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Smoke Test for Vacuum Leaks - N00b
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Smoke Test for Vacuum Leaks - N00b
I've got a few CELs on my 1998 cab related to vacuum issues. I borrowed a friend's smoke testing machine, and I'm stuck with what's next.
Could you share a good walkthrough for testing vacuum leaks?
I've checked youtube, the DIY forum, the technical pages at PCA, etc. Maybe I'm missing something! The videos found are earlier 911s that look a little different. I think I take off the airbox (done), and plug some other lines (which ones??) Get me started and I'll put together a video on how to hook it up for the next guy!
Could you share a good walkthrough for testing vacuum leaks?
I've checked youtube, the DIY forum, the technical pages at PCA, etc. Maybe I'm missing something! The videos found are earlier 911s that look a little different. I think I take off the airbox (done), and plug some other lines (which ones??) Get me started and I'll put together a video on how to hook it up for the next guy!
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Joined: Nov 2002
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From: Chicago
Its described in the shop manual. Then just go to Home Depot and get a big rubber cap, drill a hold in it, insert a bike valve, then attach it in place of your air box. Add air at the valve and listen for leaks. No smoke needed.
p.s. youre not talking about a vacuum leak, but rather an intake leak. Two totally separate systems, parts, symptoms, tests, and fixes.
p.s. youre not talking about a vacuum leak, but rather an intake leak. Two totally separate systems, parts, symptoms, tests, and fixes.
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 40
Likes: 10
Its described in the shop manual. Then just go to Home Depot and get a big rubber cap, drill a hold in it, insert a bike valve, then attach it in place of your air box. Add air at the valve and listen for leaks. No smoke needed.
p.s. youre not talking about a vacuum leak, but rather an intake leak. Two totally separate systems, parts, symptoms, tests, and fixes.
p.s. youre not talking about a vacuum leak, but rather an intake leak. Two totally separate systems, parts, symptoms, tests, and fixes.
You have me second guessing my test. Experiencing rough idle, occasionally high idle, and codes:
- P1124/P1126 - Fuel/air lean
- P0410/P1411 - SAI
Perhaps thats 2x different tests? One on the intake side, and one on the SAI system?
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Smoke testing the intake is very simple. Remove the airbox (the black plastic housing the air filter sits in). Cover the end of the MAF with a shop glove (latex, etc). You'll have to put a big rubber band around it to hold it on. Then plug the smoke in. At the center rear of the varioram manifold (closest to you when you're standing behind the car) you'll see two rubber fittings sticking off the left side. One has a vacuum line, the other is just a cap. Pull the cap off and plug your smoke in there.
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From: The Nook
Had similar issues. Have you cleaned your idle stabilization valve? Simple to do. https://p-car.com/diy/isv/
The P0410/0411 likely means that you need you SAI check valve replaced (best outcome) or the system cleaned out (more work). There are many "How tos" for this, but this is a good start. https://p-car.com/diy/sai/1/sai.htm
The P0410/0411 likely means that you need you SAI check valve replaced (best outcome) or the system cleaned out (more work). There are many "How tos" for this, but this is a good start. https://p-car.com/diy/sai/1/sai.htm
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Joined: Nov 2002
Posts: 12,230
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From: Chicago
First off, ignore anything AI says; that's a completely useless waste of time.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Last edited by TheOtherEric; Apr 2, 2026 at 02:41 PM.
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Thread Starter
Intermediate
Joined: Oct 2022
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First off, ignore anything AI says; that's a completely useless waste of time.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Edit: Actually you are in Chicago! What part? I'm way out in Geneva (Western burbs) and could use some Porsche friends. Do you get to events, tracks, cars+coffee etc? I am also looking for a friend to turn wrenches with occasionally, but I think we might be in very different leagues of skill
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Rennlist Member
Joined: Nov 2002
Posts: 12,230
Likes: 104
From: Chicago
God I love you guys. This .pdf is incredible. If you're ever in Chicago, I'll owe you a beer!
Edit: Actually you are in Chicago! What part? I'm way out in Geneva (Western burbs) and could use some Porsche friends. Do you get to events, tracks, cars+coffee etc? I am also looking for a friend to turn wrenches with occasionally, but I think we might be in very different leagues of skill
Edit: Actually you are in Chicago! What part? I'm way out in Geneva (Western burbs) and could use some Porsche friends. Do you get to events, tracks, cars+coffee etc? I am also looking for a friend to turn wrenches with occasionally, but I think we might be in very different leagues of skill
Three Wheelin'
Joined: Feb 2010
Posts: 1,437
Likes: 106
From: Midwest
First off, ignore anything AI says; that's a completely useless waste of time.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Second, get the special PDF document "On-Board Diagnosis" specifically for P1124/P1126 faults. I'll try to upload, but no idea if it'll work.
Third, if that didn't help, review the diagnostics/symptoms table (Section 24 of "DME Diagnosis") to match your symptoms to what tests are called for. And see Oxygen sensor issues there too.
If you test the intake system for leaks-- it is covered in either that P1124/P1126 document or the shop manual Section 24 of "Fuel System, Electronic Injection." Those docs show a cover plate but you can go to Home Depot and get a mixture of PVC caps, rubber sleeves, hose clamps, and a tire valve to make it yourself. Easy peasy. Pressurize to 7 psi and listen for leaks.
Its not too hard. You got this.
Thanks for that Eric, Very Nice.....
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 40
Likes: 10
Smoke testing the intake is very simple. Remove the airbox (the black plastic housing the air filter sits in). Cover the end of the MAF with a shop glove (latex, etc). You'll have to put a big rubber band around it to hold it on. Then plug the smoke in. At the center rear of the varioram manifold (closest to you when you're standing behind the car) you'll see two rubber fittings sticking off the left side. One has a vacuum line, the other is just a cap. Pull the cap off and plug your smoke in there.
Rennlist Member
Joined: Nov 2002
Posts: 12,230
Likes: 104
From: Chicago
Not sure why the talk about a vac system leak when the OPs codes are due to intake system leaks. Totally different. Can a vacuum system leak cause codes? Maybe if a line near the engine became totally unattached but a failed HVAC actuator probably wouldnt throw a code. Shop manual doesnt bring up vac system leaks as a possible code causer.
Last edited by TheOtherEric; Apr 30, 2026 at 09:07 PM.