1990 240sx bogging problem

[WESIDE]

Just want to say this site is awesome and full of great information. I have been having this frequent problem for some time now and cant figure it out. I am driving about 75 mph or so and rpms are at about 3500 or so. When I start to go up a grade it will bog like I let my foot of the gas. I get no pedal response until rpms drop to 3000. This also happens sometimes under heavy acceleration, high rpms, in 3rd and fourth gears. I read a topic about a possible chassis ground and will check that out. But I have replaced fuel pump, tps sensor, plugs, wires, cap, rotor, fuel filter, o2 sensor, and more. Can someone please enlighten me. Thanks

[NISTECH]

You need to set up your car with a couple gauges you can see while driving under these conditions, But you also have to take into consideration speed and rev cuts that occur in higher gears. Set up your car with a vaccum gauge teed into a manifold vaccum source as well as a fuel gauge between your filter and the injector rail. See what kinda readings your getting and note your rpm and speed when the bogging comes on. Post your results.

You need to see weather your vaccum begins to build when under the heavy load conditions,this indicates a possible exhuast restriction. The fuel gauge will tell you weather your losing pressure at higher rpms,note though if you build enough vaccum the pressure will drop in the fuel system to around the idle spec of 36 psi as it will open the pressure regulator up.

[WESIDE]

how would I go about testing my mass air flow sensor???

[NISTECH]

with a volt meter, you back probe the wires with it plugged in and the car running, your readings should be battery voltage on one,less then .2v on another, and 1.3 to1.5 volts on the other at idle.

[WESIDE]

Also realized that it bogges in 5th gear going up a grade at 3500 rpms and doesnt come back until it drops to 3000rpms. Also, my odometer and speedometer doesnt work but all my other gauges work if that helps any........

[NismoTypeX]

hey, I had the same problem, It was due to Mass airflow problems. Might want to be 100% sure of the problem first becasue a new one cost like 180$

[WESIDE]

I was talking to a tech tonight and we prett y much ruled out a fuel problem. He suggested that the next step would be a distruibitior or maybe the ecu. any suggestions to tell if any are failing????

[NISTECH]

have you conducted any of the tests in which I recommended you do? You gotta keep focused here and post back some of those test results or I can not help you. I could guess my way through and start telling you to throw parts at your car til one of them fixes it but that could get pretty expensive as nismotypex stated.