pull dipstick - idle change?

[JHZR2]

Hi,

I have a little problem with NOx in my 91 BMW 318i. It barely failed, then it barely passed. I have checked for intake leaks, and have not been able to find any, and all seems good.

However, after an oil change, I was testing the oil cap for seal, and then I pulled the dipstick (both with the car running). Just cracking the oil filler caused the engine to sputter and almost stall, but I could pull the dipstick all the way out, and there was no change.

Shouldnt removal of the dipstick be a source of unmetered air, and result in a change in idle as the engine goes lean?

Maybe there is just slight enough of a leak thatit still can idle perfectly smooth and run great, yet its just enough to lean out the mixture so there is no CEL, but the combustion temp increases, causing NOx to form.

Sound plausible??

Thanks,

JMH

 

[Amkeer]

Nope, the dipstick tube will end within the sump so the oil level will cause it to be blocked with oil so that air will not travel up the tube.

 

[Alan]

My BMW used to run like crap when the dipstick wasn't seated right.It would easily stall.

 

[fdunford]

Not sure, but you can check for vacuum leaks by spraying carb cleaner areound hoses and the intake manifold, check ing for a stumble. You might want to check the PCV valve also.

 

[TooManyWheels]

Opening the dipstick and oil filter should have the same effect, the difference is in degree, the dipstick opening is obviously much smaller of an opening, so it is logical the effect would be smaller, or not even noticeable.

I am a little surprised though that the system is set up so that crankcase ventilation figures into mixture. Is it possible that this could be mis-plumbed, that it incorrectly enters the intake after the metering devices rather than before?

 

[Gary Allan]

My BMW used to run like crap when the dipstick wasn't seated right.It would easily stall.


Same with my 78 320i ..couldn't idle worth a crap with the dipstick pulled. Any vacuum regulation must be on the air inlet side of this engine, since you are adding way too much air by opening up the crankcase.

I don't have an answer for your NOX situation. If can can mod your timing ..try retarding it.

 

[Threeshot223]

I have an '87 325 with the M30 inline-6. It runs great, but if I crack the oil fill with it running the motor wants to stall out.

So you're not the only one.

 

[brianl703]

On my car I can watch the short-term fuel trim increase (on a scantool) when I remove the dipstick. It's that sensitive to the additional air allowed in by doing that. If I leave it out long enough the long-term fuel trim is increased.

That's the only noticeable effect. Of course...this is the same car that ran with a huge vacuum leak between the PCV valve and the intake manifold with no noticeable symptoms other than a slightly flaky idle(sometimes). Long term fuel trim was at almost 24%..at 25% is when the check engine light is supposed to come on.

 

[mechtech]

BMWs normally run crappy with the filler cap off/loose.
It depends if the dipstick tube end is immersed in the oil, if pulling the stick has the same results.

 

[JHZR2]

I can understand with regards to the oil fill.

I just have to wonder about the dipstick. Maybe if I idle and then plug the hole, with my finger, Ill be able to tell some change.

I have to wonder if its similar to brian's experiences, maybe Im leaning out just enough to fail NOX emissions, but not enough to set any codes. Not that I could get as good of info, as my car has OBD1, but sounds very plausible.

Thanks,

JMH