I've been methodically working my way through issues on my '96 4.0 XJ. Having replaced the radiator, thermostat housing and all associated pipes, it seems to run much cooler now. However I'm chasing down a persistent and intermittent stutter / misfire under gentle acceleration. I've read lots of posts on the subject and have now replaced the fuel pump, fuel filter, plugs, leads, coil, distributer cap, rotor arm, throttle position sensor, both O2 sensors, crank position sensor. Plus I've stripped and cleaned the throttle body and idle control valve, done a compression test, fuel pressure test and searched for vacuum leaks. All to no avail as it still happens every now and then (all be it less frequently than before). I had some rough running problems with a Jaguar AJ6 engine which turned out to be the coolant temperature sensor, so I figured it might be causing issues here and ordered a new one.

When I fitted the new sensor the car failed to start, just cranking without firing. Connecting the old one means it starts right up. I contact the supplier who was great and sent another out immediately. I fitted that and had the same problem.

When I check the resistance of my old sensor compared to the new ones it's a lot higher (about 13k ohms old sensor vs 2.5k ohms new). The part numbers match and the supplier assures me it's the correct part.

I'm stumped. Anyone had a similar experience or could shed some light on what might be happening?

Thanks

 

Per 1990 xj repair manual the Coolant Temperature Sensor tests at......

185 ohms = 212F
450 ohms =160F
1600 ohms = 100F
3400 ohms =70F
7400 ohms =40F
13,500 ohms =20F
25,000 ohms =0F
100,700 ohms =-40F

If you get weird ohm results, test your meter battery. failing meter battery can give erroneous ohms values

 

Thanks for the info. I'll test the replacement sensor tomorrow as I refitted the old one when the Jeep wouldn't start with the new one installed. I'm guessing I must have the wrong part. I'll pull the old one at the weekend and test that too.

TBH I'm chasing a random miss-fire / stutter which only seems to happen after you've driven for a while with no discernible pattern and goes away if you floor the throttle, so I'm systematically trying to eliminate things that could cause it. I've changed the throttle position sensor, front O2 sensor, crank position sensor, leads, plugs, rotor arm and cap and also removed and cleaned all the injectors.

 

clean and tighten the engine block ground point located at the motor oil dip stick mount. Some of the injection sensor ground there.

 

He has a 96 though.

 

While I don't have a '96 specific FSM, both the '95 and '97 list the same chart.

At 68F, the resistance should be 11,370 - 13,610 ohms.

2500 ohms would be about 140F.

Did you check the resistance when they were both cold?

TEMPERATURE RESISTANCE (OHMS)
°CEL. °FAHR. MIN. MAX.
-40 -40 91,490 381,710
-20 -4 85,850 108,390
-10 14 49,250 61,430
0 32 29,330 35,990
10 50 17,990 21,810
20 68 11,370 13,610
25 77 9,120 10,880
30 86 7,370 8,750
40 104 4,900 5,750
50 122 3,330 3,880
60 140 2,310 2,670
70 158 1,630 1,870
80 176 1,170 1,340
90 194 860 970
100 212 640 720
110 230 480 540
120 248 370 410


OK, so the text table would align the columns. Hope you can read it.

 

Uh oh, I didn’t realize the 1990 and 1995 had different temperature sensor resistance ranges.
I just ordered the same temperature gauge for my ‘95. Is this a common thing and can I hope there are jumpers or switches on the back of the gauge to compensate? If not, I guess I can try adding an appropriately ohm’ed resistor in parallel or series to adjust.

 

I doubt adding a resistor will work as senders and gauges are matched and not necessarily linear

it may work somewhat, but an inaccurate gauge is not satisfactory in my book

Therefore, if I understand your issue correctly, fit a matched gauge/sender pair, no more issue

 

How do you test your sensor...the only accurate way i know is to remove it and put the sensor end in a-pot of boiling water, then read the resistance...first since its a 96...are we talking about the sensor in the thermostat housing...controls fuel delivery based on temp......or the sensor in back of head, drives gauge only..no controlling functions

 

I agree with all that

the temp GUAGE sensor is separate to the coolant sensor that provides info from the PCM (on a '96)

One is at the back of the engine, the other near the thermostat housing

The range is specced in the FSM, not impossible to test

be aware a pin in the connector can get pushed back, which will give a false OBD warning coolant temp too high/low