Is this tool broken?

[dville_gt]

So I had a feeling maybe my harbor freight leakdown tool might be giving poor readings, so tonight I spent some time with it. It comes with 2 gauges, 1 reads inlet psi, the other is a % gauge that you zero out before hooking it to the plug adapter. Problem is it has no numbers for psi just % and the gauge zeros at around 13psi on the inlet. Well I noticed my inlet pressure was dropping as soon as I hook it to the plug adapter thus the % gauge couldn't still be zeroed out. So I found a tire gauge and replaced the % gauge, set the inlet at 50psi and noticed as soon as I hook up the tool to the plug adapter the psi fell to 43psi. So if the inlet psi falls when it is hook to the cylinder the % gauge will no longer be zeroed out thus making 100% sealef show probably 20% leakage (since thatd be where the gauge is zeroed. I saw some videos on youtube of this tool and when others use it it doesnt appear to drop inlet psi when hooked up. Am i misding something or is the tool jacked? BCheck video

[shumpertdavid]

My experience is that it will drop on the 1st gauge (psi 1) when you hook to the cylinder after zeroing the percentage gauge. This is because the gauge uses such a low pressure, and when you hook it to the cylinder (there will always be some leakage since the cylinder doesn't ever seal 100%) the pressure naturally drops. Main thing is that it returns to zero or near it when you disconnect from the cylinder you are testing. I use a snap-on leak down mostly. Only thing I can say is that my snap on gauge will usually zero the % gauge at somewhere around 35 psi or so.

[turbostang]

So I had a feeling maybe my harbor freight leakdown tool might be giving poor readings, so tonight I spent some time with it. It comes with 2 gauges, 1 reads inlet psi, the other is a % gauge that you zero out before hooking it to the plug adapter. Problem is it has no numbers for psi just % and the gauge zeros at around 13psi on the inlet. Well I noticed my inlet pressure was dropping as soon as I hook it to the plug adapter thus the % gauge couldn't still be zeroed out. So I found a tire gauge and replaced the % gauge, set the inlet at 50psi and noticed as soon as I hook up the tool to the plug adapter the psi fell to 43psi. So if the inlet psi falls when it is hook to the cylinder the % gauge will no longer be zeroed out thus making 100% sealef show probably 20% leakage (since thatd be where the gauge is zeroed. I saw some videos on youtube of this tool and when others use it it doesnt appear to drop inlet psi when hooked up. Am i misding something or is the tool jacked? BCheck video

You answer your own question in the video and didn't even realize it.

My experience is that it will drop on the 1st gauge (psi 1) when you hook to the cylinder after zeroing the percentage gauge. This is because the gauge uses such a low pressure, and when you hook it to the cylinder (there will always be some leakage since the cylinder doesn't ever seal 100%) the pressure naturally drops. Main thing is that it returns to zero or near it when you disconnect from the cylinder you are testing. I use a snap-on leak down mostly. Only thing I can say is that my snap on gauge will usually zero the % gauge at somewhere around 35 psi or so.

This is the main part of the answer here, coupled with the fact that your compressor comes on immediately after you plug the guage in is the other.

That thing is constantly cosuming a fair amount of air. If your supply is not adequate, your inlet side pressure suffers...or if you're borderline where your compressor comes on, as soon as you plug it in, you fill how every many Cubic inches in that cylinder that are remaining and that kicks the compressor off..all while it's still 'leaking down' (consuming more air).

Imagine if that were a tire with a small hole in it and the air chuck had a trigger - you put the chuck on it, nothing happens. You start to fill the tire, the compressor comes on, but the tire still leaks. Depending on the size of the leak (leakdown), is what dictates how much air you have to keep pushing out for that inlet guage to come up and STAY up, or your tire pressure to come up...and in order to make that happen, you have to increase supply (turn up your regulator on the inlet side)



That is a VERY simple device, you cant' screw it up. Accuracy, maybe... not working - not likely.

[dville_gt]

You answer your own question in the video and didn't even realize it.



This is the main part of the answer here, coupled with the fact that your compressor comes on immediately after you plug the guage in is the other.

That thing is constantly cosuming a fair amount of air. If your supply is not adequate, your inlet side pressure suffers...or if you're borderline where your compressor comes on, as soon as you plug it in, you fill how every many Cubic inches in that cylinder that are remaining and that kicks the compressor off..all while it's still 'leaking down' (consuming more air).

Imagine if that were a tire with a small hole in it and the air chuck had a trigger - you put the chuck on it, nothing happens. You start to fill the tire, the compressor comes on, but the tire still leaks. Depending on the size of the leak (leakdown), is what dictates how much air you have to keep pushing out for that inlet guage to come up and STAY up, or your tire pressure to come up...and in order to make that happen, you have to increase supply (turn up your regulator on the inlet side)



That is a VERY simple device, you cant' screw it up. Accuracy, maybe... not working - not likely.

Then would you agree with comparing the real inlet side pressure after the tool is hooked up with the outlet side to determine % leakdown, like I did in the video?

I plugged tool into the cylinder, brought inlet side to 50psi, then compared that number to what the second gauge was showing (i.e. 50psi inlet vs. 42psi outlet = 8psi difference x 2 = 16% leakdown).

[turbostang]

Then would you agree with comparing the real inlet side pressure after the tool is hooked up with the outlet side to determine % leakdown, like I did in the video?

I plugged tool into the cylinder, brought inlet side to 50psi, then compared that number to what the second gauge was showing (i.e. 50psi inlet vs. 42psi outlet = 8psi difference x 2 = 16% leakdown).

Yeah. The inlet pressure doesn't really matter much imho, as long as your calculations are done with the correct numbers.. So, if your showing 46psi inlet and 40 maintaining, calculate off that. It should be at least close..

but, I do agree, I'd personally be looking for a standardized method/number like 50psi.

[dville_gt]

So comparing "hooked up" inlet pressure vs. "hooked up" outlet pressure is the point of the test?

Thats the problem I have with the harbor freight tool, the right hand gauge has no real psi numbers, it is basically a 0-13psi gauge but only has % leakdown on it (100% = 0psi and 0% = 13psi if you will). So when you 0 the tool out then plug it in, if the inlet side drops below the 13% that you started with there is no way you could ever possibly have 0% leakdown, best case scenario you'd show a % that corresponds with whatever the inlet side is showing, in my case the inlet side was dropping from 13psi to 9 psi when I'd hook it up, thus best case I'd be leaking down nearly 30% even if the cylinder was completely sealed up. Having two psi gauges makes it much easier since I can see exactly what the differential between inlet and out let is with the tool hooked up (thus accounting for any inlet pressure that might be lost due to hooking the tool up.

I guess my only question is the problem the tool or my air supply, I am using a 2hp 8 gallon compressor for the test, 125psi in the tank, 100psi at the tank regulator. Hard to believe it can't maintain a steady 13psi at the tool. That is my only concern, why the inlet is dropping so much.

[turbostang]

It's a million mile DOHC cobra, not a formula 1 car - There's a lot of room for error and where the car will run acceptably at imho.

My only concern with THOSE gauges would be that they are calibrated the SAME.

Your compressor simply coming on in the middle of the test is enough to skew the results considerably. Your regulator on the tool or the compressor is already set for a given amount of supply air - when the compressor kicks on, that given amount changes, and therefor your guage settings change. For that matter, they will never completely maintain a 'set' amount. Not without spending a bunch of money on some NASA type shit that's not necessary. % of leakdown varies a LOT with temperature, air supply, demand etc.. Your tool is just there to get you reasonably close.

With the numbers you've provided, it looks like it's having more leakdown with more pressure - which is what it should do, no?

If you keep digging, you'll find more bad shit than what you want. Eventually you'll work yourself into pulling the heads, and maybe evne the longblock!

[dville_gt]

Funny you say that, right before I thought to swap out the right hand gauge to see what the differential was between "hooked up" pressures I was just about to pull the radiator out and start in on pulling the motor out of it to rip the heads off. I just couldn't come to terms with putting it back together with one cylinder showing 60% leakdown. Now that it appears that number was due to a drop in inlet pressure I feel much better about it.

Last night I actually thought back to you telling me not to put a fuel pump speed controller on the coupe and me not listening and getting burned, and was like, if I rip this motor out when Brooks said just clean it up and bolt the damn thing together and it ends that the heads are fine I'll never forgive myself for being hard-headed!

It's a million mile DOHC cobra, not a formula 1 car - There's a lot of room for error and where the car will run acceptably at imho.

My only concern with THOSE gauges would be that they are calibrated the SAME.

Your compressor simply coming on in the middle of the test is enough to skew the results considerably. Your regulator on the tool or the compressor is already set for a given amount of supply air - when the compressor kicks on, that given amount changes, and therefor your guage settings change. For that matter, they will never completely maintain a 'set' amount. Not without spending a bunch of money on some NASA type shit that's not necessary. % of leakdown varies a LOT with temperature, air supply, demand etc.. Your tool is just there to get you reasonably close.

With the numbers you've provided, it looks like it's having more leakdown with more pressure - which is what it should do, no?

If you keep digging, you'll find more bad shit than what you want. Eventually you'll work yourself into pulling the heads, and maybe evne the longblock!

[turbostang]

Funny you say that, right before I thought to swap out the right hand gauge to see what the differential was between "hooked up" pressures I was just about to pull the radiator out and start in on pulling the motor out of it to rip the heads off. I just couldn't come to terms with putting it back together with one cylinder showing 60% leakdown. Now that it appears that number was due to a drop in inlet pressure I feel much better about it.

Last night I actually thought back to you telling me not to put a fuel pump speed controller on the coupe and me not listening and getting burned, and was like, if I rip this motor out when Brooks said just clean it up and bolt the damn thing together and it ends that the heads are fine I'll never forgive myself for being hard-headed!

LOL! I'm not saying I'm always right, or even part of the time - but I'd rather do a tuneup FIRST and see what kind of results LONG before i pull heads, long blocks etc.. You've certainly done some good on cleaning those runners up though, that can't be bad.

[Acrotom]

dville - What you are experiencing is normal for leakdown testers. You want your guages to be marked in psi - not some percentage figure - so you can easily reset the regulator after the airflow is established.

Another point - leakdown tests are typically conducted at a higher pressure than was used in the video. Common practice in the aviation world is to use 80 psi (flowing pressure)on the inlet guage. I will often use higher pressures (100 psi) on racing engines to make the test more stringent. Minor leaks are more evident at higher pressure settings.

With all of this said, though - don't be too quick to condemn the engine because the leakdown numbers aren't where you think they should be. There are lots of variables, and leakdown testing results can change from test to test. The leakdown test is very helpful for identifying where the leak is occurring (intake valve vs. exhaust valve, vs. rings vs. head gaskets), but don't get too concerned if the leakage numbers seem a little high.

It takes a significant leakage to make a big difference in power production. The NASCAR guys and pro stock racers are concerned about a few percentage points because the competition is fierce. Street type vehicles will not experience a large power loss because of a ten or twenty percent leakdown swing.

If the car is running pretty smooth, and not puking oil or fouling spark plugs, I would be reluctant to tear it apart.

[turbostang]

dville - What you are experiencing is normal for leakdown testers. You want your guages to be marked in psi - not some percentage figure - so you can easily reset the regulator after the airflow is established.

Another point - leakdown tests are typically conducted at a higher pressure than was used in the video. Common practice in the aviation world is to use 80 psi (flowing pressure)on the inlet guage. I will often use higher pressures (100 psi) on racing engines to make the test more stringent. Minor leaks are more evident at higher pressure settings.

With all of this said, though - don't be too quick to condemn the engine because the leakdown numbers aren't where you think they should be. There are lots of variables, and leakdown testing results can change from test to test. The leakdown test is very helpful for identifying where the leak is occurring (intake valve vs. exhaust valve, vs. rings vs. head gaskets), but don't get too concerned if the leakage numbers seem a little high.

It takes a significant leakage to make a big difference in power production. The NASCAR guys and pro stock racers are concerned about a few percentage points because the competition is fierce. Street type vehicles will not experience a large power loss because of a ten or twenty percent leakdown swing.

If the car is running pretty smooth, and not puking oil or fouling spark plugs, I would be reluctant to tear it apart.

TWO very valid points.

edit, the whole post is pretty solid.

[dville_gt]

This is why I enjoy this site. I appreciate the help from both of you.

[turbostang]

You're welcome, hope it all works out like you want.

[shumpertdavid]

Like stated above, I use the leakdown tester to find a big difference. Example, all cylinders are 30-40% except 1 cylinder that is 80%. You're basically looking for a major swing from the others to help narrow down the problem area. My car for example had about 700 miles on it when I went to the dyno last. It hurt 2 cylinders during the session. The 2 cylinders hurt didn't have the most % of leak, but when I went through and did a compression test they were the lowest.

It's a good diagnostic tool, but there are other problems that it will not catch or give indication for.

I follow the instructions and use the gauge as is says to. I think you are looking too hard into the pressure drop thing when you plug it in. I use a 2 stage 80 gallon compressor at work with a 150 psi working pressure. With all that I still see the pressure gauge on the tester drop when I connect it to the cylinder. It's partly due to the leak and partly to the regulator I would assume.

I have a cheap leakdown tester also (looks similiar to yours) and it's working pressure is a lot lower which seems to make the % readings a lot higher.


If your regulated pressure is 15 psi it doesn't take much of a leak for it to bleed down which would indicate a higher % reading than if you had a working pressure of 45 psi.

[dville_gt]

Like stated above, I use the leakdown tester to find a big difference. Example, all cylinders are 30-40% except 1 cylinder that is 80%. You're basically looking for a major swing from the others to help narrow down the problem area. My car for example had about 700 miles on it when I went to the dyno last. It hurt 2 cylinders during the session. The 2 cylinders hurt didn't have the most % of leak, but when I went through and did a compression test they were the lowest.

It's a good diagnostic tool, but there are other problems that it will not catch or give indication for.

I follow the instructions and use the gauge as is says to. I think you are looking too hard into the pressure drop thing when you plug it in. I use a 2 stage 80 gallon compressor at work with a 150 psi working pressure. With all that I still see the pressure gauge on the tester drop when I connect it to the cylinder. It's partly due to the leak and partly to the regulator I would assume.

I have a cheap leakdown tester also (looks similiar to yours) and it's working pressure is a lot lower which seems to make the % readings a lot higher.


If your regulated pressure is 15 psi it doesn't take much of a leak for it to bleed down which would indicate a higher % reading than if you had a working pressure of 45 psi.

I don't know if the last part is right. See, the right hand gauge (which I swapped out for a cheapo tire gauge) did not have any PSI #'s on it at all. Just %'s. 100% = 0psi obviously, and 0% would normally be around 13psi inlet, thus the % gauge was just a 0-13psi gauge that had %'s instead of numbers. So if the inlet pressure is now not at 13psi then there would be no way for the opposite gauge to show anywhere near 0% leakdown since the inlet pressure is no longer at a level that would 0 out the other gauge. Thats what made me think to swap out for another psi gauge, I can plug the whole thing up, bring the regulator to whatever psi I want then just compare the difference between the 2 gauges. When I do it this way all of my cylinders came out between 10-15% leakdown (on a cold motor) which seems pretty good vs. my old number which were literally all over the map from 20 % to 60 %