Okay, all 300zx pros please come out.
My 1993 300zx NA Auto has had an issue ever since I got it and I have diagnosed issues, fixed just about everything, and yet there is still a massive issue.
When I accelerate it has an enormous lack of power, it misfires occasionally at idle, it runs rich, and it has worse fuel economy than it should. It runs OK, meaning poor, but passing...not really. When accelerating slowly up to 1,800 rpm and past that, the closer you get to 3,000 rpm it will vibrate very heavily and the power will not increase much at all, I have to pull back because I feel like I’ll damage something if I just accelerate like your normal SUV, every stop light I accelerate slower than everyone else because of this, it’s a very bad and noticeable vibration and lack of power.
A year ago I replaced the fuel pump for the first time with a new TT one. For those three days following the installation of that new fuel pump that car ran as if it had 500 horsepower and was brand new. While normally accelerating the car would PULL up to 3,000 and above, the higher in the rpm the smoother it got. It was amazing. The pump was whining, but it sounded like a healthy whine. After those three days it went back to driving poorly, and it’s been crazy trying to figure out why it’s acting like this since then.

I have replaced the pump with a NA one two weeks ago (this is about a year and a half since those three days), and it makes weird whining sounds, but it did not bring my power back.
Over the last two years I have done all of these jobs:
Brand new Coil packs
Brand new spark plugs (twice within 5,000 miles)
Two fuel pumps
All the fuel lines and hose clamps in the engine bay
New fuel injectors (new style)
New plugs to fuel injectors
New plugs to coil packs
New Idle air control valve
New air regulator
New coolant temp sensor
New Power transistor unit (version 2) I relocated it to under the nose panel
New pop filter air intake
New ECU from JIM Wolf (Stock ecu just with a slight tune) (I had the issue before and after the ecu so this didn’t effect it)
I relocated the knock sensor but the knock sensor is not being read still for some reason (the Jim Wolf ECU doesn’t use that info really anyways, I talked to Jim and he said they pretty much bypass it)
I have bypassed the knock sensor with a resistor as well and it gets rid of the code, but doesn’t change how it drives
New alternator
New PCV valves
New PCV Hoses
New IACV hoses
New fuel pressure regulator
New fuel dampener
New crank angle sensor
New thermostat
I have cleaned out the fuel tank
New fuel filter
New speed sensor
New revolution sensor
Fixed Transmission control module
Used, but repaired and in working condition from Z1 fuel pump module
New valve cover gaskets
New engine mounts, not solid by any means, but not all rubber like OEM, though, it ran amazing on these engine mounts and it felt so smooth on these engine mounts for a few days to the point it felt like the engine wasn’t even on it was so smooth.
I checked timing using conzult and timing light
Probably a few other things I forgot
Yes I have cleaned the throttle bodies
Conzult says the car is running rich, and yes it is—you can smell it.
Weirdest thing is that the cars timing jumps all around at idle from 15, 9, 12, 8, 4, 13 etc. The timing jumps around in conzult while idling, I am assuming this is because of the random misfire.
Car runs rich (I also checked the plugs recently and they were BLACK, (only had around 4,000 miles on them) new coil packs and spark plugs and yet it still can’t burn the fuel.
Any ideas? I’m out of ideas. I don’t know what could cause these weird symptoms.
I’m sorry for this long post, this is just insane at this point.
The idle is shaky in both drive and in neutral, temperature doesn’t really matter.
90% of the things I replaced was after those 3 days. Before that it shouldn’t matter since it had the potential to run well, since it did. I didn’t touch anything for those three days following the fuel pump, it just randomly started doing that again and the fuel pump got really quiet. I got a new one as I said earlier and it’s louder, but doesn’t seem to change anything whether it sounds loud one day or quiet the next, both days it runs the same.
I also checked the fuel pressure at idle and it idled around 38-39PSI at idle in neutral.
When revving the car it would get up to like 45-46psi and then go back down to 38-39 right after letting off the gas pedal.

I was thinking maybe the exhaust is backed up....? I don’t know why that would change it. Some days the car runs slightly better, yet noticeably better than others. Some days it’s bad bad with like 50% power when comparing it to what it was when it ran amazing those 3 days, and other times it feels around 65-70%, and you can tell. It feels a lot smoother especially heading towards 2,000+ but it still vibrates and isn’t full power. So I feel there is potential to have that power back and fix it since some days its much better than others, but temperature doesn’t change it, it’s just random some days it feels pretty smooth and decent but others it’s terrible in comparison.

You have done just about everything except the main sensor that counts, the MAF. Be sure it’s a Nissan orange label n62.
Also, what plugs did you use, I’ve found only Nissan oem are any good for the NA.

Hi! Thanks for the reply!
I didn’t do the MAF since both my red TT 300zx and the white NA one both have the same voltage and read outs according to consult so I was thinking that would mean it’s okay...?
I used the iridium plugs for it, I couldn’t get my hands on the OEM ones. I’ll try those next time for sure. Someone put copper plugs in it before I got the car *facepalm*

I also changed the TPS as well. It’s set at .46.

1. Since you mention replacing the TCU I'm assuming its an automatic. I don't know much about how the auto control interacts with the ECU but it's something you should look into.
2. An item I dont see listed is the NVCS/VTC system, if inoperative it would make your car run less than perfect, especially on an NA ECU because it is responsible for low RPM driveability (low range is when the system is engaged on the NA).
3. As for the MAF, you need to be taking live data readings not idle readings, a lot of the time the sensors will behave properly at baseline and go bonkers when the go pedal is applied.
4. I don't see a new EFI harness on the list, this could also be an issue since the old brittle harness could potentially have a break or a cooked wire somewhere along the way.
5. You need to use process of elimination and check EVERY system at the sensor/motor/actuator/etc. and at the ECU, basically confirm that the signal at the beginning of the wire is the same as at the end. Without checking every system methodically you'll end up replacing the rest of the car and still may not find your issue.

NolimitZ32 wrote: ↑

Thu Sep 19, 2019 5:40 am

1. Since you mention replacing the TCU I'm assuming its an automatic. I don't know much about how the auto control interacts with the ECU but it's something you should look into.
2. An item I dont see listed is the NVCS/VTC system, if inoperative it would make your car run less than perfect, especially on an NA ECU because it is responsible for low RPM driveability (low range is when the system is engaged on the NA).
3. As for the MAF, you need to be taking live data readings not idle readings, a lot of the time the sensors will behave properly at baseline and go bonkers when the go pedal is applied.
4. I don't see a new EFI harness on the list, this could also be an issue since the old brittle harness could potentially have a break or a cooked wire somewhere along the way.
5. You need to use process of elimination and check EVERY system at the sensor/motor/actuator/etc. and at the ECU, basically confirm that the signal at the beginning of the wire is the same as at the end. Without checking every system methodically you'll end up replacing the rest of the car and still may not find your issue.

Thank you as always for the helpful response! I greatly appreciate it! I’ll look into those sensors like you said and definitely the VTC system, I can literally feel it when the car is cold at around 24-30mph, engine gets smooth and you can tell by the way it sounds, only around then. Didn’t think much of it though.
It is an automatic as you said.
Thank you again for your help!

Have you used the troubleshooting section in the FSM? If you haven't you've been missing out, check the link in my signature, there is a consult and a non-consult procedure for each system.

Yeah, I have unfortunately and nothing. It’s the weirdest issue ever. I’ll probably go back to it again, but so far it hasn’t helped with this issue. I’ve already replaced all the parts according to the FSM that failed the tests and nothing haha.
Thanks!

Can you pinpoint the behavior to a certain gear?

If VTC's look good , MAF,MAF,MAF Go-o-olly !!- Also have NO "un-metered" air being sucked into intake ducts (ie."sucking" occuring after the MAF,of course). Other Vacuum leaks ? Maybe go shutoff after the "bad" run (before TOO hot,still "cool" - yet running "SUPER-Bad") and IMMEDIATELY pull ALL plugs for inspection?? Cause NO LIVE DATA from conventional ALDL scantools here

Hell, as somebody else mentioned ,ya spent a fortune yet ?? I hope one of the experienced 300 zx'er's here probly figure out - proper- what you've got.

NolimitZ32 wrote: ↑

Fri Sep 20, 2019 11:10 am

Can you pinpoint the behavior to a certain gear?

Transmission was rebuilt. It does it more in second gear but I’m assuming that’s because of the lack of power, if I give it more gas before the gear change it’s smoother. Not bad though. It isn’t a rough gear change it just vibrates more right before it shifts, probably because it’s in a higher RPM. It does it in neutral and park as well.

macgiver wrote: ↑

Fri Sep 20, 2019 1:18 pm

If VTC's look good , MAF,MAF,MAF Go-o-olly !!- Also have NO "un-metered" air being sucked into intake ducts (ie."sucking" occuring after the MAF,of course). Other Vacuum leaks ? Maybe go shutoff after the "bad" run (before TOO hot,still "cool" - yet running "SUPER-Bad") and IMMEDIATELY pull ALL plugs for inspection?? Cause NO LIVE DATA from conventional ALDL scantools here

Hell, as somebody else mentioned ,ya spent a fortune yet ?? I hope one of the experienced 300 zx'er's here probly figure out - proper- what you've got.

Checked for vacuum leaks, all good. I’ll definitely check that MAF soon. You may be right haha. Thanks!

What about the torque converter? If the solenoids aren't working properly either upshift/downshift or lockup it could be creating extra drag on the car. Who did the rebuild, were all new electronics used?

Nolimit's point should be checked out.And if the bad running vs Ok running is climate dependant ,ie. humidity. temps change , super windy , whatever - may point attention to MAF , in addition a very intermittant / clog in a fuel injector (typically one - just needs to be one) can wreak this kind of act, and beware just checking a good resistance,AND the 'clicking sound' does NOT mean it sprays WELL nor at volume - thus the plug examination after some "pedal-pumps" and then a quick shutdown. I got same motor in J30 ( 93) and again we have no OBDII , ??

NolimitZ32 wrote: ↑

Tue Sep 24, 2019 11:33 am

What about the torque converter? If the solenoids aren't working properly either upshift/downshift or lockup it could be creating extra drag on the car. Who did the rebuild, were all new electronics used?

Unfortunately it was AAMCO. It has a new torque converter, though, you are right it does sound like that though, but the car runs weird in neutral and does all the same stuff in neutral or park as well. When it runs well you’ll notice it when it idles in either neutral or drive. It shifts fine in all gears, just when it lacks power it will shift a little harder going into second, but it’s fine if you give it a little more gas or if the car is running smoother. Added a bit of fluid to it and no change. TCU was repaired and fixed my old issues. (The tranny was slipping and it was due to the TCU not doing anything but being a brick) The fluid temperature sensor on the transmission is bad, I’ve known that for a while, I don’t know if that effects anything though. I don’t know if it would cause the 40mph issue where it does engine braking if you let off the gas if you are over 40.

The TCU doesn’t read the closed throttle switch, I think that’s why I have that issue when I let off the gas and part of my idling issue in park. It isles poor in neutral but a little worse in drive, again, the engine RECEIVES THE CLOSED THROTTLE SWITCH INFO but the transmission doesn’t. The sensor itself is brand new I bought a brand new TCU and the engine reads it, but the transmission doesn’t.

The fluid temp sensor reads ridiculously hot temps all the time and the voltage is way out of range from the time you start the car to when you turn it off. Car runs the same no matter the weather, some days it’s just different, but the weather hasn’t seemed to effect it.

THOUGH: I was talking to another 300zx owner and he said he had a similar issue and it was caused by his fuel pump relay connector being messed up and over time frying his wires. It would cause his pumps to go bad and make that whining sounds I hear on occasion. What do you all think about that theory?
Thanks again for your help, I apologize for the super late response, I’ve had to help a family member recently with quite a lot due to an emergency, and I’m moving all at the same time.
I appreciate you all again.

Sounds like you've isolated some issues that need to be fixed before you go searching for more. a combination of issues can make the car do odd things. Like I said previously it looks like you may need to go check all the wires for resistance and voltage drop (power and grounds on this one).

NolimitZ32 wrote: ↑

Thu Oct 10, 2019 8:15 am

Sounds like you've isolated some issues that need to be fixed before you go searching for more. a combination of issues can make the car do odd things. Like I said previously it looks like you may need to go check all the wires for resistance and voltage drop (power and grounds on this one).

I’m going to do that at the fuel pump and check the fuel pump relay connectors and all of that stuff. Thank you as always for your reply! Will get on that tomorrow!

Update: I’ve checked everything above and yet, still nothing. I’ve bypassed the carbon canister by removing the vacuum lines and capping them off—nothing changed there, but I still smell lots of fuel at the carbon canister from above when I smell near the front driver side headlight/driver side throttle body and that’s where I smell RAW fuel. I’m baffled. The car also is hard to start when it’s cold now. That’s what has changed over the last few months. I now have to prime the fuel pump three times before I start it unless the car will try to turn over for 5 seconds and then will barely start. If I turn the key to the on position, let the fuel pump prime, take the key out, put the key back in, let the fuel pump prime, and repeat that 3 times then it’ll start after a second—much faster. Though, my main complaint is that the car still runs rough. It doesn’t seem to misfire, it just feels like it’s not getting the right fuel to air mixture so it’s not burning cleanly.

I read some of the thread so far but not all of it. Have you done fuel injector flow test or pressure the rail and let it sit to see if there is a leak in the injectors? Sounds like its being flooded now after it sits or looses prime hence its better after you cycle the ignition and prime it again

chieftolly wrote: ↑

Wed Feb 05, 2020 10:12 am

I read some of the thread so far but not all of it. Have you done fuel injector flow test or pressure the rail and let it sit to see if there is a leak in the injectors? Sounds like its being flooded now after it sits or looses prime hence its better after you cycle the ignition and prime it again

It has new fuel injectors OEM, but when I replaced them I didn’t see any leaks. I haven’t tested it, but the injectors are new. When I hook up my computer on ConZult it says that the car is running lean, but by the smell of the exhaust it definitely seems to be running rich.