Bad penny here.So I took the plunge and managed to take her out for a drive to the garage and had her plugged into their diagnostics. An hour later I had the results...well sort of...they couldn't put their finger on it and by the end of the hour she wouldn't even stay running. Because they had been given the long story by myself they thought that the ECU wasn't compatible...and in there experience it was very unlikely to be able to swap them over....ever get the feeling that Jaguars just seem to be a step to far for some mechanics...a breed apart I would like to think.They also said that the alternator was kicking out just over 16v and the MAF was giving a minus figure..which he had never seen before....they kindly allowed me to leave the car parked in their parking spaces until I could arrange to get her back. In the meantime I found another ECU which had the same part number as the original and waited for it to be delivered. My gut feeling was that the ECU was not the problem and something else was being overlooked. So the ECU arrived today and I fitted it and.....almost the same as before....started fine and then got progressiveley worse to the point of not ticking over at all.....this is good in one respect... I am now assuming that the ECU is not the problem..something else is throwing a spanner in the works. Whilst it was running I put my meter across the battery and got 14.5/6v consistently. Next to MAF..Previously I had disconnected the MAF to see if that made a difference whilst running and the engine had cut out almost immediately....this time I disconnected the MAF prior to starting and she fired up and sat ticking over nicely. I remember someone possibly saying that if there is no reading form the MAF then the ECU makes some assumptions to allow the engine to run...like a default...Is this true? A used replacement is between £30-£40 so worth it if that is the cause of the problem. Is there anything I can do to the existing MAF or are they not worth bothering with.? LHE1620AA is the relevant part number. Thanks.

 

I recall the same comments about MAF disconnect on the V8 boards, so might be worth the swap. But first check the pins for corrosion/damage.

 

It's true that default values will be substituted for MAF. This is from the X300 Electrical Diagnostics Manual

"No signal (open circuit) at any time with the ignition on, or a high signal output below a set engine speed, will be registered as a fault. ........... when faults are present a default value of airflow, calculated from throttle position, engine speed and inlet temperature, will be supplied."

But how did we get to here from previous post where there was a concern about the ECU connector. Has that now been eliminated? If so how, if not then I would carry on with that line of diagnostics first.

Did you get any diagnostic live data from your garage? I'm assuming there were no fault codes logged?

Could be the MAF but it was working OK before the ECU incident wasn't it? So seems unlikely it would curl up and die while you were working on something else.

I would recommend getting yourself a diagnostic tool. You can buy an ELM327 type interface from Amazon/ebay for about £10 (or less) and then use a free/cheap app to connect your smartphone to the car and get some readings. It's invaluable.

I have one of these in the glovebox of each of our cars (works just fine with the X300)
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

(You need Bluetooth for Android phone and Wireless for iPhone)

 

Thanks for theinfo re: code reader I will be getting one asap as the one I have does not communicate with the x300 and it does seem like an invaluable tool. I've obviously surged ahead without logging any findings and got lost along the thread. With regards to the connectors (the original ECU had two broken pins as previously mentioned) there was one broken female connector which I have removed and replaced and spliced back into the loom. All other connectors appear present and correct and I have made sure they were seated and cleaned up. Worth pointing out that I haven't done any checks with a multi meter though. The diagnostics that were run showed codes for the immobiliser system and were cleared and did not come back so assuming they were historic. There was an ABS fault which I knew about and has been present all the way through. The garage couldn't find any issues with the O2 sensors and were getting 'proper' readings,whatever that is. The MAF readings were coming up in minus values which apparently the technician hadn't come across before and the alternator was throwing out 16v+....they said that until the ECU was ruled out as not being an issue then there wasn't anywhere else for them to look at present. So I've swapped out the ECU for one with the same part number. I also checked the voltage at the battery with the new ECU in place and it was at a steady 14.5/6 so I'm hoping that issue has been ruled out. As the diagnostics had shown odd readings from the MAF and that the engine ran sdo much better with the MAF disconnected I thought it was worth swapping it out to see what happens...if nothing changes then I at least have a spare one which can't be a bad thing. I shall try it out later and report back...in the meantime I still have some giftcard credit on my Amazon account so will be purchasing a reader.Thank you for the link.


Poorly connector.



New one,also soldered and insulated before splicing in.

 

Nice, that looks like solid work on the connector. Let us know the outcome with the new MAF then.

It is a good idea to maintain a stockpile of parts if you're in for the long term. I have loads in the shed - including 4 BPMs!

 

Always looking for a silver lining.So putting the replacement MAF I managed to knock off the coolant sensor...but that was ok because when I took off the header tank and investigated I found that the sensor housing wasn't actually broken,a previous owner had put some adhesive on but turns out they needn't have bothered because a push and a turn and a turn and the sensor clipped into place..who'd have thought? Always learning. So before I removed the tank I fired her up and she ran,not overly well, but did mange to tick over and over the ten minutes or so she was running there was improvement. 'b1mcp' you were right, I don't think the MAF was the problem and probably the replacement MAF was just in a better state than the original one thus allowing for a better running condition but not curing the problem.
Remember the days of old when you tried to start your car on a cold morning without the choke...and it coughed and spluttered until you either pulled the choke out or just kept featehring the throttle until it warmed up? That's what its like....so all this got me thinking back over everything that has been done since the initial 'non-starting' issue arose. I tried to think if anything I had done that I haven't put back to the way it was originally. I have a theory which I won't share until tomorrow when I can verify something. Not really a cliffhanger just need another day before I possibly show myself up for a right fool...if that is the case I shall take the ridicule.

 

Right, trying to make sense of it all and using the famous quote:"How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?" I have been trying to work backwards over every step to see if there was something that I have done that I haven't taken into consideration.
After each part was changed in the initial 'immobiliser issue' I put back the original part.
I think I was thrown a couple of red herrings with the damaged pin for the O2 sensor and the diagnostics at the garage coming up with minus figures from the MAF and high charge from the alternator.
I am getting to the point. So to briefly recap.Everything working as it should-parked on drive for about a week and then had trouble starting(turned over and fired a few times then wouldn't turn over at all-no CEL)-changed everything I could think of associated with immobiliser-finally removed ECU found water ingress and two broken pins-put another ECU in-started up but gradually ran rougher and rougher to the point of not ticking over-put a second ECU on and repaired connector on loom into ECU-ran but was still very rough-changed MAF-ran better but still not perfect. Inbetween removing the original ECU I removed the battery to put on charge for a few days and put 10 litres of fuel in as the gauge was halfway between quarter and empty....there is a chance that what I thought was petrol was in fact diesel..there are many cans around and we don't always stick to green/petrol black/diesel and there are two other diesel cars in the family.....working on that assuption I have since filled up completely with fresh petrol and today the car ran better than it has done since the beginning of this sad saga. If I had made the connection right at the beginning I would have drained the tank but hindsight is always 100% so I have gone the other way and diluted down to the minimum. So that's my working theory...I have removed all the plugs today and cleaned then up...four of them were black/sooty and two were quite dry and clean. I'm guessing the next best thing to minimse long term damage would be to change the fuel filter and clean out the injectors. Anything else I can do to minimise the long term damage? If anyone needs any clarification as I tend to waffle feel free to ask. Name-calling will also be tolerated in the short term.

 

Well I hope that's your answer.

I've never done something like that (smug smile on face) so I can't say from experience.

I would think that draining the tank is obviously still the best thing to do but you will probably get away with just running it down as quickly as you can (got any trips to Penzance coming up soon?).

I would think that residual diesel in the filter or injectors will be cleaned by the fresh petrol. But it's just my theory.

 

Apologies for the time lapse,not sure where it's gone. So the end of the story finishes with a happy ending. The more I drove her the better she got,not perfect but certainly improving. I was resigned to selling 'as if' warts n' all and then fate played its' hand. I had been selling some old Vectra bits, a legacy from my son, when one of the buyers who was collecting some shock absorbers turned out to work for a Jaguar specialist down in Reading...."While you here would you mind etc." After a quick look he was 99.9% sure it was the MAF...I'd already changed it once for a 'working' used one. So I bought a new one (Not to bad at £85) Put it on and she finally purred. Job done and she is now in the hands of a new owner who is building a small collection of X300's as part of a pension plan...nice. Hope this has been helpful, I for one have learned many lessons. The new project is an XJ40 without any keys...but that will be another story.