[Windhund]

A few miles from home today doing about 70 mph the car suddenly shuddered or hiccups for a few seconds like a downshift but not as harsh. It recovered then about a quarter mile later did it again for about the same duration. No warning messages were displayed like Trans Program
I turned around immediately and drove about 5 miles home without further incident.
Anyone have an idea what might be causing this problem?

 

[u.nanimous]

Electrical disruption like an engine ground strap?

 

[Windhund]

Yeah that sounds plausible but as we know tranny issues can be tricky to diagnose. The list of potential suspects goes on and on.
I've replaced the input and output shaft sensors and changed the fluid and filter a few times but that's the extent of work done on the tranny. The wiring harness with all the plug ins has never been replaced however.
Could low fluid do something like this? Again, it hiccuped only for a few seconds both times and only at highway speed

 

[Mayorchuck]

My first E38 would do this and sometimes completely shut off for a full second or so. Never got a warning light of any kind. I joined one of the forums the next day and someone suggested it may be the cam sensor. I replaced it an it never happened again. Coincidence maybe, but I didn't care as it never happened again. I also learned over time that a bad cam sensor will not always throw a code. It's been my experience that a transmission or torque convertor issue will present itself at lower speeds initially. Just my personal experiences.

 

[lenwib]

Another possibility could be a slowly failing fuel pump and/or low fuel level. The pump can live "forever" but after 100-150k you never know. (Which, of course, basically is true during its complete lifetime.)

//Len

 

[Windhund]

Thanks guys for the insights. Well, the fuel level was over 1/2 tank so it wasn't low fuel but I've never replaced the fuel pump and I've owned the car since 2008 so I suspect it's original. Could a semi-clogged fuel filter be the problem? I'm just thinking off the cuff that this could cause the fuel supply to blip for a few seconds? I replaced it once but that was several years ago.

Camshaft position sensor? That's intriguing. I never would have thought of that and I've never changed it. Would the cam sensor or fuel delivery interruption (for whatever reason) throw a code? If so, would I need a special BMW code reader to see the code(s) or could a trip to Autozone accomplish the same thing?

 

[mattmar1]

fuel delivery issue wont cause a code specifically of its own, but there will be symptomatic codes set such as lean running codes. a generic scanner (OBDII such as the ones part stores have) will detect cam sensor codes, p0340 or p0341 iirc depending on which one it is.

 

[Windhund]

OK then I'll take it to the local Autozone at some point to see if any codes are detected and report back to the board

 

[mattmar1]

one additional thing....many of the OBDII readers wont see a pending code, only codes that are hard (enough iterations of the failure). BMW specific scanners normally do

 

[Mayorchuck]

The cam position sensor (CPS) and MAF are odd ducks. I've had INPA for many years and I would say the CPS generates a code about 50-60% of the time. They are two of several sensors that send info to the DME (ecu). I believe what happens is the CPS briefly stops sending data or sends something so far out of range the DME just stops calling for fuel/spark for a brief second while it tries to figure out how to compensate for the erratic readings coming in. The DME does not want to fire the coils if it doesn't know where the position of the piston.
If you take it to have the codes read, have them cleared after they read them if there are any. Old codes will remain, even after repairs are completed, if they were never cleared. So you always want to clear the codes and drive the car to see if a code will come back after enough cycles.

Clear as mud?

 

[Windhund]

Great insights Mayor Chuck. I know the local Autozone will read the codes but that's it, they don't clear them afterward. I'll have to find a shop that will do that which is no big deal. I read somewhere that both the crank and cam position sensors communicate with the DME but the most likely culprit in my case seems to be the cam sensor. As you said, the MAF, I understand, can also be the problem.

Couple questions. If it's the MAF, is it just a matter of decarbonizing it or would it have to be replaced? This is another part in my car that I'm certain is original. If it's the cam sensor, is this an easy swap out for a non-mechanic like me or is it best replaced by a professional?

Also, thanks to everyone who has posted!

 

[mattmar1]

MAF doesnt get carbon covered, its way pre-combustion. they can be cleaned, some have had success with doing so, use a specific MAF cleaner, not carb cleaner. an OBDII code reader can be had for around $20, i carry one in the glovebox always just in case. itll also allow one to clear codes. crank pos sensor signal is essential to being able to start the car, without a signal from it to the DME, fuel and spark wont be enabled. the cam pos sensor signals are also sent to the DME, if one is in error, hard starting, no start, rough running etc can result.
which engine do you have? the difficulty of replacing the cam sensors depend on which engine, it its a 6 banger, the intake sensor is easy to replace, exhaust a bit more of a trick but diy doable.

 

[Windhund]

Sorry, my bad. I was thinking about the throttle body not the MAF when I mentioned carbon build-up. I didn't realize basic OBD II scanners where so cheap so I will take your advice and buy one, thanks. That will really come in handy. It's an M62 in my 2000 740il.
If either one of these (MAF or cam sensor) ends up being the source of my problem, is it a OK (or not) to drive the car until I can get it repaired? In other words, I don't want to do any harm or end up at the side of the road. I haven't driven it since the incident.

 

[Windhund]

I see quite a few scanners advertised "for BMW". Do I need one of these (and most are over !50 dollars) or just any old garden variety OBD II scanner? Do the BMW scanners give more specific or detailed information or maybe it's just hype.

 

[lenwib]

For an easily understandable, but still very potent DTC scanning (present and "shadow") tool, with quite a few more abilities, I can recommend BMW Scanner 1.4.09, in the US often referred to as "P A Soft" (the poor developers who got ripped off).

With that, and INPA (a BMW original tool), on a Windows laptop, you will be able to be on your own, when it comes to diagnosis and, as well, if necessary, coding.

Both are freely available nowadays, but there is a lot of crap around, so try to find a trustworthy supplier. You also need cable(s) and software(s).

And operating from the 20-pin "Pacman" contact under the hood (if there sill is one on US models). Otherwise from the OBDII contact in the cabin.

//Len

 

[mattmar1]

^^ what he said....overall, youll be better off going with a BMW specific scanner, with a generic scanner, youll only be able to read DME codes with limited ability vs a specific one, which will give you the ability to read codes on all modules in the car. its a bit different of a learning curve, but necessary for a diy'er. either p a soft, or inpa, require a laptop installation, and the cables (each has its own). plus, youll see more detailed error codes, nice to have access to. both can be gotten free, just the cable cost (40 or so). the OBDII reader i carry is torque, its a droid app, loads on your droid phone or tablet, its about $7 from google play, plus about $40 for an elm327 bluetooth port adapter. there is an app for ios, i just cant remember the name at the moment. depending on the year of your car, if its an early model with the 20 pin underhood connector (round connector near the ABS module) youll need the 16 pin underdash to 20 pin underhood adapter (around $10) to read all other modules than the DME (engine) and EGS (trans), theyre read at the underdash 16 pin OBDII connector. if you dont have the 20 pin connector, all modules are read thru the OBDII connector.

 

[Windhund]

Wow, that's a lot of information,( some of which I actually understand lol). It will take me some time to sort through it all or I could just take the coward's way out and pay my local indy a few bucks to scan it for me lol

 

[mattmar1]

aint the cowards way out....if you dont have what you need to get the readings, and as it will take you some time to get em and set em up, probably your most cost efficient method for the time being. if you plan to getting on to diy'ing as much as possible in the future, depending on how long you wish to keep the car, a good scanner is a necessity. and as stated, theres a learning curve. and it also depends on how much money you wanna shell out over the life of the car on getting it scanned. one time purchase of inpa or pasoft scan is one quarter of one scan.

 

[Windhund]

Good points for sure. I hope to keep the car as long as possible but, as everyone who owns an E38 knows, it's a constant battle to keep up with repairs so it's a precarious situation. The "to do" list of things that should be done to the car never gets shorter.
I don't want to invest in a BMW scanner because for one I'm not a diyer and two the car is one major repair away from being sold "as is' or even junked ,although I'd rather not do that.

 

[u.nanimous]

Good points for sure. I hope to keep the car as long as possible but, as everyone who owns an E38 knows, it's a constant battle to keep up with repairs so it's a precarious situation. The "to do" list of things that should be done to the car never gets shorter.
I don't want to invest in a BMW scanner because for one I'm not a diyer and two the car is one major repair away from being sold "as is' or even junked ,although I'd rather not do that.

And where are you located?