not sure how many of you are familiar with the 88 sentras set up for tbi but carb on em but this is what i have.the other day it started running just bad i assumed it needed new plugs and the wires were old so grabed a new set of thoes too. i know i know assumptions are the mother of all f ups.well i get em in start the car same problem feels like its skipping something awful. ok so i yank each plug and make sure im getting fire. ok got fire. check em for fuel smell got fuel. this is the number 1 and 2 cylenders not fireing couting drivers side as 1 passenger side as 4. 1 and 2 both dead. not blowing smoke or anything like that but i deside i hear a kinda clank at certain speeds so figure got to be the valves. so today i rip the head off it (mind you just replaced the head valves ect a year ago less than 12k miles). head looks beautiful well not pristean but it was a junk yard one. but no majior scareing nice and smooth where the seal goes plus gasket looked great when i yanked off the heads. valves are seating properly no cracks in the head valves or the plug area on the head. check the cam and yes the valves are working right and in proper order.ok i think perhaps i heard a rod banging (gulp) nope movement of the pistons is smooth and quiet when i run em by hand at least feels smooth as silk. so i check the intake intake looks fine no obstructions and the carb seems fine too. no obstructions in the exaust either. so here is the question. if my valves timeing fire fuel exaust and pistions are all ok and the head was sealed and not cracked what in the world could make both cylenders die at once and side by side? i could i guess put it back together but seems like a waist to just put it back and try it again till i fnd a problem. but unless the crack is so small i cant see it even after re polishing the head to get a good view and make sure it was smooth. is this possable? i am just at a loss but to re run it down for easier reading.

got two cylenders not working 1 and 2 (1 as drivers side 4 as pass side)

got working fire

got working fuel

timeing is good

got working pistons

got working valves

got working cam

got no scaring on the head and no visable cracks

head was replaced about 11k or 12 miles ago

seals all look good
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why would this happen?

help please
thank you in advance for any ideas.

did you perform a compression test on those cylinders cause your piston rings might be bad if your valves are all good bring it to a shop and have them perform a leak down test and that would be able to tell if you have bad rings or bad valves. well good luck.

+did a compression test was a little low but not that low at the moment i have the head off it and dont remember the reading but was only a few pounds low plus if that was the case from rings wouldnt the car smoke alot? it only smokes a tiny bit under full throttle and not much then at all. like i said this thing is driving me nuts i winder if perhaps the head or the lower case is somehow slightly warped between 1 and 2 that could explane it also possably and not show dmage to the gasket ??? but i would not trust instagasket there and really dont wanna replace the head again the car just is not worth much money hate to spend more in repairs on it than its worth lol.

if you have a leakdown tester that would tell you exactly were its leaking, but if I were you i would take off the head and bring it to a machine shop and have them check to see if the head is warped cause from you told me that sounds like the only thing left that could cause it to run and smoke like that. cause you have no idea what your buying when you buy parts from a salvage yard and possibly the engine that head was on could of overheated and cause that head to warp. well hopefully you dont have to buy another head but it sounds like you do i would search online part stores and find a remanufactured fully assembled head for a resonable price and also check with your local nissan dealer and try and stay away from engine part off of salvage cars cause you dont know what your buying.

was not smoking hardly at all was the wierd thing... but i riped the head off replaced the gaskets. but im with you felt like a warped head or block right between em, so i replaced all the gaskets and added just a very thin and very narrow line of instagasket high temp on the head gasket top and bottom today. not on the metal but between it, where it acctuly touches the head only. slaped it all back together. and bam now its working. now just to get a new computer for my 78 z lol and ill have all my nissans up and going.but on the 88 sentra i am assuming it had to be a very tiny gap between em casueing the valves ot be open or something with blow past at higher temps or something i just dont know.
anyways thanks yall for the help.
if yall ever need a z question answered on 240's though 280zx's let me know i know thoes inside and out lol.
oh one more thing the engine is very loud with valve knocks i have re timed it and readjusted the vales to specs and its still loud. are all sentras loud? and is the breather on the govener on the at trans soposed ot have a vac hose attatched to it or is it only a vent?