1994 Nissan Maxima GXE with S.O.H.C. engine that is completley stock with 221,000 miles on it. The car was purchased over a year ago and has ran great until 1 month ago. The car ran very rough and the check engine light came on. I ran the code on the ECM which came back as a code 51 - fuel injector circuit signal fault. I checked the wiring harness coming from the ecm to the injectors with a NOID light tester and found no problems with the harness. I did locate a bad injector on the # 5 cyclinder which I replaced. Drove the car for another 3 weeks and the # 1 injector went out which I replaced. Drove the car for about 4 days & the # 6 injector went out so I replaced all of them. Now the car runs smooth for about 15 to 30 min. At idle the car is running very rough but has no engine light at this time. I replaced the plugs, wires, cap, rotor button, pcv, water pump, timing belt & fuel filter 1 year ago. I removed the catalytic conveter to see if it was stopped up but no change. I ran a fuel pressure gauge in line past the filter to the injectors and got good fuel pressure from 38 psi @ idle up to 50 psi while driving.The car runs good while it is cold but after driving it for awhile it is has to be cranked several times before it will start again and runs/idles rough with no power on the low end. Could this be a TPS, MAF, Coolant temp. sensor or what.....??????

Had the same stupid problem on my 93 GXE! Replaced pretty much the entire top of the motor trying to fix it. The engine NEVER showed a code or had ANY of the warning lights come on, but ran like it was missing. Replaced pretty much the entire top of the motor trying to fix it. It was the voltage regulator on the alternator! Seems as though the alternators for these particular cars are not built very well. Replaced the alternator and have not had the problem since. GOOD LUCK!

O.K. this morning I checked the voltage on the battery posts with the engine off the meter displayed 12.38 volts. I started the car & it immediatly began running rough. I checked the voltage again on the battery with the car running & the meter read 14.20 to 14.70 volts depending on engine rpm. I disconnected the alternator wire and the voltage obviously dropped but the car still ran rough so I think that rules out the voltage regulator. It is now starting to emit alot of grey smoke which tells me it is running rich. I have'nt checked the TPS, sensor or MAF sesnor but I would think it would throw a code and I still do not have any codes on the ECM ????????????????

I have a 92 se with pretty much the same symptoms, had the car 2 months and have replaced air and fuel filter, plugs, temp sensor, ran sea foam twice which made it run erratically on that tank, then better than before. No codes, also replaced O2 sensor. Have seen the gray smoke you talk about, only after idling for extended period. Suspected dirty/bad fuel injector, used sea foam. Seemed to eliminate the smoking, but the idle is still rough, and it still runs erratically as it did originally. I am leaning towards the knock sensor being the culprit..... I am not sure if your tests on alternator would conclusively rule out a bad regulator, and if your battery or any other connections in line were faulty the ecu might flip out. From what I am seeing online the ecu is not reliable at sensing faults. Good luck, I would be interested to know the solution!!

Alright , I replaced the TPS & coolant temp sensor since both of these ohmed out a little higher than they should have but were not open....still no change. I allowed the car to warm completely and checked the primary & secondary ohm readings of the coil for the distributor. My readings were way off base so I replaced the coil but still no change. Now another injector has went down again on the # 3 cylinder.I replaced the injector but still no change again !!!. I ohmed out the 02 sensor which checked fine. I ohmed out the power transistor and it checked bad. The parts store will have one at 2:30 today. Just wanting to know if anyone else has had this problem ??? I will update this post if this fixes the problem ?

My 94 Maxima with 230,000 miles has had this problem on three seperate ocassions. I am not sure if each one was related as the problems arose several months or a couple years apart. This is how I fixed them, in order in which they occurred.

My mechanic recommended I replace the MAF sensor (about 1.5 years ago). Instead I took it out and cleaned it out with throttle body cleaner, very carefully and thoroughly. I read somewhere that electrical cleaner is recommend. Have not had to replace it since and I have passed two smog tests.

A year later I again took it to the mechanic and he replaced the ignition wires; I know I should have done this myself. You live and learn. Fixed the problem for the time being.

About four months ago the idle problem reared its ugly head again. I read the trouble codes it had to do with the injectors. Now three years ago a mechanic told me that my injectors may be going out soon so this did not surprise me. I took all the injectors out and sent them to Bill at http://www.mrinjector.us/. He rebuilt them all and replaced two bad ones (free as he had two cores laying around) for under $100. The car runs great. I would strongly recommend this on any car with high miles. He will send you a printout of the injector flow before and after. My good injectors where not flowing to bad, however, they now flow like new.

What I discovered in the process was that my Maxima has more vacuum lines than any other car I have owned. I replaced many lines a few months back, but I discovered that I had missed good number of them hiding under the 3 piece intake and under other wires, etc. I have thrown in engine treatment and other engine cleaners. My gas mileage has been increasing and is currently around 26 mpg. Not bad as my driving habits vary greatly. Good luck.