Driveability issues

[nissanfreak12]

First off sorry for the long post as Im just trying to bounce ideas around. Ok, for the basics, 92 300zx 2+2 auto, all stock except for cone filter and ptu relocation.

Issue: this is all under load, idleing the car shows no issues, no missing or roughness

From a standstill the car is fine goes from first to second without any issues at all throttle range. It likes to really bog down when I dont stop completely and try to hit the throttle 1/4 to 3/4ish till roughly 3000 rpms then it gets up and goes, like it shifted to fourth gear and wont down shift. if I barely touch the throttle it has decent response, but shifts before I can really get up to speed, almost like its starving for fuel. If I full throttle it downshifts and goes, it has no problem going to redline why I don't think its a fuel delivery problem. Timing is set at 15btdc

Another issue, the idle, the stupid idle. warmed up the car, disconnected the connector for the idle, and I was able to get the idle down to 700ish, but the minute I connected it back up, it jumped up to over 1000rpm. Any ideas?

things i have done:

replaced all gaskets, seals and so on
replaced-TPS, CTS, pcv valves, all hoses(and I mean all fuel, coolant, vacuum), plugs(pfr6g-11, got these from conceptz), timing components, VTC springs, O2 sensor (I have to splice the wires, pretty sure I didn't mix up the white wires, but not ruled out), and Detonation sensor/wiring
Cleaned AIV or AAC which ever it is behind the plenum and tested all good and all connectors
Injectors tested 12-14 ohms cold, have not tested them hot,
I know I am missing a few things, so if I remember, Ill post it

The TPS: Even though this is new I have my doubts its working correctly

Adjusted it .45v closed and came to about 4.4v open.
Here is the odd thing, I adjusted it the first time to .45, opened the throttle and when I closed it the voltage changed to .52, reapeated and it went up some more. So I adjusted it again, yes I made sure it was tight during the opening of the throttle, same thing, I did finally got it to stay at about .45, but still didn't like the adjustment.*I honestly think this is huge factor of the issues*

I don't believe I have a vacuum leak, its not ruled out though, but looking at the trouble shooting in the FSM, everything points out to vacuum leak, so it is a possibilty. I did check the ecu and good old code 55 came up, tonight I will check out mode II, see what comes up. I have not tested the MAF sensor, everything "looks" good, but doesn't mean it is.


Guys I'm lost here, is it possible the trans could be causing all the issues? Have not pulled the codes for that. I really suspect the TPS because of the throttle response, maybe Ill put the old one on and see if it changes at all. Ill take any ideas and let you know if I tried it out. Thanks in advance.

[BigTDogg (MA)]

Test the MAF and check for vac leaks. Don't pressurize the system more than 5 psi, 8 or so absolutely maximum. The environment needs to be pretty quiet to listen for leaks.

Disconnect the IACV (idle valve) and adjust the setting screw to get the idle to 750-800ish, then reconnect it. If I misread your post and that's what you did, nevermind.

[nissanfreak12]

Thanks Bigtdogg, I am gonna do all the testing tomorrow, if all else fails, monday Im gonna take it down to pit stop to diagnos it. Hopefully they find something out.

With the idle, I can get it down to 750-800, but the minute I reconnect iacv, it jumps up to over 1000. I talked to COZ at concept z, and he said it sounded like its bad. Maybe the $40 for the 30min diagnose isnt sucha bad idea.

[Ace2cool]

I think it's your TPS. Was reading someone else's post where it acted like an upshift mechanism instead of a kickdown when he pressed the throttle, and it turned out he had reconnected the TPS plug backwards. If the voltage is changing after you go WOT though, sounds like a bad TPS, assuming it was tightened down all the way after you adjusted it. I'd check your TPS plug and make sure it's not reversed before we start throwing parts at the car.

Also, a maladjusted TPS can cause high idle. Just food for thought....

[nissanfreak12]

Yeah Ace, that was my post. Its just little thing now, but the bogging is the one thing thats just irritating me right now. I keep reading about injectors, what are your guys thoughts on those? I guess checking the fuel pressure is definitely on the list tomorrow. I was also thinking if the MAF was going bad or is bad, it would have a hard time idleing or even starting.

It has to be something I have overlooked or even looked to much into. Just cause the car idles very nice and smooth, just high, and all my problems are under load.

[BigTDogg (MA)]

Your idle would typically be erratic with a bad MAF, cycling from 300 to 1500 for example.

Check the FSM and adjust the TPS accordingly. If you've set it correctly per the FSM, and can't get the proper voltages, swap it for another known working one.

[nissanfreak12]

I know I had that issue when I got the car, but only coming to a stop after driving on the freeway. just coming realize I had a whole mess of vacuum leaks. After redoing all the gaskets, im sure I got the leaks taken care of, but I am gonna test in the am. I will keep you guys posted.

[nissanfreak12]

So I broke down and took it to a shop for z's, the only thing that came up was the comp kept retarding the timing when gas was applied only under load, idle showed no issues. Everything checked out fine, timing was a little off and he set my tps to .5v, but he said the car sounded great, do need an engine harness, but alread knew that.

Possibilties:

Cam off one tooth-very possible
Cats could be clogged
Transmission could be causing all the issues
Comp could be taking a crap

He did say it was not a sensor causing the problems and the balance test and injectors have no issues. I will post when I check the belt and make sure all is correct, that is the first place Im gonna check

[nissanfreak12]

What could cause the timing to retard while driving? I checked the timing belt and its on there correctly, I even took it off and re did it as per the manual. It sill does the same thing as before, its really starting to just piss me off. Give me some ideas, im up for anything.

[nissanfreak12]

Ok, so I thought about it and kinda have a theory. Even though the detonation sensor is new as well as the harness, what if its falsely saying the engine is detonating? This would make sense since I have read somewhere that the sensor doesnt read above 3500rpms(this could be wrong, justremeber seing this in an article) or something along this effect. I know tt's need the sensor, how much does the na need it or will the bypass method be sufficient enough? I just dont want to take the engine apart again if this is the problem. I have not actually found if this is my problem, it was just a thought I had last night. Let me know what you guys think.

[BigTDogg (MA)]

I know tt's need the sensor, how much does the na need it or will the bypass method be sufficient enough? I just dont want to take the engine apart again if this is the problem. I have not actually found if this is my problem, it was just a thought I had last night. Let me know what you guys think.

I don't post much on the weekend, sorry no one else has replied. Try the bypass and see if that works. Otherwise it could be your AT controller as well. I'm unsure on the diagnosis process for that, might want to check the FSM.

[nissanfreak12]

I was gonna check the trans codes and see what comes up, and its all good man. Not your fault noone realy post, Im sure most people have no idea what the issue could be. Now, is the car safe to run without he knock sensor, cause I know the tt's need it for detonation, but will i be ok wihout it for a while if that is the problem?

[nissanfreak12]

I tried disconnetcing the cats and still had the problem. have not checked the det sensor, cannot find a resistor to bypass. I did however find out that the kickdown switch and idle switch are not reading correctly. Idle switch is just reading zero, and kickdown switch is measureing 12.7 closed and 12.9 full throttle, which is nowehere near correct. I am having a hard time locaing either swittches or where connector can be, any will be appreciated

[robomatic12]

You will be "ok" without a det sensor on an NA aslong as you use good quality fuel. You need a 1k ohm resistor if I recall correctly, you can order online.

The switches you are describing sounds like the TPS which is located on the left hand side of the intake plenum, looks like a black box behind the throttle plates.

[nissanfreak12]

Thanks Robo, I finally found out thats what it was. Apparently what was going on was even though the tps was in spec per voltage, the front part of the tps wasn't showing continuity with the throttle closed. so all This issue was the tps, I'm guessing the comp never saw the throttle actually closed, so there for never dropped down to the correct gear. I have a new tps on have it set at .41, and all is good now. I do feel i have some hesitation at about 2k rpm, but nothing drastic, almost feels like I still have a flat spot in the tps, and it seems to shift a little hard from 1st o 2nd, but Im just thinking cause it sat for so long.

I just want thank you guys for your help, hopefully the car behaves for awhile. I have also decided a name for it "The Pit", cause my god Im glad I have not kept track on how much i spent cause I know it was well over a grand maybe closer to 2k. It sad cause I even knew what I was getting into, but these cars are gorgeous. Next up is a 5 speed swap, just time to start scavaging parts.

[robomatic12]

Good to hear you got it figured out! A flat spot will feel like a jerk, on and off throttle quickly as it is in the dead spot, you can check for either voltage or ohm increasing in a linear motion with a dmm.

[nissanfreak12]

Well, the car is running better but no fixed. It drives great as long as I keep the rpms above 3k, but I did noice even in first the car didnt want to get out of its until about 3k rpms. I have also noticed that I am getting horrible gas mileage maybe 8mpg or less, pulled the plug and noticed they were wet(I only pulled #2, but will find out about tomorrow night about the oher ones after driving it a bit).

What could be the cause of it running rich when under load, cause there is zero issues when no load. Is it possible the o2 sensor test out good, but be bad? They are new, but am worried I mixed up the white wires when I spliced the new O2 to the old connector. Could this be an issue?

Im getting somewhere with this, but what am I missing, any ideas I will take.

[robomatic12]

Could you explain what you mean by switching up the white wires? You hooked it up to one of the other wires instead?

Try unplugging both 02 sensors and see how the car drives, the Z will run off a safe richer fuel map and can show you if the 02's are throwing bad readings.

[nissanfreak12]

When I bought the sensors, they did not have the connectors on them and have to connect the old connectors to the new sensors. the new sensors had two white and one black wire coming out of them. I believe the wires go to each specific part of the sensor, and Im wondering when I spliced them if they got spliced wrong? Im not sure how else to explain it, but I may connected it wrong, this is just a possibilty. If I unplug them the car should act different, am i correct? if it doesn't then does it mean that the sensors are bad, or do I have this backwards. Im tryng not to make this confusing in any way, its just frustrating to spend all this time and money for the car to have this problem.

[robomatic12]

Sorry, not too sure on the wire splicing, never have had to splice them before.

If you unplug the 02 sensors and the car runs fine with no stumbling below 3k, then the 02's are giving a bad reading to the ECU. You could even try one side at a time.

Could you perhaps describe more what is happening when you encounter this problem, what it feels like, sounds like, power loss?

[nissanfreak12]

Sorry, not too sure on the wire splicing, never have had to splice them before.

If you unplug the 02 sensors and the car runs fine with no stumbling below 3k, then the 02's are giving a bad reading to the ECU. You could even try one side at a time.

Could you perhaps describe more what is happening when you encounter this problem, what it feels like, sounds like, power loss?

I unplugged the O2's and nothing really changed, it did get a little more choppy but still had the same stumble. I did switch the white wires on the sensors one at a time and did notice that the stumble is better, still there but better. I also noticed that The idle seemed to kinda hunt nothing major, maybe moving up and down 50rpms. After switching both, still felt the same as just doing one. When I got home I pulled the 2nd and 3rd plug and they were not wet anymore, #3 had black soot which tells me it was rich, but that could have been from before. i did mode II on the ecu and when reving it at 2k, I noticed the light continously blinked, same pattern, nothing changing, like when you get code 55, the first 5 blinks. I know before I switched the wires, it had I think 3 long a couple fast then back to long and so on. What do you think about that?

I did notice when I kept it in first, and hit the throttle about half way it stumbled, like if you put your car in 5th and full throttled it, for a second or two then it started to go, but still had the stumble up to 3k.

Describing it, when taking off in first, it feels like that its in like second or third, and has a low rumble type feeling like as described above in 5th gear, has no power, every now and then I do get an intake pop(I beleive), until you hit 3k, then all seems good. If driving, it has the same effect like your in the highest gear and trying to take of, still no power. I know its switching gears without any problem, but it definitely should have more power than that. Could an intake leak cause this issue with an idle issue? I did notice I had a vacuum line disconnected, plugged it back in and it actually drove worse. Upon looking over the engine I noticed that i had one injector leaking, just a slight leak like condensation for the cap. Yes going to replace that so no more leak.

thanks for all your help btw, i really do appreciate it.

[robomatic12]

I'll try and tackle things piece by piece but normally they will all add up to one bigger problem.

It sounds like you have made the 02 sensor wires in the correct spot now, if you are getting a constant blink which means the ecu is receiving a fast switch between lean and rich. Versus the longer pause you had before. So I would keep them the way they are. You could try throwing in a cheap set of copper plugs and run them for a while to judge the rich/lean condition in each bank.

If fixing the vacuum leak makes the car drive worse to me it would seem the engine is running very rich. As a vacuum leak would normally cause a lean condition, it is evening out the rich condition making it semi-normal.

If you have an injector leaking externally, it could be dumping too much fuel into that cylinder which would cause an overrich condition the ecu cannot account for. Was that the same cylinder that had the black sooty plug?

[nissanfreak12]

You know cause I have been obsessing about this, I didn't even think of that about the plug and injector. yes it is the same cylinder, I just randomly picked that one cause it was the easier one on that side. I am going to try and replace the orings first cause i don't think its an actually injector issue maybe just a sealing issue. If I still have the issue after the o rings, Ill do the cheap plugs in and see what happens then, if it has the same issue then Ill go to injectors and so on so forth. I will defifnitely keep you posted, thanks again.

[nissanfreak12]

Well the problem has been resolved, and I was ready to just give up the car. I decided to get three new injectors well due to pulling them out one decided to go topless and the other two decided to lose its basket around its waistline, showing its goods to everyone. I even decided to replace the lower plenum gaskets with, I don't know the kind that are suppose to go, really taught me from going cheap again. It really wasn't the removing the two bolts going through the egr, it was putting the damn things back in(yes my friends, engine was still in the car).

Got everything back together, everything with fresh seals, timing in the correct location, car started first time, then I was missing from the #2 cylinder, checked everything. About put my head through a wall, then I realized the PTU wasn't connected all the way. Plugged that bi*** in and nice and smooth. Added antifreeze, drove it around, notice I was leasking coolant from the bypass hose, so I made it quick. Yeah, car still doing the same thing. decided to stop in a parking lot, cuss at it for a few minutes, drove it home and locked it in the garage.

Decided to go out and do something and came back home, went back down cause I had a few ideas. Started driving it unplugged a couple things, plugged up FPR and EGR, I was fishing here. Nothing changed, then Im like lets check the timing, you know for s**ts and giggles. Remind you I did the timing through the PTU wire thingy, and I even had a shop "supposibly" check and correct the timing. HOoked the gun up to the #1 coilpack, sure enough, it was at 5btdc. I was like no way, this was my issue all the time, adjusted, drove away with a huge smile on my face. Thats all it was. I have no idea why I didn't check this to begin with, but I feel really, really stupid for this. I guess when you take it to a shop that specializes in Z's, you would hope that they would have caught this. This is the very last time I am taking anything to a shop, only exceptions are AC, alignment, and rebuilding of transmissions(yeah, opened on up before, NEVER doing that again, not my cup of tea). But all is good now. Tahnk you ROBO, ACE and Bigtdogg for all your help. I will get some pics up soon to show the beast.

[BigTDogg (MA)]

D'OH! Yeah, that's basics of hesitation, I thought you mentioned you checked that in your first few posts. Sorry dude!

After I rebuilt my car I thought I set the timing correctly, but turns out it was at 10°BTDC. What a difference 5° makes, I can't even imagine 10!

[nissanfreak12]

Oh it was horrible, but all is good now. The funny thing is I did check it, but it was through the PTU, yeah thats the last time I do that method. Its funny the things you over look when your frustrated.

[Ace2cool]

Wow, can't believe we missed that one..... 3000 RPM should be about where the VTC starts to engage. Glad to hear you got it sorted out, man!

[nissanfreak12]

I really think the VTC was what was throwing me off, even though I knew that it was kicking in. I was just so mad at myself not checking that. Oh well, lesson learned hopefully this will help someone else that may have a similiar problem. I bet most people that have some type of hesitation issue is going to go home and check their timing from this post. I just couldn't believe how much tunnel vision you get from this type of situation.

[robomatic12]

Good to hear you got it figured out! It feels good to figure it out doesn't it?

[nissanfreak12]

Oh it feels GREAT!!!!!! I do feel like I know this car on a very personal level though and a lot better understanding on why they designed the car the way the Japanese did. i will tell you what, This has been the hardest car I have ever worked on. I have always heard that rotories are the hardest engine to work on cause no one understands them. Once you take one apart, everything makes sense. I have built a few of them, port and polished the housings and so on, but this car takes the cake. I couldn't even imagine the TT, there is barely enough room for what the 300na already has but add intercooler, piping, turbos and what not, I does make sense why Japanese have little tiny hands though.