stuttering when cold ? fine when warm

[frankiman]

i look around here all the time, reply to other's problems and such..

but theres one thing i havent read about,

its an issue i had last summer on my GTR and now a buddy of mine has the same problem with his GTS-T

when i drive the car with the engine cold, its stuttering alot, very low power, even turbo shuffle, when i get it into boost its not as bad, but still

even when its acting up like that its totally driveable, just weird

but the bizarre thing is, i clearly feel a huge difference as soon as the thermostat opens,
i keep monitoring my engine temp, and as soon as the temp needle stop moving and the thermostat opens, every issue goes away instantly.... like ON/OFF

so i got the habit of letting the engine warm up on idle before driving it


my friend is reporting similar symptoms

any input ?

[DreadedFist]

Drive it accordingly? Mine does the same thing with a test pipe on it, with the cat on, it doesn't do it.

Shouldn't be trying to go into boost when it's cold anyway :P Mine feels like it's hitting a wall of zero power at 2500rpm until it's up to operating temp. Just drive slow and shift before it starts stuttering?

[archaeic_bloke]

never heard of that problem before...

I have a couple of guesses though.

I want to say ignition system, could be anything from igniter, harness, coils, and even spark plug gap.... my first test would be on the igniter and the harness, since your coils are new right? so test the igniter, and if thats not it take the ignition harness off, put it in the freezer, and use an ohm meter to measure resistance across all the wires end to end... then put it out in the sun and heat it up and measure resistance again.. normally resistance increases with heat, so its kind of backwards thinking.. but hey, you never know, there could be a micro crack in a wire somehwere that only makes a better connection once the harness is warm and the copper has had a chance to expand, which would probably be happening right around the same time your thermostat opens.

a far out guess... could it be the headgasket? expanding and contracting with heat?... have you done a cold compression test recently? vs a hot one?

just throwing ideas out ther....

[DreadedFist]

I figured it probably only happens on cars that still have the OEM cold start maps intact. They sense a ton of extra airflow from bolt on parts and get all upset.

[M13]

I figured it probably only happens on cars that still have the OEM cold start maps intact. They sense a ton of extra airflow from bolt on parts and get all upset.

no....


ecu's don't have emotions.

[frankiman]

if it was like josh says, than i guess the change would be gradual, but in my case its instant

even without the cat egt sensor in place.. i don't know

what you trigger the tune to change suddenthly when the thermostat opens?!

[derbeck]

Sounds like open and closed loop. A car runs more air and fuel to warm it's self up then once warm it drops the idle fuel and air

[TrevoR32]

same thing happens to me, its always been that way. i can be on load... and all of a sudden its like a restrictor turns off and rushes power in,.
i actually never really thought of it until now....

[frankiman]

Sounds like open and closed loop. A car runs more air and fuel to warm it's self up then once warm it drops the idle fuel and air

but how can the ecu know i'm at operating temp? i have the nismo thermostat that opens at 64deg instead of 78 like stock

same thing happens to me, its always been that way. i can be on load... and all of a sudden its like a restrictor turns off and rushes power in,.

exactly

[andy66]

I've got the same issue. As soon as the thermostat opens all the symptoms just instantly vanish

[bellis_GTR]

Mine does the same. Feels like it struggles to climb RPM. Once the thermostat opens, its like boost just came on.

[frankiman]

well dam, this seems much more common than i tought
might even be "normal"

i guess mine didn't do it 2 summers ago, just last summer and i tought it as strange
neways

[nelsonmxmarc]

Yup, same thing since day 1..

My best guess is that the cold enrichment values on the ecu are on until water temp is at a certain degree. If you look at Nistune, theres a cold enrichment map above running maps as well as timing for this table. So, basically, you'll read RICH AFR's at first, and probably be running 20 or 15btdc until the map swaps over to running maps. It's just a safe, enriched table that allows the car to ramp up to operating temps quickly; also note the elevation in rpms.. I typically try not to drive it until it's off the map from idle, but since we dont have ALL the time in the world, i simply just keep it below 2200 rpm on shifts and puts around..

[nelsonmxmarc]

Also, the kick in the pants of the turbo and intermittent "okay" conditions during this phase are due to retarded timing (or is it advanced.. i forget).. And the rich AFR's. So you'll hit the power and it wont do anything, sort of like what happens when you initiate knock maps.. Actually, the exact same thing..

[M13]

same here, I don't mind it at all. Just drive accordingly until it warms up.

fool proof IMO.