#4 won't fire after warming up

[doctorj240]

I recently put a s13 engine into my s14, swapped all sensors from s14 engine to s13. She started up fine, set the timing ~18 btdc. After she warmed up I noticed that the EGT (probe is in runner 4) dropped basically to zero. The idle also got very rough, which led me to believe that it wasn't firing. This is a gradual thing that happpens every time I start up. I also checked compression. I got 150-150-150-120. So something is definitely wrong. The headgasket has about 50 miles on it. Everything else to my knowledge has 120k. I just want to know why the idle goes from great to crap after a couple minutes. I really don't have a good guess.

[NISTECH]

The EGT dropping to zero indicates your EGR is flowing. At idle it should not flow. My best guess is your vaccum lines are routed incorrectly giving EGR vaccum at idle. The BPT should prevent that. Go over your vaccum routing closely.

[NISTECH]

note though this will have 0 effect on compression.

[doctorj240]

Could this be a valve lash clearance issue?

[C-Kwik]

If your compression tester has a quick connect connector, you should be able to connect a compressor to it directly. Pressurize your #4 cylinder at TDC on the power stroke and you should be able to hear where you are losing compression. I'd put the car in 5th gear and set the parking brake while doing this as it can drive the piston down. You don't need to use a whole lot of pressure either. 50-70 psi should be sufficient.

If you hear air out of the intake at the filter, your intake valves are leaking. If you hear it at the tailpipe, your exhaust valves. If bubbles are coming out ot he radiator nozzle, it;s likely a head gasket issue. If the air is coming out of the oil filler cap, it may be your rings or a head gasket problem.

[Q45tech]

Running compression test vs cranking compressionhttp://www.misterfixit.com/dyncompr.htm

Some interesting reads:http://www.misterfixit.com/autorepr.htm

[doctorj240]

Sent it to the dealer today. Bore scope didn't reveal any scuffed cylinder walls. Leakdown test showed that the problem is most likely in the valves and they also said its about a 20 hour job to inspect the head. So, I don't think I'm going to spend $1500 on it right now.