Methods of finding a vacuum leaks
 

So I have a vacuum leak. Diagnosed from AP data logs only (during MM Custom Calibration, I trust the diagnosis). There is no CEL, and there are no major problems with my engine operation. However I could see it explaining a few things about how my 8 runs, namely being quite rich all the time.

I have searched the site via Google and am only finding individual vacuum leak threads looking for a specific leak or known problem with physical symptoms. In none of these threads am I finding any method of how to look for a vacuum leak in the first place, other than "is X line attached" or "are your LIM nipples still on". Anything visual like that I have checked and rechecked several times. I have gone over the chart JON colored up, and everything is connected and in place.

I assume it is a cracked hose somewhere, but since assumptions are often not accurate, I can't rule anything out at this point. So rather than asking "what could it be?", I'm asking "give me methods to use to locate it"

The quick and easy one is CARB cleaner. Hose down stuff while the engine is running and look for bubbling /spurting (air exiting), or the engine starting to stumble as the carb cleaner is ingested (air entering).

I've done that. 2 cans worth in sprays here and there trying to find it (no, I didn't just empty 2 cans and hope for a reaction, anyone on here that knows me knows how thorough I am.)

So, what other options or methods? Sensor data, liquids, tools, etc...and what to do with them.

Tools at my disposal:
- AccessPORT
- common hand tools
- IR laser thermometer
- Flashlight
- Anything available at local autoparts stores

I'm assuming that you have listened for the telltale whistle of a leak?

Grab yourself a vacuum tester and check your actuators, vacuum accumulators, hoses, check valves etc. for leaks.
When visual checks fail then the vacuum tester is a great tool.

If you test the vacuum accumulator under the UIM then you know that the solenoids are holding.

Sounds like a plan. How will I know when it is picking up a leak or not? Is there a manual/chart/data which shows that pressure each item should be at?


And yes, no whistle.

Use smoke :)

http://www.aa1car.com/library/vacleak.htm

Sub

remove the air cleaner assembly and jam the end of a vaccum cleaner up the intake . Stuff a bunch of rags in there as well to block it off . Now get a spray bottle and put water and a little detergent in it .

Spray it all over the intake while pressurising with the vac. Watch for bubbles ...

I started reading that, but I got to the part about piston engines and just stopped.

Creative tip, might try this first.













Don't worry 9k, I only stopped so I could post that, I am continuing reading :D:

^ :lol:

You simply attach the vacuum tester to what you want to test and pump up a vacuum

If the unit you are testing holds the vacuum then there is no leak.
If you see no vacuum on the gauge or it drops over the next minute or so then it is leaking.

From what you are saying though about picking it up on AP logs then it must be a fairly large leak...

Ah, understood.


Finished reading the link 9k, thanks for that, quite a few methods to use. Using smoke appeals to me the most, but probably the least viable without paying a shop to do it. (I get the feeling grabbing a smoke bomb from the local firework's shop probably isn't the best idea :lol: )

I would just buy a vacuum tool, it will come in handy, and they are not expensive. Then individually test connected sections in your system.

The method my father taught me which has always worked is to use a can of carb cleaner. Start the car and then proceed to spray carb cleaner around the engine bay. Well really just the intake, vacuum lines, spark plugs, and such. If you spray a certain spot and hear the engine rpms increase thats where your leak is. Works wonderfully and engines are very responsive to carb cleaner. Its a great way to start an old lawn mower and such.

Yeah, that was the first method given to me, and 2 cans later, still no change detected anywhere.

+1 on pressurizing intake via vacuum cleaner or air compressor (make sure not to exceed 14psi or so). Starting fluid works ok but nothing beats knowing that your system can hold the pressure.

Sorry to restart and old thread, but it seems woefully incomplete.

Did any of these methods work? Which worked best? Where was the leak?

This is what SARX put together and it works perfectly.

RX-8 Hymee Supercharger Install - Smoke Tester

More proof I need to move to SARX area for my 8 ;-)

Fogger is what I used when trying to see if I had a crack in my air intake causing my rough idle. Foggers like this typically produce very thin smoke. If you run it through a cooling chamber it will produce a very thick easy to see smoke.

Bumping because its relevant.

So I airsealed the throttle body and started blowing into the yellow marked hose, and it happened without any resistance (aside from the hose thickness that causes the resistance). Now I don't know if the intake and exhaust port were both open at the same time, which would explain why there was no resistance to begin with. In any case, when my car runs, I hear pretty much the same air puffing noise like a steamtrain would make and it's louder as the throttle opens and faster as the rpm's increase.

What is a truly reliable backyard test, if there is any?

If you're trying to find a vacuum leak (?) just use the method below. Otherwise what you posted makes no sense.

On a stock Renesis there is no overlap of intake and exhaust ports. Not sure what yellow marked hose refers to, but if you hear puffing in time with rotor revolutions, you have compression escaping somewhere. Logically there are only 2 places this can happen: the oil injector and the spark plug holes. No other removable parts see compression. But even the oil injector doesn't really see compression, it's just after the intake port.

Video would help.

Thanks! I mean, certainly when a Renesis loses compression because of seals, it's not something you would hear so clearly through that thick housing. Here's a video of the sound. I will definitely check it out, but I don't smell any gasoline, I don't really hear it from the side of the sparkplugs, rather behind the Upper Intake Manifold, which is why it's so strange. When I crank the engine and a cut off fuel supply, the compression sounds very steady, not your typical hiccup with engines that have a dead cylinder.

Pull one plug then the other and listen for smooth evenly timed pulses . Or better still....do a compression test .

The other thing is, you have vacuum nipples under the upper intake manifold. Have you checked that those are still connected? It's hard to localize the sound via a video, but if it's coming from that general area, get a feel for those nipples.

Giggity.

Best advice :D:

So I took a look at the plugs with my phone camera, and noticed that between the gearbox and the engine there is a huge wet trail of some fluid (giggity giggity, oh no!).

I haven't investigated it thoroughly yet, could be just from the last time I changed the oil filter.