torque one. Was a gap between the motor and trans.. Bolted tight now it won't stay running, looks like the flex plate scraped up the tip of te cps.. I'll report back after work. I'm going to look much much more thoroughly at the wiring.
 
Have you checked closely for wiring damage where the O2 sensor/CPS sensors wires get close to the front drive shaft, exhaust manifold areas. A 12-14 volt power line to the Or sensor heater could have melted in the harness near those sensors wires and causing the high voltage codes on the sensors.

Definitely going to look closer when I have some more time, thanks for your patience.
 
Found a tranny bolt had worked its way out.. Guess I forgot to torque one. Was a gap between the motor and trans.. Bolted tight now it won't stay running, looks like the flex plate scraped up the tip of te cps.. I'll report back after work. I'm going to look much much more thoroughly at the wiring.

Flex plate may be cracked :(
 
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