On top of my tranny issue, I noticed today that around 3.5K rpm, the truck will flat out fall on it's face under acceleration....and then about 4K, it will speed up without hesitation!!What gives? Bad O2 sensor? Fuel pump? Fuel pressure regulator? I just replaced the fuel filter....so who knows. Does anyone here?

If it's an automatic I wonder if it's not the overdrive in the transmission?

Maybe you should get the codes read on it by someone with a scanner.

Let them take it for a drive and see if the code(s) appear under the conditions you described.

Don't know if it help's but i had a similar problem, i had the tank cleaned, fuel lines cleanned, and nothing. Connected to the workshops computer the air mass measuring unit was fine and the injectors as well. The mechanic told me that the injectors could have some problems that could only be tested outside the engine on a test bank.

just when i was about to do it, he connected his small unit to the truck and took it for a ride. It came out to be a small 25€/$ sensor that was ruined on the top of the gear box, easely accessible from the inside of the truck. it would keep saying to the car that it was on neutral and that would cut the injection momentarily, only between 2500 and 3500 rpm. As this sensor was fine on the thorough test it would give good information, but when he drove the truck, and browsing the sensors pages, he saw that particulary sensor going from 1 to 0 and back when the fuel injection was cut out.

25€ later, (aprox 30 usd), it was fixed.

I own a 2002 manual transmission Nissan Navara, (that's the europe name for the frontier), with an Y25DDTi diesel engine.

Marco

I haven't even begun to look for the diag plug on this, pretty sad for a former Nissan Service Advisor huh?? lol. I'll put forth the effort and try to get a scan done though, wasn't sure about a 97 model anyway.it could be the neutral switch on the tranny, I'm unsure but yesterday, it popped the service engine light on me and NOW, it runs 100% better like the day I picked it up cheap. When I reset the light via the old "undo the neg. battery" trick is when the problem really reared its head.Someone also suggested the TPS so I'm going to look into that as well.Thanks for the information gentlemen!

well now that you have one more symptom this should help narrow the problem down.

Post your findings when you find out more.