Stock LB9. It's a PITA to get to the plugs in some spots. I want to test compression. What is the least painful tester and way to do this?

 

There isn't. You can buy a cheap compression tester from Harbor Freight or a high end one from Mac/Snap On/Matco etc. They'll do the same job. Depends on how much you want to spend?

 

It's not the money so much as the PITA.

 

Stay away from Hobo Fake tools for anything that needs accuracy! I had one of their fuel pressure gauges that would stick mid-range right where I needed to use it. Also got rid of their torque wrenches after they kept snapping off small bolt heads.

I've had good luck with Summit tools.

Sometimes you can find an accurate gauge gauge to verify the compression tester gauge with. Many industrial type work places will have a calibrated gauge to the maintenance crew to use.

Good luck.

 

There's few, if any, good quality analog style testers made anymore. Even the Snap-On and MAC stuff is off-shore. Everything is going digital in the professional world. Why pull out every plug and go through that nonesense when I can put a pressure transducer in an easy to access hole, put an amp clamp on the starter draw, plug in the firing order to my picoscope and get a bar graph of the cylinder pressure on all 8 in about 10 minutes?

GD

 

Wow. Never though of using a transducer for a compression tester. Why not. Just need one calibrated for a high enough reading and some sort of adapter for the plug hole.

Too bad the majority of what I work on is diesel and very few diesel engines use glow plugs any more. The diesel compression kits are not designed for the newer engines. High pressure common rail injectors don't easily come out to install some sort of dummy injector to test compression. Even older HEUI injectors can't be easily removed for a dummy injector.

 

You can still easily do cylinder balance with starter amp draw and an injector voltage trigger to track the firing order. This will not show absolute pressure, but will identify problem cylinders and if you have a known good reference for cylinder pressure from a similar engine you could work out a close approximation of pressure. Generally you are only interested in cylinder balance as relates to troubleshooting anyway. Absolute numbers are rarely useful.

GD

 

I have to say that long before anyone could get a transducer setup ready to use a good old gauge would have it done and for less $$. I'd like to see the circuit the promoter here uses to convert a tr ansducer output to a usable value and how he calibrated it. My guess it's his own fantasy yet to be accomplished. Using one's imagination to suggest how to measure something is not what I call advice. Let's see this device in action if it possibly/actually exists!

 

There's not really much difference among testers in how hard the plug holes are to access. You're not going to go to the store and find some other tester that's going to revolutionize that aspect of the job. Hardest thing about doing a compression test almost always, is getting the fitting into the spark plug holes, and the hose hooked up to that. You'll probably figure that out during the process; wouldn't surprise me if there's a few you won't be able to do in-chassis, or that will take some extraordinary contortions to get. People always recommend it as a first-line troubleshooting kind of thing, but in my experience, the info that it provides, can often be satisfactorily obtained otherwise. Just turning the engine by hand with a crank socket, and the plugs installed, and listening to the leak-down in each cyl, for example. The starter draw approach also works well; even without an ammeter, just listening to the motor turn over can be informative. If it sounds like one cyl doesn't load the starter as heavily as the others as the motor spins, then … you do the math. Having "numbers" is only a means to an end, not the end in itself; and there are often many other means to the same end.

 

If you have compressed air available I would recommend buying a leak down gauge set in it's place. They are more useful in the that if you do happen to have an issue the compressed air escaping can help point you toward the cause. IE bubbles in the coolant, whistling in the intake or exhaust or deep in the engine. They can also be used on engines that you can't rotate over or hear run, making them very popular with the used engine LS crowd. When I was looking for which leak down setup to buy this is the one that everyone on the message boards was recommending:

 

It exists and frankly has existed in high end scopes since the 1980's at the least. Both my early 80's full size SUN machines can do cylinder balance calculations based on starter amperage draw and ignition triggers. SUN was bought by Snap-On and continues on as Snap-On diagnostics.

What I was referring to is more modern capabilities offered by PicoScope and others. Specifically their in-cylinder pressure transducers, amperage clamps, and software integration. You can see many examples on YouTube, etc.


Setup is VERY quick and you can have cylinder pressure from all 8 cylinders by only removing one spark plug and attaching an amp clamp. Setup the software on the laptop and crank the engine. It takes mere minutes to get compression on all cylinders with one 5-10 second crank.

Sorry but the old mechanical gauge technique is not used in most high end professional shops anymore. Why? I paid $14k for my Snap-On ZEUS...... might as well use it to speed up the shop and make me money. Right?

GD

 

That's a mountain of disinformation. That PicoScope starter kit is $1700. And still doesn't measure compression pressure. It uses math calculations from the ignition to make relative comparrisons of the cylinders.
I can tell it's BS when I read the top end shops don't use a gauge anymore. To suggest to someone rebuilding a 305 he needs thousands of dollars in equipment and he needs a relative comparrisons of his cylinders is a real pile.

Maybe a dealership that wants to diagnose bad/weak cylinders fast where training is common and equipment are shared.

I'm wasting my time here. I hope the OP and others don't fall for this fantasy suggestion.
Ten minute hookup and data log? After several hours of training maybe. What a misrepresentation!

I really don't know how someone can even suggest that method unless they trying to give the impression they have a better shop than they actually do. Any busy shop has no time for internet blogging by management or employees.

 

I have a Lisle 20250 compression tester which works very well; IIRC, it cost me about $30 several years ago. You'll still need to remove all the plugs and access each cylinder, and yes, it can be difficult but not impossible to get in there.

 

My point was only that decent quality mechanical gauges are pretty scarce. All the ones in the $100 category are off shore crap IMO. And yeah I have several - in fact my transducers utilize the mechanical gauge adaptors for the spark plug threads. I think my Snap-On mechanical gauge set was around $400.

You can do the same thing with an industrial 200 psi transducer, and a cheap USB scope. You just get 4-20 milliamp or 0-5v transducers and wire them up. They are cheap - like $25. You monitor voltage drop from the starter and cylinder pressure and do some math. Relative compression based on the solid number from one cylinder is all the information you need. The actual compression numbers are pretty useless and that's widely known.

I could setup a system for probably less than $200

GD

 

While there's nothing wrong with suggesting innovation it's actually malicious to suggest highly expensive equipment and extensive skills while a simple accurate gauge was requested. Your point now has changed from thousands of dollar worth of equipment without training to now a cobbled up makeshift substitute that would only take the amateur further into left field of self learning. Why do you do this? I don't understand. But you insist on this system that I know of no home mechanic using - none. I have to question who your trying to help here. You post like a scab vendor using the forum as free advertising masking your services as state of the art accomplishes. Chad Spier, Carl Hinkson you find them posting looking for business on most performance auto forums looking/fishing for business. And They claim to know/use the latest and greatest while their right on everything also. Read this soliciting everyday.

 

cardo0 , In my opinion your outta line here because General Disorder has not once tried to sell anything beyond the viability of his method .

Sure , his method may not be something the average home/hobbyist mechanic may want to equip oneself for and spend the time learning , but it is a viable method for those "techies" with an interest in both electronics and mechanical devices .

With all this talk of accuracy I gotta add this ; Anytime I've done a compression test on an engine running bad enough to be suspected of compression failure (once all external causes of the skip/misfire had been ruled out) , if there actually was a compression issue in a cylinder causing the problem , the lack of pressure was punch in the face obvious (As in , all the cylinders were well over 100 PSI while the bad one was barely 70 PSI) .

Seen being used here on a friend's modified AMC 390 , here's the one that's worked well for me all these years .....

 

I don't sell any of this stuff. I suggest ebay and Amazon as sources. I have not offered to do any testing for anyone. Most people on this forum do their own repairs. I don't really do any e-commerce.

I'm just telling you where the industry is headed and why there aren't quality mechanical gauges available inexpensively anymore. The demand for digital data acquisition far outstrips the demand for analog gauges that some monkey has to walk by and look at. Just the way of the world friend. I'm not selling anyone anything. And yeah I do have time for message boards in addition to owning and running a shop. It's called employees.

GD

 

I'm missing the point of an expensive compression tester or why one would need to be expensive to be good. It's not much more than a tire pressure gauge.
I'd rather buy 8 compression gauges at a volume discount, screw them all in and rotate the stater once than buy a $1700 electronic setup.
But still, a leak down gauge set is what I preferbecause after you use a fancy wizz bang gadget or inexpensive compression gauge you'll want to know where the air is escaping and you'll end up with a leak down gauge set.

 

Tootie, if you want an accurate gauge you only need to have yours calibrated. If you Google calibration services for Los Angeles you will find a large number of those companies that can help you and most likely nearby. A simple single gauge cal shouldn't be more than 10 bucks. The companies I have worked for use Transcat (in LA) but you may find cheaper closer to you. Any cheap gauge once calibrated is as good as any expensive gauge for what it's reading.

Hope this can help.

 

But why does a calibration matter if you are just comparing one cylinder to the next cylinder? You are looking for precision, not accuracy.

 

It's not that expensive, and who can't use an oscilloscope?


200 psi transducer:


Harness:

https://www.ebay.com/itm/Pressure-Tr...t/362772784942

5v power supply for the transducer:


Spark plug hose adaptor:


Those items and a little time wiring it up..... $130.... call it $150 with misc. adapters, wiring, etc.

And afterwards you have a 2 channel scope with thousands of uses for diagnostics, a compressor adapter for doing valve springs and stem seals, etc, and a transducer that can be used for fuel pressure, oil pressure, and a host of other things with a few pennies worth of adapters and hoses.

GD

 

A have a pressure transducer that I use with my labscope for performing in cylinder pressure testing. I've used it to quickly pinpoint valve timing faults, stretched timing chains and VVT faults without having to turn a single bolt. A running in cylinder pressure test will also point out valve sealing problems and even poor ring seal. I don't use the scope for basic compression testing. I perform a cranking/relative compression test on any motor with a misfire. If I find a low cylinder, I test that cylinder using a gauge. General Disorder detailed the same method I use, with an amp clamp and the labscope, to point out a low cyl. To identify the low hole, Just pull one plug and use the firing order to find the weak cyl in relation to the cyl with zero pressure. With a two channel scope you can also connect to #1 plug wire with an inductive probe and use that as a reference.

I have Snap On gauge that is pretty nice stuff. I for years had a KD tools gauge that worked just fine. Just be sure to keep the check valve clean and never remove the valve for a running compression test as that will quickly destroy the gauge.

 

My WiFi Oscilloscope using a laptop for display.
Well thanks for sharing that doc. So I busted out my WiFi connected Oscope displaying the 2V pk-pk test signal and attached a photo here. It uses WiFi so I can leave the Oscope connected in the engine bay and data log with the laptop from anywhere in the shop/garage (in a comfortable chair). Well I love that Oscope and have a high voltage inductive probe that will monitor individual ignition wires also. But how can I recommended that to someone on bottom of a learning curve? How could I do that since mine has sat in box since I bought it over a year ago. I think I'm over $300 without the laptop. In fact it burns my but when I read of others trying to convince new enthusiasts of something that expensive that also requires a whole nother skill set. Even more so when a $50 gauge will do what's required.
Suggesting is okay and sharing what you know or are using should be encouraged. But insisting on a patchwork cobbled system must have some other motive rather than advice.

 

So he's at the bottom of the learning curve? What's that got to do with using technology? Modern tools, equipment, and techniques work just as well on a car from 1985 as they do on one from 2019. So because he has an Antique car he MUST use antique tools too? Thanks but I prefer my 90 tooth ratchets, digital torque wrench, and USB scope.

Look it's nothing that wasn't being used 30 years ago. Scopes were a lot bigger and more expensive. I think my computerized SUN machine was around $35k back then. But now even a hobbyist can have this technology. That's a huge win for the hobby mechanic community. And the components have many more uses than just compression.

GD

 

I think the OP is long gone.
He just wanted to dig a hole and you guys are talking about 45 ton excavators.

 

Well where on the learning curve do you think he is? Right now he's having trouble finding a good gauge. You have a better description of his experience? Let's hear it?

And why do you exaggerate so much? You say gauges are antique? Sorry but they ain't going away. 30 year old gauges if calibrated are just as good today but it's apparent you don't have a clue about the need for calibration. But try and use a 30 year old Oscope on your car and you have to support 20 pounds near the engine bay that can't record any events displayed on a CRT screen. How many $300 tools do want sitting around in your tool box for years maybe decades before you use them again?

The OP said in his first post "I want to test compression. What is the least painful tester and way to do this?". So how can you possibly insist on a pico scope and pressure transducer? How can you say he will set it up in 8 to 10 minutes if he has no idea how to fabricate/assemble/perform a cranking/relative compression test? More like several hundred dollars and several weeks.

You exaggerate to much for some reason! And you don't seem to care much about how that could affect the naive and uninformed. You don't seem to offer new tech/equipment as suggestions but rather insist your advice is compulsory/essential/indispensable. BS!

 

That seems like it could be a fun little setup but the problem is that in itself would be a project. Covering and securing the power source and all the cords and pieces together. Many of the reviews for the Oscilloscope discuss how it didn't work with their ___ version of windows or they had to run it in Linux or there were no real instructions. Maybe if you could post a site that has directions or a list of all the tests you can do with this and how to do them I'd be inclined to try this. Flying solo and rolling your own with iffy product installation reviews is a killer for me.

 

I think y'all scared the OP away...