How to perform smoke test on a 951?

Talk and Tech about turbocharged 924/944/968 cars
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Fejjj951
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The OP asked about performing a smoke test on a 951.


#11

mikee30
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Hi all, thanks for all the comments. I ended up connecting the system and found a few leaks. This pic is not of my car, but helps explain the issue. I noticed that the hoses going to this yellow part circled in blue were leaking at the joints. Also, it seems like the cap itself is leaking around the edges. I did some research but could not figure out what this piece is for?
Does anyone know if the seal under the yellow cap is replaceable? Also, are the hoses connecting to it (specifically those towards the bottom part of the blue circle) available for replacement (mine are nylon)? Lastly, can those hoses be replaced without removing the intake manifold?
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#12

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Tom
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That's the cycling valve (aka the stock boost controller valve). I've never heard of anyone resealing one, though that does not mean it's impossible necessarily. A lot of people remove them to install manual boost controllers, so you can find replacements on eBay, etc. They are still available new, but silly explensive.

https://www.paragon-products.com/Vacuum ... 117.01.htm

The hoses are available from Porsche, though there is nothing all that special about them, so a rubber or silicon hose of the right diameter is fine. The ports for the hoses LOVE to snap off when you try to remove the old hoses. So much so, that I don't even try to remove the old hose, but instead cut them off with a razor blade.

Some people have claimed to replace them with the intake still installed, but to me and most normal mortals, it is a virtual impossibility. Certainly much easier just to pull the intake...


#13

mikee30
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Hi all, thanks for all the comments!
I thought I'd report back should someone else go through the same process...

So after running the smoke machine through different connection points, I ended up finding a few leaks. However, I am not sure if some leaks are considered normal or if the system should really be 100% leak free when doing these tests.

Here are some examples:
1) The smallest port on the jboot is leaking. It has the original squeeze clamp - it is either the clamp or the joint of the hose entering the port that is leaking slightly. I would like to replace the hose and clamp but cant seem to find the hose part number. Can I use a regular screw type clamp versus the squeeze clamp here?
2) The intercooler tube has a hose connected on the left side. The other end of that hose connects to a hard line if I recall correctlty, again using one of those squeeze clamps. There is a leak at the clamp...I will replace the clamp but wonder if this is normal when doing a smoke test?
3) Throttle body - there is a leak at the spring on the right hand side. The smoke seems to leak at the joint of the spring. I have no idea if this is fixable or normal... thoughts?
4) There was air coming out of my idle stabilizer valve at the two small openings in the metal body. Is this ok? One hose connecting to it has a small leak at the joint - again possibly the clamp.
5) one hose going to the cycling valve was split - I replaced that, but the cycling valve cap still shows smoke around it

It might be worth nothing - the issue I am trying to resolve on my car is that I need to keep giving it gas on a cold start until it warms up or the engine shuts off. If I don't give any gas on cold start up, the car will seem to "catch" for just a split second and shut off. Tom and others provided some guidance on testing and so far I have ruled out my air flow meter (I did the tests and also swapped with a known working one), DME temp sensor is new, DME temp sensor wiring has a short that was repaired, new FPR, new check valve, new fuel filter, new air filter, TPS tested fine, cleaned out my throttle body, new spark plugs....

For those of you interested - here is the link to the other post:
viewtopic.php?p=28428#p28428

I am wondering if I have a vacuum leak, but the car starts fine once it is warm...maybe a tad rough :) Another symptom I have is a smell of gas coming from the rear of the car when it is parked. Lastly, I did also notice a frayed connector going to my idle stabilizer, but the wires don't seem to be shorting (however I will fix it).

My thinking is:
1) Resolve the vacuum leaks....
2) Can my fuel system be losing pressure which is causing the cold start issue? If yes, what can I check here? Fuel pump?

Thanks!


#14

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