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Idle/starting issue

553 views 9 replies 4 participants last post by  trol1374 
#1 ·
Posting this here because even though my jeep is a TJ it's still a ZJ engine. With that said, I've had a rebuilt 5.2 in my jeep for about 4 years now. It's been great. This past week I went on vacation and my jeep sat for about 6 days. I tried to start it today and the only way it would run is if I gave it some throttle, even then it literally sounded like it was firing on 2-3 cylinders, but it ran. As soon as you let off the gas it would stall. I remembered my 4.0 acting this exact same way when my battery died and got a jump start but this is a good battery. I ended up driving it around my neighborhood and now it runs great. Any ideas what happened? I don't want to assume it's fixed because I did nothing to fix it. If I don't know what the problem was to me it's not fixed and can happen again anytime. Thanks.
 
#3 ·
jrcromwell said:
Not sure what else you did when you stabbed the 5.2 in there. PCM etc but IAC, TPS, CPS come to mind right away. I would search the dirty dozen and go from there.
My jeep is a 5spd so I'm running a pcm from a 99 ram 5.2 manual trans. All my sensors are newer and all mopar. It's just odd that once it's driven a 1/4 mile or so it starts and runs great. I tried again to start it this morning after running it and have 10-15 perfect starts last night and it runs terrible again. The iac and throttle body are clean enough to eat off of, battery cables are clean and tight, and battery itself is great.
 
#6 ·
Update. I did a hard reset on the pcm (unhooked battery cables, touched them together with the head lights turned on for 1/2 hr). While the terminals were off the battery I cleaned the posts and terminals. It ran great for 3 days. Started perfectly. This morning it wouldn't start again.
 
#8 ·
jrcromwell said:
When you did this swap did you utilize the OBDII connector? If you did you could scan it looking for code and more importantly you can look at live data. like the Crank position and pickup coil as well as LTFT and O2 sensors.
Yes I retained the obd2. Everything is as if it came from the factory with the V8 installed. It's not throwing any codes, I've already scanned it. I have an sct tuner for it that I'm scanning it with. Pardon my ignorance but I'm not sure how to data log with it.
 
#9 ·
Here is a walk-through for data logging on the device using the X3.

•Plug in the X3 to the vehicles OBD2 port.
•Scroll down to Data Logging, Press Select.
•Then Scroll down to Setup Monitor, Press Select.
•Config Analog Inputs? Select Yes or No, answering yes will allow you to connect a wideband or any other 0-5V component to the device analog input
•Pick Diesel or Gas, then press select.
•You are now ready to pick the pids.
oSelect them by highlighting them and then pressing select. You'll notice that an Arrow will show next to the PID once selected.
oYou can select up to 20 Pids. NOTE: Default parameters are generated from a generic list of readable PCM parameters. It is possible that some pids shown will not be log able on your particular vehicle.
•Press Cancel to Exit from the list of Pids.
•This will bring you to a Save Data Configuration Menu.
oSelect - Save OK, Left - Back, Cancel - Exit
•Start Data Logging
oSelect - OK, Cancel - Exit
•A Message will display stating to make sure the vehicle is running, press Select to Start Recording.
•Once The Log has started, you can press LEFT/RIGHT arrows to view additional PIDS.
•Select will Stop Recording.
•Cancel will Exit the Log.

•You can Review this Log using a Computer with Livelink 4.24 or greater installed.
•Once 4.24 is installed and open…
•Then press: File/ Import Data log file from X3/livewire.
•A pop up box appears, Select Datalog0.dat from the list, then Press Ok.
•This will open and display the saved datalog.
 
#10 ·
Just food for thought, my 95 ZJ 5.2L acted the same. The first start of the day wouldn't happen unless I kept giving it some gas and then it would back fire, sputter, surge, drop rpm and die if I let off the gas. Restart, give some gas and it would eventually start. Then for rest of day it started normal. I replaced the PCM and all starts were then normal.
 
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