Post by
Mckeeduran »
https://forums.nicoclub.com/mckeeduran-u296057.html
Wed May 06, 2020 12:23 am
Hello!
We have a 1995 Nissan Truck XE, 2WD 4 cylinder. It hasn’t been driven in about a year due to this problem I’m about to explain, so we decided to fix it.
THE PROBLEM-
So- when we start it, RPMS jump to about 2000, fall back down, and never really go above 2000 after that, not when accelerating, pedal to the metal, nothing jumps the RPMs above 2000. It will jump between 1000 and 2000 consistently, like the engine doesn’t get power. However, when we pour gas into the carburetor it runs like a charm, not a problem at all.
WHAT IVE DONE
1) Knowing that when we pour gas into the carburetor ourselves made it run great I thought the air to fuel ratio may be off, so I adjusted the carburetor to no help.
2) From there I thought it may be the fuel filter, so we unhooked the fuse to the pump to relieve pressure, took off the hose to the fuel filter, and gas seemed clean coming out. From there put the fuse back in, kept the hose on, and turned over the truck, gas started spraying with good pressure out of the fuel filter, so I assume it wasn’t the fuel pump.?
3) After starting the truck I realized the check engine light was on, so I took out the passenger seat and checked the ECM codes. First code was code 14, for the speedometer which I knew was out. The second code I got however was code 41, which is for the Intake Air Temperature Sensor. Upon inspecting the IAT sensor I found that the wires leading to the actual sensor hooked in to the air filter had broken off. So, I headed to O’reillys and bought a new IAT, as well as a new air filter.
3) Came home and installed the new IAT sensor and air filter. Fired it up to no help. It actually made it worse. Before hand we could rev it to 2000 rpm, now it wouldn’t pop over 1000 rpm. However, the new IAT sensor made the code coming from the check engine light go away. Now it was just the speedometer code remaining
4) I pulled out my DMM and began checking for voltage going to the wiring harness of the IAT. The power wire tested at about 3 volts (I believe it’s supposed to be around 5?) and the other wire tested great.
5) From there I thought there may be a problem coming from the wiring between the ECM and the IAT, so I disconnected the battery and tested the resistance from the power wire as well as the ground wire, from the ECM side of the wire to the sensor side of the wire, and both tested out perfectly, at about 0.5 ohms each. Both wires graded out perfectly so I assumed the wiring harness to the IAT sensor was not the problem.
6) finally, I thought maybe since it had sat for so long that the gas may be bad, and with the new IAT it may be causing it to run poorly. So, I poured in about 3 gallons of new fresh gas (the old was almost gone), and let it run for about 20 minutes, nothing. I was getting a really strong gas smell so I dialed back the fuel to air ratio and, believe it or not, I was able to get the RPMS all the way up to 5000 and 6000. The catch is, that was only on a slow acceleration, lightly increasing the throttle. Anytime I would try and accelerate quickly it wouldn’t jump past 2000 rpms again. I turned off the truck, put on the air filter again, started the truck up, and back to square one. No matter how slowly I accelerate it won’t exceed 2000 rpms.
WHAT NEXT?
I am not sure where to check next? There’s a number of things going through my head that it could be, so i figured I’d come here for help! I know this was a long post so thanks for taking the time to read, and thanks in advance for any help!