Knocking with oil filler removed?

[PaulB81]

So my 330ci has been playing up (misfiring on one cylinder). There is a thread about it in the BMW section but this is more general

So I was telling my friend about the issues Ive been having and he does a bit of mechanics but primarily on old cars

He tool the oil filler cap off with the engine running and held his hand over it to see if he could feel a slight 'blowing' (wasnt hapening) which he showed me happened on his fiesta. After about 10 seconds or so the engine started knocking quite loudly. He put the filler cap back on and it stopped.

Im guessing that is not normal and also not good news!! Anyone experienced anything like this? Is it even advisable to run the car with it off?

[Prof Prolapse]

Knocking from bottom end?

Or tapping from the head?

[PaulB81]

Not entirely sure. Im completely mechanically inept. However, it was quite a loud knocking noise.

[Daston]

Get a long screwdriver hold the handle to your ear and then place the head on the engine. You will then hear any knocking noises through the screwdriver. Move it around the head and if it gets louder then that will tell you where the problem is in the engine.

[PaulB81]

Whether its at the top, or the bottom. I'm assuming it means its a fairly serious problem and probably related to the misfires I have been having

[Ozzie Osmond]

Sounds to me like a classic case for going to the dealer and asking them to run diagnostics on the clear understanding thet no repair work is to be carried out unless specifically approved by you.

A mate who knows a bit about old cars is no substitute when you're staring at a computer-controlled engine!

[Prof Prolapse]

This is probably the least helpful advice I can give but I would suggest whacking it into a garage for a diagnosis.

ETA: I've read that old school mechanics use the method to look for air escaping past the rings.

However on a modern car I would think it would just make it run crap, especially if you already have ignition problems!

[freecar]

there is a crankcase valve on an E46 (or so a quick google tells me) that will cause strange issues at idle with oil cap removed.

http://forum.e46fanatics.com/archive/index.php/t-2...

Similar symptoms there and a fix!

[EDLT]

I've never taken the oil filler cap off to listen for knocking. Not sure what he was even trying to check tbh, I've never heard of anyone doing it in my time as a mechanic.

If you can only hear knocking when the filler cap is off then its probably because the filler cap is off.

[PaulB81]

EDLT said:

I've never taken the oil filler cap off to listen for knocking. Not sure what he was even trying to check tbh, I've never heard of anyone doing it in my time as a mechanic.

If you can only hear knocking when the filler cap is off then its probably because the filler cap is off.

Lol good advice from all. I actually have it booked in at a local BMW specialist tomorrow anyway to investigate the ignition issue. I will mention this.

The main reason I was running this past you guys is because as EDLT says, it might just be because its not meant to run with it off like that

[EDLT]

PaulB81 said:

EDLT said:

I've never taken the oil filler cap off to listen for knocking. Not sure what he was even trying to check tbh, I've never heard of anyone doing it in my time as a mechanic.

If you can only hear knocking when the filler cap is off then its probably because the filler cap is off.

Lol good advice from all. I actually have it booked in at a local BMW specialist tomorrow anyway to investigate the ignition issue. I will mention this.

The main reason I was running this past you guys is because as EDLT says, it might just be because its not meant to run with it off like that

I have had to explain to people in the past that their engine sounds slightly tappety when the the bonnet is open because the bonnet is open. They don't cover the underside in foam and plastic for fun.

[Basil Brush]

Engines are part of the induction system on a lot (most?) modern cars with pcv type breathers. If you open the filler cap you'll be introducing un-metered air into the engine causing it to run lean, so possibly pinking/detonation you heard.

I assume he was trying to test for excessive piston blowby/burnt valve symptoms, which you can do that way on a motor with a passive breather.

[farazafzal]

PaulB81 said:

So my 330ci has been playing up (misfiring on one cylinder). There is a thread about it in the BMW section but this is more general

So I was telling my friend about the issues Ive been having and he does a bit of mechanics but primarily on old cars

He tool the oil filler cap off with the engine running and held his hand over it to see if he could feel a slight 'blowing' (wasnt hapening) which he showed me happened on his fiesta. After about 10 seconds or so the engine started knocking quite loudly. He put the filler cap back on and it stopped.

Im guessing that is not normal and also not good news!! Anyone experienced anything like this? Is it even advisable to run the car with it off?

Hello Paul. I have e46 325i, and I am suffering Misfire and ignition fail in Cylinder 1 since more than a week. I have tried everything, like changing spark plug, ignition coil, ignition coil boot, air mass meter, intake suction boot, the lower boot (attached to idle control valve and throttle body) but unfortunately the misfire in cylinder one is killing me. Just today When I turned on the car and thought to see the oil level from dipstick and heard a strange noise. Then I removed the oil filler cap and heard the knocking noise that was weird. I know this is not Normal. I have been topping off the oil an check the oil level and have never heard this voice.

Looking for answers I saw your thread. You never posted he diagnostics result and what possibly went wrong with your car. Can you please share your findings so that I can have clue.

Thanks

[BritishRacinGrin]

farazafzal said:

Hello Paul. I have e46 325i, and I am suffering Misfire and ignition fail in Cylinder 1 since more than a week. I have tried everything, like changing spark plug, ignition coil, ignition coil boot, air mass meter, intake suction boot, the lower boot (attached to idle control valve and throttle body) but unfortunately the misfire in cylinder one is killing me. Just today When I turned on the car and thought to see the oil level from dipstick and heard a strange noise. Then I removed the oil filler cap and heard the knocking noise that was weird. I know this is not Normal. I have been topping off the oil an check the oil level and have never heard this voice.

Looking for answers I saw your thread. You never posted he diagnostics result and what possibly went wrong with your car. Can you please share your findings so that I can have clue.

Thanks

Welcome!

This thread was over three years ago so you might be better off starting a new thread in the 'Technical' section of the forum.