Thread: TEST, don’t guess...

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I am a HUGE proponent of TESTING, not guessing to find solutions to problems.

A small investment in testing tools and diagnostic skills will in most cases pay for themselves in a short time. With just a few testing tools, you will be able to tune like a pro and better understand what your vehicle’s motor and electrical systems are or should be doing. While there are many more, in most cases these basic test tools will get the job done;
1). Compression tester (type that screws into the spark plug hole)
2). Vacuum gauge (with numerous hose fittings and adapters)
3). Fuel pressure gauge (with numerous hose fittings and adapters)
4). Timing light (with advance feature or timing tape to check total advance)
5). Electric multi-meter (volt and ohm scales minimum)

There are numerous sources available for teaching you how to use testing tools, your local library and the internet are just a few, you may even have a friend that knows how.

A compression tester is a vital tool, it will tell you the condition of your cylinders and combustion chambers. Low pressure on one or more cylinders indicates a problem. Testing the cylinder(s) in question again using a squirt or two of motor oil (usually 30 weight) in the spark plug hole will usually reveal if the problem is at the rings or valves, pressure will increase if the rings are suspect as the oil temporarily seals around them. Usually two cylinders low adjacent each other is a sign of a head gasket problem. Here is a link to help you get familiar with a compression tester’s uses (and there are many more sources); Compression Testing

A vacuum gauge is a very handy tool, it will assist in tuning and help diagnose valve and ignition problems. Use to set your carburetors idle circuit and see if ignition timing is late or early (note, large cams can make vacuum readings erratic at idle). Here is a link to help you get familiar with its uses (and there are many more sources); Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

A fuel pressure gauge is another handy you will need, it will tell you what your fuel system is doing, keep in mind carburetors usually require less than 6 psi (some even less). Very low pressure may indicate a restriction or pump problem, high pressure may indicate the need for a regulator or adjustment. Here is a link to help you get familiar with its uses (and there are many more sources); Mityvac

A timing light is another vital tool, it will assist you with ignition timing, initial, total and where the timing curve is set. Here is a link to help you get familiar with its uses (and there are many more sources); How to Use a Timing Light | eHow How to Use an Advance Timing Light | eBay

A electrical multi-meter is a handy tool, it will help you diagnose electrical problems. Use it to test for correct voltage at your coil and other equipment, also test for restrictions to the system and grounds. Here is a link to help you get familiar with its uses (and there are many more sources); Automotive Multimeter Golden Rules on YouFixCars.com

Now, with your new knowledge use the test procedures and collect the data. Write it all down and analyze it. If you’re still stumped on what your problem is, use the data, include your car, transmission, motor type and any other pertinent information we may need, then ask the questions. We’ll be glad to help, but we’ll need all the data to help you intelligently…

I also like cylinder leakage testor-after the compression test you can chase down the finer points of the low pressure

Thanks for the link, Denny - whole lot of good information. Just saved it as a pdf for future reference. This ol' dog really appreciates learning new tricks. I remember my father used a vacuum gauge for a lot of things. He had an old brass one that measured + 30 and - 30 with a glass face that came from something he worked on in a steel mill. It was his prize possession.

Glenn

Good job guys, exactly what I'm hoping for out of this thread, SHARE the knowledge. Bring it on!

Then I'll share one of the most mis-understood parts on a american car since the 60's. The simple PCV valve.

Originally Posted by DennyW

Hope it's ok to post a link to these here from mine. (if not, please let me know).
Here's a couple pages I did up some time back about using a vacuum gauge, and things you can tell has a problem by using one.

This first one is an animation of using the vacuum gauge, and things that it indicates...
Vacuum Readings !!

Engine testing with a Vacuum Gauge

Great info Denny, but you might want to check the #3 and #4 animations in your first link.(Poor Rings/Poor Oil and Poor Oil) It appears they are switched.