Help please, xjs 1994 2+2 with 4.0 6cyl. crank but no spark. I have tried 4 crank position sensors of which 3 never worked and one only let the engine run for about 30 minutes and then quit. Fuel pump is new and I have 50lbs at the fuel injector rail when cranking. Ignition coil is new and there is 12.2 volts going in and 12.1 volts coming out of the coli, and 12.1 volts to the distributor cap. I have back probed the inertia switch and it is not tripped. I have two ecm's and swapped them out with no difference So other than a crank position sensor what could cause the spark to not travel from the distributor cap to the plugs? Spark plugs and wires are new. Of the 4 crank position sensors 3 were after market and one was sng barratt.
Thanks in advance, John

 

Have you verified sharp blue sparks at all the plugs?
You could have bad HT wires even as new.
Can you try starting in a dark area where you can observe any spark leaks?
Does your car have HT leads or not.
Are the plug wells dry?

 

Have you checked the pins on your ECU to be free of corrosion?

30 minutes of runtime before quitting....seems odd.

Inertia switch kills the fuel pump, so it would not have any effect on spark.

Your car is pre-OBD2, but if you had a trip computer, you could have a code stored....

 

No spark at all and I am not sure if the plugs wires are HT but they are high quality . Plugs are wet and new. I also connected a spark tester to each plug wire and nothing. Before the engine quit is was running perfectly and also idled perfectly when the one CPS worked for about 30 minutes. Distributor cap and rotor look very good upon visual inspection and very few miles on them.
John

 

Could it be that the distributor has gotten out of time? if so how can I check that?
John

 

I know to bring the number 1 cylinder to tdc and then see if the rotor is pointing to the number 1 wire, but maybe a toothed gear is damaged where the distributor feeds down into the engine.
John

 

Thanks V, the onboard trip computer shows no dtc error codes. What about the ignition amplifier located behind the front right headlight, so near to the ignition coil? I am not familiar with this part or it's function?
John

 

So I have 12 volts at the ignition coil, but does the ignition amplifier pulse this 12 volts to the ignition coil at the proper time to send it to the distributor the fire each plug?
John

 

I went ahead and ordered an ignition amplifier from Moss motors. They have some original jaguar dac 10923 ignition amplifiers available. So whether the one in the car now failed or not, it is 31 years old and I can replace it with an oem part, not after market.
John

 

It seems unlikely that a number of crankshaft poistion sensors are bad. Given the car ran then quit I would suspect the wiring. Check the plug to the cps for continuity, then the continuity from the cps to the ECU

According to my wiring diagram:
Red wire to pin 13
Blue wire to pin 24

wiggle the wires to see if the continuity changes

And as mentioned before look for wny corrosion on the ECU plug

 

Check ECU pins for corrosion.

 

Stuizzy and V, Thanks!
I did the continuity tests and had continuity and the ECU pins are clean. However today I went to remove the ignition amplifier and the pins and connector had really bad corrosion. It all cleaned up really nice with some contact cleaner. I am going to reinstall it and maybe that was the cause of no spark. I have to get some thermal paste first though, to apply between the amplifier and the mounting plate. Thanks again for your help.
John

 

I am new to the Jag 4.0 AJ motors so I may be crazy. From my general knowledge of ignition systems the statement above seems like a problem to me. The coil should NOT have 12V coming out. The coil's purpose is to INCREASE the 12V in to many thousands of volts out. 12V out will not spark a spark plug.
How are you measuring the 12v in and out of the coil? Is it steady state DC or pulsed AC? It needs to be pulsed (AC) in or the coil will not do anything.

 

Thanks David, Yes you correct and on the 4.0 engine it is the function of the ignition coil amplifier to pulse the coil voltage and send the voltage to the distributor cap. I cleaned and tried the existing amplifier today with no results, so I will wait for the new one I ordered last week. All other components on the spark side are new, crank position sensor, ignition coil, plugs and wires, and distributor cap and rotor look good. In the 2 + decades of owning this jag, I have never changed the ignition amplifier.
John

 

dealing with this crank but no spark for many weeks, I was not aware of the ignition coil amplifier until just recently. So alot of research later, I now understand it. Jag man downunder in one of his videos shows that on his xj40 that if one or both of the crank position sensor and the ignition coil amplifier fail it will cause a no start . He also says this has happened to him more than once. So I am hopeful the new ignition coil amplifier is the answer.
John