Xjs 2+2 1994 4.0 straight six
I am still having a no spark condition. I have replaced crankshaft position sensor, ignition coil, ignition coil amplifier, battery, distributor rotor, and ECM. I have cleaned all grounds for the battery and ignition system, and I get a strong crank. Spark plugs, spark plug wires and coil wire are relatively new and test good. Distributor cap looks good. I have checked the CPS gap and it is good and the gap is not adjustable anyway Any ideas?
John

 

John,

You've mentioned that a number of the components "test good", I assume that's just continuity rather than when cranking? I would now start to look at the signals that are going to the ECU and then from the ECU to the ignition system. You'll need to backprobe the ECU plug to see what's happening. The electrical diagram shows you all the input and output terminals and the conditions / values that are expected. It feels that perhaps ECU power, or crank sensor input conditions are not being met, or else output conditions to ignition amplifier and coil are not being delivered?

Good luck

Paul

 

Thanks Paul I will do that today and report back.
John

 

[QUOTE=miamijohn;2890992]Xjs 2+2 1994 4.0 straight six
I am still having a no spark condition.

John,
What did you do to check the SPARK?
Sounds like you have the earlier type 4.0. (not coil on plug)
Did you check good fuel pressure at the rail?

 

You are correct it is not the coil on plug and is the one with ignition coil, and ignition coil amplifier. I checked the spark with an inline spark tester connected to a spark plug and I have good fuel pressure as fuel pump is new. Question! When I test for resistance on the 3 wire crankshaft position sensor, do I put my probes on the power in pin and the sender pin back to the ecu? Right now with probes to power pin and sender pin I get 142 ohs and with probes on power pin and ground pin I get nothing.
John

 

Let me be clear, DID YOU CHECK THE FUEL PRESSURE AT THE RAIL????

 

John,

Can you just explain the "...checked the spark..."? Presumably you have no spark when the engine is cranking?

As regards the crank sensor, as you'll have seen from the electrical diagrams, you need to know that it is generating the correct voltage to the ecu whilst the engine is cranking. This can be difficult as you must remember that the crank sensor signal is a small AC voltage not DC. You must have a meter that can read small fluctuating AC volts. Also I would measure it at the crank sensor as well as at the ECU.

Good luck

Paul

 

Hi Paul,
The spark tester plugs into a spark plug wire, it then has a light bulb in the middle and on the end it attaches to a spark plug. So you can test for spark in the cylinder or out by grounding a removed plug while cranking. So you can visually see the light energize and a spark at the plug. Oh! my bad the ohms reading was in the 20K scale so 1,452 ohms. Yes, my next test will be to back probe the ecm connector on the yellow low voltage connector. Pin 13 is power to the CPS and pin 24 is signal back to ecm and yes test as ac voltage. I wanted to focus on the CPS and it's wiring first, as we all know the CPS is a problem very often. The CPS in the car now is new. Am I testing the CPS resistance correctly?
John

 

Paul,
That is a good idea to check the ac volts to the CPS at the ecu and at the CPS connector. Thanks, John

 

John,

As I understand it (and I may be wrong), the sensor doesn't have a power input. If you look at the electrical diagram, it's not showing that pins 13.or 24 are power inputs to the sensor. 13 & 24 are both inputs to the ECU. The sensor itself is, I believe, a self-generating device that generates its AC voltage output through electromagnetic induction.. That's why you can disconnect the plug at the sensor and measure the AV voltage output at the sensor when the engine is cranking.

My apologies if I'm wrong.

Paul

 

Hi Paul,
As I understand it, and I could also be wrong the ecu sends approx 5 volts to the CPS via low power pin 13 (red wire on cps) and the magnet in the CPS reacting to the teeth in the harmonic balancer sends a signal back to the ecu via low power pin 24 (the blue wire on cps) This oscillating signal lets the ecu coordinate everything with fuel injectors, throttle position sensor, distributor, ignition coil amplifier etc and even some transmission functions and mass air flow. No wonder when a cps or its wiring fails there is no spark. Many of the pins on the low power side of the ecu send power out and that is why pin 1 on the ecu is 12v power from the ems relay. That is also why pin 13 must be checked with ac not dc current on the multi meter, because of the electromagnetic oscillation.
John

 

John,

That's not my understanding, although I may be wrong as always. The 4.0 crank sensor is an electromagnetic induction sensor that generates its own voltage, not a Hall effect sensor that would typically take a 5v or 12v DV power supply.

And if you're looking at the Electrical diagram, you'll clearly see that pins 13, 17, & 24 are all marked as input signals to the ECU, with 13 being the AC voltage, and 17 & 25 being Ground signals, Are you looking at a different diagram to me?

Paul

 

Thanks Paul I will try and test both ways today. My Jaguar electric schematic does not show input or output on the ecm, or any sensor or part for that matter. However if you look at CPS it shows a coiled (spiral) line between the red and blue wires. This is what AI says about that coiled line, " This coil symbol (a green spiral in some diagrams) shows how current creates a magnetic field, acting as a component, not the source.
I will do an Inspector Clouseau today lol
John

 

Hi Paul, I am curious, how does your diagram show input and output?
John

 

My diagram is the XJS (4.0l) 1994 electrical guide published by Jaguar
John

 

OK, John, Paul.

I have been thinking on this all day, and yes, I have fell off this limb I am on a few times.

But

That single col will need a 12v Ign HOT wire at the Pos termonall.. That is a solid White wire on the Vqw, and others.
I dont have the XJ40 nearby, its 3000kms away until late Jan, hence the caution with my suggestions.
Check for that 12V, and ensure it is still there when cranking, as the infamous Ign Switch Electrical Section dropping that connection at the Start position is becoming ver common.

That sensor etc is for triggering the EFI and the coil, much like the V12 Mareli system.

 

John,

Not sure which diagram you have? The attached link is the official Jaguar Cars 1994 Electrical Manual for the XJS:

94 XJS 4.0L Electrical.pdf

If you go to Fig 25, you'll see the diagram with the PIN ids showing as 3 INPUTs from the crank sensor to the ECU.

Slightly confusingly, if you then scroll down to the second page of the Fig 26 data, you'll see the reference data and that it is 2 Grounds and one AC voltage feed to the ECU, with the relevant AC volt figures.

As an electromagnetic inductive sensor, rather than a Hall effect sensor, my understanding is that is why it doesn't use an input voltage. That's why, in theory, you can disconnect the plug at the sensor and measure the AC voltage direct from the sensor. I've never done this myself, mind you.

Hope that helps

Paul

 

Paul, that is the same diagram I have. What definitively are you seeing that you think is input or ground, or output?
John

 

John,

Fig 25 shows you the picture and the components such as the ECM and the sensor etc.

Then just scroll down a couple of pages to the 2nd page of Fig 26 Data and it tells you the Inputs and Outputs of the ECM.

Paul

 

Hey Paul,
I never scrolled down that far, cause as soon as fig 26 appeared I looked .no further. Thanks that is a big help. I guess I was just being a knuckle head. lol
John