Calling all TJ gurus. I have a 2000 TJ 4.0L with 127k miles that is driving me nuts. It is hard starting cold, when it does start and run, the alternator charges spuratically(guage bounces all over), RPMs bounce all over, runs rough until it warms up. Once warmed up you can pull over and turn it off, Then turn it back on and its a perfectly normal running jeep. You must turn off ignition switch and back on or it will continue to act funny.
No warning lights, no check engine light, and its not throwing any codes? As long as its warm out it will run great all day, unless it cools down to much, then the crazy problem starts all over again. So far we replaced, Alternator, O2 sensors, Crank sensors.
Pulling our hair out. Any suggestions would be much appreciated.
Battery is a little old but has 12.8volts. Alternator is brand new and tested after putting it in the jeep. Works fine after jeep is up to temp (180 degrees) but you do have to pull over and turn key off and back on for everything to work properly.
I had the same issue with my 2003 TJ 4.0 probably around the same amount of miles. It ended up being the computer. Found a used on that plugged and played been doing good ever since.
Put a new battery in just because the old one was 4 years old. Alternator puts out 13.9v once the engine is up to temp and running smooth, checked with a multimeter. It does not appear to be a charging problem, rather some other wierd problem. Thought it was crank senor because in the morning sometimes it will just turn over and not fire, thats what it did when my crank senor went bad 6 months ago. What stumps me is after the jeep is hot and you turn it off then back on everything works and jeep runs great.
The computer I replaced is mounted on the fire wall. It started doing the same crazy stuff I put it in the shop they checked the battery and alternator both were good. He told me the only thing else I could be was the computer I found one replaced it no more problems.
Is this the 4.0 with coil rail if so since it always fires two plugs at once it is more sensitive to which plugs you use then the pre 2000 4.0 with a distributor that only fires one plug at a time
Also check cold resistance of temp sensor
But my best WAG is a loose intermittent wire connection in battery cables or wiring to alternator try some wiggling of wires and connectors
Replaced the computer on the firewall under the hood with a known good one, checked all ground conections. The problem is get bigger. At this point the jeep is very very hard to start ( just turns over), when it does fire it runs rough then just flat out dies, like the key is shut off. I have to keep doing this until I get the motor warm or open the hood and let the sun hit it for 30 minutes. Then it will run but kind of rough, alt is charging spruratically still. Again once up to full temp, I can turn the jeep off, then start the jeep again and she runs fine the rest of the day. Unless it cools down, but since it is still 90 degrees here I am fine. This is driving me nuts. STill no codes being thrown.
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