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Swapping the ECM does work even when the car is warm and can start with its own ECM. That is why they will be “registering” or whatever it is called by Jaguar (with VW is component protection) so that the donor ECM works on my car. Then when it gets cold they will try again with it and see if the car still only cranks. Then it will definitely not be a problem with the ECM.
The crank and cam sensors were double and tripple checked They do read correct RPM while cranking, and as I said before, while the car is cranking the spark plugs are actually firing with timing. For them to work is enough to get a ground for the relay which provides them positive signal. The spark coils are still controlled with ground signal, but not like the fuel injectors as there are two modules after the ECM that run them. So the ECM is properlly sending a signal to these modules to make them work, gives them timing and so on, but doesn’t send ground to the fuel injectors and the ignition coil relay.
Just to make one thing clear. When the car gets warm the ECM would now provide the ground for the fuel injectors and the car would start, but only if the “fake” ground is attached to the ignition coil relay. That ground from the ECM never comes.
I do hope it is the ECM, but we will see.
The only error the car gives is with the park neutral switch. Which she gives even when the car starts. The switches actually work fine and I have no idea why it is showing.
PROGRESS! Apparently they started working on the car very early in the morning and they already have some positive results First now the car works with the donor ECM. The car still wouldn't start without the ground to the ignition relay (she was warm, being in the garage all night). So the car will start with the new ECM and the "fake" ground. If then, while running, the ground is removed the car would continue working. Thus that ground is only missing while the car is trying to start = some kind of a check. Also the fault code with the park neutral switch remained with the new ECM, so they found out that a positive wire was missing/cut going to the park neutral micro switch. Fixing that fixed the problem with the missing ground for the ignition relay, solving the original issue of this thread
Now we wait for the car to cool down, hopefully it won't be sunny today so they can see if the car will still not start when cold with the new ECM.
The ignition coil relay is the one in front of the ECM. It supplies power (positive signal) to the ignition coils directly. Apparently it is part of the failsafe in case the car is not in park/neutral.
And to specify, the micro switch I was referring to as being the problem for this relay and the error in the ECM is the one on the gearbox itself, no on the J-gate. The mechanic quoted two wires that need to short out when the car is at park, but they don't on mine. I went and took off the one from the donor car and am waiting on the result of the swap
Edit: Just got the call. The new switch works and the car starts without the extra ground to the relay. Hopefully the temperature tonight will drop enough to see if it will start tomorrow too.
Interesting! Did you notice if you had the “P” light indicator when starting the car and did you ever attempt to start it in “N”? I would find it a little strange if you had the lights and that was the cause. I would think if the shifter selector switch had failed it would also lose the indication However, I have seen stranger things… Please keep us posted on the progress.
The lights were working. The car would not start on N. The car would rarely complain that the shifter is not in Parkl when I get the key out, but it still will light up P
You should keep in mind that the shifter selector switch send the signal to the transmission control module (TCM) then to the ECM. The problem could be somewhere in between.
The mechanic checked the wiring on the switch and it was faulty for sure. The missing ground is now present. We will see tomorrow or on Friday (if it is too warm) if the other missing ground to the fuel injectors will disappear again. They have my spare TCM too so it will be a quick check to swap them (unless it needs to be reprogrammed too as the ECM )
The training guide says:
"...ECM receives OK TO START signal and transmission P / N signal, hard wired from transmission, (= rotary switch) and enables fueling and ignition.
ECM outputs a SECURITY ACKNOWLEDGE signal to the BPM via a serial data link..."
which I took to mean that the ECM needed to see both the OK to start and the P/N state before it signalled the BPM to crank. Apparently it will quite happily tell the BPM to go ahead even if it doesn't get the P/N signal - but won't bother to enable fuel & spark. Nice one. I can't think of a reason why it would behave this way.
I do hope and believe that you're nearing the end of this saga.
"Good news everyone"! This morning the car started up at 0C. It was in the outside for about 12 hours, so I am still not jumping in happiness, and we will leave the car out until tomorrow just to make sure. It shouldn't get warmer than 3-4C and there is not much sun, so it should be a definitive result by tomorrow Fingers crossed!
Second chilly day in a row and the car starts without a hitch Thank you all for the help and emotional support on this more than 7 months journey The mechanic is a neighbor of mine and if he manages to assemble all trims today will drive her home to me tonight and I will be finally able to put its new winter tires and drive it
Once I get a nice talk with him about all the details I'll update the thread with a recap of everything done, learned and solved
I am not sure about the specific fault code, but the park/neutral switch fault was present since the car first refused to start. The first thing the shop checked was both the rotary switch and the J-gate switches. They ruled them out. They only found out that the ignition coils are not receiving a postivie signal. When I found that this was caused by the ignition coil relay not receiving ground, they just got a ground from somewhere else, the car started and called it a day. Fast forward several months, the temperature drops and the car does not start again, but now due to another issue - no ground to the fuel injectors, while the workaround for the coils is still working. My shop wasn’t very interested in pursuin this further and I went to the dealer. Finding shops which do electronics is hard around here and basically impossible for jaguars... they can do only the rebranded fords The dealer took their time too... a month and a half, mostly because of their very particular pricing policy - diagnostics of any issue is basically free if they will be fixing the issue or you pay only for 1 hour of work. So electrical problems then take hours and days to diagnose but minutes to fix. Thus my car was pushed back in line a lot The mechanic there actually needed 4-5 days of intermittent work to pinpoint the issue and because he new how to properly test the rotary switch, he was certain all was its fault. I brought him my spare from the donor car, he changed it and voila it worked I was then billed the staggering 43$/38€ + he delivered the car home as we live in the same building. Of course I did pay him on top of that as much as it would have cost in a normal shop... Just to compare I was then billed exactly the same amount of 43$ to change my tires to the winter ones (new tires, same rims). There is still a mistery of what the temperature was changing. Probably it further affected the rotary switch... I don’t know. The important thing is that I drove her tonight for the first time in months
You can see that my brother does have a similar taste
I can absolutely confirm now that the main issue of the thread is fixed. Like I mentioned before, the first thing we checked months ago, but was green-lit as fine, was the actual culprit - the transmission rotary switch mounted on the right of the gearbox - as suggested by @Gus way back in the 17th post of this thread . To be more precise, the issue was that the switch was faulty and it wasn't registering the car being on Park, which then leads to the no starting situation that I found a way around.
The whole ordeal was at least very enlightening I learned way more about how the car works, than I would have anticipated. However I also found another issue - the weird no start when cold issue
Things now became more interesting, as the issue still exists, but the kicker is... the car starts and runs However when cold... GEARBOX FAULT When it heats up - the error is gone, and the gearbox works, mind you in a weird state, but shifts, then later in the day works absolutely fine.
I am waiting for a simple code reader to arrive so I can check what is happening and will create new thread for this.
Still, thanks to everybody who helped, even with just emotional support during the "no start" saga
02-06-2019, 01:09 AM
They do read correct RPM while cranking, and as I said before, while the car is cranking the spark plugs are actually firing with timing. For them to work is enough to get a ground for the relay which provides them positive signal. The spark coils are still controlled with ground signal, but not like the fuel injectors as there are two modules after the ECM that run them. So the ECM is properlly sending a signal to these modules to make them work, gives them timing and so on, but doesn’t send ground to the fuel injectors and the ignition coil relay.
so they can see if the car will still not start when cold with the new ECM.
