1991 D21 Gutless Highway Hill Climbing

[ManzanoNissan]

Seems when I search online about losing power going up hill, the D21 has a few entries that have cause people problems, I'm one of them.
I've got the 4 cylinder 2.4l and I cannot maintain highway speeds climbing steep hills. Dropping to fourth and pinning it to the floor, I still lose RPM and speed if it's a long grade or steep.

I've changed out the belts, the air filter, fuel filter. Spark plugs, spark plug wires, coil. Removed the old O2 sensor that wasn't even connected any longer and reconnected that to a new one.
I can see the throttle body has no problems opening all the way and the gas pedal opens the throttle body all the way. It's dirtier then original sin but it opens all the way.

So I'm just stumped at this point. She idle's fine, no issue's at all.

[mdmellott]

My guess is a cylinder compression test may show you the root cause of this issue. My old '91 Pathfinder had the same issue on long uphill grades and steep climbs. Although I wasn't burning oil due to worn out piston rings, I had poor compression because of the worn out rings. Under load, my old Pathfinder's get up and go, got up and went years before it was finally retired.

[ManzanoNissan]

Ugh. That's one thing I just can't fix. I suppose if I had the inclination to want to bore out cylinders and put in new pistons and rings....but on a 2.4l ? I mean....cool job if you're working a 455 or a 350 or ... about anything other than a 2.4l 4 cylinder.

I'll go ahead with the IAT sensor replacement recommendation from the other post and then a compression test. If she's bad ... screw it. I'll drive her until she's done. Maybe toss another 4 in.