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Occasional Miss Or Lump On Idle

sturb25

By sturb25,
in Four Door Family & Wagoneers

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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

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  • 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 :)

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