Hello, ive got an extensive issue i wanted to bounce off you guys and see if we can make heads or tails of what im dealing with. i have been having issues with my 90 N/A 300zx for sometime now and have just recently got the funds to start work on it again. the issue being, between 1500 rpm and 3000rpm i get severe hesitation and loss of power. so much to the point, it begins to stall, and backfire. once i breach the 3000 rpm mark, it takes off like a bat out of hell. it even seems to idle kinda rough. when i free rev it in neutral, it revs just fine. when i put a load on the engine(drive it), that is when the problem manifests itself. ive recently replaced the injectors, fuel filter, and spark plugs, in an effort to fix the issue. the old injectors were completely shot, the new however all ohm out at between 12 and 13. the injector connectors and coil pack connectors seem to be in pretty rough shape and i can tell need replaced and cleaned. but i figure if that were the problem, it wouldnt free rev as well as it does. am i wrong on that? other than injectors, injector/coil connectors, spark plugs, and coils, all of which are things that can be easily tested. what could it possibly be? Vacuums hoses, TPS, knock sensor, cranks sensor? im just guessing things that are a possibility, from my past experience working on toyota supras and rx7s. any assistance you could render would be greatly appreciated. if there is anything you could think of that commonly goes out on these cars, that might cause this. im all ears. thank you

I would start with the most simple things

-Check ECU codes
-Clean ALL electrical connections (especially crank angle sensor, PTU, MAF, IACV, TPS)
-Clean MAF with MAF cleaner (not carb or brake cleaner)
-Clean TB's

ECU code check
300zx-z32-ecu-diagnostic-t249406.html

Cleaning electrical connectors
http://www.300zxclub.com/showthread.php ... connectors

Thanks for the input. i appreciate your time. i cleaned everything except the MAF sensor and the crank angle sensor, and coated the connectors in dielectric lubricant. it seems to be an intermittent issue now. also when i remove the connectors to the TPS, it does not shut off the engine or anything. all that happens is it seems to idle slightly higher.

I had the same issue a while back with my 90 n/a. It turned out to be the fuel injection dampener, not the pressure regulator but the secondary dampener. The diaphram was shot and fuel was spraying directly into the intake balancer. Rough idle, hesitation, but around 3k rpm it was like a shot of nitrous! Hope this helps...

thanks zmishchief, is there way to test the dampener to see if that is indeed the case? i figure i could just remove the vacuum hose to it from the balance tube while the care is running it would be wet with fuel, if bad. is that incorrect?

This was going on with my car too actually. It really took off like a bat out of hell around 3000. I always assumed it was VVT. Then last week I went over a curb in a parking lot at around 5 mph. I didn't even attempt to slow down because I had no idea it was there until after. After getting out and looking for flat tires or any other obvious damage, I started the car back up and heard a bunch of really nasty rattling so I shut it off. Then I started it up again and everything was fine, except that it no longer seems as hesitant at low RPM's but it doesn't seem to have any sort of extra power at 3000 RPM. Maybe I am just being overly paranoid but it just seems overly slow. I want to keep this thing for a long time so I have been flooring it very, very rarely but it would be nice to know that everything is working properly and the power is still there if I need it. I'm not sure what is causing your problem (or my problem) but that is my experience.