So............. I did the test today. Got itchy, can't help it.
01. The test is to understand that a vacuum leak from our camshaft driven vacuum pump, can and will effect crankcase pressure ( negative pressure ), because the vacuum pump
dumps its exhaust air into the engine crankcase. So it is basically fresh air injected into the crankcase by a leaky vacuum pump.
Leaky vacuum pump defined as the 2 hoses of the vacuum pumps, one is to brake booster and one more to some vacuum actuator your engine will need....those hoses being leaky is what I meant.
As how one's engine will react to such extra ( un-metered) fresh air input ? If your engine is MAF based, it will be more effected.
If your engine is like mine a MAP ( speed density ) engine, its not so bad, the MAP will read total pressure anyway.
02. My vacuum pump is still very healthy, so when I unplug the smaller hose from my turbo boost controller solenoid to make that small port of the vacuum pump then becomes totally leaking ( sucking fresh air ),
it does not yet impact a great deal on the brake booster vacuum reserve and also to crankcase vacuum pressure. Its the diameter of the port that matters and where the leak occurs.
If the leak occurs 1 meter away from the vacuum pump small port ( turbo boost solenoid ) , that leak is not as bad as when the hose which got removed/torn is the one exactly at the port of vacuum pump itself.
More distance from the vacuum pump will reduce vacuum pressure, thus less fresh air being sucked.
03. Brake booster vacuum reserve consumption is the biggest one, with its hose ID bigger by 400% compared to the smaller port... and the size of the brake booster membrane's
air space behind the master cylinder....no wonder it eats up lots of vacuum reserve.
AA. The test set up : Read Crankcase pressure from oil dipstick hole.
BB. Make a leak from turbo boost controller input side port, using a Tee, where this input port is served by the vacuum pump small port.
CC. Make a small leak at brake booster testing/inspection nipple ( mini pipe )
Note : That blue silicone hose is to my Banks pressure sensor to monitor brake booster vacuum pressure.
I label it as CCP in Banks gauge. I can't find other suitable provided name/ID for this sensor on the unit database..
Sorry the audio is not too good.
Interior camera : GoPro Hero 5 mic is muffled.
Engine bay camera : Hero 9 is not too bad its mic but it is at engine bay with engine noise.
Summary for those confused watching the video due to the muffled audio :
Video time 02:21 is me using brake pedal to introduce fresh air into engine crankcase via vacuum pump.
Brake booster membrane hold -14.7 PSI gauge pressure provided by the vacuum pump.
When we depress the brake pedal, we introduce atmospheric air aka fresh air at zero PSI-gauge.
There then we get the boosted pressure of 14.7 PSI equivalent pushing on the master cylinder because we now introduced zero PSI fresh air and in return
the master cylinder pushes the brake fluid towards the brake caliper.
Ignore the ABS for now.
When you watch the video pass 02:21 minutes, you will see STFT ( short term fuel trim ) will react towards the fresh air I keep pumping into the engine's crankcase which is then sucked by PCV system
and injected back into intake manifold. The STFT reacts because the front wide band o2 sensor is reading that there is more air than fuel and thus more fuel is needed.
At 06:33 minutes up I do more brake pedal test and there at 90C coolant temp, the engine is already in a good hot/warm state, you will see STFT more reactive.
STFT is not super instant reactive vs brake pedal .... it takes a few seconds sometime. If I use Xentry and read its Lambda value of front o2 wide band, that will be instant value change I am sure.
Before I depress multiple times the brake pedal at 02:17 minute, the brake booster has full -14.7 PSI-gauge or near zero PSI absolute and the engine already quite warm at 65C coolant temp,
has -32.6 millibar of vacuum pressure courtesy of the engine's PCV system ( positive crankcase ventilation system ) which its job is to suck all the dirty/bad piston blow-by air from the crankcase
and inject it back to intake manifold.
Observe those values in RED arrow.
The whole test is to let us understand that :
01. A vacuum pump leak cam effect fuel trim, up to a point. Treat it like a mini leak after the MAF aka un-metered air.
02. The same leak : will also reduce your crankcase vacuum pressure and probably rendering your PCV performance a bit reduced.
03. The same leak : Your brake booster vacuum reserve will be effected too.
One unlikely cause I’ve seen impacting these issues is an obstruction or malfunction in the Positive Crankcase Ventilation (PCV) system itself. A clogged PCV valve can create a buildup of pressure, which may mimic or exacerbate symptoms of a vacuum leak. Additionally, don’t overlook the possibility of a malfunctioning MAP sensor; if it's not reading correctly, it could lead to incorrect fuel trim adjustments—especially in a speed-density engine like yours. Another factor might be the condition of the intake manifold gaskets; if they’re degraded, they could introduce small leaks that will throw your fuel trim readings off.
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