Hi, I recently purchased a 300 and I have the current problem with idle and black smoke 

300zx TT black smoke and bouncing idle 500-1750rpm when warm 

when it’s cold it sits at 1500rpm but as soon as it’s warm it just keep bouncing up and down from 500-1750rpm with black smoke 

 

any help or suggestions or anyone who has had this problem before please let me know 

 

thanks 

Black smoke is running rich. The car isnt getting the right fuel/air mixture. This could be a few things, but MAF springs to mind first. These often die or stop working properly. Have you tried running the engine codes? That should tell you any problems and create a list to start from.

The codes can be grabbed with this walk through:

http://twinturbo.net/nissan/300zx/forums/technical/view/1105629/The-Ultimate-Guide-to-ECU-Diagnostics.html

Welcome to the club and hope you get your 300zx sorted soon. 

Hi, thanks for the reply’s 

 

I ran code testing today and code 34 came up which is the knock sensor, I have the right resistance on the loom to the ecu so I used a 1m resistor to see if the code did go away which it did, so only have code 55 which is all clear 

 

any other suggestions ? 
 

thanks 

The codes only show when certain monitored voltages are out of the pre-determined range. If the MAF or another component is failing but still within that allowed range it won't flag an error. Annoying! 

I'm currently suffering an over fueling issue with one of my zeds and have slowly been replacing bits (either bought, borrowed or swapped off my other zed) to narrow down the problem. 

Can you check all the pipe work and make sure no air is sucking in anywhere it's not supposed too? Try taking the plugs out and check them? Check the injectors to hear them clicking or not (there is a walkthrough on how to do that somewhere on the web), basically check all the air and fuel systems for leaks/wrong mix/etc.

failing all that, jimmer and jeffTT (although retired) are a wealth of knowledge!

Edited July 24, 20205 yr by TheRealNips

As a quick check, you should be able to unplug the MAF and run it on the base map to rule out if it’s causing the issue.

As mentioned above, it’s quite possibly an air leak. The small hoses around the engine bay, on the sides of the head etc are classic for perishing and developing tiny splits.

Could be a multitude of things. From one simple issue to multiple issues. Has it ever run properly during your ownership? 
Id really look at giving it a really good look over, depending on your experience this may be better left to a professional. 
Where about in the country are you? 

Thanks for all the responses, I’m waiting on another MAF and should be able try that mid week, I’m also waiting for Jimmer to have a slot as I’m based in Bristol and his unit is only a few miles away, as soon as he has a slot I’ll drop it up to him I was just trying to see if I can find any obviously faults before hand 

I can’t visually see any problems with pipes, I bought the car with this issue, the previous owner had the engine out refreshed quite a lot of stuff but then had the problem and just left it on his driveway 

 

thanks 

Just an update still no difference 

 

I have fixed 4 boost leaks, reset the TPS to the correct range 0.44v, I boost leak tested it and sorted 4 leaks out, I’m still idling around 1500-1600 rpm and then it will start bouncing still 

the hard idle switch is working fine on the TPS as I have the Nissan app and have checked it’s opening and closing 

 

the car won’t start at all if the maf is unplugged though someone said it should run with it unplugged, any idea what could cause this ? 
 

thanks

Have you tried unplugging the MAF with the engine running? It can be difficult starting them without it plugged in from what I recall.

Were the four leaks you’ve fixed all easy to find / get at? As you might find there’s more in more obscure places.

 

 

I had found 2 leaks from the hard pipes which were blocked off with a screw and 2 short pieces of silicone, I could blow through them where the screws were to small, i think they’re blanked as I have a electric boost controller 

one leak was on a DV valve pipe had a small slit in it, one was a upper intercooler hose which needed snugging up 

 

if I unplug the maf while it’s running it does within 10 seconds and runs rougher 

 

thanks 

Hmm.. ok. Well if you’ve got a new MAF on the way you can eliminate that.

My next move would be the O2 sensors if you haven’t already.

The maf has came already and it’s the one in currently, is there any way to test the O2 sensors ? 
 

thanks 

 

there’s no errors codes 

The diag software should give them.

No errors on the app at all 

The O2 sensors have a value have a look at this page.

https://conceptzperformance.com/wiki/index.php/Consult_Quick_Reference#O2.2FOxygen_Sensor

 

https://imgur.com/gallery/RthfJyv
 

would this be the value in my app under 02 ? Uploaded a picture on the link above thanks 

Yes looks fine there are 2 I had changed 1 now both you can see the difference. 
 

I will have a look tomorrow if I can see 2 sensors on the app, cheers 

Isn’t this car booked in with Jim? 

Yeah going to ring him tomorrow to confirm he never gave me a date yet but hopefully this week just trying to do what I can 

Just an update, not sure if the maf is playing up still because when I check the voltage it’s 1.7V at my idle speed it 1350-1400

i have 2 Oem mafs here one reads 1.71V one reads 1.8V

also have a Chinese maf that reads 1.89-1.9V 

the car is fully warmed up and idle is 1350-1400

 

im under the impression the voltage should be a lot lower ? 
 

any input welcome thanks 

Because your idle is high the voltage would change. You can try the IAA idle screw and see if you can get the revs down, as I did then sorted the problems and turned it out again. I had black smoke but changed a lot of parts, now it’s fine.

Edited August 9, 20205 yr by Bones28

I’ve seen some comparison videos at 1200-1250 rpm and there mafs are at 1.4v 

i haven’t tried the screw yet seems quite awkward to get to but may try within the week, do you go counter or clockwise to get the idle down ? Also how many turns does it go ? 
 

thanks 

Apologies if you’ve tried this already, but have you tried an ECU reset? You need to do it on the Z32 if you make any modifications.

7 minutes ago, 300zxfishy said:

I’ve seen some comparison videos at 1200-1250 rpm and there mafs are at 1.4v 

i haven’t tried the screw yet seems quite awkward to get to but may try within the week, do you go counter or clockwise to get the idle down ? Also how many turns does it go ? 
 

thanks 

Long screwdriver not that hard, if you need more space take battery out. Clockwise to bring revs down cuts air flow if you have a leak somewhere.

Bottom of page http://twinturbo.info/63104/157335.html

Edited August 9, 20205 yr by Bones28