jej3

I did an intake refresh almost a year ago on my white 928 and my car hasn't left the driveway due to not running correctly and needing to devote all spare energy to a full rebuild of a 924S for my son.

Well, I had a chance to dig in a little this weekend and did a smoke test. I had smoke come from under the intake but honestly, I couldn't 100% say where. I partially removed the intake, tightened up what I could and discovered a couple of vacuum caps/junctions that could stand to be replaced (yes, I used all new vacuum lines when I did the intake.)

Buttoned it up and replaced the now permanently dead battery. Ran solid for a few minutes and then started acting like it was sucking wind. I think the leak must be back but it would be insanity to repeat the process without asking for advice and

How do you check for vacuum leaks?

Thanks!

SeanR

Pull the intake and checked everything again.

jej3

Thanks, @SeanR ! Is it normal for the intakes to go on and off? Just feels like a major PITA if I am doomed to keep repeating the same issue. Any more likely things to cause issues?

Guy

Sean is the expert but I would attempt the smoke test again and see if you can narrow it down somewhat. This way you will at least know where the potential failure is at. Take your time. Seal the air intake well prior to testing.

worf928

jej3

Do most people smoke test through the line coming off the brake booster?

Assuming it only makes sense to pressurize air through the MAF similar to one of these setups....





And probably wouldn't make sense to smoke through the MAF (contamination???)

drscottsmith

jej3

@worf928 - Dave - Thanks for the idea on the boroscope. I may just order a cheapo over Amazon Prime and use it to check things out. I likely will do another smoke test.

@Guy - Thanks for the encouragement!

@drscottsmith - Thanks for the question. I have capped off two unused lines from the 7 way junction shown in Dwayne's photo below....



and since I deleted the Air Pump, I have capped the elbow shown below circled in green (I only have one vac connector here) for the Air Pump Diverter Valve Line...




I struggled to keep this Y into the MAF boot sealed when reassembling and see in this Dwayne photo that it looks like some type of sealant was used (anyone have any experience here???)...





Keep the comments coming. I essentially have the month of February to get two 928s and a 924S ready for the WerksReunion (and my 15 year olds 16th B-DAY!)

Michael Benno

Petza914

No, it's the opposite. You use a smoke machine to pump smoke through the air intake (engine off) and see where it leaks out from. I'm sure there are YouTube videos on smoke testing you can find.

jej3

That's right, @Petza914 !

@Michael Benno - here's a YouTube video which shows smoke testing a 944. Super cheap but I'm questioning whether one wants to blow smoke through their MAF to test on a 928.


I'll post back my technique with pictures the next time I smoke test. I plan on getting a pipe to replace the MAF and using a hookup like below but with boot on pipe instead of MAF....

bureau13

When I do this, I remove the MAF (well...sometimes...sometimes no....I was not considering that baby oil smoke was a problem for it? Someone tell me if I'm wrong!) and seal off that area, and then use my cheap Ebay smoke machine to pump smoke into one of the vacuum lines that I disconnect...usually the front fuel damper. Then look for where it comes out.

I have one of those borescopes that hooks up to my phone, but frankly I usually have a hard time making sense of what I'm seeing with that. When I've found leaks this way in the past, they've been fairly major leaks, and so fairly obvious as to wear they were coming from. I can see where that won't always be the case though...

dr bob

I wouldn't waste any worry on blowing baby-oil smoke through the MAF, so long as you aren't powering the MAF during the test. If you are seriously concerned, puff a little MAF cleaner through it when you are done to remove any possible ash contamination. Remember that you aren't blowing baby oil through it, just the particulate vapor that is smoke, so it's not like you are leaving it coated with a K&N oil film.

For the intake-oscopy cam, look at one that has a mini webserver and connects via wifi rather than a hardwired cam. As Dave C. mentions, serious junk rides along with software these days if you aren't careful. At least with the wifi and using a browser for the video, your virus protection software has a chance to look at anything that that comes in. Installing from a disk or an online source, your permission to install essentially says that anything goes and you are OK with it. Or dedicate a cheap Kindle or Raspberry Pi to the duty, and never connect it to anything you consider private, like your home wifi network. I have a Pi Zero W on an old monitor hanging on the workbench wall, running everything from a micro-SD card. Maybe $40 all in, and a relatively hack-immune Linux OS running it. If it does get diddled, just write a new image to the SD card and it's a new clean system again. It has the WSM's as PDF, the bolt torque spreadsheet, and an archive of other interesting 928 stuff on the card.

I've used a setup similar to the plumbing-parts kit, sans smoke, to listen for leaks. If you want to get real specific, tape a length of vacuum hose to the camera, other end of the hose in your ear, and the hissing sound in the hose will guide you to any leaks.

Last but not least, avoiding vacuum leaks in the first place is the best solution. That means replacing the tired rubber underneath. Use care when tightening clamps so that connections remain square, and resist the urge to over-tighten. Take plenty of pictures and video as you disassemble, so you know exactly where things connect. Remember that the oil vapor connections are un-metered into the engine, so leaks anywhere in the engine itself will offer symptoms of vacuum leak. A loose oil filler cap, a cracked filler housing, anywhere that allows air into the crankcase is allowing un-metered air into the intake. If you are down to smoke-testing, puff smoke into the crankcase via the filler neck and see where you have breaches and vents. Enlist help when placing the intake, and use spacers and small blocks to get the connections all secured before that final drop onto the heads. Use cardboard strips to protect the intake ports from falling junk as you do the final install, strips you can pull out just before bolts start going in. Extra meticulous care at assembly time will save a ton of leak-searching later. Virtually all leaks will happen in pieces that you can only get to by lifting the intake again; I'm sure there's an allegory of Fig Newton's electrical laws that applies to engine plumbing.

Read Dwayne's intake refresh treatise a few times before you even start your refresh adventure. Make sure you understand the whole process before any wrenches touch the car. Take lots of pictures as you disassemble, and keep track of every bolt, clip and connector as you get things apart. Master co-worker on my own intake project dropped a FI connector spring wire, which of course went immediately into an intake port and past the valve. We stopped everything to recover the wire, using a magnet, before proceeding. Stuff will happen.

Taguid

I have removed my intake 6 times to find possible vacuum leaks. If you removed the coolant crossover it is possible that it could be in the way on the pass side and preventing the intake from making full contact with the gasket. I'd try the borescope to try and pinpoint if possible. I did not have ant trouble with the Y you may want to readjust or replace again if not fitting properly. I did see where Dwayne used RTV there but I did not.

Ramp

How did you cap that elbow ?