The 4.0 motor has no VCM codes setting. There is spark, but honestly it appears yellow and not blue-white. It is yellow and that has bothered me from the beginning. Fuel pump pressure was monitored while it was a no start as well and I don't remember the reading but it was right where it was supposed to be, I think 35 to 45 psi. The injector pulse was normal with a noid light on all injectors. Adding alternate fuel does not help. Disconnecting the sensors one at a time did not seem to help. I can eventually get it to start, runs with hesitation for a minute or so after it fires over, let it run for 10 minutes until temp creeps up and the car runs normal now. Shut it off, restarts ok right away. Let it sit until tomorrow and maybe it will start with no problem, maybe not. seems like if it is not gonna fire on the first crank, it is in its no start mode and will remain that way until you start disconnecting the MAF and try it, then the CTS and then try it and then the IAT and then try it. I checked the TPS with DMM and readings were normal, no voltage interruptions throughout the scale. I initially had only about an erratic .6 AC volts on the crank sensor. I replaced the crank sensor, voltage did improve to just past 1 volt but did not solve the no start. I removed the MAF sensor and did the Alldata detailed bench test using a DMM and an air blower and all readings were as predicted for a good MAF sensor. I replaced the ignition coil just because of the yellow spark bothering me, no change in starting. Plugs are new, fuel filter new, coolant sensor is original but passes the resistance tests perfectly although I have a new one that I will try next time I work on the car. I am curious if the ignition module can fail and cause my yellow spark? Cap and rotor and wires are all perfect.

Recap key details

Yellow spark, consistent and does jump but seems like it should jump further than it does. ** Bothersome

injector pulse ok - battery voltage feed ok

fuel pressure ok

MAF sensor ok

CTS ok

IAT ok

ignition coil new

It will crank and crank and crank like a bad fuel pump but the whole time there is proper fuel pressure and injector pulse. Plugs appear to be getting wet sometimes hard to tell. But since it starts eventually and even runs normal after a minute of running you don't focus as much on the bothersome details

compression ok

crank sensor new 1 volt AC +- while cranking

intake boot not torn

When it starts (very hard start) and runs a few minutes, you can drive the car with no issues whatsoever. Shut it off start it up, like problem gone. let it sit overnight and you are back to square one with a no start.

So tell me, is the cause the yellow spark or got any other ideas for me?

Thanks.

I am a working mechanic 35 years. Jaguars beat me up, not much else.

 

Far from any great Jaguar expertise here.

The clue of yellow spark indicates insufficient current through the ignition coil. The question is why?

I would proceed with tracing out the ignition coil wiring and the grounding for the various associated modules.

Also would check the various engine and battery grounds.

 

Boy, I'd love to know if you ever figured out your problem. It sounds exactly like mine. I have a 90 Jag XJ6 that started having starting issues, rough running and hesitation. I checked the fuel pump, fuel filter, cps, etc. I replaced the fuel pressure regulator with no improvement. After she warms up, she runs fine but if you let it sit for a while, she might not start. The problem seems to be getting progressively worse to the point that I can no longer trust it's reliability. Worse, the car only has 65K miles on it and it is in mint condition.

During one of it's down times, I was unable to get any spark.

Helpless in Minneapolis

 

HouseCall,

Holy crap you've been thorough! The CPS's are well-known one these cars for failure, and there are even stories of brand-new replacements being bad. This is a common source of the no-start issue. You may want to double check that. Otherwise, if the car is getting all the fuel it needs, shouldn't the problem be with the spark? What about the ignition amplifier? Otherwise, I'm at a loss.
Hang in there. There is a solution! We just don't know what it is yet.
cheers,
Scott