compression check, findings,valve test findings

[sil80forme]

well i did a compression test, on my newly swaped dohc w/ 260k miles, 1st cylinder =165, 2nd= 165, 3rd=170, 4th=170, so i am guessing that is good considering the milage, well anyway i had a lil missfire so i put a dollar against exhaust tip and every so offten the dollar got suked back into the tailpipe, so my conclusion is that either i valve is siezed or bent, anyone have any comments on this, and or how i can fix the problem or diagnose which valve is exactly bad. thanx

[orion::S14]

Seized or bent valve would not give decent compression numbers...I had a valve shim that was .005" too thick (holding the valve open) and had only 50psi in that cylinder.

And the dollar bill thing is an old school trick that does not work well, too many other variable involved.

Did you compression test on a warm motor? Holding the throttle wide open?

And the fact that they are all consistent is good...the PSI is a little lower than normal, but that could be gauge error...or from a cold motor, or improper test.

- Brian

[sil80forme]

thats one thing i didnt do was hold it at WOT, :bash: how whould this effect the results? a friend said it the comp should go up if its at WOT. is this correct? if so my numbers are goin to actually be better, which is suprising since i have so many miles. the car was warmed to op temp soo thas a plus, i guess whenever i get back to school i will do it again and see what happems, now onto the missfire, each cylinder is firein fine, while runnin and missfireing i pull the plug wires and all do the same thing, and make car run on 3 cyl which is good, so i determind from that, which was that a valve is messed up somewhere, so i did the dollar thing which sometimes doesnt work, my next thing to do is a leak down test, but if it was hold comp and comp was good then there really shouldnt be a dramatic loss in psi right? anyone else have any advice to see why my car is missfireing thanx

[orion::S14]

Yes, the number will go up once you hold the throttle open and repeat the test.

As for the misfire...how are the plugs? What kind, what's the gap?

Have you measured the resistance across the plug wires, to see if one is extraordinarily high? How old are the wires? Are they OEM, or aftermarket?

??? - Brian

[s13gonwild]

have you checked timing? cap and rotor,spark plug gaping,spark plugs codition? my car backfire like a mofo when its just at idle...its my #4 plug the thread on the head is striped..so the plug doesnt go all the way in..so it stutters alot at idle...runs fine tho :) dont intend to fix it hehe

[sil80forme]

spark plugs are from i had ka-t on this motor, NGK-bkr7's stock gap, cap is new, resistence on wires are good also, the wires are aftermarket and fairly new, i am thinkin bout goin to get new plugs but not sure what i should get considering i am NA now, timing is at from 18-20 doesnt stay on the 20 line but never goes past 18 or so, so thas bout it does this help any for your diagnosis? and what should i get for plugs, these plugs are all black around the edges from when i was ka-t it was real rich for the first few times i started it! thanx

[sil80forme]

BUMP: anyone? ive been searchin since i posted and found of course nuthin WTF

[sil80forme]

well i just went out and got some new NGK bkr5's .044 gap so i hope this will help it out if not i dunno what to do :bash: :wtc:
the car runs great got lots of power but the whole missfire while at idle is very anoying. :wtf: :bash: the fact that i cant figure out whats wrong is just plan pissin me off :confused:

[sil80forme]

oh WTF I an starting to dislike my car very much, someone make and offer, i might sell it

[sr240mike]

Have you tried pulling any codes from the ecu yet? Test the coolant temp sensor resistance, and o2 sensor condition too.

[sil80forme]

so i dont know how to and i dont have a fsm, soo, also its a new o2 sensor and temp sensor works and is good, cause it was new when i did the ka-t, so i guess i willtry and figure out how to do the codes and when its not raining will try. thanx

[papershot]

http://www.zilvia.net/f/showthread.php?t=10007

[sil80forme]

ok thanx but that link makes no sense to me, i ended up finding it on 240sx.org, will post codes sooon