strange sr20det compression problem

240sxjusowned · Apr 25th, 2009, 11:02 PM

i have a strange problem with my car.i just got the sr20det(s14) motor from gs motorsports in irving texas.from a guy named german.he sold me a motor that had 19,000 miles on it. i get back to my town and drop the motor in.i turn it on and it DOES NOT miss fire,blow any type of smoke,burn oil,back fire,hessitate,or act strange.the motor runs perfect like a champ. BUT when we do a compression test it comes out 40,50,40,50. it has super low compression. we just dont get how this motor can run and drive so perfect with no issues but no compression.what could be the cause of this?i really need some help with this one.please help!!!!!

**rogoman** · Apr 27th, 2009, 09:41 AM

Try a different compression gauge. Also make sure the throttle valve is fully open when doing the test.

240sxjusowned · Apr 27th, 2009, 11:56 AM

we did try a diffrent gauge and we also kept the throttle fully open and its all the same.no compression.any other suggestions?

**rogoman** · Apr 28th, 2009, 07:31 PM

It's possible that the motor was assembled incorrectly in that all the ring gaps are all in line instead of being staggered. However it's hard to believe that someone would do this.

Another possibility is that maybe the cam timing is off.

Try doing a leak-down test to find out where you're losing compression.

240sxjusowned · Apr 30th, 2009, 10:15 AM

what is a leak down test and how do i go about doing this test?thank you for helping me.

**rogoman** · May 3rd, 2009, 09:29 PM

A leakdown or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss.

First you need to get a leakdown tester which consists of two hoses, one or two gauges, and a hand valve. To do a leakdown test, fully warm up the motor. Remove the spark plugs. On the cylinder that you're testing, bring the piston up to TDC on the compression stroke. Install one of the hoses into the spark plug hole; The other hose to a high pressure air supply. Apply a certain amount of air pressure by adjusting the hand valve. Watch the gauge which will indicate the percentage of leakage. An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.

The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.