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I was checking my vacuum connections now that I have the intake off and I checked the oil metering injectors.
The FSM says it acts as a check valve as you should only be able to blow one way.. . . .Is checking the oil injector with a vacuum pump an appropriate test method?
The vacuum lines that go to the oil injectors come from the plastic spider manifold, while that manifold, is supplied by the upper intake . .The large vacuum line was just replaced and I was trying to check if this oil injection subsystem still works like it should.. . . Thankfully, doing this check verified that the spider still holds vacuum.. . . But it raised the question as to whether the oil injectors are good.
I noticed that one injector would hold vacuum while the other 3 do not.
Do I have 3 bad oil injectors? . .What's the impact of not replacing them?. . . .
Ok, these oil injectors act as one way check valves, but they don't have to hold up to a vacuum pump level of vacuum. As shown, the level of vacuum produced by a human is plenty to test these. If you use a vacuum pump, you are more likely to blow them out if they have any age on them. If you are changing them out, just do all 4 as a set, then you don't have to worry about the last one. The one-way function is a low pressure differential application. The splitter should be fine. Replacing the rubber lines with some new silicone ones should give you some good results.
Here is an explanation to their function. First things first, the check valve isn't in there to keep the boost (or atmospheric pressure air in your case) from escaping. When the system is not under vacuum, the entire manifold, and around the injector nozzle, is at approximately the same pressure as the throttle inlet where the big hose plumbs to. When your throttle is closed, or you are running under vacuum conditions, those check valves allow the higher pressure air (pre-throttle) to be sucked through the injectors into the vacuum of the idle-air manifold. As each rotor has a vacuum cycle, it will create a surge of air through each injector. When this surge happens, it sucks the small amount of accumulated oil through the injector and causes it to jet out into the air going to each rotor. When the throttle is opened, the air doesn't surge through the injectors as much, or in theory at all. At this point, you want the check valve to keep the oil headed towards the injector orifice (high resistance) instead of the vacuum tubes leading to the throttle body (low resistance). All the check valves have to do is hold the minimal amount of pressure between the OMP and the open, but narrow, injector orifice. Think of it like putting your thumb over the end of a hose. If its only partially over, but allowing flow, you get higher velocity water with minimal force on your thumb. If you put your thumb all the way over you have to fight the full pressure. This is a low pressure application, so checking with human limits is acceptable. I'd put a length of hose on the end first though... 10-40 isn't very tasty.
These also act as air bleeds in a sense in that they allow a limited amount of air from pre-throttle to post throttle conditions when the throttle plates are closed. If they are obstructed or blocked off, that idle air has to come from somewhere, often less precise. Hope this helps.
If these units don't seal under momentary conditions of pressure delta, the effect when a unit fails is to give a continuous pathway of air to bypass the intake manifold.. . (or get pushed back depending on the pulse cycle)
How that effects the oil delivery I'm not sure.
When I checked these with my hand pump, 3 did not hold air/vacuum at any pressure. . . .Only 1 oil injector did along with the spider & new hoses.
Ultimately I'm trying to fix a bad idle.. . . ..Any air leak is bad.. . . These things might have 302k miles on them.
Ok. Let's see if I can get you the rest of the way there.
The purpose of these oil injectors is to squirt oil into the intake manifold so it can get sucked into the rotors and wet the apex, corner, and side seals because there is no other way to get oil to them. The oil for the rotor bearings is separated from the outer parts of the rotor (or should be, depending on how bad your seals are). These "injectors" are just precision bored banjo bolts. Think of it like shooting a spitball in school, with your straw as the injector. Whenever there is a pressure differential, this thing shoots a wad of oil like a spitball into the intake manifold. The air that pushes that wad also goes into the manifold. It helps the oil wad get sucked into the rotor as a moving particle rather than the oil just dribble down the side of the intake runners and eventually make it into the rotors much later. If you put a little oil in one of those, cover the banjo fitting holes, and blow, you'll spit out a little jet of oil and some air behind it. The precision holes in them ensure that a restricted amount of air goes through them as part of your intake idle intake air (provided by 4x fuel injector air bleeds, these 4x small oil injector holes, and your BAC adjustment screw, as well as additional solenoids that are model specific).
The pressure difference these see always goes from top to bottom. You won't ever have pressure come up from the bottom, pushing air back out of the injectors unless your engine just exploded. In which case, you've got bigger issues. So air pressure will always be more on the top, unless the throttle is open and there is no vacuum in the manifold. In this case, both the supply air by the throttle body, and the outlet of the injector are at the same pressure. At this point, there is no air movement. At this point oil will still be pushed into the injectors by the oil metering pump (separate from the regular engine oil pump). When the throttle closes, your pressure differential comes back, and with it comes a jet of oil out of the newly pressurized injectors. You're sucking in these jets of oil to lubricate all your apex seals because they can't get oil any other way. What the check valve is to make sure is that the oil stays put in the injector during cycles where there is no pressure differential and doesn't creep up into the vacuum lines where it sticks to the side of the hose and can't shoot into the intake manifold.
As far as a vacuum leak, this system pulls air from before the throttle body, but after the air flow meter. As long as the hoses and splitter themselves aren't leaking, this is a closed circuit for airflow and you can rule it out for a vacuum leak. The air that does flow through them does represent a significant portion of your idle airflow, as does the vacuum lines that connect near your fuel injectors. Make sure the lines are in good condition. I prefer silicone hose kits, because they seem to fit well on the hose barbs without getting crusty and dried out. If you are able to, you can pressure test your intake with an air compressor and a cap over the inlet. Make sure to disconnect your MAP pressure sensor beforehand though.
Keep in mind, a bad idle can be any number of issues. Good luck, keep us posted.
if you have the S4 style, which is like the FSM picture, you can clean them and take em apart. usually you can get them to work. the S5 and later (and replacement parts) are an assembly, so you can only clean them
10-23-21, 01:06 PM
