Jump to content
SAU Community

Occasional Miss Or Lump On Idle

sturb25

By sturb25,
in Four Door Family & Wagoneers

 Share

Recommended Posts

SMOKEYV35 Mentor

SMOKEYV35

Posted
Posted (edited)
What is this PCV valve is it present on standard RB's and Neo's or what?

PCV valve is positive crankcase ventilation valve. most cars have them - they basically release any buildup of combustion gasses that sneak past the piston rings and in under the cam covers. this is also called 'blowby'.

the PCV is the factory way of releasing that pressure. the valve opens when the crankcase is under positive pressure, releasing the gasses and any oil vapour back into the intake where it cycles back into the engine and is burnt off in the next combustion cycle.

a way that tuner's approach this is to get rid of this system and run a breathable catch can - which vents that vapour to the atmoshpere naturally, and then using a series of baffles, attempts to get the oil particles out of the vapour, where the accumulate in the bottom of the catchcan to be drained later. because it is unmetered exhaust releasing to atmosphere, they're illegal.

after that explanation, i'd be curious to see how he thinks the PCV is contributing to the miss. unless it is sticking shut, and then snapping open and releasing a big pressurised hit back into the intake - but that could only upset the AFR if it was entering the intake before the AFM?? either way, it's easy to eliminate the possibility just remove the return pipe from the intake and plug the intake hole with your thumb. if its still doing it, it's not your problem!

EDIT: just thinking this over in the back of my head, it could be stuck - yes. but it could be stuck OPEN, which would cause a vaccum leak and create a lean misfire. to check this, take the hose off at the PCV valve, and block the PCV valve with your thumb. all in all, pretty quick checks!

and if you just want to service it for peace of mind, grab some throttle body cleaner (carby cleaner) and remove the PCV. soak it in a cap full of the stuff. shake it round a bit and it should start moving freely again. do your throttle body while you're at it.

Edited by SLYLINER
Brendan&Ana Collaborator

Brendan&Ana

Posted
Posted

EDIT: just thinking this over in the back of my head, it could be stuck - yes. but it could be stuck OPEN, which would cause a vaccum leak and create a lean misfire. to check this, take the hose off at the PCV valve, and block the PCV valve with your thumb. all in all, pretty quick checks!

and if you just want to service it for peace of mind, grab some throttle body cleaner (carby cleaner) and remove the PCV. soak it in a cap full of the stuff. shake it round a bit and it should start moving freely again. do your throttle body while you're at it.

thats basically what the mechanic has said but he told me to just buy a new 1 cause it should be pretty cheap and throttle body and injectors have already been cleaned

Brendan&Ana Collaborator

Brendan&Ana

Posted
Posted
Just tried cleaning mine and still no joy.

Going to go get a new set of plugs (even though these only done 2,500) sometime soon

when i went to mechanic he cleaned mine aswell it was fine for a lil while then came back but he did say i need to replace it

  • 2 weeks later...
kidafa Veteran

kidafa

Posted
Posted

Turns out my issue was my timing on base idle was well out... I should have chucked the light on it ages ago but its been with a mate! Dialed it in on the dyno today and shes happy again :-)

  • 1 month later...
sturb25 Proficient

sturb25

Posted
  • Author
Posted

Replaced my plugs with coppers today, the miss on idle has gotten worse but it seems to be smoother on and off throttle especially noticable whilst going down hill. Am going to replace o2 sensor in a couple of weeks, i havent ever replaced it and its done 160,000km now.

This miss has got to be sorted out, its starting to shit me. The last time it was this bad was about two years ago and i tracked it down to the hose that crosses over the rocker covers at the front having a split in it. Maybe it is a hose.

When u sit there with your foot resting on the throttle giving it a flat constant rev at one rpm anywhere in the rev range its got a miss but you dont feel it when your driving.

sturb25 Proficient

sturb25

Posted
  • Author
Posted
Replaced my plugs with coppers today, the miss on idle has gotten worse but it seems to be smoother on and off throttle especially noticable whilst going down hill. Am going to replace o2 sensor in a couple of weeks, i havent ever replaced it and its done 160,000km now.

This miss has got to be sorted out, its starting to shit me. The last time it was this bad was about two years ago and i tracked it down to the hose that crosses over the rocker covers at the front having a split in it. Maybe it is a hose.

When u sit there with your foot resting on the throttle giving it a flat constant rev at one rpm anywhere in the rev range its got a miss but you dont feel it when your driving.

How do you reset the ecu?

  • 1 month later...
sturb25 Proficient

sturb25

Posted
  • Author
Posted

Yay, my cars miss is all sorted out. Took it to the mechanics about 2 weeks ago and they said the timing was out 4 degrees so they adjusted that and cleaned the air flow meter but the miss was still there, slightly better but still there.

They checked a few more things but couldnt figure out why it was there. They said the only thing they could think it would be is a dirty injector, so i pulled them out and had them tested and cleaned and re-tested.

The injectors came up 10% difference between the lowest and the highest pressure, the spray and spray angle was good. They got them within 2% from highest to lowest after cleaning them. There tolerance is 3%

My car has never sounded so smooth, no more popping. Its actually gotten quieter, Im wrapped

DaveB Mentor

DaveB

Posted
Posted

Yay, my cars miss is all sorted out. Took it to the mechanics about 2 weeks ago and they said the timing was out 4 degrees so they adjusted that and cleaned the air flow meter but the miss was still there, slightly better but still there.

They checked a few more things but couldnt figure out why it was there. They said the only thing they could think it would be is a dirty injector, so i pulled them out and had them tested and cleaned and re-tested.

The injectors came up 10% difference between the lowest and the highest pressure, the spray and spray angle was good. They got them within 2% from highest to lowest after cleaning them. There tolerance is 3%

My car has never sounded so smooth, no more popping. Its actually gotten quieter, Im wrapped

That's a great result, glad to hear. I actually developed a slightly rough idle after going to 600cc injectors (neo); this was apparently to do with not having quite enough resolution in the latency settings. It doesn't bother me; sounds kinda 'tough', and for the increase in power I'll tolerate it :)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      Nah, that is hella wrong. If I do a simple linear between 150°C (0.407v) and 50°C (2.98v) I get the formula Temperature = -38.8651*voltage + 165.8181 It is perfectly correct at 50 and 150, but it is as much as 20° out in the region of 110°C, because the actual data is significantly non-linear there. It is no more than 4° out down at the lowest temperatures, but is is seriously shit almost everywhere. I cannot believe that the instruction is to do a 2 point linear fit. I would say the method I used previously would have to be better.
    • GTSBoy
      DeAgostini 1/8 scale BNR32 Nissan Skyline GT-R Nismo

      By GTSBoy · Posted

      That's hilariously putrid!
    • GTSBoy
      R33 Fuel Pump & Brakes after alarm swap

      By GTSBoy · Posted

      When I said "wiring diagram", I meant the car's wiring diagram. You need to understand how and when 12V appears on certain wires/terminals, when 0V is allowed to appear on certain wires/terminals (which is the difference between supply side switching, and earth side switching), for the way that the car is supposed to work without the immobiliser. Then you start looking for those voltages in the appropriate places at the appropriate times (ie, relay terminals, ECU terminals, fuel pump terminals, at different ignition switch positions, and at times such as "immediately after switching to ON" and "say, 5-10s after switching to ON". You will find that you are not getting what you need when and where you need it, and because you understand what you need and when, from working through the wiring diagram, you can then likely work out why you're not getting it. And that will lead you to the mess that has been made of the associated wires around the immobiliser. But seriously, there is no way that we will be able to find or lead you to the fault from here. You will have to do it at the car, because it will be something f**ked up, and there are a near infinite number of ways for it to be f**ked up. The wiring diagram will give you wire colours and pin numbers and so you can do continuity testing and voltage/time probing and start to work out what is right and what is wrong. I can only close my eyes and imagine a rat's nest of wiring under the dash. You can actually see and touch it.
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      So I found this: https://www.efihardware.com/temperature-sensor-voltage-calculator I didn't know what the pullup resistor is. So I thought if I used my table of known values I could estimate it by putting a value into the pullup resistor, and this should line up with the voltages I had measured. Eventually I got this table out of it by using 210ohms as the pullup resistor. 180C 0.232V - Predicted 175C 0.254V - Predicted 170C 0.278V - Predicted 165C 0.305V - Predicted 160C 0.336V - Predicted 155C 0.369V - Predicted 150C 0.407V - Predicted 145C 0.448V - Predicted 140C 0.494V - Predicted 135C 0.545V - Predicted 130C 0.603V - Predicted 125C 0.668V - Predicted 120C 0.740V - Predicted 115C 0.817V - Predicted 110C 0.914V - Predicted 105C 1.023V - Predicted 100C 1.15V 90C 1.42V - Predicted 85C 1.59V 80C 1.74V 75C 1.94V 70C 2.10V 65C 2.33V 60C 2.56V 58C 2.68V 57C 2.70V 56C 2.74V 55C 2.78V 54C 2.80V 50C 2.98V 49C 3.06V 47C 3.18V 45C 3.23V 43C 3.36V 40C 3.51V 37C 3.67V 35C 3.75V 30C 4.00V As before, the formula in HPTuners is here: https://www.hptuners.com/documentation/files/VCM-Scanner/Content/vcm_scanner/defining_a_transform.htm?Highlight=defining a transform Specifically: In my case I used 50C and 150C, given the sensor is supposedly for that. Input 1 = 2.98V Output 1 = 50C Input 2 = 0.407V Output 2 = 150C (0.407-2.98) / (150-50) -2.573/100 = -0.02573 2.98/-0.02573 + 47.045 = 50 So the corresponding formula should be: (Input / -0.02573) + 47.045 = Output.   If someone can confirm my math it'd be great. Supposedly you can pick any two pairs of the data to make this formula.
    • Jarsky
      R33 Fuel Pump & Brakes after alarm swap

      By Jarsky · Posted

      Well this shows me the fuel pump relay is inside the base of the drivers A Pillar, and goes into the main power wire, and it connects to the ignition. The alarm is.... in the base of the drivers A Pillar. The issue is that I'm not getting 12v to the pump at ignition which tells me that relay isn't being triggered. AVS told me the immobiliser should be open until the ignition is active. So once ignition is active, the immobiliser relay should be telling that fuel pump relay to close which completes the circuit. But I'm not getting voltage at the relay in the rear triggered by the ECU, which leaves me back at the same assumption that that relay was never connected into the immobiliser. This is what I'm trying to verify, that my assumption is the most likely scenario and I'll go back to the alarm tech yet again that he needs to fix his work.      Here is the alarms wiring diagram, so my assumption is IM3A, IM3B, or both, aren't connected or improper. But this is all sealed up, with black wiring, and loomed  
×
×
  • Create New...