Intake manifold problem...

[digifil]

Hi how can i test my intake manifold for a leak......after taking dipstick out it has a sucking at the dipstick hole.
Worried it may be the intake manifold. perhaps a crack.......whats up to do....?
FIL

[Eaglesail]

digifil...I know others here may better help you...Generally, given the observation you have described, a leaking manifold, if the intake, (air in) will be dramatically different from that of an exhaust (air out) manifold. Because you mention a suction at the dipstick, this would suggest an '(in-take)' issue. From here, there are several components and issues that can produce this negative influence. Do you know an Indipendant BMW guy in your area?....I would at this point pay a professional indy guy his survey.....and or cut bait and move on...what is the car worth to you..etc....................It can possibly be serious...and or maybe not. Take it to a shop that has proper testing equipment and with BMW or general German car knowledge specialist.

[TonyAngel]

Just to understand, you removed the dipstick while the engine was running? And noticed a vacuum at the dipstick opening? Why would you think that this would indicate a problem with your intake manifold?

Someone, correct me if I'm wrong, but if the engine was running, there should be a vacuum state in the crankcase. When you remove the dipstick while the engine is running, you create a vacuum leak in the system, hence, the sucking sound. Or am I way off base here?

[legoman67]

To test for air leaks in the intake system shops do what is known as a 'smoke test'. They use a special machine that pumps 'fog'(the same stuff used by fog machines) into the intake system making leaks very visible.

There is no easy way to do this test yourself, and the smoke machines cost ~$1000 to buy so its not something most backyard mechanics own. A fog machine will not work as it does not pressurise the fog.

[MIKYZZ4]

Just to understand, you removed the dipstick while the engine was running? And noticed a vacuum at the dipstick opening? Why would you think that this would indicate a problem with your intake manifold?

Someone, correct me if I'm wrong, but if the engine was running, there should be a vacuum state in the crankcase. When you remove the dipstick while the engine is running, you create a vacuum leak in the system, hence, the sucking sound. Or am I way off base here?

You are correct:
Removing the filler cap causes the CCV regulator to see 0" w.c. vacuum. It then goes to maximum open trying to suck air out of the crankcase to get the vacuum back into the 4-6" range. Hopeless, but the CCV doesn't know that. Meantime, that air going into the engine via the CCV hasn't been measured by the MAF. Since the DME calculates how much gasoline to inject based on the MAF reading, too little gas is injected, the mixture is too lean which causes misfires. The same effect as having a very large vacuum leak. The DME senses the falling idle speed and senses the misfires, It opens the idle air control valve and injects more gas to compensate. Once the idle picks up the DME backs off on the IAC valve and reduces gasoline injection which reduces idle speed and leans out the mixture again. And on and on and on goes the cycling. This is the simplified version that ignores many details, but gets the main factors.

[Eaglesail]

mikyzz4....I need to shut UP....BUT...while I have practice with cars..1951-onward...51 Plymouth Cranbrook, 1959 Rover-P-4..a 1959 MGA-Twin-Cam...62 M GA mk ll...63 B, 1980 VOLVO 230 B......still then made in Sweden...today designed in Sweden...assemble in CHINA...secondary MEXICO