20psi steady is fine.
why do you say the car is missing?
what are the exact symptoms you're experiencing?

 

well i shatered a baring in the tranny. so i got more problemes. sorry bout the spelling im tired from working on my car all last night. any way its misfiring, there is alternating pressure, then vac fro m the oil fill cover, bad gas milage, losing water with no leaks that i can find, a lite tinging noise, but it performs fine ove 4.5k rpms.

 

well i got me a nice 1989 240sx 189k miles, power windows, cruse control, manual, runs and drives i got it for a steal at $400 all i need to do to it is front and back windows and clean the fuel system i could if i wanted rebuild the other engine and sell it. so i will have a 1991 240sx and a sohc engine (rebuildable or rebuit, dont know yet, but i could rebuild it) for sale but no tranny unless you feel like the tranny is rebuildable, oh yea and a short shifter.

 

those symptoms don't really point to a misfire.
the alternating pressure and vac in the crankcase should be normal. you see the vacuum in the crank case when the PCV valve opens to relieve the pressure from the crank case.
you are probably losing coolant due to a bad headgasket if you can't find any external leaks.

 

well the alternating press / vac feels like its going with one cylinder, very fast, constant, and goes with the rpm of the engine. so i realy dont know whats going on, and if there is a probleme i would guess it were bad rings sence the car was sitng for 6 years before i got it. but in the the month before i bought it the people that had it drove it once in a while to keep it up and running, as me and my dad were driving away the oil light turned on. so im guessing thay bought it put gas in it and never checked the oil. that may explain the oil ring probleme.

 

the alternating press/vac WILL be fast and of course it will go with the RPM of the engine.
if your compression numbers are good, your rings should be good also.
a steady manifold vacuum reading shows that you have no misfire.

 

well it shure sounds like it, and the car shakes alot at idle. one of the issues i had was a busted o2 sensor, got that taken care of, runs a littel better still misses though. this weekend i pulled 2 (trannsmisions, exhaust manifolds, those pipes that goes from the maniflod to the cat, and drive shafts) and put the good ones on my blue car. also i got the silver car runing good with no miss-fires but its burning oil so im going to rebuild it.

my blue one (the one with all these problems) burns a little oil on cylinder 3 and burns a tinny bit on cylinder 4 (acording to the exhaust manifold) and valves may just need valve job. i had to put 4 heli coils in the head for the rocker arm guides/ shaft, that was a pain. stayed up till 2:30 finallizing the car finaly got to bed at 3:20am

 

yay! i got a droped valve pics soon to come thats whats been wrong! lol oh and cloged water jets in the head. no cooling in the front 2 cylinders. well my engine is all apart and i have another head , valves and all, so im just going to replace the head .