Rb25 Flat/dead Spot

[Franko07]

So i've had my rb25 cefiro going for a while now everything seems fine until i discovered this little problem *sigh*

What happens is if the cars running (warm or cold) you slowly increase the revs from 8-900rpm to 2100-2500 I mean really slowly, it gets to 2200 rpm and then starts hunting like mad and you can continue accelerating pretty much to my foots flat on the floor and wont go over those revs. If I back off completely it idles fine, no hunting, then if I stab the throttle and race the engine it revs fine all the way to redline...

I don't even know where to start on this one, seems sensor related. I thought that it might be that my AFM is in the intercooler piping on the throttle body and wasn't getting enough air early on to read properly, so I put it back to where it's supposed to be and it still does it. It is a pink label AFM with a series 1 ECU? Don't know if that matters at all but when I unplug it when cars running it stalls immediately and when I start the car with it unplugged it runs but when you try and rev it, it tries to stall out again, so I'm pretty sure the AFM is doing its thing...

I wouldn't be so concerned but when you drive the car and change gears it seems to hit that flat spot when the revs die down and makes it really jerky...

Where should I start looking?

Mods are basically bone stock s2 rb25 with Freddy plenum 90mm throttle body, bcpr5es sparkplugs s1 turbo.

thanks!

[Ben C34]

Tune?

They are some hot spark plugs. What's the theory for using them?

[Franko07]

nah stock ECU atm.

Yeah i thought they were a bit hot, thats just what auto one gave me but i always ran 6's and then 7's in my Sr thought may be rb's needed a hotter spark? Might change to a 6 as I want to run 12-13psi for now...

do I want a bcpr6 or a bkpr6? one has a longer porcelain but cant remember haha.

Edited October 24, 2015 by Franko07

[GTSBoy]

S1 ecu was green label afm. Is the wiring converted?

[Franko07]

yeh id say so as i have the 3 pin clip that attaches to the AFM and when i trace the wires back to the body loom theres only 3 as well. Its a bit hard as this is a conversion and it was already done when I bought the car so its a bit of a head f**k because its a s2 Rb being run through a rb20 loom to a s1 ECU.

It was my understanding that the extra wire in the green label AFM Is another earth? From memory (this was a while ago) signal earth and earth were just twitched together to make 1 wire then I just had signal and 12v left.

[Franko07]

sorry to bring this thread back but i still haven't found the solution to this problem.

Iv'e changed the spark plugs to Bcpr6es, I've tried and cleaned two Iacv controllers, swapped out for better coil packs, changed to a different CAS. I'm running out of ideas on this one now I'm thinking it may be the ECU temperature switch that lives in the intake plenum? except i thought this would effect the engine on idle as well as this only happens when you rev the engine..? ECU idle screw is also turned all the way to the left. Can't get ECU to display codes either?

I don't think its a boost/vacuum leak as I've blocked off air coming into the turbo and the car stalls and if i unblock an unused vacuum port the car runs like a bag of shit and tries to stall. This effects the engine with load or no load but mainly only in first to second gear third and fourth it doesn't seem to effect it near as much just makes it really painful to take off. Car feels slightly underpowered as well sluggish almost.

Here's a vid to better explain it...

thanks!

[Ben C34]

Blocking the inlet in no way at all is a diagnostic thing to do.

You have to pressure test to find leaks. That's a fact.

Unblocking an unused vacuum port is weird. Not sure what you are trying to achieve there.

What ecu temp switch in the plenum? Hint ;there isn't one. I suppose you mean the one in the top radiator hose near the plenum.

Stop guessing. Get a multimeter. Check it.

[Franko07]

If you block the inlet and you had a leak wouldn't the engine try and breath through the leak? What I'm trying to do is rule out common things like a vacuum leak if i create one and there's no change to the engine then there might be a leak somewhere else but because it makes it worse then its probably not that. I have pressure tested it as well though and i cant find any leaks unless there tiny as.

Switch was probably the wrong word there's your cluster temperature solenoid and next to it is your ecu one and if there faulty your ecu dumps fuel because it thinks its overheating but this usually effects idle as well wheres my car idles fine only gets effected at 2200rpm...

[Ad's]

Have you got it tuned yet? Mine was a doey POS with a standard ecu fmic, exhaust and more boost, then installed a power fc and put a "home" tune into it witch lived it up a little over last summer. Now shes at the tuners to have her tuned by the pros and a few little things addressed at the same time.

Id get a retune able ecu or have one supplied by your tuner, save 1k and drop it off that way you are covered fr a tune and diagnostic work.

[Franko07]

yeh thats my next step when i put on a bigger turbo and all that jazz but its complety stock except for that plenum so it shouldn't be doing this and kinda want it fixed before i do that in case another ecu doesn't fix it and the tuner has to go on a hunting expedition. May be i should borrow another stock ecu before hand (seeing as i cant get the LEDs to flash on this one may be theres something wrong with it?) I just thought they either worked or didn't and not slowly failed...

[Franko07]

Stop guessing. Get a multimeter. Check it.

What am i checking for? resistance voltage ohms? google says you need the consult port to check...

Edited December 13, 2015 by Franko07

[Franko07]

another thing to add is that this problem actually disappeared one day without me changing anything except it caused my idle to be so low that when you'd come to a stop the car would stall, as soon as i lifted my idle back up using the screw on the iacv the problem came back and hasn't gone away since. I thought that this meant it was definitely the iacv and i had a spare but no change since swapping and cleaning both.

[Franko07]

I've had a small breakthrough, was going back and re checking simple things and was testing my TPS for the voltage and all was good then went on ahead and disconnected it to try and reset my idle. As soon as i disconnected it the car instantly felt better, more responsive the hunting had gone away the revs were steady didn't feel lethargic anymore, plugged it back in back to hunting and miss behaving.

1. Does this indicate that the TPS is buggered even though its giving out the correct voltage?

2. There was only one plug on my s1 loom for the TPS even though there's two ports on the sensor itself and it went in the port that's external to the sensor on a wiring loom? I figured the other one is for diagnostic reasons but i dkno what its supposed to be?

3. Is it bad to yolo this and drive with it disconnected?