Working on a 1995 XJS six cylinder 4.0 that does not start. Cranks over fine. Car had been missing intermittently at road speed but would come out of it. Then it failed to start and has been dead since.
No power to the crank sensor. The wiring diagram I have shows it as a red wire going to LI189-23 terminal on the high power connector on the Engine Control Module. There is no power at that terminal coming out of the ECM. There is a blue wire and a white wire with a tape marked "S" on it that connects with the red wire.
Is there a diagram that shows the location of terminals on the ECM? Am I looking at the right wire for the crank sensor? Any reason why I shouldn't have power at the crank sensor? Could the security system be blocking the power? It chirps when I hook the battery up and the light comes on by the cigarette lighter. Getting very frustrating. Spent many hours looking at manuals and web forums but still no closer. Feel like it is something real simple. Thank you

 

Did you check the inertia switch at the passengers door hinge? Press that button and see if anything changes.

 

Checked the inertia switch. It hasn't been tripped.

 

could be wrong on the 1995 XJS, but doesn't the inertia switch just kill the fuel system?

 

ummm lol first of all, do you know if this is a hall effect sensor or permanent magnet?

Im pretty sure the cmp is a hall effect. In the diagram it shows 3 wires. The CKP shows just two wires. So it must be generating a signal and not modifying one like the CMP is.This being the case, you won't see any signal until the crankshaft is turning.

what i am saying is that this CKP sensor generates voltage. If the engine is off you shouldn't have anything there. If you have been checking it while cranking and you have no voltage, replace the ckp sensor.

Idk if it is frustrating that you were wasting your time or if it will make you happy to finally be done with the ckp sensor. But you need to look elsewhere for your no-start issue.

Work your way back in the system. First determine if there is spark

 

Yes, that would allow the engine to crank, but not start. I think that's what the issue here is, which is why I brought it up. Simple and easy to check.

Apparently that's not the issue.

I'm also assuming there are no codes in the system.

Let's see if there's spark...

 

This sounds like a crank sensor to me. Very common AJ16 problem. I carry a crank sensor and spare coil in the trunk at all times.

 

spike thinks its common, so you should hook up a dvmm and check what the sensor is doing during cranking to determine if it is bad. I believe you should be seeing a very low voltage that alternates between negative and positive

 

Ok we put the meter on and have about .276 volts AC. Does this sound OK? The wiring diagram showed that the signal is in Ac. Am I correct? Hate to order a part I dont need, especially when it isnt my car. Thanks everybody. I am learning a lot.

 

Ac is correct, remember I said it should read negative and positive?thats what ac looks like when you read it as dc. It's AC alternating current, so it's goin back and forth

It's more useful to read this as dc because you want to observe these negative and positive pulses. They are what let the computer know where the crankshaft is. The voltage sounds fine so it sounds to me like there is nothing wrong with your crank sensor. You need to determine what point in your ignition system the power is stopping and perform diagnosis there

is there power at the coil?

 

Ok havent had a chance to work on car lately but today did more checking. No codes in ECM. The crank sensor shows about .276 volts AC cranking and that is at the ECM connector so all the wiring and connectors are intact. Switched it to DC volts but it didn't alternate polarities on my digital multimeter. It showed a few rpms on the tach. No spark. There is power on both sides of the coils. Checked grounds. Checked power terminals. Have fuel. It is as if the ECM is not grounding the coils for spark. Anybody have an ideas? Any relays that could be causing issues? All the minifuses check out ok.Thanks

 

I agree with Spikepaga. The crank sensor is a very, very common problem on the AJ16 XJS. I had the very same thing happen on mine and when the crank sensor fails you will still see the tach read 2-300 RPM's or so when cranking over engine. Do yourself a favor and put a good crank sensor on to start because they fail and are hard to figure out. I have two 95's so after getting tons of opinions on the forum I switched out my crank sensor with my other car and it started right up. I now carry a spare like Spikepaga does in the trunk-very easy to switch out and even if you have another issue this is such a common failure that it should be done any way and will get you past that possibility. I bench tested my bad one with a good one and they bench tested the same so do not be fooled with testing on these as the magnets get weak internally and just stop reading correctly or sending correct signal to ECM for spark.

 

Thanks for the advice. I had read that if the tach moves the sensor is good. I think I will order one and at least that part can be eliminated. I am crossing my fingers. Thanks

 

Good deal. I went through the same thing when my crank sensor failed reading from many on the forum that if the tach showed anything when cranking that the crank sensor was good-boy did I find out other wise. In fact before I put my known good crank sensor from my XJS that would start into the one that would not start like I said I bench tested them and they tested the same so I figured I might be wasting my time trying but it started right up. Like I said it is such a common failure and very hard to test that it will not hurt to start and get past this possibility. Let us know what you find out after you try a new crank sensor. The sensor is very easy to replace as If memory serves me it is held on with one bolt on the bracket. the thing you need to be careful of taking it off is at the connector just to make sure you do not damage it taking it apart. Time seems to be the biggest culprit on these failing as when mine failed it only had about 60K miles on it. The magnets get weak and stop reading right so age is the big issue with them and not miles from what I can tell.