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Low compression

5K views 25 replies 5 participants last post by  Battlez2rr 
#1 ·
Hi all,

  • I performed a compression test a few weeks ago and found that cylinder 3 tested out at 115. When I added about 3mL of oil and retested 2 different times with pretty long cranks, it never got above 120. This leaves me too believe there is an issue on the top end. I've started to take the head off. I am currently working on the intake side and have noticed a decent amount of oil that has built up in the intake plenums. The Y plenum actually had a slight little pool of oil where it connects to the mid plenum. Should I now consider an issue with three bottom end too? Also, while in tearing this apart, what extra stuff can I take off the car that won't throw a CEL or is something I can easily spoof? For context, I am hoping to use the car rarely on the street, and mostly for some track duty. Adding a couple pics of the plenum below? Also, any tips on general for taking the head off, and what I should replace? Thanks in advance!
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#2 ·
I had one cylinder as low as yours when i did my compression test after my head rebuild(bent valves previously). but the next morning i tried it again after i recharged the battery + reconnected the fittings for the tester and got 175 psi on that cylinder(while cold, engine was out of the vehicle). Cant hurt to recheck again with a recharged battery.

try a leakdown test if you have one available.

also if you do end up committing with taking the head off: new head gasket, arp head studs since oem head bolts are torque to yield(one time use), cam seals, valve cover gaskets
 
#4 ·
  1. Thanks for the suggestion, however I compression tested other cylinders after testing cylinder 3 twice (once with oil), and cylinders 4, 5, and 6 got up to 175, 175, and 181 respectively. I ended up retesting cylinder 3 again with oil the next day and it still maxed out at 120 which was the longest crank of all cylinders and the crank still sounded pretty healthy from a battery perspective.

    Thank you for the other recommendations! Do you have any recommendations about the process of pulling the head off, or any other recommendations of things that I can remove from the engine bay area that will make it easier to maintain\clean it up. I am thinking of doing the following: removing the ACIS contraption in the pic above, EGR blockoff plates, and possibly removing some of the EVAP stuff, but I am not exactly sure what I can do there without throwing CELs.



  2. I had one cylinder as low as yours when i did my compression test after my head rebuild(bent valves previously). but the next morning i tried it again after i recharged the battery + reconnected the fittings for the tester and got 175 psi on that cylinder(while cold, engine was out of the vehicle). Cant hurt to recheck again with a recharged battery.

    try a leakdown test if you have one available.

    also if you do end up committing with taking the head off: new head gasket, arp head studs since oem head bolts are torque to yield(one time use), cam seals, valve cover gaskets
 
#12 ·
I had one cylinder as low as yours when i did my compression test after my head rebuild(bent valves previously). but the next morning i tried it again after i recharged the battery + reconnected the fittings for the tester and got 175 psi on that cylinder(while cold, engine was out of the vehicle). Cant hurt to recheck again with a recharged battery.

try a leakdown test if you have one available.

also if you do end up committing with taking the head off: new head gasket, arp head studs since oem head bolts are torque to yield(one time use), cam seals, valve cover gaskets
Ok, running a leak down test. Did I do something wrong, or are the exhaust valves that bad?

 
#3 ·
The Y plenum actually had a slight little pool of oil where it connects to the mid plenum.
I would attribute some of this since the engine system has the PCV Valve. If you're not familiar with it, it takes excess engine oil and fuel that gets into the crankcase and filters it back up into the intake manifold to be burned off.

Ever since I installed an oil catch can (I have one of the cheap ones), I've noticed all that excess oil and fuel is being caught.
 
#5 ·
I would attribute some of this since the engine system has the PCV Valve. If you're not familiar with it, it takes excess engine oil and fuel that gets into the crankcase and filters it back up into the intake manifold to be burned off.

Ever since I installed an oil catch can (I have one of the cheap ones), I've noticed all that excess oil and fuel is being caught.
Thanks! I was thinking about that too, it just seemed like a lot. After thinking about it a bit more, I am wondering if it is possible that the oil I put in cylinder 3 for the wet compression test ended up pushing up through the PCV and back into the intake?

What brand oil catch can did you go with?
 
#14 ·
I did go back and forth multiple times trying to find tdc; what a pita! However, if you see here, the cam lobes for cylinder 3 are up, so they should be closed and sealed, right? I could easily feel air rushing out. I eventually took out the tester because it was showing 100% loss and I couldn't understand how that was possible. Eventually ran it directly off the compressor so I could hear it better.

Theoretically, could I run the test with the Piston anywhere in the combustion stroke too, right?
 
#15 ·
I did go back and forth multiple times trying to find tdc; what a pita! However, if you see here, the cam lobes for cylinder 3 are up, so they should be closed and sealed, right? I could easily feel air rushing out. I eventually took out the tester because it was showing 100% loss and I couldn't understand how that was possible. Eventually ran it directly off the compressor so I could hear it better.

Theoretically, could I run the test with the Piston anywhere in the combustion stroke too, right?
If both lobes are up. Then you may have a bent valve or one stuck. Did it happen all of a sudden?
 
#18 ·
Stainless under cut valves would be good for an upgrade. As for seals just good quality. No tricks to the intake. As for cams. That would be all you. You know what you are doing with the car in the future. If doing cams, remember to do springs and do the correct lash.
 
#21 ·
It's a weekend driver with occasional road track, and auto cross events. I'd like to get some more power out of the engine while I have all this stuff apart, if the price/gain is reasonable. I'll consider boosting it in the future, but I should really spend a little more time getting the suspension/brakes improved first. Thanks for your help!
 
#24 ·
I used oem head gasket and all oem seals besides the valve seals which were supertech brand. 1200 miles since my rebuild and no leaks so far. if you can get the oem part number and shop around online between lexus and toyota dealerships websites + ebay + amazon you can generally find some good deals on oem gaskets and seals.

Im sure felpro gaskets would work fine as well. i've used them in the past on my other cars, i just like the thought of having oem stuff.
 
#26 ·
Thanks all! I used to work at a shop and we used felpro all the time. Just wanted to check with some experienced 2jz owners to see if there was anything special. Any of you running bc 264s? If so, are you happy with them? I'm getting the itch to pick some up since the head is over at the machine shop and they are going to fix the valve clearance/lash anyways. On that note, anyone running an adjustable exhaust cam?
 
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