strange sr20det compression problem - Nissan Forum
SR20DE/DET Engines 1991-2002 Silvia

 
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post #1 of 7 Old Apr 25th, 2009, 11:02 PM Thread Starter
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strange sr20det compression problem

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!!!!!

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post #2 of 7 Old Apr 27th, 2009, 09:41 AM
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Try a different compression gauge. Also make sure the throttle valve is fully open when doing the test.

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post #3 of 7 Old Apr 27th, 2009, 11:56 AM Thread Starter
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we did try a diffrent gauge and we also kept the throttle fully open and its all the same.no compression.any other suggestions?
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post #4 of 7 Old Apr 28th, 2009, 07:31 PM
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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.

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post #5 of 7 Old Apr 30th, 2009, 10:15 AM Thread Starter
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what is a leak down test and how do i go about doing this test?thank you for helping me.
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post #6 of 7 Old May 3rd, 2009, 09:29 PM
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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.

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post #7 of 7 Old May 6th, 2018, 02:08 AM
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running rough

Just dropped a sr20 red top (supposedly recently reconditioned) car starts runs and sounds like a car running on 3 cylinders
on investigation cylinder 4 running on low compression
stats
compression test
cylinder 1 = 115psi
cylinder 2 = 125psi
cylinder 3 = 125psi
cylinder 4 = 25 psi wet test 40 psi

Leak down test
No leak from bottom end
No leak from air intake
Can hear and feel a strong leak from the exhaust

?? exhaust valve
I installed the engine using personal experience and on line research.
I still have the good red top head from my old blown big end motor
Question
Will exchanging the heads solve my problem or is the diagnosis more sordid than I thought!
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