View Full Version : How to: Build an intake manifold leak finder for about $20

11-05-2016, 09:50 AM
It took me wayyyyyy to long to build one of these! This was dead simple and helped locate a few leaks within moments.

Air compressor with a reasonable amount of capacity. Doesn't need to be much if you rely on the soap bubbles more than the sounds of air leaking.

-4" to 3" rubber coupler with hose clamps
-3" PVC pipe cap
-Male air fitting
-Pressure gauge
-Spray bottle with soapy water

I picked up the top 3 items from Home Depot and a low pressure gauge from Amazon. HD had pressure gauges but they're all too high which limits your needle movement.

How to build:
-Drill & tap 1/4" NPT holes in pipe cap
-Install gauge and air fitting. Use teflon tape, pipe dope, or other pipe sealer.
-Put cap into coupler
-Attach coupler to K-jet

How to use:
Disconnect and cap PCV and charcoal canister lines. They are guaranteed leaks that will only distract from actual leaks.
Set regulator for 5ish PSI, attach and start pressurizing.
Spray soapy water at all vac lines, manifold bolts, fittings, etc. Watch for bubbles
Fix leaks. Enjoy the lack of afterfires and stable idle.

Technically you are finding boost leaks, not vacuum leaks. Many rubber vacuum lines are fine under vacuum but garbage under boost. In my experience only silicone hose provides consistent leak-free operation under both conditions.

You will never see your intake hold pressure, it will always drop. I've only read a rule of thumb for "1psi drop per second is fine". No idea what to expect on our motors. I have to replace my "pipe of agony" because it's leaking like a sieve. Once that's done hopefully I can post my own numbers.

If you cannot hold any pressure and no leaks are found, it's possible (although unlikely) that a cylinder has valves in overlap (air going straight out exhaust). That or you have ring failure on whatever cylinder has an open valve.

11-05-2016, 10:58 AM
Better picture of the assembled unit:


11-05-2016, 06:17 PM
I like it!

I would've preferred this over the method I used a couple of years ago; I made a "smoker" using a charcoal briquette, dexron, and compressed air.

A video would be great... :thumbup:

11-05-2016, 09:13 PM
Very innovative!:thumbup:

11-05-2016, 11:18 PM
I would've preferred this over the method I used a couple of years ago; I made a "smoker" using a charcoal briquette, dexron, and compressed air.

A video would be great... :thumbup:
If you wanted to use smoke, I figured you could build a smoke chamber with a few air fittings to draft some smoke in. Honestly I think soapy water is a better detector since you aren't having to involve something smouldering. I'd think for really tiny leaks you wouldn't see much smoke anyway but I've never tried that method.

I shot one quick video but it's not interesting. Mostly you hear a fountain of air rushing out of the "pipe of agony". I'm going to install a proper hose fitting and be done with that POS design. Found a few small leaks at the vacuum solenoid (rubber hose) and one of the BAE intake adapters (probably my crappy hand-cut gasket). Not a single silicone hose leaked.

Very innovative!:thumbup:
I can't take any credit - this method has been around along time for turbo car owners. I just finally walked into Home Depot with some intake bits to find something that would fit. Turned out to be much easier than i was expecting.

11-08-2016, 12:01 PM
Thanks for the guide, and what a coincidence. I was just about to take my car into a shop for a vacuum leak test. Here's a pic of the one I made.http://uploads.tapatalk-cdn.com/20161108/1825571cfa856e2519e01be772ae4b12.jpg
A bit different but works the same.

11-08-2016, 12:34 PM
Awesome! Curious to hear your results.

I haven't had a chance to get back to mine yet. I need to go through my bin-o-fittings and see if I have a fitting that will work for the idle air attachment, otherwise I will probably pick up one of these (http://www.autozone.com/fittings-and-hose-line-connectors/heater-hose-quick-connector/help-3-4-in-hose-x-1-2-in-npt-x-1-3-4-in-long-metal-heater-hose-nipple-connector/98806_0_0/).

Plan is to drill / tap / insert fitting and ditch the factory pipe of agony arrangement. Will be doing fuel lines, plugs, etc. all at the same time for good measure.