Cylinder Compression - Help to read results

[Jan Larsson]

So got a brand new compression tester directly from the US, works well and not too bad to get to all cylinders ....

Ok, so warmed the engine, disconnected cam sensor, pulled all plugs, opened the trhottle fully and removed up pipe. Cranked engine about 5 times for each test, tested each cylinder twice.

Results

1 - 116 and 116 PSI
2 - 115 and 115 PSI
3 - 116 and 115 PSI
4 - 114 and 115 PSI
5 - 96 and 90 PSI (this was the last one I tested so battery might be slightly worse on this one but does not look good right?)
6 - 136 and 135 PSI (this is the cylinder where I had a leaking injector so guess this indicates carbon build up?)

Would the above readings be correct, I had to let the engine cool down a bit before I could connect the compression tester as it's very tight down there as you all know.

Cylinder 6 is where I had the leaking injector

Cylinder 5 does not look good .....

Comments and suggestions please.

I also ordered a leak down tester but wont have it until end of next week with some luck, got it from the US as well.

 

[87GNSteve]

How many miles on the car?

...and you have a PM

 

[Jan Larsson]

The car got 103k miles on it, Engine since a complete rebuild probabrly about 50k but since then there's been a few bits replaced like cam, lifters, valve springs etc

Previous owners been doing engine work on and off and I have no complete record of exactly whats been done, this is what I know was done at about 50k miles:
Forged Pistons, Polish Rods, Ported and Polished heads, Cam, Valve Spings, High Volume Oil Pump

And at about 80k miles the cam, lifters, valve springs been changed again ...

 

[72firebird]

well since you've changed the pistons and the heads have been ported I'm going to guess your compression has changed. But by comparing the cylinders against each other I'm going to guess you're right on cylinder 6, you might want to try and run some top engine cleaner throug it to maybe clear it all out. As for cylinder #5 it's a little too low, typically you want all your cylinders within 10% of each other. Once you get a leak down tester you might be able to find a little more out about it.

 

[Jan Larsson]

What top engine cleaner are you guys using? I can't get the GM one over here, is there a STP or other brand anyone can recommend using that I might find on this side of the pond?

I can't confirm if the pistons been changed or not as I have no old receipts showing this only go on what I was told by the previouse owner.

Otherwise would the compression be normal in the other cylinders?

 

[72firebird]

I would suggest like Techron I think is what it's called. It may not help you out too much, but it'll help clean out any carbon or anything in the combusiton chamber.

 

[zerotta]

What top engine cleaner are you guys using? I can't get the GM one over here, is there a STP or other brand anyone can recommend using that I might find on this side of the pond?

...

Seafoam makes a TEC just as good as GM's.

http://www.seafoamsales.com/

 

[j13smiley]

yes - if you want to use a TEC - i'd recommend seafoam.

 

[72firebird]

I wouldn't suggest using Seafoam, for the pure fact that it claims to do everything. There is no way that you can create a product that will efficiently do everything that it claims it'll do, and do it correctly. I would just prefer to use a product that was specifically made for the task that you're performing, that you can trust will do the job well, and correctly.

 

[Jan Larsson]

I rather use something made for the purpose.

Big problems to find something like it in this country, engine flush (to put in your engine) there's plenty of otherwise all you find is injector cleaner which you pour in the fuel tank ... I spoke to one Corvette dealer over here and they use the injector cleaner they told me, would this work the same as the top end cleaner you guys think?