Re: forum answers not helping
Called the "Propane trick" for search purposes.
Using propane to find vacuum leaks is common with professional shops that understand how to do it. Those that don't just throw parts at it until they find it or you go broke.
The trick to finding an air leak is to use something that burns similar to gasoline but won't burn the vehicle down. Some folks use carb cleaners that don't burn, WD-40, oil, or other chemicals that don't burn, even water. They don't do anything. At best they might temporaily plug the hole.
Spraying starting fluid or gasoline is very dangerous.
When a burnable substance hits the leak it causes the engine to speed up - if it was lean in the first place.
Propane is the safest and easiest thing to use.
Prepare the engine - if it's possible, lean it out even further, and slow it down as much as possible. A slow running engine with a very lean condition becomes very sensitive to adding a tad more fuel - the propane.
Take off the torch head itself, slip a long hose over the tube. It's best to remove or drill out the tiny orfice as well, to get even more propane volume.
Use the end of the hose to spray around possible leak areas -- when you hit a spot where air is not supposed to be getting in the engine RPM will increase. To make sure you know how it will react, give a little down the carb/TBI throat and notice.
You can get it in areas that are hard to reach, even harder to see - like under the intake manifolds, etc.
Try not to spray it on the distributor - there's sparks in there.
If it does ignite it flashes, scares hell out of you, but then the fire goes out. If you'd sprayed carb cleaner or gasoline around you'd have wet puddles and a big fire.
Remember, propane is heavy - it will collect in low areas.
And, sometimes the air blowing around the engine compartment can blow the invisable propane down the carb tricking you -- "Look - the fender's leaking." Use common sense.
Propane enrichment is standard operating procedure for almost all car makers.
And -- it's a great way to tell if your mixture is correct.
Normally a correct mixture will have a very slight reaction - both at idle or high speed. It should be very slightly on the lean side - meaning adding a very small amount of propane will cause the RPM to increase a tiny bit. Then adding even more propane will cause it to slow down - as it becomes too rich.
You can do that test at any RPM - even at 6000+ if you want. It'll tell you how your jets are - too big, too small etc.
Anything above idle you will have to drill out the torch's orfice to get enough propane.
Poor man's dyno -- Run the hose from the driver's seat into the engine's airstream and drive it - add propane under load to see if you can stand more jetting or less.
It's great for diagnosis too. Fuel vs Ignition? Lean or Rich?
Some folks mistakenly think propane will hurt an engine, but many vehicles use propane all the time. It's just another temporary source of fuel.
Some think it will burn it up because it's too lean - like
Nitrous - no, Nitrous Oxides make it go lean, propane goes rich - just the opposite.
I've even used it to drive my van a few bocks to the gas station in the rain when I ran out of gas.
It's probably the handiest diagnostic tool you can have in your shop short of a scope, exhaust analyzer, and dyno --- and many many thousands of $$$ cheaper! Even then I used it in combination with all that equipment in my shops.