Please help me diagnose my compression issue!

[Crazy91GSX]

I picked up a sweet 90 talon for CHEAP because it has a blown engine. Or at least I think it does.. let me run the symptoms by you real quick and see what you think.

When doing a compression test, i noticed that as long as i had either the tester or a spark plug in either cylinder 2 or 3, the unplugged cylinder (2, or 3) would create a huge vacuum and make a loud "suction" sound. Also would not reguster any compression at all! I cranked it over a few times with all four plugs out, and it sounded fine, placed the tester in cylinder 1 or 4, sounded fine and had 130psi compression in each. But, place the tester in cylinder 2 or 3, and the noise comes back. So i put all the plugs back in exept for cylinder 2, and of course, the noise arised.

My conclusion was that it either suffers from a cracked head/block or a busted head gasket. This way, when the air from either 2 or 3 gets compressed, it bleeds into the other and on the downward piston stroke creates the vacuum. Thus why it would not do so when both cylinders were empty - no compression.

the car does have a strong spark, and plenty of fuel pressure. All injectors are firing, and the timing is spot on. The car did get warm though on a long 2nd and 3rd gear pull at 18psi (didnt overheat, just rose above normal)...

What are your thoughts? If you dont mind lending me a guess.


Thanks!
Adam

 

[Big Woo]

From what you have stated it is most likely a head gasket between cylinders #2&#3. Next up would be burning or warping the head again between cylinders 2 & 3. Of course there may be valve sealing issues as well.

In any case you will need to pull the head to identify the exact problem, and repair it.

 

[fourreGsixty3]

I concure with Big Woo. Your next step should be a leak down test to pin point exactly where your problem is, but is does sound as thought the GH is leaking between the comanion cylinders # 2&3. Also your compression at 130psi is below the min tolerence, do a wet test on the cylinders that register compression, and if the compression rises 10+psi during the wet test then your rings are bad and need to be replaced.