Removing sensors to diagnose problem

[idzentity]

Hi Naxja,

I'm having an intermittent power loss issue with my xj that has gotten pretty bad this past few days, it feels like it's stalling, can be quite jerky, like it's fighting for fuel, air, or something. I suspect it's electrical as the issue is intermittent, but there's a number of issues it could be. I'm wanting to test if it's a sensor issue before moving on to other possibilities.

I'm not a mechanic by any modicum of imagination's stretch, but is there any reason why I couldn't unplug one sensor at a time to see if the power loss issue goes away? Would this help pinpoint a particular bad sensor causing my problem? For example, could I unplug my TPS and drive it to test? If so, which sensors could I do this to and still have it drive, and is there any sensor I couldn't do this with? I realise removing a sensor will cause the engine to maybe run rich/funny, but my thinking was if the power loss goes away, maybe that's a culprit.

Thank you advance for the help.

 

[Unclewolverine]

I doubt it would do much of anything besides maybe idle with the tps unplugged. Also the tps is your most likely culprit. Buy a cheap harbor freight analog multimeter with the needle and use one of the many tutorials online to guide you in testing it. A failing tps will cause all sorts of driving issues.

 

[Saudade]

Listen to your Unclewolverine. There are not any sensors that might cause your drivability issues you can simply unplug to see if it's any better.

A multimeter and fuel pressure test gauge will help.

What year is it? Auto or 5sp? 4.0l or 2.5l ? Gas or diesel?

If it's '96 or newer, is the Check Engine light on?

 

[idzentity]

Thank you very much for the replies.

It's a 1999 xj, 4.0 petrol, 5sp manual. Love it to bits, and very sad for it right now.

The check engine light comes on for a p0132 once in a while, but this comes on and off (clears itself randomly), and I've replaced the 02 sensors... both up and downstream. There is probably something triggering this CEL connected to my current issue, however the power loss happens even without a CEL popping up.

 

[Da XJ nut]

on your Code P0132 try checking the wires to the front o2 sensor for breaks, shorts or open circuit issues related to the plug or harness. I've seen this a few times on several Jeeps

 

[idzentity]

Thanks, Da XJ Nut, I'll take a closer look along the wiring harness, but I hadn't seen anything untoward when I installed the new O2 sensor a couple months back. The cables are generally in good shape, but definitely a closer scan is in order.

I grabbed my multimeter, and pulled the TPS sensor, as suggested. I checked the voltage sweep, and everything seems fine.... 0.89 to 3.88v, no drops or erratic behaviour. That said, when I pulled the plug and was checking which wires were the active, sensor and ground, I noticed the active pin and sensor pin were both giving off 5.1v. Is it normal for a disconnected cable for the sensor pin to be showing this? I expected only the active pin to have voltage, and the sensor pin to be unpowered as I'd assumed the active pin powered the sensor, and the sensor wouldn't be receiving a power supply until plugged back into the TPS. Strangely, as soon as it was plugged in, the sensor pin dropped to the above number (0.89'ish, and performed the throttle sweep without fault).

 

[Da XJ nut]

I've never Checked both sides of the harness when disconnected, always assumed the sensor side would be dead. Unless it stores voltage or your meter was set on HOLD setting

 

[idzentity]

That's what I would have thought, too, but yeah... both active pin and sensor pin showing the same voltage readings when pulled from the TPS. I checked this multiple times, before and after the throttle sweep test.

 

[wbnickens]

Have you checked the fuel pressure? Factory spec is 49.2 +/- 5 psi.

 

[idzentity]

This is a good call, I was wondering if there was a fuel issue as opposed to sensor, hence working through the sensors first as I work through the problem. I don't have any equipment to check fuel pressure, but seems pretty cheap on amazon.

 

[75SV1]

A few things I'd look at:
Clean Throttle Body
Check for vaccum leaks. Possibly TB gasket.
IAC Valve in throttle body. Maybe clean the inside cover.
Look at your spark plugs. Replace, clean and gap as needed. NGK.
The temp sensor in the thermostat housing can give issues. I have replaced mine. I think mine was other stuff. Mainly, the spark plugs.
I'd also check the spark plug wires and the coil.
Also, check the battery voltage.