E70 50i engine off when driving, perplexed and needing suggestions

[Analyte]

Hello,
The site has been helpful before so hopefully someone has an idea. I do my own maintenance so I'm familiar with the X5 and troubleshooting things.

The wife had said her 2012 X5 50i seemed to be missing so I put the scanner on it, and I found no cylinder faults or anything else. I decided to take it down the road myself to see if I could feel what she described.

The drive was fine and I felt no issues. On the way back home at a stop sign I hit it and run it up through first to 6500 and second until around 4500. I felt no miss the entire time.

Then the engine just shut off. No warning lights, no message on the display noting a malfunction, or anything else.

I coasted to a safe shoulder, and tried to restart. It acted like the battery was almost dead slow cranking until it finally started. It ran for about 2-3 seconds and shut off again.

I pulled the scanner back out, hooked it up, and run through all the modules. No fault codes for the engine other than an O2 system error, no specific bank or anything. There was still no CEL on the dash. In addition, I now had a fault on the transfer case for oil wear.

I then tried to start it again, and another slow cranking followed by 2-3 seconds of running before shutting off. I popped the hood and looked under it as well as under the car. No obvious issues so I went back in the car to check all the codes again. Just the O2 system fault as well as the transfer case oil fault again.

I cleared them a second time, and then tried to start again. This time it cranked normally and idled normally. While it set idling I went through the scanner again, and nothing new popped up over the next 5 minutes.

I pulled back out on the road, and it was not accelerating smoothly like normal the first quarter or so. After that, it ran fine the rest of the way home. I accelerated again up the hill moderately with no issues and it was as smooth as always.

Once home I looked at everything again while it was idling. No new faults, just the O2 system and transfer case wear, and I was able to start/stop it normally a few times while trying to reproduce the previous slow crank condition.

I'm at a loss as to what happened. I'm going to investigate the O2 sensor fault a little more to see if it's a specific sensor acting up and change the transfer case fluid so those are done. Beyond that, I have no idea what caused the engine to shut off.

I guess it's possible the transfer case may have been causing a stutter or slight slipping due to the old fluid which she thought was a miss. It was just changed 30k miles or so, but I'll change it again if it says so.

Any other ideas on the cause of the engine off situation? Thanks!

[ard]

Engine sub-harness issue.


Years ago I recall this a few times with a few cars.



Hard cornering/acceleration would cause torquing of the drive train, connector or wire loose or chaffed.


My guess. Do some google searched for 'engine sub harness' ... see if it matches your experience.

[Analyte]

Thank you, I hadn't thought of a potential wiring issue

I'll do some searching on it. Appreciate it!!

[80stech]

Any progress? I think the slow cranking is the big clue here.

[Analyte]

Originally Posted by 80stech

Any progress? I think the slow cranking is the big clue here.

Well, I think so

I dived in yesterday. No issues at the battery, just to confirm, but I pulled the lower plate and all the air boxes up top to look over everything well

I haven't found any wiring concerns so far. With searching, it does appear the transfer case oil wear is due to me not able to reset it myself. When I changed it last, I reset apaptations, but it appears only BMW can reset the light.

I did pull all the plugs, and I pulled the pre-cat O2 on back 1 that was throwing the code. I added new plugs and a sensor, and I kept looking for any other possible issues.

I've not found any other problems so I'm putting everything back on this morning so I can do a test drive. I'll drop the oil afterwards when warm, but so far only the plugs looked rough with 70k on them and the O2 definitely looked like it was seeing a rich condition.

Otherwise, my investigation continues

[Analyte]

Well, this is not the update I wanted to write.

I got it all back together, cleared the codes, and then started it up. It cranked fine, and I let it idle for 15min or so to see if anything came up. No codes so I decided to take it down the road.

For the first couple of miles all was ok, and then with the cruise on it started to accelerate as I went up a hill. It made a single "thunk" sound, and I turned the cruise off real quick. As I was slowing down, I heard a high pitched tapping sound. As I slowed down and pulled over, it sound more like something flopping around as the rpms settled. Maybe similar to a rock in a can, high pitched and not a consistent rhythm.

I got the wife to come get me and the X5 so it's back home now. Using my stethoscope, it's definitely on the bank 1 side and when it made the sound on the road it did trigger the pre-cat O2 bank 1 too rich fault again.

I'm going to pull the air boxes off again on that side, and I wonder if I lost the bank 1 pre-cat. I've had a cat break up before and it did sound like rocks in a can. Or it could be the turbo I guess as well.

The only fault is the bank 1 pre-cat is too rich, and otherwise the X idles seems ok other than the rattle. Nothing else seems to be affected or seeing an issue. Figures.....lol

[80stech]

With the slow cranking it almost sounds like an engine timing/chain issue.

If nothing is really obvious maybe pull the plugs on that side to see if there is mechanical damage.

[Analyte]

Ok, I'm back at it. I got all the intake and such removed on the bank 1 side. At this point I'm trying to figure out how best to attack.

I'll pull and check the plugs first just to confirm nothing obvious in the cylinders, but the noise does appear to be coming from the primary cat/turbo area. It seems to ve echoing pretty good on the scope when I listen.

I may start it after checking the plugs just to see if I can get a closer listen to it with the air box out of the way.

Is it possible to pull the bank 1 primary cat without pulling the turbo? I did some Google searches, but I didn't see a walkthrough that shows if the pipes may be replaced without pulling everything around it off or not.

I'll update later.

[Analyte]

Looking at this thing, it may be worth pulled the bank 1 turbo since that may need to be removed anyway if the primary cat has to be pulled. With the turbo out id the way, I will be able to stick a camera up the cat to see if chunks are broke off.

All plugs removed, and they look fine. A little rich on cyl2, but the rest looks ok for day old plugs. No damage to the tips or anything else.

[Analyte]

Ok, I got the O2 sensors out and pulled the heat shield off the primary catstl.

The bank 1 post cat O2 sensor was covered in white powder, that's not normal. I checked the bank 2 post cat 02 and it had some white powder on it as well, but it wasn't as thick as bank 1.

The new pre-cat sensor in bank1 still looked pretty new since it only had around 5 miles on it. Tank w pre-cat sensor had a little white residue but nothing weird like the post cat sensors.

I'm still thinking I may have a bad cat or 2? I pulled the front coupling off the bank 1 turbo and it's clean. Nothing seems to be getting up there. It did appear the rattle was coming from the upper back of the engine.

Any concerns trying to start the engine with the O2s to see if any residue flies out of the post cat sensor openings? I'll listen again for the racket, but I'm thinking if the cat is breaking apart it will be going toward the post cat sensor and not toward the turbos.

Thoughts?