1993 Nissan Truck RPM faulters at 2700 RPM


Engine Performance problem
1993 Nissan Truck 4 cyl Four Wheel Drive Manual 125000 miles

My truck starts and runs fine up to about 2700 rpm. It then falters back to 2000 and after releasing the gas pedal and reapplying it will go back to 2700. I have changed fuel filter, check fuel pump pressure, tested with an ohm meter the throttle position and mass air flow. I have installed new complete distributor and coil assemblies. I have added gas through the air intake and checked exhaust flow. Nothing has changed the rpm problem. I live 70 miles from the nearest Nissan dealer. My local mechanic shop is stumped also.
Update on 93 2.4L 4x4: I got my truck back and tried to drive it home. 2 miles or so. Under load the rpm will only get up to 1300 rpm. It does not backfire yet does make a popping noise as if the fuel is not adequate. While checking the fuel pressure I noticed the fuel pressure went up slightly when I got to 2700 rpm just as it would falter. It will still get to 2700 rpm in the driveway. My mechanic thinks the fuel one of the injector drivers in the computer may be bad. But will any replacement Nissan computer work and does it have to be programmed for my truck and engine? The mechanic said the lights (one red and one green) on the computer did seem to work properly and give the correct error codes. Where can I find out how to get and read these codes? I haven't found a source for a good Nissan truck repair manual. Any help is appreciated. GGann

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Wednesday, February 20th, 2008 AT 10:21 PM

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I still have a problem with my 2.4L but it is now worse. I coudn't get an error diagnostic code but it would start and get to 2700 rpm then fall back to 2000 and try to rev up again. I disconnected the 0-2 sensor to see if that code would show up. Now the thing tries but won't start and run. I added gas down the intake and still it tries but wouldn't keep running. Now this is scary, I pulled all of the injector connectors and tried it. I ran for almost a minute. This tells me the injectors are suppling too much gas and the engine RPM falls down. There must be sensor that tells the ECU that the mixture is too lean and to increase the gas supply. I haven't found out which sensor that is but this could be the original RPM problem. Too much gas will cause the engine RPM to decrease. If I find out I will let you know.

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Tuesday, March 11th, 2008 AT 11:10 PM

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