confusing compression and leakdown test results

[rlacasse1]

Alright, I'm posting this from my phone so hopefully this works out.

I just got confused by the compression test and leakdown test I did. So real quickly here's the results. When I did the compression test I got between 100-125 psi on all the cylinders. Obviously these are shitty results. Then I did a compression test after dumping a little oil in each cylinder and the numbers jumped up to 175 psi on each cylinder. So, that tells me that the rings are shot and I need to rebuild my engine. However, when I did the leak down test I was barely losing pressure and little to no air was entering the crankcase depending on the cylinder. And to my understanding a little blow by past the rings is ok and normal. And the guage on the leakdown tester even showed as having good compression. And I followed the proper procedure on zeroing the leakdown tester, so that's all good.

And there was no compression leaking past the valves or into the coolant system either. And the timing is correct.

Something I was considering is maybe the headgasket being burnt out betwen the cylinders. But the compression test after the oil killed that hope for me.

So does anyone have any suggestions on what else to check before I rip this bi*** down and rebuild it.

 

[Chicken Patty]

When you did the compression test was the car fully warmed up and did you hold the throttle open?

 

[rlacasse1]

The throttle was open completely but the car was not warmed up.

 

[phunny]

The throttle was open completely but the car was not warmed up.

Ding Ding! Warm, lather and repeat.

 

[rlacasse1]

I really don't think having the car warmed up is going to make a huge difference but I will try it.

Only reason I say that is because I have tried it both ways on another car and it made absolutely no difference.

But still, even with that, it still doesn't explain the compression problems vs. the leakdown test.

 

[donniekak]

A wet compression test doesn't work well on these cars, the oil just fills up the piston dish, and raises compression no matter what. The leakdown test is a better indicator than a compression test anyway.

 

[Calan]

I really don't think having the car warmed up is going to make a huge difference

You'd be surprised.

A wet compression test doesn't work well on these cars, the oil just fills up the piston dish, and raises compression no matter what. The leakdown test is a better indicator than a compression test anyway.

This ^

"Wet" Compression Test

The idea of the wet compression test is that the addition of some oil will help the rings seal. In theory, if the compression numbers are better with the wet test than they were dry then you have worn rings.

The problem is that for one thing, the wet test is dependent on the profile of your pistons. If all the oil remains at the center of a dished piston instead of out at the rings, then the results won't change much. Another problem is that adding too much oil can effectively lower the displacement of the cylinder and naturally increase compression, leading to false assumptions.

If you find that the average for one cylinder is 15-20 psi lower than the others, you can add a tablespoon or so of oil to that cylinder through the plug hole and repeat the test. If the compression comes back up, you may have worn rings on that piston; but keep the points mentioned above in mind and take the new results for what they are worth.

 

[rlacasse1]

A wet compression test doesn't work well on these cars, the oil just fills up the piston dish, and raises compression no matter what. The leakdown test is a better indicator than a compression test anyway.

That is actually what I was thinking as well and was going to ask. But I figured cranking the car over may throw the oil around a little to where it will get on the cylinder wall.

But still.

Low compression, but, no leakage. WTF?

Oh, might as well add. The cylinder with the most leakage was cylinder #4, but it was also the cylinder with the highest compression.

 

[Calan]

What pressure were you at when you did the leak-down test? Also, are you sure the valves were completely closed? (The crank should be a little after TDC in most cases).

 

[rlacasse1]

Yes the valves were closed. 100% positive of that. I had no air coming from the intake or exhaust. Plus, the leakdown test was fine. And I tested them at 95-100 PSI. The leakdown tester can't handle anymore than that.

 

[Chicken Patty]

Try it with the car warm. Buddy did it with car semi cold and he got 125 even, did it warm got 160 all across.

Plus what a coincidence that all four of your rings are worn evenly. I know sometimes compression is low and even, but that's usually the case on older motors that have wear and tear.

Try it warm, if you got even before, most likely you are fine, just gave you lower because it wasn't at the proper temp. Do that and revert bro, best of luck!

 

[rlacasse1]

I'm definitely going to do a warm test when I get the time. But the compression vs. leak down results still confuse me.

 

[Chicken Patty]

I'm definitely going to do a warm test when I get the time. But the compression vs. leak down results still confuse me.

Meh, if the compression is good, I'd say you are okay.

 

[tenn-gsx]

Did you do the leak down before or after you put oil in the cylinders? If after it is possible the oil sealed things up better. Its also possible you will get better results doing a comp test with a warm engine.

 

[rlacasse1]

I did a leak down test both before and after the oil was put in the cylinders. I got the same results both times.

 

[tenn-gsx]

Id say your confusion is most likely from doing the compression test on a cold engine then.

 

[rlacasse1]

I don't think so.

I mean think about it. Supposedly with a cold engine you will get lower compression results. That means with a cold engine you should get worse leakdown results as well.

The warm test is still coming.........eventually.

 

[TunaTalon]

A cold engine has lower compression test results because of the effect of heat of compression. Air heats as it's compressed and the heat adds to the pressure. (That's what the intercooler is good for, it removes the heat of compression from the turbo before the charge reaches the cylinder.)

A leak down test is not affected by the effect of heat of compression and will be very close on hot and cold engines.

 

[rlacasse1]

Ok that makes sense.

A nywayI just did the compression test warm and I got the same results.

 

[Calan]

Anyway I just did the compression test warm and I got the same results.

That is really strange.

I can't remember ever getting the same exact results on both a warm and cold engine, unless the rings were worn so badly that they never sealed, or there was serious leakage at the valves.

Assuming your test procedures and results are accurate, the only thing I can think of that explains what you are seeing is that you have leakage that only appears at higher cylinder pressures; and that is usually the beginning of a head gasket failure... where leakage can occur in certain areas but only at a high enough pressure. If that is truly the case, it's just a matter of time before the HG deteriorates to the point that leakage occurs at lower pressures and then finally fails.

I would keep an eye on it and do the leak-down test often over the next several miles and see if it changes.

 

[phunny]

That is really strange.

I can't remember ever getting the same exact results on both a warm and cold engine, unless the rings were worn so badly that they never sealed, or there was serious leakage at the valves.

Assuming your test procedures and results are accurate, the only thing I can think of that explains what you are seeing is that you have leakage that only appears at higher cylinder pressures; and that is usually at the beginning of head gasket issue... where leakage can occur in certain areas but only at a high enough pressure. If that is truly the case, it's just a matter of time before the HG wears to the point that leakage occurs at lower pressures and then finally fails.

I would keep an eye on it and do the leak-down test often over the next several miles and see if it changes.

Agreed. I have NEVER gotten the same results going from cold to warm.... OP did you actually re-do the test?

 

[rlacasse1]

Yes I redid the test.

Now after all this I started to wonder if it was out of time. When I bought it I had my dad check it out and he said it was in time so I took his word for it. And it was driving fine and all that and running good. However sometime in between me buying it, and the whole 10 miles I have put on it, to now, this happened.

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=16july2011176.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/16july2011176.jpg" border="0" alt="Photobucket"></a>

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Looks like in those 10 miles or so the balance shaft belt decided to break.

It threw it out of time a little. But what is weird is that the car runs smooth as hell, it's just kind of nutless. And whats even weirder is that at TDC for each piston there was no leakage from the valves. So hopefully there are no bent valves.

Tomorrow I am going to retime it and I'm going to post my results back.

 

[Chicken Patty]

Keep us posted bro, hopefully there was no damage.



I just did a compression test on mine and with 200k it has 180 all across. Bone stock 7 bolt, I'm actually very impressed.

 

[tenn-gsx]

Yes I redid the test.

Now after all this I started to wonder if it was out of time. When I bought it I had my dad check it out and he said it was in time so I took his word for it. And it was driving fine and all that and running good. However sometime in between me buying it, and the whole 10 miles I have put on it, to now, this happened.

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=16july2011176.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/16july2011176.jpg" border="0" alt="Photobucket"></a>

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=16july2011178.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/16july2011178.jpg" border="0" alt="Photobucket"></a>

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=16july2011180.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/16july2011180.jpg" border="0" alt="Photobucket"></a>

Looks like in those 10 miles or so the balance shaft belt decided to break.

It threw it out of time a little. But what is weird is that the car runs smooth as hell, it's just kind of nutless. And whats even weirder is that at TDC for each piston there was no leakage from the valves. So hopefully there are no bent valves.

Tomorrow I am going to retime it and I'm going to post my results back.

That would definately explain things. I think your good once you re time it. You already did a leak down and it passed that so your looking good on valve condition.
Make sure you put new timing components on. No sense in reusing old parts.

 

[rlacasse1]

Ok, so some more info.

I busted out my manual to look up the timing on it and saw that there are two different timing marks depending on whether your car is a 90-92 or 93-94. My car still has the 90-92 timing mark so I figured I would line it up that way. But the cylinder 1 wasn't at TDC, so I tried following the timing for the 93, and cylinder 1 still wasn't at TDC. What the hell??????

So I pulled the crank sprocket off and this is what I found.

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=15July2011001.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/15July2011001.jpg" border="0" alt="Photobucket"></a>

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=15July2011002.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/15July2011002.jpg" border="0" alt="Photobucket"></a>

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=15July2011006.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/15July2011006.jpg" border="0" alt="Photobucket"></a>

<a href="http://s860.photobucket.com/albums/ab162/rlacasse1/?action=view&amp;current=15July2011007.jpg" target="_blank"><img src="http://i860.photobucket.com/albums/ab162/rlacasse1/15July2011007.jpg" border="0" alt="Photobucket"></a>


Apparently the last genius that timed the car forced the crank sprocket on even though it wasn't aligned properly. The crank doesn't have any damage so that's good. I just need to buy a new sprocket and back plate and retime it and hope to God that nothing is bent in the head.