What's this spark plug telling me?

So if I were to do this test, do I just check 3 & 4? & I imagine I use my regular motor oil. Always best to double check.... cupful = quart bottle cupful?
& I gota brace myself.... Breathe.... I mean piston rings are pretty major, correct?

 

The pressure on the gauge should not drop after you stop cranking the engine. There should be a release valve on gauge to release the pressure and be able to do the next cylinder in your test. In my opinion, I would redo the test. 1- make sure ignition and fuel system disabled. 2- remove all 6 spark plugs. 3- install compression tester. 4- hold accelerator wide open ( gas pedal to the floor) this allows full air into the engine for a proper test. 5 - crank engine 10 revolutions ( you should hear a different noise every time the cylinder being tested gets compression) so 10 times hearing that different noise. 6- stop cranking and check gauge. write down gauge reading- it should not drop on gauge unless something is wrong with gauge. 7- repeat for every cylinder cranking 10 revolutions and write it down.
They should all be within 10% of each other. If you have one or two cylinders that are not within 10%, put 1/2 teaspoon of engine oil into spark plug hole - wait a minute and repeat compression test. The compression will always rise a few pound because of the oil but if it goes up considerably, then there is a issue with your piston rings because the oil is acting as somewhat of a sealer for the rings. If it does not go up but a pound or two, then it points to a valve issue.
With everyone helping and the compression turns out ok, you should be able to get it right and running well.

 

Soooo.... I retested dry right before doing wet

3 - dry - 130 wet - 160
5 (typo - should be 4) - dry - 150 wet - 170

 

ok. just saw this. I had looked up how to do this as you suggested & there sure seems to be a variety of ways, or rather particulars regarding how many cranks or gas pedal to the floor or this is not mentioned at all. One had that you should crank the engine once or twice after putting in oil & before putting on the tester because of hydro flooding? (I know the term, just can't think of it). Then there was 1 tsp, 1 tblsp.... etc.

 

It's not really complicated. A little challenging trying to figure out how to get the most accurate results being the first time I've done this & such a variety in the particulars. I kinda picked the middle ground & went from there. Tomorrow's a new day. I'll get an early start & do it again.

 

Something is not right here. Your dry numbers don’t match what you had before. Cylinder #3 and #4 were the lowest before. Why did you test #5 dry and wet? In order to diagnose your compression test correctly, DO A COMPLETE 6 cylinder dry compression test as I described above. If any of the 6 cylinders does not meet the 10% allowance, THEN do a wet test with 1/2 teaspoon of engine oil on only those cylinders. When testing compression in each cylinder, EVERYTHING must stay consistent. Sorry for the extra work but you want to make sure and not have to guess at anything. Think like an MD (motor doctor)

 

That was supposed to be 4, not 5. I mean I wet tested 4, not 5.

 

Question - the tester

Couple of questions before I get started (later than I had hoped, but nonetheless) -
1. There is an adapter with the tester. It is about the length of my plugs. Do I need to use this? The tester threads in as is with less threads, so seems easier, but easy doesn't matter if it throws off the accuracy.
2. "you should hear a different noise every time the cylinder being tested gets compression" - does this mean, 1st crank sounds different from 2nd crank, up to the 10th? Or 1st cylinder should sound different from the 2nd cylinder? Or it should simply sound different from a normal crank?
3. This is one thing that did not vary when I looked up instructions. A difference of 20-ish psi was normal from dry to wet, even on the cylinders that were good. Significant jump was, well, more significant. & no jump or minimal was an indicator of a valve problem as you put. I am not stating that there is not a problem even if 3 & 4 it does go up 20-ish. Just confused & when I understand the why's, I get how to be more precise. More of a "Motor Doctor" - MD

 

That plug is indicating that it works.

 

1. Usually, yes you need the adapters. Read the instructions, you will need to use the one that fits your threads (14mm?). ONLY HAND TIGHTEN. You do not want to have the adapter unscrew in the engine...

2. I usually just watch the gauge; it usually moves since compression is being pumped to it. However, I also do not count compression strokes. IMO we are testing for max compression; not compression at a defined number of cranks. The issue with only doing 5, 6, 7, 8, etc. cranks is that the battery tends to sag causing unreliable results. I'm sure the others have a good reason for including this in their instructions, but this is my opinion. I just crank until the needle on the gauge stops increasing. Back to your question, the pistons should make a compression in every crank cycle; not the 2nd, 3rd, etc. Here's a video: https://www.youtube.com/watch?v=DKF5dKo_r_Y

3. If your cylinders are reading below 10% dry, but increase wet, there is an issue, most likely with the rings. All cylinders usually read higher with the wet test, akin to what lefthook mentioned about the oil acting as a seal. Basically, the rings are what seal in the compression from the piston. If they are worn, they will not hold as much compression. If the wet test shows no change, it means that the rings are most likely not the cause since the oil would act as a seal. In this case, the valves, which are not affected by the added oil, are a likely cause. The valves open and close to let fuel in and exhaust gases out. If they are stuck/bent/broken they will let air escape during the compression cycle, which is not normal. Usually a leak down test would be the next step in determining this. Other possible causes in this situation could be a bad headgasket. Another issue with bad rings is that they can let oil through from the bottom of the cylinder (think the attaching rod part) to the top of the cylinder head.

If you test again, make sure to clean the spark plug threads. I like to use brake cleaner and a rag/screwdriver combination. A warm engine can make a huge difference... I once tested a 1974 911 cold and it read over a 20% difference between two cylinders. Checked it again warm and it was within 10%.

Also:
The actual compression numbers are usually meaningless. An engine can come from the factory with 200 psi compression and now have 140 and be perfectly fine, or, your testing equipment may be off. Unless the compression is extremely low, you usually are looking for differences in compression between cylinders; 10%.

 

As stated above, the separate threaded adapter for the tester you may want to use if the threads are correct? you crank the engine with all spark plugs removed and the tester is in a cylinder, the engine cranks fast but when the cylinder with the tester in it compresses, it makes a different sound while cranking. For example di-di-da. Count that ten times for each cylinder test.

 

So what is the point of counting the compression cycles? I was always taught to crank until the gauge stops reading higher, so I am curious. I've heard of counting how many cranks it takes to build max compression (as this could mean leaks are more present), but never to limit the test to a number of cycles.

I would almost just say use the adapter if one of them fits. Many kits I have used require them as the threaded end that is attached to the gauge is ONLY for connecting those adapters as it is much shallower. Hopefully, OP's problem is not the rings, replacing them is usually a PITA and not worth it. If the rings are just stuck, you might have luck getting them to unstick by soaking the pistons and an Italian Tune-Up.

 

Both, with & without the adapter fit. I will say though that without goes in smoother. This is why I ask.
Now I get the wet/dry difference. I guess i’m now baffled at the misleading info out there. Not that i’m that ignorant to think it doesn’t happen. Just how often I saw that a rise of 20-ish was normal.
Ok. So grain of salt since I am doing this with a cold engine. It’s too bad one of them is number 3 seeing’s how that is the only one I can’t get to without dismantling stuff.
Oh, & I will try to set it up so I can watch it. I had a helper yesterday. Not the case today.

 

Ha-ha! I have put waaaayyyy too much work into the truck over the past couple of years to give up. I mean I can’t say if this will hold true once i’m knee deep in, but for now I must let my sometimes unrealistic hopelessly hopeful do its thing.

 

Just realized what I stated has no bearing. It matters not which one is problemed since they all have to come out anyway. Had a moment is all.... happens....

 

& This sounds so painful to the engine. It makes me cringe. Just had to let that out....

 

I did not mean to imply that you should start drawing conclusions. I merely meant to express my disdain towards replacing the rings. Imagine rebuilding an engine with bad rings and rod bearings only to have the shop improperly wash the block and have the entire thing blow up on the first start-up due to microscopic debris leftover. I have no experience with any Tacoma engine, but I do have quite a bit of experience with Japanese motors. They can be fixed if you have the patience, swapped if you don't. Generally, this can be done in your own garage.

If you didn't have the rough idle, I wouldn't even bother messing with anything and would just run the crap out of it to loosen anything up. Your compression is not terrible on the other cylinders. #3 is the only concern, but since the others are good, there is a chance the rings are just stuck and not worn. If you haven't done this already, try doing the compression test without counting the cranks. Crank it until the gauge hits max and refuses to read any higher. There are a number of things that can cause lower compression, so I would be interested in seeing what maximum the cylinder can reach. Failing that, look up some guides for unsticking piston rings.

The reason why the compression is lower when the piston rings stick is that the engine is made of metal which expands and contracts, and on top of this, the cylinder walls are not perfectly round. The rings create a seal by compressing (like a spring) in and out to combat these slight imperfections. If these rings get "stuck" in a certain position and refuse to move in and out, they will let compression escape to the crankcase. More videos:
https://www.youtube.com/watch?v=Wadmzv1Vs0Q

 

Weirdnesses with my phone. Anyway. The adapter came free from the tester & while I got it unthreaded, it’s still down the shoot & I have no idea where my magnet is. It is a different size from my spark plug socket which is magnetized. Funny, not so funny cuz i’m seriously frustrated, is I did not have to force it to thread in. If that happened I would not have used it.
Anyway, there’s a hold up if anyone is on the edge of their seat just waiting in anticipation....
Kidding. I’m sure all have way better things to do....
Off to find a magnet....

 

Just to clarify why I said to crank it ten times, 1- we have someone doing it that has never done it before (easy way to do it). 2- If you crank the engine until you get your highest reading, this may not be accurate for diagnosis. Just say 4 cylinders get highest compression on three revolutions and 2 others get it at 15 revolutions. There still could be a problem. I was taught that actually you want to see how high the compression is on the first second and third revolution (how fast it comes up to maximum as opposed to maximum. 3- Trying to get a compression reading that is done the same for each cylinder with someone who has not done it before and wants to learn how to fix the truck is in my opinion more beneficial than all the technical data. Other people can help out with that. I believe looking at the spark plugs that it is running very lean. Get the test done, drive it and see how it runs. If the CEL comes on after driving a few days, people will help with that issue.

 

Ok. So way better than yesterday. I think....
2 things I did different. Gas pedal & 10 cranks, not 4.
1-205
2-205
3-215
4-200
5-190
6-190
Why such a huge dif though from 3 & 4 if I did them all the same way yesterday? 4 cranks & no gas?