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good to doo
06-19-2013, 09:30 PM
someone told me that I can find a vacume leak on my 91sc auto using a propane torch.he said to move the unlit torch around the engine compartment with the engine running. if the engine gains rpm there is a leak in that area. can any one comment on this. thanks good to doo.

LIVipers
06-19-2013, 09:35 PM
Why not just make yourself a DIY smoke machine? There's plenty of info here on how to do it, and they can be found at your local party city for under $35 and will spot every leak

dthompson
06-19-2013, 09:36 PM
Yes it is true. Gotta love Ericthecarguy videos...

http://www.youtube.com/watch?v=9CPqbaSgcok

elanoresc
06-19-2013, 10:46 PM
Yeah it true smoke machine works better but if your in a pinch and don't have 35 to spend you can do that and starting fluid as well that's what I used in a pinch on side of road dang elanore was puttering and not wanting to stay running at idle but if your car is running fine and you only have a small boost leak or something use smoke test for sure

gaetz1985
06-20-2013, 02:47 PM
I thought that you would use smoke to locate a boost leak as it would be pushing the smoke out at the leak, but use propane or accelerant of some sort to locate a vacuum leak as the vacuum would be sucking at the leak

David Neibert
06-20-2013, 03:13 PM
I thought that you would use smoke to locate a boost leak as it would be pushing the smoke out at the leak, but use propane or accelerant of some sort to locate a vacuum leak as the vacuum would be sucking at the leak

Most of the places that leaks occur see boost and vacuum, so the smoke test will work for either one. I like the spraying with carb cleaner while idling method, but since it's highly flammable most people aren't comfortable doing it.

David

gaetz1985
06-20-2013, 03:16 PM
Most of the places that leaks occur see boost and vacuum, so the smoke test will work for either one. I like the spraying with carb cleaner while idling method, but since it's highly flammable most people aren't comfortable doing it.

David
thank you for clarifying David, I figured there were holes in my "theory" :)

TbirdSCFan
06-20-2013, 03:27 PM
Another technique is to use a mechanics stethocope and you can actually hear the sucking sound. For me its a lot faster and easier than locating the propane jar, attaching the fitting, opening the valve.. but not toooo far :rolleyes:, and trying to angle in the hose that you have shoved into the tip of the torch fitting to reach where the possible vac leak is. :)

Ddubb
06-20-2013, 05:59 PM
The propane enrichment test is also a good way to check if your o2 sensors are working correctly.


- Dan

ThunderRoad
06-20-2013, 06:22 PM
won,t it suck in and cause motor 2 stumble ???:confused:

S_Mazza
06-21-2013, 08:06 PM
won,t it suck in and cause motor 2 stumble ???:confused:

I don't know ... I think it takes a lot of water to make the motor start stumbling. With propane or starting fluid, when you find a leak and the engine does rev up, it's pretty obvious.

David Neibert
06-21-2013, 08:24 PM
I don't know ... I think it takes a lot of water to make the motor start stumbling. With propane or starting fluid, when you find a leak and the engine does rev up, it's pretty obvious.

Especially if your working with a motor that's already stumbling because it has a vacuum leak.

David

Ddubb
06-21-2013, 08:46 PM
won,t it suck in and cause motor 2 stumble ???:confused:

Probably .. it will also clean your heads / valves - steam clean. Oldschool trick to pour water down the carburator to clean the engine - also a good way to hydrolock your engine and destroy it if you add too much.


- Dan

XR7 Dave
06-21-2013, 10:54 PM
I take it most of you guys don't have a very good track record with actually finding small vacuum leaks on your SC's.

Most average vacuum leaks, when subjected to a fuel source, will not result in a raised rpm. The reason for this is that the EEC targets idle speed using rpm and spark advance adjusted at a rate of 3x per engine rotation. Yes, it can and does respond with up to a 40 deg timing swing faster than the engine can rotate one time. If you've ever set the timing on an old distributor car you probably know that you can cause idle to change from 600 to 2000rpm just by turning the distributor. The EEC does this faster than you can blink.

Watching a vacuum leak on the datalogger when using propane or brake clean on a vacuum leak will show up instantly in dramatic swings in commanded timing and AFR in the EEC without ever generating even a 25rpm fluctuation.

If timing were fixed like on an old carburated car or maybe if you pulled the spout connector first, then absolutely rpm would jump around a lot with the introduction of fuel into a leak source, but on our cars you would have to generate an rpm fluctuation outside the EEC's ability to adapt in order to observe any rpm change at all.

I'm not saying that you can't find some vacuum leaks with propane or carb spray, but that is an extremely unreliable method of leak detection.

S_Mazza
06-21-2013, 11:12 PM
Watching a vacuum leak on the datalogger when using propane or brake clean on a vacuum leak will show up instantly in dramatic swings in commanded timing and AFR in the EEC without ever generating even a 25rpm fluctuation.

If timing were fixed like on an old carburated car or maybe if you pulled the spout connector first, then absolutely rpm would jump around a lot with the introduction of fuel into a leak source, but on our cars you would have to generate an rpm fluctuation outside the EEC's ability to adapt in order to observe any rpm change at all.

I'm not saying that you can't find some vacuum leaks with propane or carb spray, but that is an extremely unreliable method of leak detection.

I have actually done it, and observed the change in engine sound and vibration. I wasn't watching the tach, so I couldn't tell you how much the RPMs changed, but it was a noticeable difference in the running of the engine.

In those cases, the vacuum leaks were not tiny. They were a little bit audible.

I understand that the method is not the most precise, but it can work in certain situations.

the-big-e
06-22-2013, 09:01 AM
I use the poor mans stethoscope. Three feet of vacuum tubing.:p Put one end in your ear and probe around the engine with the other. I found an intake leak on my 90 XR-7 using this method.:D

terralex
06-22-2013, 09:26 PM
I'd stay away from starting fluid and just stick with the propane, carb/brake cleaner. Starting fluid can give you a nasty fire if it hits something too hot and flares up. Propane is weak and blows away, carb or brake cleaner don't pose anywhere near the fire threat IMHO.