Testing procedures

Is there a single site dedicated to bench testing sensors, circuits, switches and relays. I am getting back to my 86 XJS v12 project and want to test any component capable of being tested. Was wondering if there is one place for that info and also an explanation of each component. Thanks in advance.

No, but a circuit diagram, a 12v power supply and a multimeter is all you need.
See what the said component is supposed to do and replicate it at the bench.
For special things like the TPS, CTS, Ignition Amp etc, you will find lot’s of info at Kirby’s book and the archives.

Here are some info from my archives:

Coolant Temperature Sensor (ECU)
0 C 5.9 kOhm
10C 3.7 kOhm
20C 2.5 kOhm
30C 1.7 kOhm
40C 1.18 kOhm
50C 840 ohm
60C 600 Ohm
70C 435 Ohm
80C 325 Ohm
90C 250 Ohm

Coolant Temperature Gauge Sensor
DAC2583
20° 980 Ohm
30° 600 Ohm
40° 400 Ohm
50° 290 Ohm
60° 210 Ohm
70° 150 Ohm
80° 105 Ohm
88° 80 Ohm
90° 75 Ohm
100° 56 Ohm

Wiring Colour Codes
Brown: non-fused battery supply
Purple: fused battery supply
Brown/colour: always powered, but switched by some device
White: non-fused ignition supply
Green: fused ignition supply
White/colour: powered with ignition ‘on’ through some device
White/pink: ignition position I & II
White/yellow: ignition position to crank
Light green & green/colour: auxiliaries
Black: ground
Black/colour: indirect ground through some device before grounding
*-/colour: wire is routed through some item

fed_wiring

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BS-AU7 gives most, and mostly accurate colour info and so do the diagrams. Relays and switches are best tested with a test lamp and power source, sensors with a cheap multimeter. Testing all components isn’t really worth the effort, only test parts that might be broken or that are known to be fragile.

Please forgive me as a total novice and and old woman. I have someone who can help me, but some of the photos and things are overwhelming. I do have a Service Manual for the future, but I just want to diagnose for now. I have a 1994 XJS 2 x 2 4.0 six cylinder. I have been told there is an OBD, there is no ODB, and there is an integrated system of some sort. The person who sold it to me said there are codes that will flash on the dash board and the code he saw was FF15. I am not concerned about the code right now, but getting some diagnostic equipment. There is a photo on page 112 of my manual that shows a piece of test equipment called an Epitest with an Epitest Adaptor. BTY is has a connecter that looks like an old parallel port on an old PC. Can someone help me sort all this out and tell me how to diagnose at home? I am not going to a dealer yet. Thank you and thank you for letting me join. Carole52577

Welcome to the forum Carol.

I would be better that you open a new thread.
Your car is also quite different from Rodney’s so the above does not apply in yours.

Best regards.

Testing ‘on the bench’… You will probably damage half or relays doing so. The real pain of XJS also known as The Rainwater Bucket - is the corrosion and oxidation of the terminals/plugs. You will damage only 25% of these while trying to unplug and clean them. That makes no-brainer. Cheapest lab power source is really handy with relays if you must follow the dark path…

Carole,
If it works fine - don’t touch it. OBD stands for on-board diagnostic, nobody said you will have OBDII socket installed. Jag system is really primitive and Epitest ‘adaptor’ is nothing but poka-yoke device for Jag mechanics… While Japanese cars were having real diagnostic computers available in 94’ - Jaguar was forced to improvise with few wires and some Christmas tree lightbulbs… Still, your Jag system will show you most of the typical engine faults. BTW, there os no FF15 on your engine. At least it shouldn’t be.

I apologize and thank you so much for leading me in the right direction. I did not realize they were that much different. I appreciate it. Carole

You guys have been kind, but I think this is beyond me. But I will start a new thread as advised. Before I go though, I don’t know what you mean by “cheapest lab power source.” Also, I have never seen where the faults are displayed in the system because I don’t know how to get to it and the car has never run long enough for me to mess with display buttons. The seller said he had seen the “FF15” but I have never been able to find or duplicate it. However, a friend told me he thought maybe he said FF11. I changed the plugs and added new gas and a fuel cleaner. When jumper cabled to the battery on my Honda, it runs! But pretty rough, after a nice smooth start up. So I am going back to my original plan. I have ordered new wires, distributor cap, rotor ad coil and install those and check timing. I also have a new fuel filter. I am ignoring relays for now. I really appreciate your help and now will start my own thread after any response you might want to offer to this. Carole52577

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Hello Carol
you really need another thread as your car model year (94) is very different than the OP one (86), and your engine is a 6 cylinder, not a V12

to answer some of your uqestions :
-cheapest power lab power source" :could be any way to get a DC voltage compatible with automotive parts . This is probabaly overkill for your tests

a 12V battery could do : - )

  • to see the codes on your car, you need to set the ignition on , without starting the engine the code should be visible on the central display of the car “computer”
    as only one would be visible, you can clear them all by disconnecting the battery for a minute, then reconnecting
    if you start the engine, and it fails again, , cut the ignition, reactiate it and read the code on the display

smooth running on cold, going rough after a while could be a temp sensor going wrong, or one of the various devices added for emissions control : that’s why a specific thread would be more efficient to hep you

I don`t know why my fonts come out screwed up like what was pointed out to me. Now they look fine. Oh well. Thanks

I sent a message thanking you for the info and explaining that Im on hold testing. Im back to square one trying to start it again. Clean fuel through rail , good spark, power to injector but wont start with starting fluid. May have sucked bad gas is all I can think of so Im pulling injectors to test and clean. Also has been pointed out to me my font is weird. But I guess I`m stuck with it. Thanks again

Thank you so much! As it is not clear how long the car has sat,I bought a distributor cap, a coil,wires, MAFS, and will clean gas, and next move to correct forum. Thanks again!