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Discussion Starter #1
My e39 M5 has been off the road the past 6 months and during this time I had the exhaust off and replaced all four lambda sensors with the correct bosch items, this is the only thing that was touched on the car. Whilst fitting the exhaust back I also noticed that the EGT sensor wiring was not in the best of condition and was frayed and the connection may have already been broken but during refitting the cable came away so is definitely now not connected.

Anyway I had started the car up and moved it around the drive on occasion over the 6 months with the lambda sensors removed.

Last night was the first time I had driven the car and it now has a major loss of power and very slight hesitation, I can barely pull away especially with heavy throttle.

From what I understand if the EGT is disconnected/faulty then a warning light should show on the cluster which I do not get, so im guessing the EGT connection was already broken/ the ECU has been re-flashed at some point to the newer version which no longer required the EGT.

This leads me to think the issue is around the lambda sensors, I need to ensure I have definitely fitted the pre-cat/post-cat the correct way round but 99% certain I will have done although I would be surprised if that would cause the issue?

Could it be that when I ran the car and maneuvered it around the drive with no lambda sensors connected that it has caused the car to go into some kind of limp setting, although the car does rev past 2600rpm, so maybe not as apparently limp mode sets the rev limit to 2600rpm.

I am in the process of ordering some diagnostic cables from cable shack on here and will be checking the codes this weekend and resetting them, perhaps this will resolve the issue.

Can anyone offer any other advice?

Thanks
 

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Definitely will want to see what codes are stored, clear them and see what comes back after another drive. Is the check engine light on?

Also, was the exhaust dropped hard at any point, in particular up near the cats? It's possible but unlikely that the catalyst broke inside the cat and is causing an obstruction in the exhaust flow.

Edit - Also, I am not too familar with the EGT system as mine was disconnected long ago and the cat on that side was replaced under warranty so I don't even have the bung anymore. That said, I would think if the sensor was still active and disconnected that it would at least set a code if not set the CEL.
 
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Discussion Starter #3
I have no check engine light or any other warnings on the cluster, I also understand it may be worth resetting the adaptation values which I can do once I receive my diagnostic cables and software as the lambda sensors were 135k old so well past their best.

I didn't drop the exhaust hard at any point but I did have to trailer the entire exhaust to my local garage and they may have done so but highly unlikely given the size and weight it's not the sort of thing you'd just let drop on the ground and also it was at a friends garage.

As you say with the EGT disconnected I would expect the CEL but perhaps the ECU had been re-flashed at some point to the later version which did not need the EGT.

I will update this thread once I have got my diag cables and got to grips with using the software :M5thumbs:
 

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There is no message for a bad EGT sensor on the OBD display. You may be under the misunderstanding that codes show up on the OBD display. They don't. You need a special code reader like the Peake one.

There are quite a few threads on here about people getting the O2 sensor connectors mixed up which causes problems, obviously. I haven't got my head around how this actually happens but it HAS to set codes as the DME must be totally confused. And the codes may not switch the SES light on. I suggest you get the codes read.
 

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Discussion Starter #5
I double checked for leaks last night and felt no blowing, I also checked that the sensors were not back to front and can confirm the precats (part no 0258003477 iirc) were in the correct position at the front of the car and plugged into the loom correctly as they have different male/female connectors so they can only be connected correctly but you could obviously have them physically in the wrong section of the exhaust . The only way you could physically connect the wire wrong way would be to connect the precat lambda male to the postcat lambda female.

Anyway I took the car out for another drive and for the first few minutes of driving it seemed relatively normal to drive again, however after about 3/4 minutes of driving the car started to hesitate, feel lumpy and not willing to build up speed easily.

I shall hopefully be reading the codes this weekend once the cables/software arrives.
 

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Without too much detail, the common error is plugging the two sensors together and the two feeds together. You get a code for the heaters only and it takes a few drives before the SES/CEL lights.

In any event my guess is you just need to drive the car a few more miles. You can clear the adaptions but you will still have to drive it just as far to get them correct. You have to understand the reading has to peak and then the adaption drops a bit then repeats. It never makes big adjustments.

There have been many a conversation on this, but likely 200 miles gets you close and 500 miles you are there. Some argue much less, but I say BS.

Here is a fairly common problem. The PO does not do a lot of maintenance so as the old O2 sensors age air leaks in the intake system form. Could be aging MAFs and O2s acting together too. Oddly each of these two things balance each other as the years tick by keeping the performance acceptable. New owner changes the O2s and the car runs like crud. It is because now the other problem has nothing on the other side to balance it.

While you are driving the 500 miles do several MAF test runs and see how the numbers change. That will also give you an indication of adaption changes. The MAF test is really a fuel rate test so when it stops changing your adaptions are close.
 

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Discussion Starter #7
Just to update this, havent tried driving the car since last week and last night I plugged in INPA, cleared the error codes and drove the car and no problems whatsoever. Dont get how clearing the codes would make any difference or if it was just driving it again that helped as it happened to be the third time i've taken it out for another short drive since putting it back together and it's managed to now adapt to the new sensors.

Once I got back after a good 15 minute drive I checked INPA and no errors whatsoever and engine pulls really well as expected.
 

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Just to update this, havent tried driving the car since last week and last night I plugged in INPA, cleared the error codes and drove the car and no problems whatsoever. Dont get how clearing the codes would make any difference or if it was just driving it again that helped as it happened to be the third time i've taken it out for another short drive since putting it back together and it's managed to now adapt to the new sensors.

Once I got back after a good 15 minute drive I checked INPA and no errors whatsoever and engine pulls really well as expected.
Good news! Thanks for updating the thread and certainly revive it if the symptoms return.
 
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