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compression test and then seafoam

S

S2Knott

Hard-core CEG'er
Joined
Jan 29, 2005
Messages
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Location
Sandwich, Massachusetts
ok so i did a compression test today and first noticed that i definetly am running ruch, so my tailpipe AFR has to be wrong, my front 3 plugs which i replaced last week look liked they had been in a car for 20,000 miles.... all carboned up.

anyways, so heres the compression numbers.

Cylinder 1 - 220psi
Cylinder 2 - 230psi
Cylinder 3 - 230psi
Cylinder 4 - 205psi
Cylinder 5 - 210psi
Cylinder 6 - 220psi

now seeing the downwards fluctuation in cylinders 4/5 raises an alarm but i believe they are still in spect, i have zero luck with alldata, the compression numbers were all over the place in this huge grid which made no sense, even my teacher didnt understand it, it said that in spect compression numbers were 175psi to 230psi which i didnt understand that seems way too broad, also alldata, had the incorrect fuel pump relay location, so i pulled the relay it said to and i still had fuel coming in so i to pull all the ones near it until i found which one made the fuel pump not come on..... so with the compression, my teacher said just take the highest psi divide by 10 and then subtract so tecnically,

230 divided by ten is 23 so that would equal, 207 which is 2 psi above the lowest 105psi.

so i need to get some reasurance here, my teacher said it was fine, but i doubt the guy sometimes, not doubt his skills but hes just really old and it just seems like hes not 100% on the ball sometimes.

anyways, i didnt have time to do a leak down test, but i think ill do that later next week.

after school i seafoamed my car again, i had done it a few weeks back but my teacher told me not to shut off my engine so all the stuff just went right through the engine and it smoked for like 10 seconds.

so i got another bottle and this time added it through the main line right by the TB, last time i added it through a vacuum line near the coil pack, anyways, so i cut a water bottle in half so i could see what i was doing, added about half and then wait about 5 minutes and then fired her up! man it was awsome so much smoke, it almost caused several fights actually, i tried to do it away from people but the smoke blew on the few cars and some jackass kids got pissed off, it was quite hilarious actually. i added about half the bottle and then added a bit in the oil fill and the gas tank to see if it did anything.

so about 10 minutes later i left, and gunned it up the road, and looked back to see nothing but blue smoke. so it was apart that oil was coming out the exhuast but the best part was drowning the poor lady behind me in a cloud, she pulled up next to me screaming!! it was great.

anyways, thats my day. throttle response is much better after foaming, but doesnt feel any faster, yet.
 
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While I respect the fact that you're buckling down and making progress on the car, you still really need a tune. That should be your #1 priority...:shrug:
 
the compression numbers dont look so hot on those two cylinders. did you try putting some oil in the spark plug holes?
 
Those compression readings are fine. The rule of thumb is that the lowest and highest should be within 25% of each other. With a high of 230. that would mean that the lowest needs to be above 172.5. Compression readings are seldom completely even.

Now I'll go a step further. Even if the readings do vary more than 25%, it is not a problem unless there is an actual misfire in that cylinder. And the 25% difference is a rule of thumb. If the lowest cylinder is only a few pounds less, but there is a misfire in that cylinder, and there is no other explanation (vacuum leak, plugged injector, ignition problem), you could still have a compression problem with that cylinder.

Also, you really didn't use the cleaner properly. You need to find a way to slow down the cleaner ingestion as well as make sure that you get it into the cylinders evenly. You may have uneven readings because most of the cleaner went into those two cylinders.
 
I knew they could vary, but didn't know that much. I was initially concerned about mine, then found that they could vary by a decent margin. I'm at: 225, 220, 223, 222, 223, 226
 
25%? i always read the lowest shouldn't be more than 10% lower than the highest
so if you have a high or 220,the lowest shouldn't be lower than 198:shrug:
 
tune will be happening within the month.

and i used the seafoam after i did the test, and i did the compression test and didnt have time to do a wet test over again.
 
ive always learned 5% either way with not more that a 10% total difference. i was taught this at many different places. high school, tech school, and an engine building shop.morbids is what you want yours to look like. the first set of numbers kinda threw a red flag but as said before it could be from the cleaner, or if theres no misfire its fine.
 
I guess that I will need to attribute my recollection of 25% to be tribal knowledge. I know that it is the standard I applied during my many years as a tune-up technician.

When I tried to go back to some of my old texts, I can't find anything definitive. I have found 10% to 15%, 10%, 10 0r 15 lbs, and so on.

I agree that even numbers are best. I really like it when I find readings within 5 lbs of each other.

I also know from personal experience, as I said before, that it is only an indication and that it depends on other things as well. You can have a low reading with no other symptoms and so no reason to open the engine to figure out why. You can also have a very slight low reading with other indications and find a burned valve.

I still remember a regular customer that put a lot of miles on his car. He was in twice a year for a tune up. One cylinder, and only one, read about 70 lbs, but the engine ran fine. It cranked smoothly with all the plugs in, had no miss, had good power, etc, so there was never a reason to open up the engine to figure out why.

I have also had engines with what looked like reasonable compression readings with one cylinder only 5 or 10 lbs low but with a miss and uneven cranking with the plugs in. Upon tear down, they had leaky valves in the offending cylinder.

I didn't make up the 25% number. It was commonly taught as I was learning the trade.
 
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