Xj electrical voltage issue help please

I have a 2000 xj Auto
For the last three months i have had issues with starting and then when running the car will
1. fluctuating Idle 700rpm -1800rpm when stationary
2. Car Dying at running speeds 100
3. Backfiring
I have had fault codes for tps, Idle air control, Map sensor both low, and high voltage then no voltage, idle temperature control, have replaced tps, idle control,Map sensor no improvement
Found the wiring harness was brittle at the back of the block had many cracks in the wires and many melted and touching each other .
so i replaced the harness and still have the same problems.
The computer has been replaced as well. Disconnected it for 24hr to reset it
went for a drive same problems
Any ideas? please

Go through the grounds just to be sure. What voltages do you have at rest and at idle? Need more data...

found the new tps to be faulty so replaced it. The car ran well for an hour or so now I have had it throw the code p1296 manufacture control. I understand this to mean no voltage to map sensor.
but as already stated I have replaced the wiring harness and it checks out okay.
Any ideas

Since you had starting problems, maybe the contacts in your starter relay are dirty and not making good contact. This could cause voltage fluctuations in some circuits. Either spray clean it or replace it. They're inexpensive and something to try.

Best regards,

CJR

How does the starter relay affect a running engine ?



P1296 - No 5 Volts to MAP Sensor. Loss of a 5 volt feed to the MAP Sensor has been detected.

A P1296 suggests that you still have some wiring harness issues to resolve. Loss of 5 volts could be an open circuit, a shorted circuit, or a faulty ground connection. All the 5 Volt sensors are on the same circuit so the problem could be a fair distance from the Map Sensor itself.

Tim MN,

I just went through a problem on my 88XJ somewhat related to my starter relay. There are many wires/splices attached to the starter relay lug that affects fuel pump, starter solenoid, ignition, etc. Apparently, the previous owner had installed a fuse (ATC plug-in type) in the battery(+)voltage supply wire that goes to that starter relay lug. The fuse got dirty and started causing intermittent voltage supply to the starter relay lug, which in-turn affected voltage to the starter solenoid. Then after studying the wiring diagrams, I discovered that the voltage also went from that starter relay lug to a wiring splice where the fuel pump was attached. So, the XJ would start up and run normally, then while driving down the road the engine would suddenly die. I'd turn the key and nothing; i.e. no starter solenoid or fuel pump clicking. Likewise, the battery voltage was normal. I'd let it sit and it would fire right up and run awhile before repeating the shutdown. Eventually I found the problem when one contact, of the installed fuse, finally melted. Apparently, as the fuse spade contact got more dirty, it lost contact momentarily. Eventually as it got dirtier, it heated up and melted, but the fuse never blew.

I don't know what other circuits may be on this 2000XJ's starter relay. But changing the starter relay may at least solve the starting problem. I just picked up a 2000XJ so I'm also interested in how this gets resolved.

Best regards,

CJR

sadly, the later model starter relays are a separate circuit from the other circuits controlled by the Renix starter relay (EGR, ignition, fuel pump)

probably doesn't have anything to do with the OP's problem

Tim_MN said:

P1296 - No 5 Volts to MAP Sensor. Loss of a 5 volt feed to the MAP Sensor has been detected.

A P1296 suggests that you still have some wiring harness issues to resolve. Loss of 5 volts could be an open circuit, a shorted circuit, or a faulty ground connection. All the 5 Volt sensors are on the same circuit so the problem could be a fair distance from the Map Sensor itself.

Click to expand...

I'd check the wiring harness at the rear of the intake/exhaust for chafing or burned spots. It's real tight back there and all of your 5V reference signals travel through that harness.