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rover_75
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Discussion Starter #1
Hi all,
After reporting my problems with the rev counter and temperature gauges rarely working I called Digi-Dash this morning and was told that they could take the chip from my old pack and transfer it to a new (secondhand) one but it would have to be the same type i.e. without message centre.
I decided to go to the breakers today to see if they had a basic instrument pack from a diesel but 2 I found there (one in a shed, the other I had to climb up to one still fitted to a car to remove it, I got fairly dirty but was good in a way as I was in control!) were both message centre types from newer cars than mine.
I was allowed to try each in turn on my car (as long as I left mine in their office while doing so) and found the following:

1. The rev counter and temperature gauge did not work on either of them, just as with my own.

2. Everything on the others seemed to work OK, didn't see any lights on that shouldn't have been etc.

3. The mileage of both message centre models showed the original mileages from their own car in each case, both much lower miles than mine has done.

So I don't know what to do next. It can't possibly be a faulty instrument pack now, can it? If not faulty, what else could be? Canbus connections have been checked by resistance reading across the 2 terminals at the instrument pack, a few ohms over 120 ohms with the pack disconnected, and a few ohms over 60 ohms with it connected. I have not isolated the 2 wires and checked each from one end to the other yet. The ECM has been tested on Bosch testing equipment and apparently found to be OK.
Could anything else interfere with the way the system self tests?
Before I went to the scrapyard I had to go back to my home to collect something I had forgotten, a distance of about 6 miles. During that trip both gauges started working and stayed working all the way home. The air conditioning worked and the HRW worked, both have not worked for months. As soon as I restarted the engine to continue the trip the gauges no longer worked and did not work at all for the rest of the day.
My son has done exactly the same trip a few times in my car and found that it is the only place he has seen the instruments work properly and that was on at least 2 or 3 occasions. So for some reason the gauges will not work anywhere else, but might work on that stretch of road. Very odd!!
Any comments on what I should be looking at next will be gratefully received.
Regards,
Charlie Hall
 

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Very strange!

Daft I know but are there any obvious radiation or wireless sources-could interference from in the car or external to it be the problem?

Mike
 

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rover_75
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Discussion Starter #3
Hi Mike,
Thanks for that suggestion, not that I hadn't already thought of it myself as a possible factor, but the fact that it might have occured before to someone else would be quite encouraging. It could also make sense of the stretch of road having some kind of effect, maybe a cancelling effect of rf signals or something like that?
Looks like I might have to isolate (or replace entirely and perhaps screen them in a separate new run) the Canbus wires and do some tests there.
I can't think of anything I have done to the car in any way that would change anything, BUT a short while before it started happening my mechanic friend had worked on a fuel problem (he replaced the MAF sensor, a fuel pump on the bukhead, and the tank fuel pump with a later type at my request after having read other threads about it) and fixed it. He had also removed the ECM to check it was dry. I'm now wondering if he could have disturbed something unknowingly. Inside the plastic box that houses the ECM there is a smaller box that has a nut and bolt that attaches a wire to it. Do you know what that box is please, and whether a bad connection via the nut and bolt could cause anything I am experiencing?
What do you think of doing something to modify the Canbus wires?
While I think of it, when the instrument pack is removed there is a silver coloured small box behind it with 2 or 3 wires connected to it. Any idea also what that box is please?
Regards,
Charlie Hall
 

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rover_75
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Discussion Starter #4
To add to my last message, the ECM is housed in a metal container with a removeable plate held by a number of keyed head screws (the same type of keyed head screws that fix the back plastic panel of the instrument pack). I assume that the metal container has to act as a screen and would not do so if there was a bad connection to it.
When I took a quick look inside before sending it to be tested I did not notice any connection to the box, although that doesn't mean there isn't one, only that I didn't notice one. Maybe one of the board fixings is supposed to connect to the box via one of the screws?
I would be grateful if anyone can confirm the correct mechanical configuration of the ECM board and its metal box. It is a Bosch ECM.
Regards,
Charlie Hall
 

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rover_75
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Discussion Starter #5 (Edited)
Just spoke with the service manager of the dealer who looked at it before. The car is booked in on Wednesday and they will be concentrating on the ECM. He insisted that to his understanding the mileage is logged in the ECM. The only way that makes sense to me after all I have read and heard elsewhere is that the 2 instrument packs I tried did show the original lower mileages of the cars they were taken from.
I thought this might be interesting to some of you.
Regards,
Charlie Hall
 

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rover_75
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Discussion Starter #8
If they are fitting a new ECM could it be programmed to give the 135 performance, or at least increased performance? Or is that only possible with an X Power (is that the right name?) add on?
I know I could ask them the same thing but I'd like back up opinions if possible please. Thanks for any help.
Regards,
Charlie
 

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Discussion Starter #9
The car is with the garage right now. They had decided that the Body control unit was the problem (since it controls both the aircon and the HRW even though they said they know the problem is the Canbus, I assume Testbook confirmed that) and fitted a new BCU yesterday, no difference. At least they took it off again, so I don't have to pay for it.
They have suggested that it still could be a wiring fault since the gauges do occasionally work but I know that the Canbus connections are good. What I don't know however is whether the Canbus wires are properly oriented e.g. picking up interference.
As mentioned earlier I had already tested both Hi and Lo Canbus signals with a scope and there were patterns as expected but no movement of the patterns when revving the engine. I realise that they are trying to save me spending money on a new ECM if that isn't the problem, but finding a bad wire could take a lot of time (at £60 an hour) especially if there isn't a bad wire.
So I have asked them to fit a new ECM which hopefully will be on Monday as they haven't let me know of any problem obtaining one. Of course once fitted, I've got to have it.
Would anyone think it could possibly be a faulty wire or connection other than the Canbus (and possibly disabling transmission or reception of some parts of the Canbus signals) before I commit myself to the ECM once fitted and programmed?
I personally think not, but I'm not an auto electronics expert (beginning to wonder if anyone is though, since having the ECM tested on Bosch equipment and found to be OK, supposedly). I'm thinking that because the ECM was tested off the car it might make a difference to the diagnosis since the Canbus signals are probably not connected to an actual Canbus, but of course I don't know anything about the Bosch test equipment other than it cost thousands.
What I really mean in simple terms is, has anyone heard of bad wiring on a 75, where replacement units of all kinds did not fix a problem? Any thoughts on this would be much appreciated.
Regards,
Charlie Hall
 

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rover_75
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Discussion Starter #10
Just to bring this to the top in case anyone missed it.
Has anyone heard of any wiring failures (as opposed to electrical component failures) on 75's?
Looking forward to any info to help me to decide whether I am doing the right thing requesting a new ECM (since it is probably the only component left to try), having virtually eliminated everything else component wise.
It is so annoying having what seems to be a minor fault (although probably within a major component) stopping so many important things from working properly.
 

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Hi Charlie,

Myself I have never heard of a wiring failure on a 75. It doesn't mean there hasn't been one but sounds like a real one off. I wish I had a suggestion for you but I don't :( What's the betting it turns out to be something really simple!

Good luck and do let us know.

Regards

Mike :)
 

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Discussion Starter #12
Hi Mike,
Thanks for your reply. It probably is something simple, but my guess now is something like a faulty component in the ECM that is in the Canbus send or control circuit. I'm going on the basis that since the car runs fine, and that the Canbus is for communications between modules, then the Canbus has nothing to do with the engine performance from within the ECM. I might be wrong though. Also, the fault first occured in damp foggy weather and that would point to something where the damp weather would easily reach.
I've got the garage fitting a new ECM since I just can't think of anything else, it's all been practically eliminated. They said the new ECM was about £460 or £480, I forget which but that's probably without VAT. I will also ask if I can have the old one back as a spare in case the new one develops a fault in future.
My mechanic friend has had an ECM tested before (Japanese make I think) and was said to be all OK, but replacement of it was the thing that cured the fault.
I'll report here on the result when the new ECM is fitted.
Regards,
Charlie Hall
 

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Discussion Starter #13
Got the car back while they wait for a new ECM to arrive.
Meanwhile I find the radio no longer works, it switches on but there is no reception, as if there is no aerial.
Could removing and refitting the BCU cause this? It was working before up to when the garage collected the car. I have already told them about it so they can't say it must be a separate fault.
 

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Charlie Hall said:
Got the car back while they wait for a new ECM to arrive.
Meanwhile I find the radio no longer works, it switches on but there is no reception, as if there is no aerial.
Could removing and refitting the BCU cause this? It was working before up to when the garage collected the car. I have already told them about it so they can't say it must be a separate fault.
The aerial cable runs from the hu to the front n/s and then down along, up the n/s 'c' pillar and to the rear screen. So the cable does first run in the BCU area and they may have disturbed it or even pulled it out of the unit. Do you have a double din size Harmony or Symphony? Instructions on how to get the hu out are in the how to forum-you could thern see if the aerial has just come out the back of the unit.

Good luck

Mike :)
 

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Discussion Starter #15
Hi Mike,
Thanks for your reply. I think it's a Harmony unit, just radio/cassette. Car is a 75 CDT Club. Incidentally, since they removed the dash to check for bad earths a while back, the cassette dust flap is missing. I've told them but they say that the whole thing comes out as a unit and can't see how removing the unit from the dash would cause the flap to be lost. But it was there before!
Do you know if the aerial is a separate cable/connection or within a connection block along with other wires to the BCU? Everything else seems to work OK.
Seems like the car is gradually disintegrating faster than it can be put right, even in the hands of a former dealer. I don't want to fall out with them since they have said they have written off some of the hours spent on it, and they have been more than helpful as far as possible.
Regards,
Charlie Hall
 

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bare with it Charlie, im sure the problem(s) will be solved soon. The stereo problem is just a result of slightly sloppy workmanship from that one ex dealer, you shouldnt have to put right any faults they cause, so keep on at them. Politely but firmly is the way to go, they are taking enough money off you for the work for it to be a quality job.
 

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Discussion Starter #18
Thanks MattL for your reassuring words, and Mike for the cable info.
Sounds then like the cable might have been unplugged by accident.
Still no news of the ECM arriving yet. At least the car is driveable until it does.
Regards,
Charlie Hall
 

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Discussion Starter #19
To those concerned or interested?!
Heard nothing yet from the garage.....
I went to work today in the car as I do most days, a trip of 0.6 miles! As I switched off I noticed the sound of a fan winding down (something I only hear if everything is working properly) and thought I saw the rev counter needle move to zero. I immediately started the engine again and sure enough the rev counter was working. Tried restarting several times, still working. Went back an hour or two later to try again and worked every time I started up.
Then I noticed that the glow plug light was not staying on for long each time I switched the ignition key on (I am almost certain that the glow plug light had been staying on for a lot longer over the last few months, whether the engine was cold or hot). Tried switching ignition on and off many times to see if glow plug light was on for short period each time and always was. After switching on and off for so many times the wipers did one sweep! The wipers were not switched on. Carried on switching ignition on and off and after 24 times the wipers did one sweep again, then after 24 times they swept again, then only after 36 times they swept again, then after that, nothing.
I wonder if I have somehow successfully reset something as the rev counter (and everything else that was not working before) has worked properly since, even late this evening it was still working after a cold start, but also noticed that the glow plug light was not lit for long, just as when the engine was slightly warm earlier today.
Now I am wondering if the engine (or rather water) temperature sensor (ECT?) or some wiring fault with it has been playing up and causing all these problems I have had over the last few months. The sensor would probably control the glow plug control module and cause the different length of time I am seeing now that everything works again. I just wonder how long it can keep working OK, particularly as it went wrong already of course.
Any comments are welcome of course, because now I am wondering whether to cancel the order of the ECM, and look at either the ECT or the glow plug control instead.
Edited: to add that the radio still does not work as described earlier, that must be a separate fault and never thought otherwise.
Regards,
Charlie Hall
 

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Discussion Starter #20
Everything still working this morning. Glow plug light stayed on for a lot longer from first cold switch on of the day so there seems no fault there. Temperature gauge at 6 o' clock to begin with, yesterday it was always a little past that point even after several hours.
My son has just been on a 30 mile round trip and everything worked all the way there and back.
Can anyone confirm that switching the ignition on and off several times as I have done would reset anything, particularly the ECM, on a 75CDT?
Seems incredible that the dealer with Testbook was not able to pick up on this, unless it was a case of waiting for the right thing to happen before anything could be done.
Will have to see how long it stays OK for now as my luck doesn't usually last for long with such things. Can't believe if this is now fixed. Maybe something the dealer had done has allowed the fault to clear somehow.
Regards,
Charlie Hall
 
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