1996 Nissan 300zx NA (won't accelerate past 2k rpm)

[07mike07]

I'm all outta ideas, I've been doing a lot of research and no one seems to have to exact issue I'm having. I have a 1996 Nissan 300zx NA manual and when I first got it the car was great, it drove strong and idled almost perfectly. About a month ago it started to have an issue where while accelerating it would cut out at 2k rpms and backfire really bad until about 1k rpms and it would let me accelerate again, I can only go about 40mph if I balance out the throttle around 1.9k rpm. I have no clue what's wrong with it and I really don't wanna have to end up selling the car. I've tried everything from replacing the MAF and testing it, along with replacing the TPS and testing it, I pulled the ECU and checked the codes and the only code the consistently pops up is a code for the fuel temp, but I've had that code since I've got the car. If anyone could help it would be much appreciated.

[VStar650CL]

That sounds like maybe a bad CAS. If the optical wheel gets crudded up or is tilting due to a mechanical issue, it will often read okay at low RPM's but go completely bonkers when the RPM's rise and the signal speeds up. The ECM kind of has to trust the signal, the firmware isn't very good at detecting a signal that's lying as opposed to flatlined. You could also have something simpler wrong in the ignition, like a coil with bad insulation, a dying power transistor, or just crappy PT grounds.

[07mike07]

Ok thanks, I'll check the CAS again. Last time I checked it, I loosened up the 3 bolts and it was barely able to move freely, I had to tap it with a flat head and hammer to get it to spin slightly. I have no clue if it's supposed to be like that as this is my first time dealing with a CAS system. All the cool packs and fuel injectors are new, and I tested them before I put them in and they all tested good. I'm also going to check all the grounds.

[07mike07]

Also, I forgot to mention, I hooked up a scanner to the vehicle to see if I can spot any noticable things when I look at the live data as the car is running and at idle the spark ADV sits at 10* and as I accelerate it goes up. Until it hits the 2k rpm range as I mentioned and shoots to 63* and sits at 63* until around the 1k rpm range and it shoots back down to 10* sometimes 0*. Does this mean anything?

[VStar650CL]

That does sound like the CAS signals are getting confused. The ECM relies on it for both ignition and injector timing, so like I said, if it starts lying, the ECM is usually in trouble but you may not get any codes.

[07mike07]

I almost replaced everything I could think of and the issue still persist. Hits 2k rpms and bogs down without letting me give it any form of gas to about 1k rpm then I am able to rev the vehicle again until I hit 2k rpms again and the issue repeats, I'm losing hope slowly as I keep throwing money at the car and nothing seems to change, I've done everything that I've seen on the forums, to cleaning the iac to replacing spark plugs to even cleaning the throttle bodies. I've replaced all the injector and coil packs and anything I can think of that has to do with fuel or spark and nothing changes.

[07mike07]

Yesterday I drove the car out with hope it would do something different and give me a sign, when I took off same thing was occuring, then I parked and started it back up a couple minutes later and then the car starts driving fine, goes past 2k rpms and everything. I've now noticed the car drives fine when low on gas or atleast when my gauge reads low on gas but as soon as I put gas in it the issue starts again until I can manage to get it low on gas. I have no clue what could cause that. Maybe a bad pump? Maybe a bad sending unit? I've also noticed that on the level side of the tank, the floater is missing on one of the metal pieces, I don't know if that has anything to do with it.

[VStar650CL]

Dying fuel pumps usually misbehave worse when the tank is empty, because they're cooled by the fuel. That sounds more like a problem with the evap purge system or the evap vent valve. Try driving with the filler cap removed so the tank can vent freely, if that makes it behave itself then you probably have a plugged canister or a stuck evap vent valve that's causing vacuum to be pulled on the fuel tank. If that doesn't help, try pinching off both purge lines into the manifold and see if it behaves itself, if so then you may have a stuck-open purge valve or a fuel-flooded canister.

[07mike07]

Yeah I thought so, and I replaced the fuel pump before with a well knows working one. Thanks for the reply, next time I have time to work on the z I'ma try the methods you mentioned and report back what I find.

[PapaSmurf2k3]

Try driving with the filler cap removed so the tank can vent freely, if that makes it behave itself then you probably have a plugged canister or a stuck evap vent valve that's causing vacuum to be pulled on the fuel tank. If that doesn't help, try pinching off both purge lines into the manifold and see if it behaves itself, if so then you may have a stuck-open purge valve or a fuel-flooded canister.

Solid advice.