Effects of difference in compression numbers?

Hello,

I just did a compression check on my 2003 Taco. Apparently the difference should be less than 15psi.
What are the effects of having a difference of more than 15psi between cylinders?
I can't seem to find this info anywhere.

Thank you kindly

 

Usually you’ll get misfire and rough running,What are the numbers you got?

 

Rule of thumb, over 100 and a 10% variance high to low. Say your highest is 120, your lowest then, should be no less than 108ish. This is not set in stone, just a guideline.

 

1: 150
2: 160
3: 170
4: 160
5: 170
6: 175

Engine was cold, battery was not hooked to a charger, also throttle body wasn't opening all the way? and number 1 was tested second to last so...

I am almost 6000 above sea level so numbers seem good minus the variance between cylinder 1 and 6 hence why I am asking if there are any issues with a larger discrepancy.

Originally did the compression test because I got a P0304 code, but after taking out the plugs number 4 was much looser when I started to loosen it vs all the others. I think it was loose and letting oil blow by.

Everything was OG except the plugs so I replaced coils, wires, plugs, PCV (surgery performed after it fell into the engine), cleaned MAF and throttle body.

Started right up and is sounding smooth. Purring like a kitten.

On to replacing much of the front end steering.

 

You're good to go, no worries.

 

The difference should be no more than 20.

Dynaic compression numbers should reflect a difference of no more than 5 psi. Do you have a misfire?

If you are not misfiring now it sounds like you are good to go. Don't worry about it too much for now but remember that next time you have a misfire on the cyl with the lowest compression you found, you will likely be missing on #1 due to poor compression issues.

Proper diagnosis procedures are still in play, however, and if you find a source of misfiring elsewhere then fix that and recheck.

 

Cold start idle was rough and so was reverse. Once it warmed up it was fine. P0304 came on so figured something to do with that cylinder, but as the compression test showed it is within range on that cylinder. Also as mentioned I think there was blow by because of a loose spark plug.
Everything seems to be fine now after one drive.

I am not really asking what my numbers should be, those are all fine as even the 150 is really roughly 176 @ sea level, well above the minimum.

What I am asking is what are the effects of having cylinders with such a difference above 15psi? If all the numbers are above the minimum does it really matter?

 

Mileage ??????



cylinders on any engine rarely fire / wear the same

a good dozen reasons why thats true
1 cylinder each bank ( ghost cylinder ) is affected by harmonics & flow

a leak down test would give U another perspective

save for the 150 cylinder 1.......i see nothing of concern

good luck

 

210,000

 

Yes it matters. If you are at 220 psi on one cylinder and 200 on another, the compression is still high but the variance tolerance threshold is too great which can cause misfires. You are 25 in between variance, but as long as you don't have misfires drive away until the wheels fall off and don't worry too much about it until a misfire emanates again.

 

Cool, so all the variance does is cause misfires?

How does that happen if the compression is good? Isn't a lack of compression taking place because there is a leak in the system some where? So if compression is good, then no leak? Why the misfire?

Hope my posts aren't coming off as argumentative, I am just curious and trying to learn more. I just can't find this info anywhere. People just post their numbers and others chime in and say do a compression/leak down test and this or that could be the cause.

Nothing on what and why the effects are of a large discrepancy in psi are.

 

Valve guides and or pistons ring wear is why you get a loss of compression. They just wear out because the engine is in a state of constant movement and they are critical for compression sealing.

The flip side to that is that carbon can also cause the valves to not seat properly causing a loss in compression. When is the last time you did a "fuel induction" service on your engine? You may benefit from cleaning out your combustion chamber which can in turn up your compression numbers across the board.

 

You talking about some Seafoam? I have not done it as this truck is about a week old to me.

 

Well if you have a tool for it (which I'm sure you don't) it would be WAY more effective to use simple water which essentially "steam cleans" your internals.

I'm sure you would benefit from a few seafoam sessions though.