official_style

the weather has finally started to cool of a little here, and i have noticed something. when i start my car the first time of the day, if its kinda cool, it runs rough for like 2 mins. like i can kinda feel the engine shaking and see the antenna vibrating more than normal at idle. it kinda feels like failsafe, but the car doesnt failsafe. i didnt notice this at all during the summer, but it has been so hot, and it finally just cooled off. i kept having a problem with a bad 02 sensor causing a CEL, and i changed it, i thought that could have been causing this problem, but it still happens. so far CEL is staying off. is this just part of having LTs on this car? is there something i could tell my tuner to adjust? i drive the car all year round, and dont want to have starting problems if its really cold out.

2006GT500

I'm not sure that we are having the same problem but it is similar. When I start my car warm or cold it will start right up and drive fine but soon after taking off my car will start to back up like my cylinders are loading up. Not sure what is causing it but I'd love to hear what you guys think about it.

traffic142

Shoot, It is still in the 90's here most of the time, coldest in the am is high 60's

official_style

well it started fine today, i also cleaned the MAF, but it was hot today.

jtgrantm3@hotmail.com

my car is doing the same thing.

2006GT500

Can anyone help or have any clue what could possibly be wrong with my car?

Cleveland

it isnt enough info to just tell you what to adjust.

Like with anything else the only proper way is to watch a datalog and adjust from what you see. You have an Xcal, why dont you actually use it?

-Dan

official_style

i went to mustang magic today and they scanned my car. everyones having this problem with the longtubes. the problem is that the o2 sensor is way down under the car now, and with the stock manifolds it is right inside it. they are not getting hot quick enough, and this is causing the rough running/check engine light when cold starting. do any of the tuners know if there is anything that can be adjusted to help this? i have mine set to the o2s are as far down as they can go in the computer. i was thinking it would help to have the car not start reading the o2 sensors for a longer period of time, but my tuner told me i couldnt do this. anyone got any info?

ski

It's my understanding that the O2 sensors will not cause a rough running engine or a CEL during a cold start, because the ECM is in an open loop mode when the O2 sensors and the engine are both cold, and it does not accept signals from the O2 sensors.
It's only after the O2 sensors and the engine heat up that the ECM go into a closed loop mode, and it accepts signals from the O2 sensors.

I'm thinking that if the engine does not have a custom tune that's programmed for LT headers either from the supplier or from a dyno tech, then the headers may be causing an overlean A/F ratio which is getting even leaner with the colder, denser air, and possibly causing the cold start roughness.

official_style

I was talking to the tuner yesterday, and he said that the computer doesn't read the o2 sensors for like 30 seconds after starting the car when its cold. Since th o2 sensors were inside the stock manifolds, this was enough time to heat them up, but since they are way down in the long tubes, this is causing the problem. The car thinks they are warmed up and starts reading them and this causes the rough running. One solution is to drive up the street in 1st gear lol. He said he can't change the timer before it starts reading them. Setting it to idle high while in the cold start mode might help I guess? What has everyone else found out?

2006GT500

All I know is that after my car has sat for over 30 minutes and I start it back up it will start fine and drive fine for a few minutes but then it will start to backup like the cylinders are loading up. Usually if I shift throw the gears it will go away but that's not always the case. I didn't have any problem with the long tubes for the first 4 or 5 months I've had them and I'm curious as to why I'm having them now. I emailed Doug about this because he's the one who has done all my tunes and he said that the issue is with me having the JLT 1 intake as opposed to the JLT 2. I'm not entirely sure why that would make that big of a difference.

Cleveland I'm not Xcal expert so how do you datalog? I agree that would definitely help.

official_style

here ya'll read this, this chick posted it on another forum. http://www.aa1car.com/library/o2sensor.htm
now after reading that, it seems to me that what we need to do is have our cars run in open loop for longer at startup. can this be adjusted?

65sohc

Now you all know why LT headers are illegal. The other problem, besides the increased distance of the O2 sensor, is the fact that the thin header tubing dissipates heats far more readily than the thick cast iron manifolds. This results in a less precise realtionship between the sensor and the ecu since the exhaust gas temperature is lower and less consistent. Insulating the headers with something like Thermotec might help since more of the exhaust energy in the form of heat will be retained within the exhaust system which will tend to increase exhaust gas flow.

2006GT500

Official Style that article makes since, and seems to sum up what is going on with my car. Now like you asked how do we fix it? I know for a fact that my rear O2 sensors are turned off so....I don't know.

official_style

i have heard horror stories about header wraps. what i am doing now is, start the car, run for 1 min, then drive up the block in 1st gear at 3000rpms. then i have no problem, they get hot, and i get to **** off all the neighbors lol. thats my solution till a tuner figures it out. when it starts to stumble, give it gas and it will warm up and if u do it in time no CEL