Leak down testing, and valve job?

[argniest]

When you have a minute can you pop over here and read this. I wasnt sure where to post this one. Since its really related to the engine, I thought I should have probably listed it here instead in the engine area, after I had already typed it in over there

http://www.classiczcars.com/forums/showpost.php?p=354558&postcount=32

or read it at the end of this page, that is, post #32 and the end of page 2

http://www.classiczcars.com/forums/showthread.php?t=40938&page=2

Edited February 18, 2011 by argniest

[Gary in NJ]

If a cylinder goes instantly to 0, then that cylinder can not support combustion. If the engine really has three dead cylinders, you'd know it. The engine would be rough running and more then likely smoking from the exhaust.

Re-run the differential pressure test, but this time do it with the valve cover off the engine. This will allow you to confirm that both valves are closed; and if air is getting by the guide you can feel it at the source.

I'm not sure what tool you are using for the leak-down test. I use an aviation style differential pressure tester. I believe the inexpensive lead-down testers accomplish the same thing. I usually use 80 psi for a leak-down test. Any cylinder that can hold 72 psi is a-ok. Below that I start to look for a source of the leak.

[argniest]

Sorry, I am not sure what you mean by 72 psi? Because during the compression tests I saw them holding 140 to 155 psi. When you say 'if it holds 72 psi you are a-ok' are you talking about just for leak down tests? I bought a higher quality leak down tester, and I do think its working fine. I was pushing about 100 psi into the cylinders from the leak down tester. And I will be retesting a few times just to be sure. And OK, I can pop off the rocker cover next batch of tests. Then as you said, I can see if they are really closed or not.

he he I was just talking to my cousin about this on the phone as I was explaining what I did, and he said the same thing :-) take off the rocker cover, and make darn sure the cam lobes are pointing up. And make sure there isnt much play between rocker arm and cam, and that the valves looked closed. He really thinks if I redo the tests this way, that I will find out that cylinders 1,3,5 are actually OK :-))))) I sure hope so.

Edited February 18, 2011 by argniest

[FastWoman]

Argneist, I already responded to your other thread. Check there.

[Gary in NJ]

Sorry, I am not sure what you mean by 72 psi?

When I use my leak-down tester I first set a reference pressure, i.e 80 psi. My tester holds this pressure within the gauge itself while I fill the cylinder. A very good cylinder will hold about 78 psi, about 98%. An acceptable cylinder will hold between 72 to 77 psi or 90% to 97%. So my leak-down tester has two gauges, a reference gauge and a cylinder gauge.

When I'm done testing all of my cylinders I have a record for each cylinder that looks like this:

#1 78/80 #2 76/80 #3 78/80 #4 77/80 #5 78/80 #6 72/80

The next time I run the test I can compare these figures with the current reading. The longer the history, the more validity to the test.

This is the common practice in the aircraft industry which is where I have my mechanical training.

[sblake01]

Argneist, I already responded to your other thread. Check there.

Sarah, I'm glad I saw this post about your other post. It saved me from posting an almost duplicate post in this thread

[argniest]

When I use my leak-down tester I first set a reference pressure, i.e 80 psi. My tester holds this pressure within the gauge itself while I fill the cylinder. A very good cylinder will hold about 78 psi, about 98%. An acceptable cylinder will hold between 72 to 77 psi or 90% to 97%. So my leak-down tester has two gauges, a reference gauge and a cylinder gauge.

When I'm done testing all of my cylinders I have a record for each cylinder that looks like this:

#1 78/80 #2 76/80 #3 78/80 #4 77/80 #5 78/80 #6 72/80

The next time I run the test I can compare these figures with the current reading. The longer the history, the more validity to the test.

This is the common practice in the aircraft industry which is where I have my mechanical training.

Well my leak tester goes up to exactly 100 psi. And now that I know how to use it correctly (read my other post to see good results I got!!!), I see that the reference side is calibrated to be 0% loss at 100 psi.

That cruddy leak down tester from harbor frieght was all messed up. It was my only local option. And it least I learned a little more while playing with that cheapo leak tester. The new one I got from amazon was much better and calibrated correctly.

[Jennys280Z]

argniest: What brand is it from Amazon? I'm hoping you're going to say Actron because I got an Actron compression tester from Amazon and I hope this thing works well.

[Gary in NJ]

A compression tester and a leak-down tester are two different tools. The compression tester uses the pressure within the cylinder (through aspiration) to check the total pressure within the cylinder. It is a dynamic test of the cylinder and combustion chamber.

A leak-down tester uses external pressure from an air compressor. Since the piston is held in place (or selectively moved for advanced testing) during the test this would be considered a static test of the combustion chamber. With a leak down test you can determine the cause or source of any failed or out of tolerance components.

While more difficult to conduct and more time consuming to perform, a leak down test is a more useful tool for diagnostics.

[cozye]

FWIW The harbour freight leak down tester is fine if you replace the 2nd gauge with a 100psi gauge.

[argniest]

argniest: What brand is it from Amazon? I'm hoping you're going to say Actron because I got an Actron compression tester from Amazon and I hope this thing works well.

yes my actron compression guage have worked fine. But the leak down tester from amazon wasnt actron. I dont think they make one.

Here is the leak tester I bought. It worked exactly as I expected. Practicing with the harbor freight leak tester (which I returned) taught me what I needed to do.

http://www.amazon.com/gp/product/B000Q6P7GU

The last thing I had to finally figure out and understand, is that in order to do the leak down testing, I had to manually position the piston at TDC on the compression stroke. Because for example, cylinders 1 and 6 are at TDC at the same time. But only one of them is on the correct compression stroke, and the other one is on the exhaust stroke.

So when I did the leak down test with the [piston at TDC on the exhaust stroke, welllllllllll I got 100% leakage. I was like OMG what is wrong!!!!!! But after advice from my new z friends, I realized my mistake. So I just rotated the crankshaft pulley nut, until the piston went down and back up again to TDC. And then I knew I had it in the correct position for the leak down test of that cylinder. And then I found out THANK GOODNESS, that all my cylinders and pistons, valves etc are fine. They are basically around 18%. And I believe even a new average car has 15% leakage on such a guage.

So after sweating bullets wondering about this, until I verified all this myself (after learning how to do all this myself too), my Z car engine is healthly.

And the compression tests also proved that. They were on average around 150 psi. Also, my cousin who restores cars, asked me if I held the gas pedal to the floor during the compression tests. I was like ummmmmmmm nope I didnt do that. He said if I had done that, the psi readings would have been even higher. So worst case scenario I got 150 psi.

Sometime after I get all the new parts installed (fuel injectors, PCV valve, etc), I will try the compression tests again with the pedal to the floor, which will open the throttle body and let more air in there. Is what he explained to me. It does seem to make sense. That would be nice if I actually had 155 or 160 psi instead of 150. But hey 150 is fine too.

WOW it was not easy or fast for me to learn all this stuff and how to accomplish all the tasks, but now it all seems so easy to do the compression tests, fuel pressure tests, vacuum tests, and leak down tests. And I am also cleaning all grounds in the engine, and have cleaned all sensors and electical connections in the engine compartment. And I cleaned the fuse box, and replaced all fuses too. I read that if too many electrical connections (or even just certain ones are causing resistance from corrosion, it can accumlate and cause the engine to run rich or lean). So I am trying to eliminate those kinds of issues from the equation over my wintertime projects

***********************************

I know this stuff is a little off topic, but I am so happy about all of it, I cant help myself.

And as a major victory, just last night at 958PM , I got my gas tank off. It was full of lots of nasty rusty gunk. After taking out the fuel sending unit, I could see down in there, and was horrified at all the junk in the tank!!!!!!!!! SO I read and read and read, and figured out what I needed to do. I encountered some rusty screws that were very difficult but once I got them off, I was home free.

So once my cousin restores the gask tank (boils it out, acid, and sealer) in about a week, I will put it back on (well after I clean, seal, and paint the outside). It should be better than new, and outlive me by 100 years. Also, I am probably going to install an inline fuel screen between the fuel tank and the fuel pump. Because I am 99% sure the screen in the fuel tank is toast. Or will be once he works it over. But I have been told by several people in past few days this is a working solution, to deal with losing that screen in the fuel tank after its restored. And the other nice thing about the inline screen, is that its serviceable since it lives outside the gas tank where you can get at it if needed.

And then once new tank is on there, I will install a new fuel filter, and then install my new fuel injectors. After talking to my mechanic friends and Z friends, I believe my car will run a lot better. The last thing will be to tune the AFM to the new fuel injectors. Everyone who is helping me, agrees those old injectors are toast. God knows how long that car has been running with a tank full of nasty rust!!!! And we know the car sat for a while. And that would leave gas sitting in the injectors (probably for a few years we figured). Which of course is not good for them. A few bad fuel injectors can wreak havoc on the runnability of the engine. And I didnt want to touch the gas tank, or injectors, etc until I knew what was going on with the gas tank. Check. Done! ANd also when I cut open my fuel filter I was horrified once again at how much stuff came out of it. But I did that before I opened fuel tank, which is what was the final tipping point, to make me need to remove fuel sending unit and look into the tank in the first place

One of the next fun things I am doing is using my fog machine, and compressing the air in the car, to see where any seals are bad. And replace the rubbers. Some look newer some look old! I saw a thread on here about how to do that test :-)

Edited February 23, 2011 by argniest