ok i have a big problem i hope someone can help.
about a week ago my mom picked me up from college in my 1990 maxima. we drove home on the highway the car ran great no problems, but when i started it later to go to work it ran horrible the noise comming from the exhaust (which also is shot) sounded like the engine was missing, carbon smoke also came form the exhaust pipe (the first 2 times i tried it it doesnt smoke anymore). i opened the hood and the engine seemed to be shaking, not viloently but more than usual and it sounded as if it werent getting a steady flow of feul it would rev then die then rev then die.... my friend looked at it today and said my intake manifold is probablly cracked because u can smell gas int he hood outside the car and when you turn the heat on.

I'm not sure weither this is the real problem if anyone thinks it might be something else, please tell me.

i also told my girlfriends father about it he said with an engine with the miles i have (93000) it was either abused which i doubt it was a one owner female before me, and i only put 7000 on it) ot it is a bad engine. he said id be better of changin the whole engine if its thew manifold because more and more htings will just go wrong. my questions about this are, do you think it would be worth replacing the whole engien, and if so can i put a 4th gen v6 3000 in or is it too much of a hassel to do so, or impossible..

please give me imput keep in mind i dont make very much money so if you could offer the most cost effective way to approach the situation it would be appreciated.

thanks in advance

 

heres my take on it..
fuel smell in your case could be two things...

1. your underhood fuel lines are cracked. this is no big prob since the cracks are hairline and only really open up when cold its an easy fix, just replace the two underhood fuel lines and no more smell

2. the smell could also be a fuel leak at the injector. I say this because the other symptoms you described, backfiring, almost stalling w/o pressing gas kinda relate to that. is there any fuel coming out the exhaust?

also you might just have a bad injector(s).
you might wanna measure the OHM of the injectors to check that out

thats ny best shot at it...IMO intake manifold crack would be more pronounced by a high pitched leak "whine" when the car is running

 

no feul leaks in the car as far as i noticed, i would agree however that it is a feul prolem, it looked like dark grey borferline black smoke comming out of my exhaust when it did, which people have told me can signify burning gas, and smells like gas too.

 

yeah then I'm gonna say you have a leaky injector(s)...thats my guess.