91 300zx TT running poorly, please help!!

[Robert mudd]

I bought my 1991 300zx twin turbo about two weeks ago. Was told it needed new injectors because it was misfiring. Indeed one injector was out so I decided to just replace all 6. This job was terrible first off lol. (this is my first Nissan) however I completed it today. While I had the plenum off I replaced all the injector connectors, new plugs, new fuel filter. New PCV valves. Checked all coil packs. I Put it back together, then started it today and it ran great for about 30 minutes. After that it started to run funny. At low ish Rpms (0-3600) it seemed to not want to run. At lower rpms it would feel very underpowered and it would buck and run very rough. However once you get it above 3600ish rpms it accelerates very nicely and smoothly. When I got home I shut it off. When I went to restart it is was extremely difficult to start. And is now very difficult to start. Before I replaced the injectors it was very easy to start. I checked the fuel filter and it was free flowing, the old one was filled with rust colored gas, and I checked the fuel pressure regulators and they seemed good. I think the engine is being starved of gas but I'm not sure what to check??? Maybe a mass air flow sensor??? Rust in the tank??? I'm at a loss here. Maybe be worth noting that the car sat for about a year or two before I got it. I also filled the tank with fresh gas when I got it, so it shouldn't be bad gas. I've only had the car for two weeks so I'm still learning about them and any help you guys can provide is greatly appreciated. Thanks for replys or any question

[nissanfreak12]

Do you have all the grounds connected on the back of the plenum?

Did you adjust or check he TPS?

Are you sure there are no vacuum leaks? How is your idle, is it high or does it bounce?

Are you sure you didn't pinch an oring on installation? Pull your plugs and see if any are wet after you run the car.

Have you checked the ECU for codes?

[Robert mudd]

Hi thanks for the response!
Yes I connected the two grounds on the either of the back of the plenum and I also connected the fuel rail ground. Are there others I might have missed?


No I didn't check the TPS, I'm not sure how to do that. It is reconnected lol

I'm not sure if I have vacumm leak. I printed out a vacuum diagram but I can't say 100% I don't have a vacuum leak. It may be worth noting I did a coolant hose delete and an egr delete while I was in there.

The idle is low and rough, when I come to a stop light the idle drops down to around 500, the car acts like it's going to die, the the computer kicks in and raises it to close to normal levels. Then it slowly goes back down.

I'm not sure what o rings you are talking about. I will check the plugs when I get back to the car on Monday.

No I haven't checked the ecu yet, I'm going to do that Monday,

Weird question but do you think the timing could be off by a little. Would that explain it not running right under 3500 rpms then when timing is changed it starts running smoothly?
Thanks again for the reply.

[nissanfreak12]

Timing isn't changed at 3500, VTC is activated and things are spinning faster so it is harder to notice "issues", but the timing could be off should be 13° +/- 2°. The intake cams open the valves longer so to say. it could be possible the CAS was bumped and caused the timing to be off a little.

Checking TPS;
https://z32.wikispaces.com/Throttle+Position+Sensor

Make sure the black sensor on the TPS is plugged in correctly, it can be switched, but there is only one way it connects.

Lower O-ring on the injectors are very easy to pinch, which cause a fuel leak in the combustion chamber. Pulling the plugs will tell you if you have a leak. If they are wet or one is wet and smells like fuel, there is an issue.

Those are basically all the grounds, you are fine there.

Have you done a power balance test? Unplug one coil pack at a time and see if there is any difference or change in the engine. No change will mean that cylinder is not firing. Which could be injector, coil, plug, etc

Even though you probably have the right one, which PTU do you have? Old style is silver fins on the front, old style is all black? This could also be an issue if the old style. There was a recall on it years back.

[Robert mudd]

Hey thanks again for the reply,

I'm not really sure how to check timing on this vehicle, but I will do some research.

Thank you for the link about the TPS I'm going to check that after work today.

In regards to a pinched o ring, it ran great for about 30 minutes before it started acting up, it would seem to me that if an I ring was pinched it would have been apparent from first start up?? does this sound correct or am I wrong??

After work I'm also going to do a power balance test assuming I can get it started.

I'm not sure what exactly a ptu is or where it is located but I do know that there is a silver sticker under the bottom side of the hood that says power transistor service completed under nissans serice campaign.

Someone bolted down the cowling in between the headlights so I haven't been able to check the maf or air filter. I'm also going to try and do that today after work.

I will post with results of some of the things listed above after I attempt then.
Thanks again

[Robert mudd]

Alright so after work I went to start my car thinking is would be hard like yesterday, however it started up very easily today, weird. Then I hooked it up to my bosses computer that can turn off individual cylinders, the power balance showed a miss in cylinders 4 and 5. Before I replaced the injectors the miss was in 2 and 5. Took both coils out and tested them for spark, took both plugs out and they had gas on them but when plugged into the coil and ran they sparked aswell. Then I hooked up a pressure gauge to the fuel lines post filter and when I turned the key it spiked to 40ish then slowly went back down to 0. When it was running it was at around 38ish PSI. When shut off if again slowly fell back to 0 which took around 15-20 seconds. I'm really at a loss. These symptoms seem to change daily. Like states before the weird part is that after I put the new injectors and plugs in it ran fantastic for about 30 minutes. Idk
Any help is greatly appreciated.

[nissanfreak12]

Check your connections and make sure they are not corroded with green "crud". Bad connection will cause issues that working one min, then not the next. Or just stop working completely.

[Robert mudd]

Thanks again for the reply nissanfreak,

Ya I have cleaned all of the connectors associated with taking the plenum off. But tommorrow I'm going to pull them all apart and clean the connectors especially the MAF, I'm also going to test the MAF using a volt meter. I really appreciate your help.

[RubyRed300ZX]

Considering you pulled the plenum, you probably disconnected the Coolant Temp sensor. Obviously re-check to ensure that it is connected securely; however, you should also check to see if the sensor is reading properly. Does your multimeter also measure temperature? If it does, takes only a minute to check it. Could be just coincidence that the temp sensor failed at the same time as 30minutes after you started it back up.

[nissanfreak12]

CTS doesn't measure temp to the ECU, it measure resistance. Any normal Multi-meter will read it.

MAke sure you check the ECU for codes. That would be the best thing to do before removing anything. It could be as easy as a sensor, bad PTU, CAS.

PTU is located, stock, on the passenger side timing belt cover. If it go moved, normally it got moved to right by the headlight or where the air filter is. It will have about 7 wires going in and out of it.

[nissanfreak12]

Also, pull the vac line from the pressure regulator. See if there is any fuel in the line. If it has any fuel smell, it needs to be replaced. If it doesn't, that doesn't mean its good. If it holds pressure at idle, then its fine. If you lose pressure after the vehicle is shut off, then you fuel pump has a bad valve in it.

It could very well be your pump is going out and when it warms up or gets hot, it could start failing, causing bad fuel PSI. These pumps can show signs of going out, then all of a sudden working perfectly, then failing.

If you do have to replace the pressure reg, replace the fuel damper as well, they normally don't fail, just as a safe measure.

[Robert mudd]

Hey thanks again guys for your help.

To rubyred the coolant temp sensor is the yellow clip in the front of the engine correct? I checked it to see if it was corroded, which I wasn't, however I didn't check it with a volt meter, what should I do to do that, and what should I expect to see?

Nissanfreak, when I did the power balance I also ran a whole system check and my car threw 0 codes, not even a hicas code, I will look for the PTU tommorrow, I'm assuming I can test those sensors with a volt meter?

Also I have pulled the vacuum lines off both fuel pressure sensors while the car was running and neither seemed to have gas in the lines.
Also based on the fact that the car has two misfires now all the time, not just when it's warm, do you still think it could be a fuel pump? I was told to hook up a pressure gauge and clamp off the return line for a sec or two to see what it spiked to. My pressure spiked to 71ish psi, so this person told me that the fuel pump seemed to be working correctly, however it is losing pressure after the ignition is turned off. I'm not an expert by any means so just asking?

When I opened up the connector today going to the MAF it has dielectric grease in it and it was in great shape so it was making contact, I started the car with it disconnected, it ran about the same with it off, then I plugged it back in, the Rpms dropped very low but then crept back up to normal idle level, however the car was still missing with it off and on.

So what should my next step be guys? I'm really at a loss here so any help is greatly appreciated.

[Robert mudd]

Does this scenario make sense to anyone? So it had an injector problem, I fixed that(presumably), it ran great for about 30 minutes, then like rubyred said maybe the coolant temp sensor failed, now it is running bad again all the time, however the day I drove it, after driven for about 45 minutes it was extremely hard to restart, this was when it was warm, now when it's cold it's very easy to start, does this sound like a coolant temp sensor problem, could a malfunction of that cause a miss in two cylinders?

[nissanfreak12]

The fuel pump is just the valve going bad, normal on older pumps.

On the MAF did the connectors have dielectric grease on them or the seal? That could be throwing it off if on the connectors.

One thing to check out is are the injectors actually working? Take a long screw driver or stethoscope to each one and confirm they are clicking. They will click if working. It can be possible they are intermittent or bad even though they are new. Happened to me before. Are they old style or new style?

On your spark plugs, if they had gas on them, your issue could be the injectors, again, even though they are new. When you state new, where did you buy them? What brand are they? Stock size or larger? Conditions are completely different outside the combustion chamber, so if they had a little but of gas on them, they will foul in a combustion chamber because remember everything is controlled in there. Outside they get plenty of air, so they will spark. Those chambers are running rich.

CTS could cause a condition to run rich, but it wont be to specific cylinders unless there is already an issue in those cylinders, bad/fouled plug, weak spark, injector issue(sticking open, pinched oring). You can test the resistance with a ohm meter on the car or in a pot with gradually warming water and a thermometer

Want my honest opinion what is going on. I think your injectors are the issue, even though new and on the assumption they are old style(which are prone to failure with ethanol in gas). You can test them to make sure they are between 10-14 ohms and verify they are clicking. Hard start when hot can be a CTS issue but also too much fuel in combustion chamber. Try unplugging it when its hot and see what it does, but you obviously have a rich condition in certain cylinders( or all if all plugs are wett) They should be dry if timing is set correctly, fuel pressure is correct 43.4 psi, injectors spraying correctly, and sensors working correctly. CTS can cause a rich condition(wet plugs) in all cylinders, not specific cylinders.

[Robert mudd]

The MAF had the grease caked on everything, I will clean that.

The injectors I got where from Z1, they where brand new not reman, stock TT size, 370cc, but they are the old style. And I also put in all new old style connectors as well.
Yes what you're saying makes sense, after work today I will do the screwdriver method to see if the are clicking and if not I will try and ohm them or use a noid light if they seem to be working.

Thanks for you're honest opinion even though It's not exactly what I wanted to hear. But I will keep you guys updated on what I find out, thanks again.

[Robert mudd]

So when I got into work today I moved my car, it was pouring white gas smelling smoke out of the pipes....
Maybe an injector stuck open?

[nissanfreak12]

I know I stated this before, I bet you have a pinched o-ring. Maybe it wasn't bad at first, or very small, but as it got warmer the o-ring expanded, which caused a leak. Might be two.

You can use a 9volt battery to test click the injector to make sure there isn't a fault in them. Also, do not rely on the noid light, that just tells you you have electricity to them. Just make sure you do the screwdriver/stethoscope test.

I would remove the injectors and reseal them with new o-rings. Make sure you use oil or grease when installing them. Its a lot of work you just did, but it may solve your issue.

[Robert mudd]

okay, ya im going to take it back apart and get new o rings, what is the proper way of putting them back in the rail? what i did was i sprayed my fingers with a little penetrating oil then rubbed the injectors O rings, then threaded one side of the cap on a little. then i push the injector by hand down and screwed in the other side. (kinda crude). is there a link or site you can recommend with correct installation methods? also how much should i lubricate it and what lubricant is safe for the injectors? i think i might have a CTS out too because that would explain hard starting and lean ratios when warm. also there looked to be rubber rings where the injector tips sat down into the engine. those looked pretty rough however i didnt have new ones and wasnt sure where to get them, any ideas what those are called, because if im taking it apart again i will want to replace those.

Nissan freak, thanks again for the help, i really appreciate it. im going to buy these parts, install them (hopefully correctly), and i will keep you guys updated with what happens.

[ArmedAviator]

When you perform the surgery, move the #4 and #5 injectors to #1 and #2 cylinders. If misfires continue, you know those two injectors are bad.

Do the same with the coils except move them to #3 and #6. Again, if the misfire follows, you know what to replace next. Just because it sparks out of the cylinder, doesn't mean it has enough potential to overcome the fuel air charge and spark.

[Robert mudd]

Ah thank you, that is smart thinking. Will do

[nissanfreak12]

HArd starting and lean conditions may also be from the possible pinched oring(s) or fuel injectors. Too much fuel in the combustion chamber will cause a hard start. But the CTS is cheap enough and easy to replace. You can test it to make sure it is doing what it is suppose to do.

Fuel rail insulators Z1 or conceptzperformance will have them.

https://conceptzperformance.com/czp-bun ... _10061.php

These also break easily, just be careful and you will be fine, but just incase

https://conceptzperformance.com/nissan- ... _p_724.php

[Robert mudd]

Ya that makes sense. I'm going to take out and replace the orings and fuel rail insulators, is there any videos or links you guys use to explain the proper process so I don't pinch an o ring?

Thanks again

[nissanfreak12]

Read toward the bottom
https://z32.wikispaces.com/Fuel+Injector+Replacement

I just disagree with vasolene and wd-40, this could cause the o-rings to swell and deteriorate. Motor oil or MArvel Mystery Oil works great. They should almost "pop" in when they go in. You can use a slow twisting motion, but again, don't use the caps to get them in. Like they even said, it will cause a pinched o-ring.

[Robert mudd]

Okay parts are in today, will probably have the job done early next week, will update you guys with questions or results, thanks again.

[RubyRed300ZX]

Nissanfreak12 my comment about a meter that will probe temperature: Yes almost every meter will read resistance; however, the resistance of the Coolant Temperature Sensor is dependent upon the coolant temperature at the time it is tested. At 176 degrees Fahrenheit, resistance should be 0.30 to 0.33 K-ohms. That would be near operating temperature assuming the thermostat and cooling system are functioning properly. Or, check the coolant temperature at the housing adjacent to the Coolant Temperature Sensor with a probe on a digital multi-meter. Consult the FMS for various temps such as ambient temperature if the car won't start. It's a cheap and easy fix, if it is the problem. I wouldn't rely on just correct resistance at ambient room temperature though. The car supposedly ran fine for 30 minutes. Maybe it took that long at idle to reach full operating temperature.

However reading the additional posts, which tend to suggest inexperience with fuel injector installation, it sounds more probable that it's the o-rings as you suggested.

[RubyRed300ZX]

Original poster: Yes, the coolant temperature sensor is the one with the yellow connector... two leads back to the ecu.

[Robert mudd]

Began disassembly and noticed in the plenum under where the driver side balance tube sits there was gas sitting in the bottom of the plenum. Is this consistent with leaking o rings or would they leak only into the cylinders. Again I did take the fuel pressure sensor vacuum lines off while the car was running and there was no gas in the vacuum line indicating they were still functioning.

[Robert mudd]

Update 2
Got the plenum off, much easier this time, thanking God, alah, (other gods I forgot the names of) spirit animals, ancient ancestors etc that I did the egr and coolant deletes lolol. Gas was sitting on the valves on cylinders 4 and 5 which are the ones that currently had the miss. Will keep updated.

[Robert mudd]

Update 3
Got the injectors out of the rail, the o rings looked in decent condition, cylinder three large ring had a little damage to it. Could they be pinched and not damaged looking when you take them out?

[nissanfreak12]

Yes and no. Fuel sitting on the plenum is a sign of a pinched oring. Orings will either leak in or out of the cylinder. The small oring would cause it to leak in, harder to notice the damage of a pinched oring. Larger ones leak out of the cylinder to the lower plenum. Easier to see the pinch. If you see a crease or line out of place on the o-ring, that is the sign of a pinched o-ring.

Sometimes the o-ring has a "casting" line that runs along the edge of the ring, that is when it will ok, but still could be pinched.