When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Did some sleuthing and wrenching. I was getting ~30 ohms on the multimeter, but that was after I moved the Jeep so I could work on it easier. After it cooled down, I swear I was getting more like 3-4. I took the same reading on my 98 and was getting 3.2. My wife added some more info saying every once in awhile, the coolant temp and oil pressure gauge would go really high. I decided to go ahead and swap the alternator. That was less than an hour out and in and ready to go.
Did some revs and a short test drive trying to rev the engine as much as possible. No blown fuse after a short trip. What a pain. I'll remeasure resistance after it sits overnight and it's stone cold. ay need to get an amp guage so I can watch it from inside. The fun of old Jeeps. I wonder what a professional mechanic would do with this situation.
Finally got to recheck resistance this morning. Was reading ~3 ohms. The heat must linger for quite awhile. I am really not sure what else to try at this point. Only other thing I can think of is insulation inside the harness periodically shorting. Seems like ti would show up more frequently if that was the case. If it keeps happening, will go to an amp meter to see what is going on there.
Well, the alternator was not it. Fuse blew again. Next step is disconnect the front sensor, then the rear sensor separately. Also going to figure out how to wire something in the cabin that will show a light or something when the fuse blows to know what/when is causing it. It hasn't blown when I have taken it on test drives but blows when my wife drives it. I hope there is a mechanic critera when deciding if we go to heaven or hell. I have to imagine I have assed the test to relax in heaven. This seems like one of those hell tests.
Well, perhaps when you and your wife go out again together (dinner, shopping, whatever), you should let her drive. If it happens, you may be able to see what was going when it blows.. I'm not suggesting she's doing something wrong, just that witnessing the event yourself can help diagnose the cause. Sometimes, going over speed bumps, up or down driveways, etc., can flex harnesses and blow fuses.
When you had your harness open, did your visually and physically verify the integrity of all the crimps/splices in there?
Once I had an intermittent #3 injector. I'd be driving around just fine, and then suddenly, the engine ran rough, and lost power. I'd pull over, lift the hood and look around to see if something "came off" or any other signs of trouble. I'd see none, drop the hood, start the engine and it's fine. However, this got progressively worse. Bear in mind it's an '88 so no codes. It would "misfire" again, back under the hood, and double check injector connections, make sure the harness didn't hit anything hot and burn through. I finally figured out that moving the harness around often "fixed it". So now I know I have a wiring issue inside the harness. Turns out on a Renix, all FI grounds come together in one big crimped corroded splice wrapped in tape. The #3 injector was barely connected. I ended up replacing all of the FI connectors and ran fresh ground wires further back and did a staggered solder joint to make the bump for the splice smaller. Been running fine ever since.
So if you can, go back and check continuity or voltage and start shifting the harness around. Tug on the splices and see if they hold.
Next step is to go into the harness. Rainman Ray just did a good episode on a melted O2 sensor wiring harness. Gotta be something stupid int he heater harness.
In the immortal words of Russell Ziskey - Son of *****, ****. I pulled the wiring harness for the downstream oxygen sensor up through the engine compartment to get a good look inside. Nothing out of the ordinary. I had already looked at the upstream but will go through that again. I was not able to see everything on the downstream though. Resistance readings make sense. When cold I get 3.2 ohms on the heater circuit. No shorts to ground from the powers side. Once it wams up, get 30-40 ohms.
One thing that I am seeing is it seems to be ok until it gets warm. Once it warmed up today, the fuse would blow the instant the key was turned to on. I need to do some research on how the heater circuit works on an O2 sensor and what changes once it is hot. I am still back to my original thoughts:
1. Monitor the amps flowing. Since I am seeing it blow once it is warm, I should be able to setup monitoring under the hood and not need it when driving.
2. Possible run alternate power/ground wiring and bypass the harness to test for a shorting condition somewhere. Wiring inside the harness looked good Pulled apart and din't see anything frayed
Been thinking about this problem. As I thought, it seems like it blows the fuse instantly and repeatedly once it is warm. My wife had driven it and it was hot and was blowing the fuse repeatedly. I unplugged each O2 sensor and it still blew with both unplugged. Will let it cool off and watch as it warms up. Next step will be to run alternate wires to the O2 heater circuit. And research the FSM more to see if I missed anything in the wiring.
The other weird thing that started happening: I disconnect the battery when I do electrical things. The last several times, the power door locks have locked he doors when I reconnected the battery. And tonight, I didn't disconnect the battery but the doors locked. No idea if there is any connection but going to look through wiring diagrams.
Hmmm... Have you checked the harness that passes into the driver side door? Flexing and chafing can cause all sorts of problems with power windows/locks, speakers, etc. Not clear if that's related to the O2 sensor issue but those gremlins are really sneaky.
Good suggestion. Will probably pull some other fuses and see what happens. I went through the wiring diagrams and don't see anything else on that fuse. The only other diagram that seems relevant is the splicing diagram where some wires come together.
More data. Replaced the fuse, jeep was stone cold. fuse blew as soon as I started it so the temperature angle is eliminated. Then I unplugged all unnecessary fuses in the PDC, fuse blew instantly. Was down to 1 fuse left so I ordered a 15 amp breaker fuse and more fuses from amazon. I was only able to get the Eaton ID fuses from the local auto store, about $1/fuse. Will move onto running alternate power and ground wires to the O2 sensor heater circuit. Will definitely dive into the door lock wiring too. Seems like if there was a short there then the power locks wouldn't work right either and those worked fine tonight. Grrr.....
04-24-2024, 07:41 PM
