87 maxima won't start

Hi, I have a headache for 4 days now. Well is about my 87 nissan maxima that died while my wife was dirving. I have checked the ecm codes and replaced a maf and fuel pump. I have also replaced the tps and idle up solenoids. The car ran like it was new and then two weeks ago while I was gone on a trip it shut down on my wife while going home by my block. The battery is brand new and I had the alternator check good. I really need some help. By the way the only code now that pops on the ecm is 44. Again engine cranks but does not want to fire. I also checked the firing on the coil/spark plugs checked good.