My XJ Is not running right!and my mileage is about 12MPG Any Help!!!

Hello My fellow Jeep & XJ lovers,my jeep hasn't been running 100%. Let me give a little bit of background on her, 1987 Xj 4.0 I6 engine with Renix FI and my mileage is 154,108,4x4,NP231 Transfer case and I love my Jeep XJ. Original when I got my XJ she had a blow by, the ccv system was saverlly clogged. So I removed the valve cover and tored it down and cleaned it out completly out, and replaced the rear grommet for the CCV system, also cleaned out the throttle body. I given her a complete tune up about 5 months ago.Spark plugs,wires,cap,rotor,fuel filter,air filter(all oem replacement parts). Recently I have replaced my Intake/Exhaust Manifold Gasket, I noticed before replacing the intake/exhaust manifold,she was running rough(idle somewhat unstable),I figured possible vacuum leak. So i purchased a can of carb and choke cleaner and did some sniffing around and found the intake gasket have a leak, so i replaced it. Ok so i noticed that when i first started her she ran Fantastic, but then after about 20 minutes the idle stumble came back. So i armed myself with my digital multi meter and a copy of the renix fuel injection service manual. I first started by checking my ground wires at the pass side of the block and for the TPS sensor, no resistance to ground found. So I went from sensor to sensor attempting to find the colpript. All sensors tested fine except for the sync signal generator A.K.A cam sensor. According to the renix manual the this sensor is supplied with 7.01 volts from the ECU, not the case with mine. My voltage to sensor is 5.02 volts, problem? ok next i decided to unplug the sensor and see if she would start and she does and the idle still stumbles. So i need some help on how to further test this sensor. Ok next i noticed that if i disconnect the vacuum line from the fuel pressure regulator there is no change in idle. Any Advice will greatly appricated. Please forward any and all thoughts and info... Thanks JR

Check your o2 sensor.

Check for any exhaust leaks upstream of the o2 sensor.

HI Joe, I do have an exhaust further back in the system, i dont have any near the O2 sensor. Am going to try to do a repair this weekend. Now getting to the O2 sensor, what be the best way to test the sensor? I have a digital DMM, not an analog one. Thanks.

Hallo. To test the O2 sensor you have to tell us how many wires and what colors does it have?
Is it a Titanium or a Zirconium one?
When the fuelmileage is bad, you can also check the CTS Coolant temp sensor. (choke function).

'92XJwim

Here is everything you need to check the Renix sensors:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

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