G4+ Link ECU Timing, RB25DET

[eric240sx]

48 minutes ago, Duncan said:

Have you tried to adjust the airflow at idle by turning the big screw on the AAC? As you've cleaned it, it may be letting significantly more air through than when the the ECU was tuned

Hi Duncan,

 

Yes, I have turned the screw all the way in (currently set at this) and backed it all the way out (increases idle into the 3k rpm). Could I have assembled it back wrong? Any way to test it?

[Duncan]

OK great. So with AAC turned all the way in you should have minimal airflow. Does the throttle close fully?  Do you have the other cold start valve connected as well, it might be downstream of the AAC? 

 

[eric240sx]

34 minutes ago, Duncan said:

OK great. So with AAC turned all the way in you should have minimal airflow. Does the throttle close fully?  Do you have the other cold start valve connected as well, it might be downstream of the AAC? 

 

Hi! 
 

I removed the ACC, going to verify all components are installed correctly.
The  throttle body doesn’t close fully, it is slightly open. Should it be closed? I can try closing it further. I don’t believe I have a cold start valve, just the AAC. 

[Duncan]

I'm not familiar with the rb25 throttle, but yes I would expect it 100% closed at rest. My stagea has a little stopper screw on the throttle which can hold it slightly open, if you have the same try and back it off until the throttle is closed at rest. There is probably a proper description in the workshop manual how to deal with all this

[joshuaho96]

37 minutes ago, eric240sx said:

Hi! 
 

I removed the ACC, going to verify all components are installed correctly.
The  throttle body doesn’t close fully, it is slightly open. Should it be closed? I can try closing it further. I don’t believe I have a cold start valve, just the AAC. 

If you try to close the throttle body more by adjusting the throttle stop you're going to cause it to bind against the housing. Don't do this. The throttle stop is set at the factory for a reason and unless you know the correct adjustment specs it's a bad idea to try and mess with it. I'm speaking from experience as someone who has messed with that stuff before. I would only do it on an engine where you're installing your own custom throttle/intake and therefore the adjustment spec is no longer valid.

Once you have ruled out external vacuum leaks you have to start chasing internal vacuum leaks. This is considerably more annoying. What I mean is stuff like this where you have some old worn part allowing air to bypass the throttle so the ECU can see the excess air but it can't control the idle: 

I had a mildly high idle on my RB26 and some combination of having the intake manifold resealed and the throttle bodies rebuilt likely went a long way to curing my high idle issues.

[eric240sx]

Hi @Duncanand @joshuaho96

So… looks like I read this too late. 

I rechecked the AAC and it’s 100% in tip-top shape. 

The bolt Duncan is describing is one I had to remove to paint the outside of the throttle body. For this, I used regular automotive paint, no powder coating. Once I reassembled, I returned the screw to what I thought it was set at. But today, I screwed the bolt on the AAC all the way down, and fully closed the TB, I DEFINITELY felt the binding of the plate. But the car stopped fluctuating and dropped RPM to 900 as @robbo_rb180set it up. It ran as it should, even the air to fuel went to 14.5-14.7at idle. I checked timing at this point and it was running at about 10 degrees, not the 15 I set on the ECU and crank speed timing.  Once I changed the offset to match 15 at idle, rpm rested at 1,300 still higher than what @robbo_rb180set. However, the fluctuating stopped. 
 

In order to open the throttle body at this point, it did require a bit of a push to unbind the plate and have it move freely. However, as soon as it was free, the fluctuating idle started again. I will be looking for the procedure to appropriately set the scree. Yikes! 
 

Not really sure what to do at this point, but I’ll check for internal leaks. Thank you for the video, @joshuaho96!

[eric240sx]

2 hours ago, joshuaho96 said:

If you try to close the throttle body more by adjusting the throttle stop you're going to cause it to bind against the housing. Don't do this. The throttle stop is set at the factory for a reason and unless you know the correct adjustment specs it's a bad idea to try and mess with it. I'm speaking from experience as someone who has messed with that stuff before. I would only do it on an engine where you're installing your own custom throttle/intake and therefore the adjustment spec is no longer valid.

Once you have ruled out external vacuum leaks you have to start chasing internal vacuum leaks. This is considerably more annoying. What I mean is stuff like this where you have some old worn part allowing air to bypass the throttle so the ECU can see the excess air but it can't control the idle: 

I had a mildly high idle on my RB26 and some combination of having the intake manifold resealed and the throttle bodies rebuilt likely went a long way to curing my high idle issues.

This is a good pointer, my base timing is all over the place because my idle is funky. Look like when I cut out all external air supply, it was happy. Hmm.
 I’ll be researching how to detect internal leaks for the RB as we continue to brainstorm : ) once I achieve a stable idle, I’ll do the timing again. It’s hunting time 

[Dose Pipe Sutututu]

39 minutes ago, eric240sx said:

This is a good pointer, my base timing is all over the place because my idle is funky

It's probably your idle control strategy on your Link trying to control the idle speed with timing.

Have you recalibrated your TPS at 0% and 100%? Don't try use the OEM method to do this, as it won't work.

There are two factory leak valves. Try block off the one that's under the plenum and  disconnect it. It isn't really needed with a modern ECU controlling idle.

 

[eric240sx]

1 hour ago, Dose Pipe Sutututu said:

It's probably your idle control strategy on your Link trying to control the idle speed with timing.

Have you recalibrated your TPS at 0% and 100%? Don't try use the OEM method to do this, as it won't work.

There are two factory leak valves. Try block off the one that's under the plenum and  disconnect it. It isn't really needed with a modern ECU controlling idle.

 

Hi @Dose Pipe Sutututu, welcome to the forum! Yes, I have recalibrated my TPS to read 0-100. 
 

I’m going to be looking for internal leaks and see if that can repair the issue. 
 
This is my current setup. It looks more like an RB26

 

[eric240sx]

Hi everyone,

The research and videos I’ve watched, also with @Duncan suggestions, it all seems to point towards the throttle body, TPS, and AAC. But my AAC is working. Plus, after forcefully closing the TB all the way, the engine idled at 900.

Tomorrow I will do the following:

1. Remove the intercooler piping to look at the TB plate to ensure it’s closing properly. 
2. make sure my TPS is set at .45V 

3. recalibrate TPS

3. ensure my throttle cable isn’t too tight 

 

I will keep you updated 

Edited October 10, 2022 by eric240sx

[Dose Pipe Sutututu]

If you're going into that much effort, might as well convert it to DBW.

No more stuffing about with AAC, IACV slow reacting leak valves.

[robbo_rb180]

10 hours ago, eric240sx said:

 

 

Hi Everyone,

Up to date status:

I checked for leaks using a smoke detector. I started by inserting smoke from the turbo intake side, held my throttle body open, and let the pressured (6psi) smoke fill my entire system. There were absolutely no leaks of any kind. 

I cranked the engine and set it to 15 degrees, then I started the engine and set it at 15 degrees (when cold it doesn't fluctuate), but when it warms up enough, it starts idling from 1,300 up to 2,500 RPM. I also noticed the timing moves with the idle. Maybe the timing isnt set and locked properly?

How I set timing:

1. Unpluged TPS

2. Cranked engine without starting until CAS lines up with 15 degrees 

3. Plugged TPS back in

4. Turned engine on (has high idle of 2,000rpm)

5. Adjusted timing offset on g4+ to read 15 on timing mark (still high idle)

6. Engine idle starts fluctuating and timing ranges from 10-25. Idle goes down as it approaches 10, idle goes up as it approches 25. 

I'm not sure how to stop the erradic timing or is it supposed to be that way? Or does that stem from another problem?

I've PM'd you
For everyone following:
There is definitely issue with more air and it wouldn't actually go into Idle as wasn't meeting all parameters so I have gone a Closed Loop idle and Ignition control conditions changed to hopefully get some good data.

Reason was showing 10-25 as its targeting what is commanded on Ign 1 Table at those rpm.

Adjusting offset won't help
It only locks timing when setting the offset.

Hopefully once throttle stop is adjusted and new file is loaded and logged we'll have him sorted.
 

[eric240sx]

Hi @robbo_rb180,

Thank you for taking the time to look at my tune and explain why the timing was ranging. I'm currently at work but once I get home, this is my current plan:

• 1. Remove the intercooler piping to look at the TB plate to ensure it’s closing properly. 
• 2. Make sure my TPS is set at .45V at close
• 3. Recalibrate TPS
• 4. Ensure my throttle cable isn’t too tight 
• 5. Load new tune file and log

I'll report back tonight. 

Thank you all for helping me sort this out. It is never required and yet you take the time to do it.  

[Dose Pipe Sutututu]

If all the above fails, block off this stupid thing:

 

They seem to like to jam up and seize randomly. Typical Nissan leak valve BS, honestly imagine they just used a stepper motor for idle control (like their JZ cousins with some brains).

[eric240sx]

Hi everyone,

 

I ended up running out of daylight, the family came over today.  But I was able to remove the throttle body and yes, there was air getting through, I have adjusted the TB screw and aligned the TB plate. 
This is the current close position. MUCH MUCH better. I put a light behind the TB in a dark room to see how much light was getting through and this is fully closed without biding. It’s just a slit at the top. Is this good?

Fun Fact: I tightened the two bolts a little too hard the first time and ended stripping one when removing. I ended welding a screwdriver tip to take it off  

[eric240sx]

Correction, I inserted the two bolts and now there is a very very very, like hair wide or less slit on both sides. Before it was a pretty big gap compared to this. I’m excited to try it tomorrow! 

[eric240sx]

Hi Everyone,

Okay! After adjusting the throttle body, throttle cable, calibrating the TPS, and setting the AAC, I finally got it to idle at 900RPM! It was definately the way the throttle body was reassembled. I had a pretty big gap allowing air past the plate. 

For anyone that ever has an idle surge/fluctuation issue with an RB25DET, or probably any RB, please do the following:

1. Perform a vacuum test leak. My favorite method is to use a smoke test, but you can use "start yah bastard" fluid around gaskets, vacuum lines, intake manifold, etc. . . 
2. Clean Idle Control Valve or AAC (Clean with carb cleaner, brake cleaner, or whatever else parts cleaning solution). Also ensure the set screw is properly adjusted to allow air in or to block air out. Turn on the engine and turn the screw in or out to hopefully adjust your idle at the correct RPM. Don't be afraid to turn!
3. Make sure TPS (throttle plate sensor) is between .45 - .48V at idle or calibrated using an aftermarket ECU software 
4. Ensure throttle body plate is fully closed, check throttle plate screw. The screw must allow the plate to fully close
5. Ensure your throttle cable is allowing the throttle body plate to fully close, not too tight, not too loose. 

Thank you everyone for all your help! Looks like all I need now is to dial in my tune. I will be consulting @robbo_rb180 for guidance. 

 

[GTSBoy]

4 hours ago, eric240sx said:

Turn on the engine and turn the screw in or out to hopefully adjust your idle at the correct RPM. Don't be afraid to turn!

With the caveat that some IACV/AACs have plastic screws and can be damaged by hamfisted turning.

4 hours ago, eric240sx said:

Make sure TPS (throttle plate sensor) is between .45 - .48V at idle or calibrated using an aftermarket ECU software 

With the caveat that RB20DET and 26DET do not work this way for detecting idle condition - they have an actual throttle closed switch.

[Dose Pipe Sutututu]

1 hour ago, GTSBoy said:

With the caveat that RB20DET and 26DET do not work this way for detecting idle condition - they have an actual throttle closed switch.

And this all goes out the window with an aftermarket ECU as you calibrate 0% at whatever voltage and 100% at whatever voltage. 

[joshuaho96]

On 10/13/2022 at 1:12 AM, GTSBoy said:

With the caveat that some IACV/AACs have plastic screws and can be damaged by hamfisted turning.

With the caveat that RB20DET and 26DET do not work this way for detecting idle condition - they have an actual throttle closed switch.

I still have no clue how the RB26 TPS closed switch works. As far as I can tell it has one but when adjusting it for the factory ECU you go purely off of the voltage and then unplug the TPS to reset the voltage the ECU decides is the magic number.