87 Maxima won't rev up
87 Maxima won't rev up
I'm working on an 87 Maxima that will not rev up. It acts like a bad MAF, but I've replaced it and no change. The signal voltage from the MAF to the computer remains constant and doesn't change with airflow. Adding fuel does not help, It is already running rich, but the CHT sensor is OK. It appears to have no spark advance. I've verified the valve timing and initial spark timing, voltage and ground to the MAF. The ECU is not getting 12 volts to pin 18 from the throttle switch at closed throttle. I've tried to adjust it and I can only get 7.5 volts to it. I've tried another throttle switch and it is the same. Someone has been working on this car before me and may have mis-wired the throttle switch. I cannot find a good resource on how the throttle switch gets it's power, but in the wiring schematic, it is somehow hooked up to the the fuel pump relay. I don't want to throw any more parts at this car, but I suspect either a problem in the throttle switch circuit not allowing spark advance or a bad ECU. Can anyone help me with this? Sorry for the long post.
you say the MAF voltage on the signal wire never changes? Even when you snap the throttle? does it pop through the intake when you try to throttle it? How much voltage is available to the MAF? How much voltage drop do you have on the ground to it? and what is the actual signal voltage your getting out of it? I do not have a wiring schematic available to me to look over the circuit or I would.
Thanks for the quick reply. It does backfire through the intake. I have 12 volts on the Y/R wire at the MAF. I have no measurable voltage drops at the ground wires between the MAF and ECU. I also have no measurable voltage drops at any of the ECU grounds. I know that Nissans are very sensitive to ground side voltage drops, but they are all less than .05 volts. I can adjust the CO on the MAF all the way from 1 to 4 volts but the engine runs the same.
I totally agree with you. It has the classic symptoms of a bad MAF. I believe I'm checking the right wire. It is the very end pin on the pigtail and has anywhere between 1-4 volts on it depending on how I adjust the CO screw, but the voltage does not change when you throttle it. It is a reman. unit and it acts the same as the reman. that was on it before. I haven't ruled out the idea that I have two bad units. I've seen many reman. parts that were bad right out of the box. I'm assuming that without the proper voltage sweep from the MAF, that the computer will not advance the timing. I was just wondering if the TPS was causing any of this.
hmmm Its older then I typically work on, I have done a hell of alot of the injector campaigns on them but never have really done any drivability diagnostics on them.They may be wired slightly different. Can you scan your diagram and post it. You can upload it to here http://www.nissaninfiniticlub.....php?
then link it to this thread. That way I have a better visual of the circuit.
then link it to this thread. That way I have a better visual of the circuit.
Well, I figured it out. I was checking the wrong pin. On the pin that I was checking, it had voltage that I could adjust from 1 to 4 volts with the CO adjustment screw, but it never changed when revving the engine. The pin that I needed to be checking was the one next to it. As it turned out, it had 0 volts. I ohmed the harness and it was OK. I ohmed both sides of the connector and it was OK too. Finally, I decided to cut the wire and then I had 2 volts. Although the Nissan flow chart said that the MAF was bad, the ECU was stepping on the voltage and pulling it down to 0 volts. I've ordered an ECU for it and I'm 99.9% confident that it will be fixed. Not one you see every day.