Please help, I was doing a compression test on a vehicle I just bought and I am experiencing low compression in all cylinders, 110 and then in the middle cylinder on the driver side there is absolutely 0 compression.
One thing that has me extra scared is when I was taking the spark plug out of that cylinder I acidentily hit the posititve cable on the battery and it caused a pretty decent spark. Please help me I have no idea what I did and am extremely scared now.

Also to note it was running 100% fine, no cel or anything before I tried to do the compression test. Also does it matter if it is due fpr an oil change ? The shop put in synthetic and I want to switch back to normal, would this be why the cylinders are low?

id say oil was not changed the greatest on this vehicle. Piston rings could be stuck. you can do a wet test (pour a small table spoon or 2 amount of oil down the plug then do another test to see if they come up) that will tell you if its rings.

Id say bent valve on the cyl that has 0 compression. maybe but pretty rare hole in the piston.

do a wet test on the pistons.

Also pour a another bit of marvel mystery oil down the cyl and let the oil soak in the rings to help free them up. and let that sit for a day, crank the motor and set another day.

after the vehicle is up and running again you can do a sea foam in the intake, gas tank and oil.

Lets see what others have to say as well as your wet compression test numbers.

So I didn't mess anything up with the spark that occurred when o was taking the spark plug out?

Is the car running fine? If you have super low compression and one with zero it would not run that well. I would be missing, hard to start, very low on power. Are you sure you did the test correctly?

Now I started it, got a check engine light , pulled the code with my ultraguage and it's p1300 . I never had this before I did the compression test . What did I do ?

Well now just started it and no cel, everything seems to be completely fine. One thing I did notice was the wheels were tough to turn when not moving? Maybe from not enough power to them yet ? Idk

Yarr your wheeling bearing is probably going bad and that caused you to have 0 compression in CYL 02. (Sarcasm)

I would just suggestion you don't mess with your working engine anymore unless there is a good reason.

Is that a 4-cylinder or a 6? How many miles?

Here's why I ask:

In my experience with a 135k 4-cylinder 2RZ in my Tacoma and a 195k 4-cylinder 3RZ in a 4Runner (they're essentially the same engines) at about 120k the exhaust valves begin to lose clearance and must be checked and re-shimmed every 20-30k after that.

I've examined four of the 6-cylinder, 5VZ-FE engines with 150-250k and valve clearances seem to be largely unchanging in those engines. My guess is that Toyota specified a higher quality exhaust valve in those engines. Good thing : the driver side bank requires a lot of surgery to access. You wouldn't want to do an examination every 30k.

Thus, a 4-cylinder may have a tight valve - zero clearance - and this could be the cause of no compression on your engine.

Also in my experience, mechanics may apply what they've seen regarding valve clearance on the V6, i.e. unchanging even at high mileage, and applied that same logic to the 4, without a proper examination. More than a few mechanics - and shops - don't like to mess with shim-type valve adjustment. Likely because customers are shocked at the cost.

it's a 6 cylinder with almost 160k, I'm thinking I did the test wrong, I know they say to do it on a warm engine but how are you supposed to get all 6 plugs out before it goes cold? So would that be a reason my numbers are low ? I've also read that gauges range and as long as they are all close to each other they are good. But with one reading 0 I'm confused because something would be wrong when operating normally that I would notice if one cylinder wasn't getting compression. I think I'm going to take it to a shop tomorrow and get them to do a dry and wet test so I can know for sure.

I have to ask why you didn't perform a compression test on the 4runner before buying it. At least you would have had much more leverage to haggle the owner over the asking price.

If there was zero psi in cylinder #2 I would assume you would have a misfire, CEL for code P302 and possibly P300.

Once both the wet and dry compression tests are performed, and if the numbers for cylinder two are still sketchy, then have the garage perform a leak down test or use a scanner to see if all cylinders are firing.

That's why I'm confused as to why I got 0 in just that one cylinder, everything seems to be working completley fine. I guess I'm going to have a shop do a compression test and I'll ask about a leakage test then see where it goes from there. I really wanted to supercharger but now that's looking out of line

So should I chalk it up to me just doing the compression test wrong since all cylinders were reading low, and the one wasn't ever reading at all. Or should I be seriously concerned ?

Spot on. I just opened up my 192k 4Runner with the V6 (5VZ-FE) and literally every valve was perfect. As in middle of the road FSM perfect. I love this engine.

The 3.0L 3VZ-E engine? Terrible. Some Toyota dealers refused to adjust the valves because it's so difficult to access and an absolute pain to do.

As one who has owned a vehicle with very poor compression, (before mentioned 3VZ-E), you should have the following if you really do have 0 compression:

1. The engine would shake violently from side to side at idle. Like it's about to fall off the engine mounts violent.

2. You would have a terrible vibration in the cab at low RPMs (under 1000).

3. You would have terrible acceleration until about 2000-3000 RPMS.

If this is not the case, I would agree that yes either the test was done wrong or your gauge is faulty. The Harbor Freight ones are known to be faulty, sometimes right out of the box.

If you want to have it done at your mechanic's shop for peace of mind then by all means please do. My shop has done it for free for me before since they know I try and work on my vehicles myself when I can. But it doesn't really sound like you have 0 compression or low compression on any of your cylinders.

I'm all for learning how to work on your own vehicles, but be careful you don't take on more than you can handle! BTW the positive side of your battery should have a red cover that goes over the terminal so you don't accidentally short out something like what happened to you.

Thank you, I got the gauge as a rental from auto zone so I think it may be faulty. But this still does not explain why one cylinder has 0 compression. I think I may just take it to a shop, get them to do a compressuon test and if they find what I found( I'm praying I did the test wrong) I will have them do compression test and a leak down test if need be.
And no from what I notice it runs completely normal and no rough idle or bad acceleration.
And as far as the battery, I have extra connections to the terminal so the cover does not shut fully.

Thank you so much !