bad computer? 1998 altima

[dirtrider5001]

well im just wondering if anyone has ever seen this? im dont seem to be getting a reference voltage to my crankshaft sensor (with key on). Car runs good for about 10 seconds after starting it from dead cold but quickly starts to run like crap. Ive litterly tested and/or swapped out nearly everything except the pcm.

[ricebike]

what were the trouble codes?

or you were just randomly changing parts hoping to relieve this problem?

[dirtrider5001]

there are no trouble codes!!!!!!!!!!!!!!!!!, sorry i should have said that. cel light does come on when i turn the key to on but goes off when i start the car

[dirtrider5001]

and i think no reference voltage to that sensor is definiatly an indication of something that in non sensor related like a bad pcm or something

[ricebike]

click on the following link to test-verify if you ecu/ ecm is bad:

http://www.nicoclub.com/FSM/Altima/1998/ec.pdf

but you should have got a code P1336 see page EC-331


what else you changed out?

IACV cleaned? as seen on page EC-433

[dirtrider5001]

I DID!!!!!!!!!! I pulled three codes when i bought the car,
po1335
p1336
po100

Well get this i just found out that both of the wires going to the crankshaft positioning sensor are GROUNDS, this cannot be right. So something shorted to ground?
I assumed that the codes were from the previous owner tampering with things.
the codes did not reappear after i cleared them
There was a misplaced spring in the distributor that was causinng it to arc out when i bought the car (it wouldnt even run for more than 5 seconds untill i put the spring in its proper place) thats what i assumed the codes were brought on from.

i ran the car for some time in the driveway and i was unable to get any codes to come on. It really isnt driveable as it had no power so i didnt wanna drive it to try and get codes to come on. THe car runs like its on 3 cylinders but when i pull plugs/injector connections one at a time the power on each cylinder drops equally.

I litterly tested and ohmed every sensor on this frekin car, all come up ok, i swapped out distributor from a sideswiped car in junkyard, swapped mass airflow, checked temp sensor, ect. and today i just swapped the pcm and still im not getting that 5 volt reference, although i did take it out of a car that had 197k miles on it. i just was able to find the wire that goes to the crank pos sensor down by where it plugs into the ecm and i tested it for the 5 volts there and still no reading so im puzzled, thanks for the replys, also i just found out today the car is a 1997 although it has the distributor like the 1998s, it doesnt have that coil pack next to it. also the plugs and wires were replaced by previous owner

[dirtrider5001]

no i didnt mess with the iacv, from the looks of it and the name of it im geuessing this is like a collant operated idle air control?? believe me i was looking at it and wondering about it, i should have grabbed one from the junkyard today as it would be the only sensor on this car that i havent changed out! WHat about the reference signal issue to the crankshaft positioning sensor, why are both wires that go to the crank sensor showing me that they are grounds!? The book tells me that with the key forward that i should have a 5 volt signal.

[ricebike]

for the CKPS, yea the link i gave you on page EC-328 explains it... it generates a V when it spins...

start from the beginning, like a good connection to the battery, grounds, and follow the charts page EC-99

[dirtrider5001]

well i did do quite a few of those test from the link you sent me. There is continuity in both of those wire going to the ckps. The strangest thing though is that both of those wire are grounds as they come out of the computer( i cut the wire down at the computer and tested it and it STILL came up as a ground! when according to the manual the one wire is supposed to have 5 volts!????) I guess its possible that i got another bad computer, its either that or my book is wrong.

[dirtrider5001]

IACV

well i just sprayed all around the intake again and i find no difference in how it runs when i spray. I am now taking a serious look at the iacv. That has got to be the most pain in the ass of an iac ever made! coolant! back of the motor!! im hoping its not gonna be too much of a bear. I unplugged it with the motor running and it did start to run worse like it eventually starts to run if i let it run longer. Im gonna look in the book and see if theres any vacuum test or anything to test it but i dout it. LIke ricebike said they get dirty, well see.

[dirtrider5001]

well my vacuum guage test led me to this. It was not to much fun, it had a bad vacuum leak at the intake manifold right by the iac, everyone on the internet was saying it was by cylinder number 4, well it was cylinder number 1 the opposite so thats why i couldnt find the leak with carb cleaner also everyone was saying to spray it from the top and the leak was on the bottom. im just glad i figured it out i still gotta throw this thing back together ill let every one know how it works out, thanks again for all the great advice!

[dirtrider5001]

you can see where it was leaking right by the iac port, and everyone in the world on google kept saying cylinder 3 and 4, well the iac is on the cylinder closest to the passenger side so i consider that cylinder number 1. whatever