AAC Valve operation HELP!

[GodziRRa]

Good day fellow GT-R enthusiasts!

I have been tracing my car's overnight start up problem for months I'm getting used to it. The problem is like when you leave the car sitting for a long period like overnight, it will have a hard time starting in the morning. When you crank it will sort of start but immediately stumbles, rpm drop, and dies. It will take 3 tries before it will start. But if I step on the gas a bit to make the engine catch up, the engine will start no problem even on mornings. The car rans perfect, and it will start one click just after one successful start even if it is still a bit cold.

Checked the fueling, spark, MAF, start signal. Parts like AAC, coil pack, coil pack harness, FPR, igniter all fairly new. So the other day I was fooling around w/ the consult with both the GT-R and B13 w/ SR20VET. That's when I noticed the starting behavior of the GT-R's AAC valve.

When you crank the engine, % of the AAC valve will jump to 80% but when the engine is about to start it will rapidly drop to 10% (I'll feel the engine stumble & idle drop along with it) then % will slowly rise up to around 40%. Comparing it with the SR20, the behavior is totally different. On start ups it will rise to around 80% then SLOWLY drops % (won't dive like the GT-R), thus you can feel the engine drops idle along with it smoothly. That made me think maybe this is the problem I have been tracing all along.

So calling out GT-R gurus out there, help! Any inputs would be very much appreciated.

[Skym]

ECU switches to different startup tables when starting. Some are richer (leaner with exhaust, etc), retarded and need to be retuned. Even just fitting a higher flowing exhaust can make the hard starting problem pop up.

I've found too thick oil (factory oil is 7.5w30 when new), intake airleaks before, after turbo, faulty CAS (pulls ignition timing by 1-2 degrees), ECU tune, leaking exhaust manifold gasket from exhaust manifold to head can add to the hard start problem when cold. Dirty AACV, IACV can be others (need to be cleaned or replaced, especially if turbo oil seal on compressor side has failed and put oil through intakepiping, etc).

The main cause is the warmup tables (ECU tune) after fitting mods.

[GodziRRa]

I'm running Mine's ecu as of the moment. You said something about aftermarket exhaust and thick oils can do this? I didn't know that. Car has Apexi downpipes and exhaust, and Motul 300V 15W50. How can a exhaust system do hard starts by the way? The engine has new Nismo gaskets, new Cold Start Valve, AAC, I did also try to swap CAS... I guess I'll try to have a new ecu and tune to check if I need a new start up table.

Thanks sir!

[allwheeldrifter]

did u figure it out? my car does the same thing...... but its since i changed my motor.......

[GodziRRa]

Nope matey! I'll try to tune it with another ecu and see how it goes. I'm running mine's right now and I don't want them to retuned my ecu since it's not cost effective. Every time I put something new, need to send ecu to them.

Is your symptoms very similar with mine? It only happens during mornings when car is parked for a long time? I also checked AAC continuity to the ecu and it turns out ok.

[allwheeldrifter]

If my car is parked for a fair amount of time, it very rarely starts properly, i have to hold the throttle a bit, if not, the idle gets very low car almost wanna stall (sounds bad). It stabilizes after a few seconds

[Skym]

I'm running Mine's ecu as of the moment. You said something about aftermarket exhaust and thick oils can do this? I didn't know that. Car has Apexi downpipes and exhaust, and Motul 300V 15W50. How can a exhaust system do hard starts by the way? The engine has new Nismo gaskets, new Cold Start Valve, AAC, I did also try to swap CAS... I guess I'll try to have a new ecu and tune to check if I need a new start up table.

Thanks sir!

Use 10w40 oil. Nismo now use 5w40 oil with S2 tune engines (with R35GTR? injectors) -

http://www.nismo.co.jp/omori_factory/original_menu/engine_m/s2/index.html

And R2 tune engines (racetrack, with R35GTR? injectors) -

http://www.nismo.co.jp/omori_factory/original_menu/engine_m/r2/index.html

Loss of back pressure, retarded ignition timing, running richer than it should. Pressing throttle while starting engine advances ignition timing and opens throttlebody butterfly's (allows more air to enter engine). Cranking engine longer is another way to get pistons pumping which makes engine suck in more air to comabt rich mixture.

[GodziRRa]

If my car is parked for a fair amount of time, it very rarely starts properly, i have to hold the throttle a bit, if not, the idle gets very low car almost wanna stall (sounds bad). It stabilizes after a few seconds

Do you hold throttle or like me- pumping the pedal a bit to help the engine recover from idle drop? When it is not parked for a long time will it start no problem?

[GodziRRa]

Use 10w40 oil. Nismo now use 5w40 oil with S2 tune engines (with R35GTR? injectors) -

http://www.nismo.co.jp/omori_factory/original_menu/engine_m/s2/index.html

And R2 tune engines (racetrack, with R35GTR? injectors) -

http://www.nismo.co.jp/omori_factory/original_menu/engine_m/r2/index.html

Loss of back pressure, retarded ignition timing, running richer than it should. Pressing throttle while starting engine advances ignition timing and opens throttlebody butterfly's (allows more air to enter engine). Cranking engine longer is another way to get pistons pumping which makes engine suck in more air to comabt rich mixture.

So Omori now uses oem 550cc CBAR35 injectors instead of Nismo 550 or 600 on S and R tune GT-Rs.

[allwheeldrifter]

I gotta pump it a little to give it a chance to recover from the ultra low idle. If i shut it off (after the idle recoverd) and start it right back up, it will be fine, but if i leave for like 20-30+ minutes, probly wont start well.... And its really frustrating because everytime it doesnt start well, i see it takes time for the oil pressure to build and the engine makes like a valve noise meanwhile...

[GodziRRa]

I gotta pump it a little to give it a chance to recover from the ultra low idle. If i shut it off (after the idle recoverd) and start it right back up, it will be fine, but if i leave for like 20-30+ minutes, probly wont start well.... And its really frustrating because everytime it doesnt start well, i see it takes time for the oil pressure to build and the engine makes like a valve noise meanwhile...

Seems like my style pump the gas a bit to help the engine recover the idle drop. But unlike yours my car will start up the whole day after the initial poor start. It's just when it is park more than 8 hrs. or so. Hmmm... maybe we have the same prob.? Have you checked your FPR?

[allwheeldrifter]

No i havent, im running the r34 fuel rail and fpg, but my tuner would have told me something if it was faulty or something kuz i got my car tuned right after my swap...

[Skym]

So Omori now uses oem 550cc CBAR35 injectors instead of Nismo 550 or 600 on S and R tune GT-Rs.

Looks like it.

I gotta pump it a little to give it a chance to recover from the ultra low idle. If i shut it off (after the idle recoverd) and start it right back up, it will be fine, but if i leave for like 20-30+ minutes, probly wont start well.... And its really frustrating because everytime it doesnt start well, i see it takes time for the oil pressure to build and the engine makes like a valve noise meanwhile...

Normal. Startup tables. ECU uses different set of startup tables on first startup vs second startup. Valve noise, check that you are using correct oil and make sure oilfilter has an anti drain back valve (factory / OEM oilfilter does) and check clearances on solid lifters vs cam lobe (might need to adjust clearances using shims or replace lifters if worn on top, which happens with them, usually on high hp engines or engines using incorrect oil). Slightly thicker oil might help with lifter clearance problem. Use factory / OEM or Nismo oilfilters if you can. The anti drain back valve keeps oil above oilfilter, so engine doesn't run dry on cold or normal startup.

[allwheeldrifter]

My head was just rebuild at the same time as my swap, valve adjustment was done, i was thinking maybe because i installed a tomei oil restrictor and a oil cooler/ filter relocator? I use motul 5w40 , but im thinking of going back to 5w50 or 15w50