Power Loss On Downshifts, Bouncing Idle And Slight Hesitation At Specific Rev Point -R34Gtt

[rondofj]

Lol....sounds like you just described

hy_rpm.... I agree fully with what you say.,plenty trolls around ;-

[rondofj]

Thread wake up from the dead...

I finally found this elusive motherf**ing problem plaguing my ride for more than a year after the PowerFC tune. To recap - R34GTT running Precision 5558 0.63a/r 290rwkw @ 22psi on 98.

Problem was a massive power loss around 60-70% for at least 4 to 5 seconds when downshifting especially going up hills and also on those low rpm drives below 50km/h- slowing down, turning and climb up a right angled incline in 2nd or 3rd. The power loss is felt after slowing and turning. Also felt in some upshifts but to a much lesser extent and generally when high rpms. The power loss was so bad that uphill felt like it just wouldn't make it if it lasted a few seconds longer.

The result of this thread was numerous tests including swapping AFM, CAS, new O2 sensor, new plugs, new oil, new air filter (general service), disconnecting/connecting MAP sensor, adjusting TPS to 0.46V, removing n cleaning IACV, disconnecting/connecting it, blocking stock plumb back BOV with plate, checking temp sensor and other voltages thru PFC controller etc, even posting up my tune file for members to check. Getting tuner to check a couple times as well. Nope even they found 'nothing wrong' with my car...really... As well as that many people suggested my BOV entry angle to turbo intake wasn't ideal and it was possibly causing reversion, change that they said. NO I said, not convinced because I know fully well under what conditions it was happening and a lot of times under no boost as well.

Read other generic stuff online about traction control, popped bonnet, disconnected TCS sensor plug near firewall and bingo - instant transformation! New car from go, absolutely NO power loss or hesitation under these conditions, tested many times to confirm, that was it! Bloody TCS sensing slip when there was non/negligible and partly closing TCS butterfly for a full 5 seconds. Yet under normal takeoff / boosting while running and shifting to 2nd or 3rd etc with lots of wheelspin it doesn't sense any slip or close butterfly as it should -( the power is there from seat feel). Thinking it aint been properly tuned around in PowerFC am I right? Or dodgy TCS. This didnt happen at all with my previous Nistune and same all else setup.

One problem with disconnecting plug is the check engine light code. So I connected that back on and removed the 15A TCS fuse instead. No check engine light now and no TCS messing up my car = win -win!

Ask why I dont simply switch off my TCS switch - when I bought the car, was told that TCS dont work, I have never seen the TCS/SLIP and HICAS lights to this day (maybe globes removed?). Even the switch doesnt lock to its new position when 'switching' it, it comes back to its original position like a spring. is this how its supposed to be? My TCS does seem to be working (from all the problems its caused me) albeit very incorrectly..

Edited April 23, 2015 by rondofj

[rondofj]

Forgot to add - with the TCS disconnected as is now, it seems like I have suddenly gained massive power and torque through the mid and high rpms especially noticeable in 2nd and 3rd, its pretty insane the amount of grunt that I was 'missing' because my TCS plate was possibly partly/slightly closed even under all driving conditions. Feels easily around 320rwkw now from seat of pants feel

[GTSBoy]

No TCS = no ABS. Be careful.

Better bet would be to remove the butterfly from the TCS TB, perhaps.

[rondofj]

I did think of that, but the ecu would have measured less air hence less fuel and with no butterfly = more air/less fuel, is it possible I will be getting lean-out /danger ? Even for 5 seconds. Even though the TCS wasnt causing this temporary power loss with Nistune it was still not stopping any wheelspin from takeoffs and spirited 2nd/3rd runs either - does this indicate a rooted TCS ecu or sensor? Didnt know about the lack of ABS with no TCS- no good this

[GTSBoy]

Your TCS system does appear to have a problem. Might have existed when you were using Nistune but the symptoms might not have been the same. or it might have developed since going to PowerFC. Can't remember the detail of when it started from your OP and really don't care at the moment either. What is important is that you need not worry about mixture problems. The TCS butterfly is exactly that. A butterfly. The ECU does NOTHING during a TCS intervention that it wouldn't do if you had just closed the main throttle. The TCS system sees slip it wants to stop, so it modulates the TCS butterfly. The ECU doesn't really know anything about this except that the AFM signal is decreased and so it will match fueling to air flow. That's it.

It IS possible that the ECU participates in a TCS event by reducing timing or something. By "ECU" I mean the Nissan ECU. PowerFCs I would expect to not give a shit, seeingas they can't even be bothered to do anything with the Knock sensor other than put up a light. So either way, not your problem to worry about.

Important point for you. Do not confuse the different parts of the TCS system with what they do. The "sensors" for the TCS system are really only the wheel speed sensors. The TCS throttle has a motor on it that is driven by the TCS system to close the butterfly. There is also a "position sensor" on that butterfly that is feedback for the TCS computer. Let's it know what angle the butterfly is at. It is essential for operation and will raise a fault code if not present. Hence why I suggested removing the butterfly from the TCS TB rather than anything else.

[Kinkstaah]

Tcs switch is a button... Not a switch

After looking at the entire system due to installing aftermarket traction control.....

TCS is entirely its own thing... It should have happened with either ECU surely...

As GTSBoy says... Check your ABS actually works. It uses the same speed sensors the Traction control does.... Which has a fault.

[rondofj]

Good point Brad, what I understand as you say it, the powerfc doesnt regard the TCS as anything so my mixtures shouldnt be affected regardless if the butterfly is there or not or if its open/close. So off the butterfly goes- two screws right? Wonder if I can do it from front with throttle body pipe fixed as I dont wana remove that, all that waiting/running round for new T/B gasket.

Kinkstaah, is the TCS button supposed to flip back to its original position right after pressing it? Mine does, like a spring, press button from left to right and it comes back to the left

[GTSBoy]

Yes, the switch is momentary. Someone designed a circuit to replace (or augment) the switch so that it would self cancel at every startup. It's on here somewhere.

[Ben C34]

What is the TCS sensor plug near firewall?

Got a pic?

Glad you sorted it.

[Ben C34]

The t body gasket is reusable.

[GTSBoy]

What is the TCS sensor plug near firewall?

He means the TCS butterfly angle sensor that I was talking about a few posts back. It's "near" the firewall inasmuch as it is on the TCS throttlebody which is broadly towards the back of the engine bay!

[rondofj]

Good that its sorted now, lots of useful lessons learnt about sensors and which one does what and when and how the system works together, even better tested and confirmed that 'most' of my vital sensors and the engines in great health, thanks in a large part to SAU members for all the great help, guys like GTSBoy, Ben C34 and some others

[rondofj]

And yes Ben thats the butterfly position sensor that GTSBoys talking about, its similar to the TPS which is on the other side

[XGTRX]

So just a question. Is there a diagnostic procedure to check this sensor or similar or is it just a matter of fault diagnosis.

[rondofj]

I would assume the same as TPS?, theres a THRTM voltage in powerfc sensor check - (throttle motor sensor).

[wolverine]

3.6v - 3.7v to pin 51 on PFC to get rid of TC light...like we did on Stagea's without TC?

[rondofj]

I just pulled TCS fuse, lights gone. Sensors all connected

Edited April 23, 2015 by rondofj

[wolverine]

Yeah sure but how is ABS?

[rondofj]

Dunno how to check that? ABS lights not on?