CAM Timing fluctuating on Idle (Sometimes)

[Skaith4224]

Hey all,

Been chasing a few little issues here and there as usual but not sure on this one.

Had a few issues with random stalling, seemed to be when changing gear (clutch in, revs drop, engine very occationally dies) and it would even sometimes stall for no apparent reason when idling. no coughing or splutters, just engine dies. electronics stay one.

The odd thing is, I have to turn the car completely off to restart and it will fire up fine. Resetting the ECU I'm guessing. (Apexi FC Pro)

Checked the usual, AFM, Idle control valve cleaned, TPS voltage, fuel filter, new sparks, boost leaks, etc etc,

The thing I've noticed recently is my timing sometimes drops below 15 degrees on idle. This can fluctuate between 9-15 degrees

When this happens, a quick blip on the throttle will bring it back to a steady 15 degrees. Seems be happen when engine braking to a slow speed so the revs are very low. 
If the car has stalled when idling, looking at the handheld I can see that even with the engine off, the timing shows 6 degrees (might vary). Turning the ignition totally off then on again so the ECU reboots, timing goes back to 0.

Another quirk the car has always had since purchase is, if I accelerate in 1st then pop the clutch in almost straight away, it will stall the engine. Don't know if this could be related.

Thing of note, using an aftermarked HKS BOV however was tuned with this and tried with this on and blocked (Don't lecture me on the Turbo wear...)

Basically, wondering if a CAS on the way out could cause the timing issues?

 

Thanks in advance.

[Dose Pipe Sutututu]

Install your stock BOV, recirculate it.

The varying timing is your ECU's idle control strategy, trying to maintain the correct idle by adjusting the timing & the idle control valve.

If you like whooshy whoosh noises, best to install an ECU that can do speed density.

[Skaith4224]

Thanks for getting back to me on this.

Purcchased the car with the aftermarked BOV so will have to have a look at sourcing another one. Does make sense.

 

It's odd that a blip on the throttle will bring it back to stable timing at the same idle, Maybe it's from engine braking to slightly below the requested idle speed that is confusing it?

Might have a tinker with the ECU to see if I can fine tune the idle and see if that at least changes symptoms.

[GTSBoy]

3 hours ago, Skaith4224 said:

It's odd that a blip on the throttle will bring it back to stable timing at the same idle, Maybe it's from engine braking to slightly below the requested idle speed that is confusing it?

No, it's because the BOV is a bloody great air leak and when you poke the throttle you probably are making it open and close and reseat properly.

 

3 hours ago, Skaith4224 said:

Might have a tinker with the ECU to see if I can fine tune the idle and see if that at least changes symptoms.

Don't waste your time. Your AFM is hating life. Change the ECU or put the correct BOV on.

[Skaith4224]

20 hours ago, GTSBoy said:

No, it's because the BOV is a bloody great air leak and when you poke the throttle you probably are making it open and close and reseat properly.

 

Don't waste your time. Your AFM is hating life. Change the ECU or put the correct BOV on.

Still does the same thing with the BOV completely blocked off so no leak there. Am I correct in thinking as the air goes back though the turbo it's "recirculated" as far as the AFM is concerned 

Having a quick look at the ECU settings, the highest Idle I can get it to go to is 950RPM but she has been idling at 1060ish. Could that be the reason the ecu and idle control valve are having an argument? If that was the case, still odd that blipping the throttle steady's it.

Saving for a new ECU but times are hard and it's fun to tinker/diagnose in the mean time 😆

[GTSBoy]

32 minutes ago, Skaith4224 said:

Am I correct in thinking as the air goes back though the turbo it's "recirculated" as far as the AFM is concerned 

Yeah, but it can recirculate "too far". As in, it goes back up the inlet and registers on the AFM again, going the wrong way, thus double metering, and not being any good. This is one of the main reasons that the factory Nissan systems used a compressor bypass valve in the first place.

33 minutes ago, Skaith4224 said:

the highest Idle I can get it to go to is 950RPM

As in, the highest that you can command? Well, yes, but the IACV, if stuck open, can flow more than enough air to rev a lot higher than that.

You should probably clean the throttle body and the IACV with carby cleaner. Might make it all behave a little nicer. IACV will want to be dismantled to achieve the best cleaning results.

[Skaith4224]

50 minutes ago, GTSBoy said:

Yeah, but it can recirculate "too far". As in, it goes back up the inlet and registers on the AFM again, going the wrong way, thus double metering, and not being any good. This is one of the main reasons that the factory Nissan systems used a compressor bypass valve in the first place.

As in, the highest that you can command? Well, yes, but the IACV, if stuck open, can flow more than enough air to rev a lot higher than that.

You should probably clean the throttle body and the IACV with carby cleaner. Might make it all behave a little nicer. IACV will want to be dismantled to achieve the best cleaning results.

Already stripped and cleaned the IACV however didn't adjust the screw, just put it back where I found it.

I'll have a look at the throttle body, Anything I need to watch out for? Seen some post mention that if you clean them, it can remove a seal or wax that helps prevent leaks? Might have been from reading about 350z throttle bodies but want to check.

 

Are there any good guides on adjusting the Idle as I know there's a kind of procedure where things need unplugging during adjustments etc however seen a few conflicting ones.

 

Thanks.

[GTSBoy]

1 hour ago, Skaith4224 said:

Seen some post mention that if you clean them, it can remove a seal or wax that helps prevent leaks?

Only on RB26.

 

1 hour ago, Skaith4224 said:

Are there any good guides on adjusting the Idle as I know there's a kind of procedure where things need unplugging during adjustments etc however seen a few conflicting ones.

Do you want to tell us which engine?

[Skaith4224]

6 hours ago, GTSBoy said:

Only on RB26.

 

Do you want to tell us which engine?

Sorry, totally forgot to mention that!

 

It's an RB25DET in an 1995 R33 GTST spec 2

 

Usual mods I suppose,

Front Mount intercooler,

new Rad,

Strighthrough exhaust,

HKS BOV,

Greddy turbo timer,

Catch Can

Apexi Power FC ECU

 

Thanks,

Edited June 23, 2023 by Skaith4224

[Duncan]

So if PFC is set to idle at say 900, and the engine is running higher than that, the ECU will be trying to bring revs down, but it only controls the fuel and spark timing.

Adjust the screw on the IACV clockwise until the revs drop to the ECU target, which reduces the air coming in. Once that is set properly the idle should settle OK, unless there is another air leak or other problem 

[Dose Pipe Sutututu]

I'm going to take a guess the AAC valve is stuck open.

This is the one under the plenum, pain in the arse to get to.

Imagine Nissan used a stepper motor like their JZ cousin or their distant friend, 4G63. Nope, they decided to use twin leak valves to control idle.

[Murray_Calavera]

I can not wait to setup DBW and pull all of these leak valves in the bin. 

[joshuaho96]

2 hours ago, Dose Pipe Sutututu said:

I'm going to take a guess the AAC valve is stuck open.

This is the one under the plenum, pain in the arse to get to.

Imagine Nissan used a stepper motor like their JZ cousin or their distant friend, 4G63. Nope, they decided to use twin leak valves to control idle.

AFAIK that's not called an AAC valve but rather an "intake air regulator". In Nissan's defense Toyota loved putting similar weird things on a lot of their cars, they just stopped doing it sooner than Nissan it seems.

[Dose Pipe Sutututu]

2 hours ago, joshuaho96 said:

AFAIK that's not called an AAC valve but rather an "intake air regulator". In Nissan's defense Toyota loved putting similar weird things on a lot of their cars, they just stopped doing it sooner than Nissan it seems.

Yeah that thing, it belongs in the bin.

[Dose Pipe Sutututu]

3 hours ago, Murray_Calavera said:

I can not wait to setup DBW and pull all of these leak valves in the bin. 

It's so good, best thing I did.

Superb idle control, superb AC idle control & operation, superb throttle curve control.

I still find it funny people that spend big bucks on builds to only use a cable throttle. 

[Duncan]

1 hour ago, Dose Pipe Sutututu said:

........superb throttle curve control.....

well there you go. I always thought the throttle was an on/off switch

[GTSBoy]

1 hour ago, Duncan said:

well there you go. I always thought the throttle was an on/off switch

It is.....in dirt rally.

[Skaith4224]

Good news, 

 

Adjusting the idle control valve did the trick. Maybe the warmer weather had some effect? 

As soon as I turned it about 15 degrees the timing settled. Tweaked to match the rpm asked for by the ecu. 

 

Just glad the Cas isn't dead :D

 

Any who, will do some testing and see if I still get any stalling. 

[GTSBoy]

4 hours ago, Skaith4224 said:

Tweaked to match the rpm asked for by the ecu.

Turn it down further. Make the ECU use more of the available IACV capacity to achieve it. Better to run in the middle of the range than at one end.