low compression in 2&4

[JacksonAuto]

I usually only do a leak down test if my compression numbers are bad and always the leak down test shows the reason why... never has it shown me less than 10% loss after bad compression numbers. It's the reason we do it.

That's not always accurate. I've seen more than a few engines with good compression numbers but horrible leakdown results.

 

[haddixjl]

I ran the compression again last night when I got home from work and it was 75 in 4 and 100 in 2 150 in 3. So its the same numbers from after the leakdown test.
I plan on checking it over again on the weekend there are some issues I want to resolve like the FIAV and maybe check out the EGR or swap it with another. ''

Should I remove the camshafts and run a leakdown? It was a pain trying to keep it on TDC without it spinning the motor over. If the leakdown stays good under 10% or so can it be rings? at that point that should prove the rings and cylinders are fine along with the valve seal. So what after that timing is the only thing right? I would think I could still get decent leak down numbers if the timing was off but the valves were shut

 

[JacksonAuto]

Yes, removing the cams is a sure-fire way of making sure the valves are closed.

If leakdown is acceptable, then that means the rings are fine. Same with the valves and seats.

If leakdown numbers are acceptable then the problem with low compression lies with the timing.

 

[haddixjl]

thats whats confusing I guess, Is if the timing was off it would make sense that it would affect these cylinders as they are paired together.
I need to check the timing again this weekend and make sure its lined up correctly. If it was off in one tooth wouldnt all the compression numbers be low? Thats what brings me back to cam shaft issues or maybe even the incorrect one if that is possible. The guy I got it from wasnt much of a mechanic, the car had about half the bolts back into it.

thanks for all the ideas and input so far its whats keeping me from selling it as is or parting it out

 

[lil corb]

Is it possible the problem Lies with your cam gears? Is it possible the the actual gear marks are off causing it to look correct but the marks are still in fact off? Just an idea, I have heard of dowels falling off before or maybe it's another oem cam gears and the timing marks are off.

 

[haddixjl]

at this point I guess anything could be possible. I think I am going to swap the cams from another motor that is on a parts car that was running fine until the belt broke. So I know the history of it and the gears. I am running a EVO 8 timing belt but I got that from the guy who did the head who is a member here.
I bought the Jay racing timing belt tools and used that to set the cam gears and then set the crank and put the belt on. I rolled it over a few cycles and everything came back to where it should be. The crank mark wasnt 100% perfect but wasnt off a tooth either. I set tension via the VFAQ here with the drill bit and the long rod.

 

[97gsxIA]

That's not always accurate. I've seen more than a few engines with good compression numbers but horrible leakdown results.

But rarely the other way around, correct?

EDIT:

Just saw your post about timing being the cause if variables are the other way around.

I would like to look at this further. Youd think if the timing was off it would effect leakdown percentage too??

 

[haddixjl]

the timing I can see could make sense being that compression test is done while the engine is cranking, for the leakdown I just had it to there the valves were closed and I could see the piston up top and pressurized it while holding the motor with a wrench to keep it from spinning around

 

[97gsxIA]

But, if the timing was off, then the valves would not be sealed when you have them at TDC for the leakdown test causing the leakdown test to show bad results... right?

 

[haddixjl]

I was not positive I was at tdc at the time it looked like it but was hard to tell for sure. I basically got the cams off lift and looked for the piston and pressurized it. So that's what I meant about it being off a little bit

 

[JacksonAuto]

I would like to look at this further. Youd think if the timing was off it would effect leakdown percentage too??

Depends on the position of the cams while the test is being peformed. The timing can still be off by many degrees but the cams will still be on the base circle. This means the valves will be closed and the leakdown numbers are good.

 

[JacksonAuto]

I was not positive I was at tdc at the time it looked like it but was hard to tell for sure. I basically got the cams off lift and looked for the piston and pressurized it. So that's what I meant about it being off a little bit

Just a couple of degrees either way will throw your results off. You either need to find a way to hold the engine from turning or you need to remove the cams. Those are your only two options. Half ass methods produce half ass results.

 

[haddixjl]

I agree. I think first thing will be to check the timing and if that checks fine I'll remove the cams and do the tests over. I plan on measuring the lobes of the current cams and I will compare them to another set. Other than that if it all checks out then I'm not sure.

 

[haddixjl]

Just pulled the cams and re did the leak down test results as follows

Cyl 1 7.5% has 150 lbs compression

Cyl 2 15% has 100 lbs compression

Cyl 3 5% has 150 lbs compression

Cyl 4 6.5% has 75 lbs compression

This is the leakdown results with no cams installed each piston on tdc.

The 15% seems high but that cylinder has higher compression then the worst so I'm not sure what to make of it really any ideas? I did do the compression tests AMD the leak down a few times

These leakdown tests were done with the motor cold as I had to pull it apart. That's the only difference.

 

[haddixjl]

Resolved


So I put a different set of cams and gears in the motor along with different rockers and lifters and the compression came back slowly first in cyl 2 then 4. So what I think happened was bad lifters not letting the valves open all the way and causing low compression. Now I have 175lbs in 4 and still a little lower in 2 at 130 something but I tested them in different conditions. I got 150 on 2 last .

Thanks for all the replies now I need to get my egr figured out