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914World.com _ 914World Garage _ How to check for vacuum leaks
Posted by: porsche913b_sp Oct 31 2014, 06:15 PM
From the last time I tried with the engine running and spraying carb cleaner everywhere and causing a big mess. I did not really see a big RPM difference, maybe I was doing it wrong, maybe I was expecting too big a change and moved on too quickly, but nothing really came from it. I still suffer from a periodic hi idle (1500 rpm), sometimes it idles fine at 800. If it was a vacuum leak why did it correct itself and sometimes idle at 800 ? I have since removed the AAR and even swapped out the MPS with another one, no difference. Stock 1.7 FI
So the discussion for today is what is the proper method, tips and tricks to perform a good vacuum leak check.
I am tempted to make a DIY homemade smoke machine from watching youtube to blow smoke in my FI system and check it that way ??
Thoughts ![popcorn[1].gif](style_emoticons/default/popcorn[1].gif)
Posted by: 02loftsmoor Oct 31 2014, 06:25 PM
From the last time I tried with the engine running and spraying carb cleaner everywhere and causing a big mess. I did not really see a big RPM difference, maybe I was doing it wrong, maybe I was expecting too big a change and moved on too quickly, but nothing really came from it. I still suffer from a periodic hi idle (1500 rpm), sometimes it idles fine at 800. If it was a vacuum leak why did it correct itself and sometimes idle at 800 ? I have since removed the AAR and even swapped out the MPS with another one, no difference. Stock 1.7 FI
So the discussion for today is what is the proper method, tips and tricks to perform a good vacuum leak check.
I am tempted to make a DIY homemade smoke machine from watching youtube to blow smoke in my FI system and check it that way ??
Thoughts
your going to make a mess, but oil out of your oil can works well
Posted by: bdstone914 Oct 31 2014, 06:47 PM
I have not tried it but using a non lite propane torch. When it sucks in the propane the idle should increase.
Posted by: 76-914 Oct 31 2014, 07:03 PM
or a spray with water and look for an idle drop.
Posted by: porsche913b_sp Oct 31 2014, 07:46 PM
I was thinking of something similiar to this with either a charcoal or just a cigar, something cheap and simple in a empty/clean metal paint can ?
https://www.youtube.com/watch?v=FFlyAqiYMro
Posted by: Jeff Bowlsby Oct 31 2014, 08:35 PM
How a bout a smoke pen? a vacuum leak would visibly suck the smoke into the leak location, no fuss no muss.
Here is one:
http://www.toolexperts.com/smoke-pen-pencil-tests-air-flow.html
Posted by: Chris Pincetich Oct 31 2014, 11:08 PM
Posted by: a few loose screws Nov 1 2014, 03:57 AM
As far as the combustible methods go, personally I'd go with the unlit propane torch. You could also try another way, and that is to use your ears. I'm not being being a smart ass. I know its almost impossible to get your head in to even a spacious engine bay. Use a length of rubber hose, hold one end to your ear and probe around all the usual places where vacuum leaks occur. You can feed the hose right in to the tightest spots too. The nice thing about this is you can cup your hand over vacuum fittings, lines, mating areas on intakes, or carb bodies, if you have carbs, and amplify the sound of even a small leak. Once found, use your fingers to bock the leak. Now you know exactly where your leak is.
Posted by: cary Nov 1 2014, 08:52 AM
I built a smoke generator out of a paint bucket. It was built to find a manifold leak on a 4.0 Ford explorer. Basically you light a rag soaked with WD40 to create the smoke. Put the lid on it and push the smoke into the intake with air pressure. Found the leaking seal in about 30 seconds.
You got me thinking what air pressure did I use. I'll have to see if I wrote it on the top of the can. I'll shoot a picture of it today.
I have a long hose attached to a torch nozzle too. I can never get that test to work.
My .02c.
Posted by: r_towle Nov 1 2014, 08:54 AM
Go back to the issue.
A periodic high idle , in my opinion, is not a vacuum leak.
I would look at cleaning your distributor advance plates and regreasing them.
Posted by: RobW Nov 1 2014, 09:00 AM
Go back to the issue.
A periodic high idle , in my opinion, is not a vacuum leak.
I would look at cleaning your distributor advance plates and regreasing them.
I have this problem. Idle pops up to 1200 or so occasionally and intermittently.
Posted by: porsche913b_sp Nov 1 2014, 11:51 AM
I built a smoke generator out of a paint bucket. It was built to find a manifold leak on a 4.0 Ford explorer. Basically you light a rag soaked with WD40 to create the smoke. Put the lid on it and push the smoke into the intake with air pressure. Found the leaking seal in about 30 seconds.
You got me thinking what air pressure did I use. I'll have to see if I wrote it on the top of the can. I'll shoot a picture of it today.
I have a long hose attached to a torch nozzle too. I can never get that test to work.
My .02c.
I was going to attach a tire pump to the can like the video, would that be too high of pressure ?
Thanks for the pic
Posted by: porsche913b_sp Nov 1 2014, 11:54 AM
Go back to the issue.
A periodic high idle , in my opinion, is not a vacuum leak.
I would look at cleaning your distributor advance plates and regreasing them.
Yeah I did that too, completely removed and rebuilt the distributor, unless i didnt greased it enough, it did move when I used my mity-vac on it ?
Maybe a different sensor then CHT or IAT confusing the ecm ?Posted by: boxsterfan Nov 1 2014, 11:16 PM
My idle problems went away with a new CHT and spacer. 1974 2.0L.
Posted by: porsche913b_sp Nov 2 2014, 12:11 AM
whats the spacer ?
Posted by: Porschef Nov 2 2014, 05:10 AM
An adapter essentially that goes between the CHT sensor and the block. Delays heating of the sensor as to trick the ECU into thinking the engine is cooler than it really is, thus keeping the mixture richer longer.
Brad Mayeur sells them. I made one but it didn't seem to help 
Posted by: BeatNavy Nov 2 2014, 05:30 AM
My idle problems went away with a new CHT and spacer. 1974 2.0L.
I like the spacer, too. It really helped warm-up by preventing engine from going too lean. But I'm not sure this will help stabilize idle, particularly after warm-up. Based on what else you've tried I'd think about the dizzy like Rich suggests.
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