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How Do You 'tune Out' Flopping Rpm?

SargeRX8

By SargeRX8,
in Engines & Forced Induction

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SargeRX8 Grand Master

SargeRX8

Posted
Posted

My car sometimes, not all the times, hits about 500rpm when clutching in. It doesn't sound like its going to stall but it doesn't sound like it should be doing it. I have a fair bit of bolt on mods with the PFC ECU. Sometimes when coming to a stop(and it makes no difference, off boost, light throttle etc) the revs come to about 500rpm and the car kicks back up and idles fine. Ive cleaned the AAC. Ive removed fuel from the cells it hits in the first column of the pfc but didn't make a difference. Its going into the first column then into the higher load cells. Something is telling the car there is a load on the engine and it kind of f**ks around a little...

Also, now don't anyone give me shit for it, if I want to remove my BOV, how do you tune out the symptoms of running no BOV? I know alot of cars who have no BOV with nice deep flutters and there car doesn't stall. My old skyline would switch off instantly even on a free idle rev and flutter. Is it about removing fuel or giving it fuel?

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rob82 Mentor

rob82

Posted
Posted

There is no way to tune a PFC around maf reverse caused from running no bypass valve. All you will be doing is fudging one section of the map to stop overfilling of another section of the map.

Ie you may help the idle sag but create a lean spot once on throttle. If you want your car to be in a proper state of tune put the bypass valve back on the car and get over it.

SargeRX8 Grand Master

SargeRX8

Posted
  • Author
Posted (edited)

There is no way to tune a PFC around maf reverse caused from running no bypass valve. All you will be doing is fudging one section of the map to stop overfilling of another section of the map.

Ie you may help the idle sag but create a lean spot once on throttle. If you want your car to be in a proper state of tune put the bypass valve back on the car and get over it.

But Ive seen and heard of a fair few skylines running power FC with atmo bov and even with a blocked BOV and some don't have the issue...

Gay piece of arse AFM.

None the less though I still get the dip in RPM WITH the BOV fitted. Like I said in the OP, I don't even need to be on any boost(all vacuum) and it still does it. Just now I was driving home 50km/h in third. I clutch in to stop at the lights and they dip to 500rpm then jump back up, it just gets worse with the BOV gone.

Edited by SargeRX8
GTSBoy Grand Master

GTSBoy

Posted
Posted

IAC and AAC are the same thing just different names.

No, not true. IAC is the one on the back of the plenum that the ECU controls the idle speed with. The AAC is the Auxiliary Air Control which is the heated thermostatic valve hidden under the plenum that is open when cold and closed when hot and allows a lot of extra air in to raise the cold idle.

The only one that matters in this instance is the IAC, but if he's cleaned it and it still fluffs around then it is probably a tuning issue as per others above.

SargeRX8 Grand Master

SargeRX8

Posted
  • Author
Posted (edited)

I cleaned the aac as per the diy. Is that cleaning the iac too? Afaik the aac lets the engine breath more air when you use things like air con, the brakes, power steering etc.

Isn't that thermostat the csv, cold start valve which is the one under the plenum?

Edited by SargeRX8
89CAL Grand Master

89CAL

Posted
Posted (edited)

No, not true. IAC is the one on the back of the plenum that the ECU controls the idle speed with. The AAC is the Auxiliary Air Control which is the heated thermostatic valve hidden under the plenum that is open when cold and closed when hot and allows a lot of extra air in to raise the cold idle.

The only one that matters in this instance is the IAC, but if he's cleaned it and it still fluffs around then it is probably a tuning issue as per others above.

Ah i see now. So the AAC is what i was calling the cold start part of the system and the IAC is the Idle control. i always knew that's what the IAC did but people always throw AAC around and gets confusing.

Yeah that's fair enough then. at least that clears that up

I changed my FC/1 and FC/2 settings and mine is fine now. used to dip a bit when clutching in and IAC has already been cleaned. set them at 1500 as suggested

Edited by 89CAL
JonnoHR31 Grand Master

JonnoHR31

Posted
Posted

good to see your being as helpful *cough*condescending*cough* as ever mafia.....

Will adjust those sells by a few degrees, +5 should be fine in each cell right?

depends what they are at the moment. i wouldnt go any further than 20-25 degrees in n01 as any more is likely to go backwards and have the same effect as less timing. unless your timing in these cells is really low for some reason this will just help to mask whatevers really causing it. its sounding more and more like a sticky iac/aac

T04GTR Grand Master

T04GTR

Posted
Posted

its abit hit and miss as that rpm range canot be acuratly "dynoed" i find wacking in some timing and similar fueling as at idle seems to help. also having a blanket 20 odd degrees around the idle area seems to smoth out a unstable idle. bigger afm,s and non return bov's do make it harder.

also raising the decel fuel cut to around 2k helps aswell. on our race car it has no idle control at all. and used to hunt real bad after giving a rev. when i turned off the decel cut it was perfect.

simpletool Mentor

simpletool

Posted
Posted

The decel fuel cut not cutting out soon enough could be the issue.

20 deg of timing around the idle is a fair bit. I run 16° at idle, 12° at 800rpm. Also 13.8 AFR 1200rpm and below. Good for clutch out at idle in traffic - crawl.

paulr33 Grand Master

paulr33

Posted
Posted

the only suggestion i have is find someone with datalogit, copy your tune

get the engine setup correctly, base timing, remove your bov or fit it (how ever you like), check the aac valve, check idle air control, check for basic vac leaks etc

then DATA INIT

perform self idle adjust as per powerfc-faq

and let iet idle for 30 minutes (dont drive or f**k around, just let it idle as per instructions)

then confirm you have good idle and stable de-accel

ie go for a fang around the block and confirm its OK

then "write" your previous tune over the top

if you dont have access to datalogit its a bit painful to do it manually

ie pay someone beer to copy your tune

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