I have a 2001 jag xk8 convertible. It has had an on and off problem of not starting. I have installed a new battery. It has 13 volts cranking. Engine has always cranked over p and n light up on shifter. Have checked relays fuel pump pressure at rail is 41 psi. Have discovered that I have no injector pulse and no fire at coils they are all brand new. Replaced crank sensor. Car would not pass smog would drive over 100 miles and computer would not reset . Every time I would reset ck engine light. I could not get the computer on board to clear all functions. Misfire on 5 or 7 would show up at times. Prior to replacing battery car would not start. It did however always turn over and had fuel pressure at rail. Car would sit and I would do the reset pos to neg or at times disconnect battery cable and car would start. One time I inserted key into car door lock did a sequence of turns put in ignition switch Bingo car would start. Replaced lower co2 sensors and another crank sensor even tried another ecm. Have ignition at coils hot only. No pulse at fuel injectors. Have checked all fuses and relays even moved them around the ones in the trunk and engine compartment but no luck. Actually car started after being sitting for a few weeks drove to the store but did not have a good neg battery connection. Was taking it on and off to do the reset. Jumped in car turned key starter engaged then click went to trunk tightened cable Turns over fine no start towed home put Battery jumper to it cranks fine has fuel at rail thinking low voltage but still no spark or coil pulse. Did bore wash a yr back no start. Shot starter fluid into air chamber and can get to run from combustion only. Similar to diesel my compression is 135 to 150 per cylinder. tried all of the resets mentioned and having no luck. Thoughts

 

Daddyo,

First thing I note, you're pretty handy in the garage, so pardon me if I say the obvious.

Have you checked the battery cables? You mention the ground cable. Does it get hot? Get voltmeter from battery positive to the cable body end and compare voltage from cable end to the body stud. Easy to replace these cables as the crimps are known to go bad. There's lots of cheap upgrades to solid copper non-crimped cables. While you're there, the battery positive cable goes to the High Power Protection box and there's a connection nut there which is known to work loose.

However this wouldn't explain your non-start due to no spark. You've tried switching ECMs so here's an excerpt from my electrical manual showing lots of other modules involved in the start. Start with those ie for testing the Security KTM, first try a second key to see if it starts - hopefully it's just the key chip that's gone bad as if the KTM is bad, you're in a world of pain.

 

From what I can decipher from the wall of text
- Crank but no start, but I can't tell if this is now a permanent no-start or intermittent ?

1) you have no injector pulse (how have you determined this)
2) It runs on easy start so you would appear to have a spark (it would not be used for diagnosis if it self ignited)
3) You have thrown a lot of parts at it which may confuse the issue.

What current codes do you have (or have when it does not start) ? Lets get some direction from that.

 

You mentioned that all the coils are new and you have a misfire on 5 and 7. Swap the 5 and 7 coils to two other positions and see if the problem follows. You can at least eliminate or confirm the coils as a problem.
If the coils are not the problem you want to see if anything is common to the #5 and #7 ignition. The answer could be in a schematic such as a common part, or physical proximity such as wires that run in the same conduit that may be damaged.

 

You mentioned trying another ECU. In another recent no start thread motorcarman said that an immobilization procedure has to be performed or it won't work.

 

Cranks over but won't start, hope it isn't the BPM or the ECM.

Mine acts weird sometimes too, but finally found a way around it. If I don't use the car daily, sometimes once in a great while it will NOT turn over. Usually tapping the starter relay on the fender with just my finger did the trick. So when that failed to work, I simply held the key to the start position for about 5 seconds and she cranked up. A little slow at first, but gradually sped up and engine started fine without issue. Shut it off and restarted several times without issue. Then went for a short drive. Sounds like it could be the body processor module causing the delay. Can't be the starter since I changed it recently and it seemed to like the new starter a lot better. Wasn't fun to get to the starters top bolt with the exhaust manifold and the motor mount in the way as I recall.