Unplug the DME (ecu) connectors and make sure there's no oil contamination. You changed everything but the fuel pump and crank sensor. Both can cause stalling. Also, do a smoke test https://youtu.be/AsgB9eBl58I

 

MAF sensors give so much more problems than expected. Any nearby junkyards where you can swap out the part for a second and check to see if it was the MAF? That may be a worthwhile option.

-Nev

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Armenh7, thanks for the quick reply. I did two smoke tests (one myself with consumer-grade equipment and one by that trusted shop with pro equipment, and neither found a vacuum leak). I'll look into changing out the crankshaft position sensor. The fuel pump has been on my mind too, but I last replaced it just 55k miles ago and it's pricey, and I figured if it were the fuel pump then it would probably fail just as readily when cold as when warmed up.

Nev, no junkyards anywhere nearby, unfortunately.

 

Sir, then you're just as rural as I am. Nearest junkyard with an e46 is 90 miles away, and I can't really drive a stalling bimmer all the way out there now can I?

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Have you ever replaced the fuel filter? Connect a pressure gauge to the fuel rail and drive the car. You can tape it to the windshield or zip tie to wiper arm so you can see it when driving. If the pressure drops when car the car is loosing power and stalling, you have a fuel supply problem like a bad pump, clogged filter or voltage/ground issue with the pump. If fuel pressure is steady, its not a fuel supply problem. Are you getting any other codes besides p0171/174 and p0300-306?

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I don't see anything in that long list that would cause you to go near the lower intake boot and throttle body. I had a similar situation to what you describe. I did a smoke test and it revealed that the lower intake boot had come free from the throttle body. It looked ok but a gap had opened up underneath. Refitted it and sorted the problem out.

 

Are the catalytic converters the original ones that came on the car? If they are, they would be highly suspect based on my meager experience.
After double checking for vacuum leaks, my suggestion would be to either do another exhaust back pressure test yourself or go to a different shop and get them to do another test. If you get a shop to do it, ask them for the results that they see. Any exhaust pressure over 0 psi at idle, or over ~1.5 psi at 2500 rpm means the cats are restricted. I know this after going through many of the gyrations and overdue repair work that you have been through and still having nearly the same symptoms as you are now seeing. Here is the back pressure tester that I bought:

https://www.amazon.com/dp/B01EMKFGZ2?tag=e46fanaticsconvert-20

Here are a couple of threads from this forum that may help with your situation:

https://forum.e46fanatics.com/showthread.php?t=1242285&page=4
https://forum.e46fanatics.com/showthread.php?t=1247005

Another way that some people have successfully tested for back pressure is to run the car without the pre-cat O2 sensors installed, but I was leary of doing that. I think that sort of test is mentioned deep into the first thread I listed just above.

I hope you find your trouble source.

 

Did you figure out the problem ? I. Have exactly same problem as above....

 

The throttle valve can jammed and the car would run fine using the ICV up until when it needed the main throttle, then it couldn***8217;t open and switched to limp mode.

 

I'm still working on it. I took the car back to my local shop and they performed another smoke test (passed), then a "multi-tiered electrical test of engine management systems", including tests of wiring harness, fuses and connectors, traced apparent cause to oil contamination of DME control module due to oil wicking from some sensor (possibly leaky oil pressure switch, but they weren't sure), tested resistance to sensors (ok), fuses (ok). In the end they recommended replacing DME and wiring harness. I declined.
I opened up DME box myself, found a little oil on the wires, pulled out the DME, but I found no evidence of any oil *inside* the connectors. Unscrewed DME cover, found no oil inside. Looked for oil at various sensors, found exhaust camshaft position sensor oil-soaked (even inside it's connector). I don't believe that sensor has ever been replaced. I ordered a new one in the hope that it's the ultimate source of the problem. I'll find out this weekend.

 

Well, I replaced the exhaust camshaft position sensor today (BMW-brand part #12 14 7 518 628, $110). Test drove it, unfortunately it's still weak and stalls under acceleration after a minute warm-up, just like before. I guess this weekend I'll do a fuel pressure test while driving and see what happens.

 

On a car this age, not even worth testing the fuel pressure. But even a fuel pressure test is not enough, volume must be verified as well. But this is usually just a time waste to check pressure. Replace the fuel pump and filter. Simple and quick repair. Even if this is not the source of your problem you eliminate this as a potential source and improve the reliability of the vehicle.

The pump and filter are not lifetime parts, the pumps are failing in these cars on a regular basis. You are looking at around $200 for a new Siemens/VDO pump and fuel filter. You may also want to swap the fuel pump and horn relay as well.

Fuel pump failures - https://forum.e46fanatics.com/showthread.php?t=929501

One thing from the video is the Transmission "Cog Of Death" is one then I think the Brake light turns yellow before you restart the engine. What is up with this? Temp gauge appears a bit high, but this may be the camera angle?? What is the charging Voltage doing during all of this? Has the Alternator/regulator been replaced with this mileage?

 

Thanks for the updates. Keep us posted. Seems like a few of us are having similar issues. Cats are still highly suspect.

I guess if a shop wants to charge you more than $50 to test the cats it would be better to just buy the tester from the above^ link.

 

Bob:

After finishing ruling out the fuel pump and charging system, please consider the following:

Is the indy shop that did the exhaust back pressure test in your original post the same shop that said the DME needed to be replaced? If so, then please consider re-reading my post number 8 above. Just a thought. Hope you find the fault, I know it's frustrating.

 

At 225k+ miles it is likely the converters could be clogged. What usually happens in more severe cases is there tends to be misfiring and then if bad enough the thottle is disabled and the engine is put into a default "Safe/Limp" mode that can often be cleared by shutting the engine off and restarting it.

One of the BIGGEST problems we have quite often is people test the exhaust back pressure and say it is 1.5 PSI or less and then they claim this is OK. Generally it is NOT. Understand that the 1.5 PSI value is a "Street Spec" that is tossed around very loosely and it really does not apply to these cars with individual catalytic converters IMHO. I still have yet to be able to capture and test a car with known good replacement converters so we could have a better baseline, but the shop that tested the back pressure may have fallen into the same trap many others do.

Remove the Pre-cat O2 sensors and drive the car under the same conditions and see what happens and also see if the car has more power and is more responsive. Ask the shop how the tested the car and what the values were as well.

But I am still interested as to what the "Cog Of Death" is on in the video. Was the MAF disconnected at this time? Or is there another problem.

 

jfoj, the "cog of death" light appears whenever I don't wait more than a couple seconds before restarting the engine after the cut-out problem occurs. Since that light never appears when I pause long enough before restarting, I assume it's not especially relevant.

I'm thinking you're right about the cats being clogged. But aside from the noise, don't I risk melting something if I run the engine with the pre-cat O2 sensors out?

 

There is not much directly in the way of the Pre-cat O2 sensor connections, keep the wires away from the holes and I do not expect you to be driving the car long enough to worry about melting anything.

 

You can remove the pre cat O2 sensors and insert a borescope and see the condition of the cat honeycomb material. Ie if its torn or plugged with carbon.

 

I removed both pre-cat O2 sensors and test drove the car about a mile. Result: woke up all the neighbors with the exhaust noise, but still the same severe power loss. No improvement there at all. I couldn't get it to stall out, but that may be due to not letting it warm up all the way.

Out of time today. Tomorrow I'll do an exhaust backpressure test (though that seems kinda redundant now) and fuel pressure test at 2500-3000 rpms.

On an unrelated note, today I learned that 45 mph is just about the maximum speed you can drive these cars when the hood is not properly latched.

 

Oh, forgot: I also test-drove the car with the pre-cat O2 sensors installed but not electrically connected. There was still the severe power loss, but after warm-up the car *did* stall out under hard throttle. Not sure what to make of that.

 

Have you cleared all codes, then run the car for some period of time, then read the codes?





podman

 

Here's what I (the original poster) have done since my last post a month ago:

1. Replaced fuel filter (Mahle KL 149). No improvement.
2. Immediately got code P2440 (secondary air injection system switching valve stuck open bank 1), P0411 (secondary air injection system incorrect flow detected). Also, secondary air pump was emitting a whine and a burning smell.
3. Replaced secondary air pump (Pierburg), secondary air pump vacuum control valve (Pierburg) and secondary air filter (BMW). Test drove, idles smoother when cold, but no improvement with the main problem (low power and engine cut-out).
4. Removed & cleaned idle control valve (was dirty & stuck). Removed & cleaned throttle body (was dirty). Ensured all connections tight. Test drove, no improvement. Noticed burning rubber (?) smell from engine compartment after test drive.
5. Replaced fuel pump (Bosch). No improvement.

After test drive where I intentionally caused the stalling problem, got 2 new codes I hadn't seen before: P0735 (power train; gear 5 ratio incorrect), P0700 (power train; transmission control system (MIL request). I also got a P16A7 code (MAF signal implausible) again. No other codes currently, although P0171 and P0174 are sure to return in a few miles.

I graphed some data from the ODBII and Torque app, showing the time right before and after the stalling. Does this provide any useful insight to anyone? Any idea what to test now?

 

The transmission errors point to the MAF.

 

I replaced the MAF just 5 months (4,000 miles) ago and it didn't help.

Today I finally checked the exhaust back pressure with a tester that beechbmw recommended (I was thinking it was pointless after getting no improvement with the run-without-o2-sensors test). Results: bank 1 ~3.5 psi at idle and ~4.5 psi at ~2200 rpm. Bank 2 ~1.25 psi at idle and ~4 psi at 2200 rpm. With higher revs in the 2500-3000 rpm range the pressure was even higher. See photos.

The first photo is bank 1 at idle. The second is bank 1 at ~2200 rpm.

Looks pretty conclusive, right? I should have heeded beechbmw's advice back in February.

Well, technically I know I should check the pressure *after* the cats, but that's not happening today.

 

As I mentioned in my post earlier, measuring the pre-cat back pressure of anything over 0 psi at idle means the cats are certainly restricted. I was getting almost the same measurements of pre-cat back pressure that you are getting. I was also getting all kinds of codes that didn't seem related to the exhaust.

Certainly do what you are comfortable with, but I would forget any checking of the MAF sensor/wiring or the post-cat back pressure. Instead, spend the time to figure out if and/or where to get replacement cats.

I am planning on keeping the car for a very long time since I bought it new and it has family sentimental value, so I bought genuine BMW cats. They are very expensive, but fit perfectly as would certainly be expected. Others on this forum have had good results with DEC new replacements. I suggest shopping around quite a bit.

Sometimes others on this forum have found used ones from people parting out cars, I think on eBay. But here in Maryland, using used catalytic converters is illegal. Even selling used cats are illegal. Again, do what you are comfortable with.

If you are going to do the job yourself, I found this thread in this forum's DIY section extremely helpful. Emphasis is on taking your time and being patient. Try to allow the penetrant you use, I used PB Blaster but there are others like WD40 in the gray can, to soak ALL the nuts over night. That means the 16 nuts on the head flanges and the 4 nuts on the exhaust pipe flanges. I heartily recommend using genuine BMW gaskets for the head flanges.

https://forum.e46fanatics.com/showthread.php?t=931323

I hope everything works out!

 

It doesn't necessarily mean a bad maf but rather the wiring is an issue. https://forum.e46fanatics.com/showthread.php?t=1256311

 

Many things sound similar to my experience with my 2005 325i SULEV.

Ultimately, the second dealer I took it to found 9 psi of back pressure on both of the cats. It is still under the 150 K / 15 year SULEV warranty so they were replaced at no charge.

I'd taken it to a more local dealer for the airbag replacement and they offered to check to see whether any parts covered by the SULEV warranty needed replacement due to my complaints about how it stumbled on grades, etc. They replaced the MAF sensor and one pre-cat sensor but obviously didn't check for back pressure from the cats.

 

Well, as extra confirmation I graphed the post-cat oxygen sensor voltage and saw that it varied up and down like the pre-cats do, which according to the 50skid video is further confirmation of bad cats. So I ordered the new cats yesterday. I couldn't find any good used ones on Ebay, so I'm going with BMW brand from getBMWparts, $814 each (not incl. refundable core charge), new BMW-brand gaskets, new nuts & bolts. I got the car up on 4 jack stands today and have sprayed all the nuts with PB Blaster and will repeat daily until the parts arrive. The car has spent almost every night in my garage since it was new, so there is very little rust, hoping for no troubles. Off to Harbor Freight to get an engine support bar.

 

If you don't already have it, I found a reversible, ratcheting 11mm box wrench comes to be very helpful for some of the nuts. 1/4" drive wobble extensions also are handy. I didn't own an 11mm 1/4" drive deep socket, so I had to get that, too.

Another hint. I tied a 4 foot piece of string to the ends of each of the post-cat O2 sensor wires before removal of the wires. That made it easier to thread the wires back up to the connections above the intake manifold using the same route. Maybe it is easier on a sedan, but on my coupe, it is absolutely impossible to get any kind of wrench, specialized or otherwise, on one of the post-cat O2 sensors. I replaced both post-cat O2 sensors since they were original with 180k miles on them. I mounted the new post-cat O2 sensors on the new cats before I installed the cats.

I found this job to be more tedious than difficult. But I found the satisfaction of driving the car after job completion to be amazing since the car ran almost like new. I had forgotten how much power and acceleration the car had before the cats got clogged.

Hope everything works out for the best!

 

I finally finished installing the new BMW catalytic converters today (and new engine mounts, and 4 new oxygen sensors). A hell of a time consuming job for someone slow and careful like me. The 16 nuts at the head all came off cleanly, though not easily. And the 4 nuts connecting the exhaust manifold to the exhaust pipe came off after a minute's heating with a blow torch. The rope trick for the O2 sensors was very helpful. The engine mounts were a SOB because I made the mistake of removing both at the same time. I had to partially lower the subframe on the right side to get the right one in.

The final verdict? Success! Full power is restored and no more stalling. So far no codes, although I've only driven 5 miles on the new cats so far.

Next project: replacing the oil pan gasket. There's always a next project with these cars, right?

Sincerest thanks to beechbmw and everyone else who offered helpful advice!

 

Hello, is there a follow up on the issue ? I have same year model and exact issue only cuts out on extreme cold days and only at full throttle maybe 2-3 gear switch.