How to perform smoke test on a 951?

Talk and Tech about turbocharged 924/944/968 cars
mikee30
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Hi all,
I recently received an Ancel S1000 smoke machine to test my car for any vacuum leaks etc...
My understanding is if I want to test my vacuum lines, all I need to do is disconnect any of the vacuum hoses and insert the smoke machine at that point. Is this correct? I was hoping for some suggestions on the best way to proceed with testing the vacuum lines. Since I have the machine, are there any other items I should be testing? I would also like to test for any leaks occuring through my jboot or hoses connecting to it and along that same path given the age of all the materials.
Thanks!


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Belgian951
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Gratz on the machine, it's great. I had one too!

Buy a PVC cap that's as big as the AFM connection. IIRC it's 80 mm. Drill a hole in the PVC cap for the smoke machine tube to sit in.

Remove the air filter box and connect the PVC cap (with smoke machine tube connected to it) to the AFM.

Be sure to open the throttle and keep it fully open so the flap is open.

Pump the smoke into the AFM and thus air intake, you'll need to pump hard.

Open the oil filler cap to check if you have smoke there.
Decouple the vacuum lines to check for smoke
Check everything for leaks!


1986 944 Turbo Garnet Rot Metallic

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cda951
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You should also pump smoke into the the crankcase via the oil filler hole, which will more quickly check the seals of the air-oil separator, dipstick tube seal, breather hoses, etc, though these would eventually fill with smoke via the breather hose between the AOS and intake J-boot if testing from the J-boot.

You can also check the turbo boost pipes and hoses for large leaks, but to check for leaks that only occur at 10 PSI or higher, you need a smoke machine that can generate that much pressure, which is not common. The factory service manual method of cutting an old fuel filter in half, clamping it in the boost hose between the turbo outlet and intercooler inlet and applying shop/compressed air is best. If any leaks are heard, spray soapy water around the suspected area to find the leak. You can also use the fuel filter at the throttle body boot to focus on the intake manifold area.


Chris A.
---'86 944 Turbo track rat
---'90 944S2 Cab daily/touring car
---'73 BMW 2002tii road rally car
---'81 Alfa Romeo GTV6 GT car/Copart special
---'99 BMW Z3 Coupe daily driver/dog car
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icb
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I built myself a pretty fancy smoke machine complete with built in regulator, 0-15 psi gauge, and 0-3 litres per minute flow meter. Used it once to track down the leak points in my intake. The smoke from the pure mineral oil stinks, and when it condenses (on every surface it comes in contact with) it leaves an oil film. Now I just use it without the oil /smoke, just low air pressure, the flow meter, and soapy water to find the leaks. No more stinking mess and just as effective.


Ian Borg
1988 Porsche 944S
https://icb-machinations.blogspot.com/

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icb
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icb wrote: Fri Oct 18, 2024 3:07 pm ... low air pressure, the flow meter, and soapy water to find the leaks...
I should clarify that the soapy water is used in a spray bottle and sprayed on suspected leaky joints, not in the smoke machine!


Ian Borg
1988 Porsche 944S
https://icb-machinations.blogspot.com/

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Fejjj951
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icb wrote: Sat Oct 19, 2024 6:38 am
icb wrote: Fri Oct 18, 2024 3:07 pm ... low air pressure, the flow meter, and soapy water to find the leaks...
I should clarify that the soapy water is used in a spray bottle and sprayed on suspected leaky joints, not in the smoke machine!
This is incorrect information. Low pressure will not reveal boost leaks at higher pressure which is where they normally show up.


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icb
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It's not incorrect at all. What is your definition of low and high pressure?


Ian Borg
1988 Porsche 944S
https://icb-machinations.blogspot.com/

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Fejjj951
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icb wrote: Sat Oct 19, 2024 2:57 pm It's not incorrect at all. What is your definition of low and high pressure?
At least 10 psi and preferably 15 psi to expose leaks.


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Tom
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I think you're both saying the same thing really. I bought one on amazon quite a while ago to find leaks on the old 450SL, which uses vacuum for all sorts of non-engine-related tasks. I used the mineral oil, which does indeed stink, but was able to find leaks I'd never be able to find otherwise, including leaks buried so deep I had to remove parts just to see where the smoke was coming from. On that car, even 5-10psi was plenty. On a boosted car, it make sense to test at max boost pressure, probably after finding and fixing all the run of the mill leaks at lower pressure.


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icb
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Exactly, Tom. Obviously you should use whatever pressure is appropriate for the induction system you're testing. 3 psi is suitable for a naturally aspirated engine like my 944S has. A forced induction intake would require marginally more pressure than what it sees in normal use for the best results.
Anyway, the point of my post was really just to say that it doesn't have to be smoke. Appropriate air pressure inside and a soapy water spray outside works great.


Ian Borg
1988 Porsche 944S
https://icb-machinations.blogspot.com/

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