Couple of SCT Livewire questions

[chromehound]

I searched but couldn't find an answer so here is my question: my livewire asks if I've changed tire size and if I want to correct for them (I do and I did); is this correction for the speedo, transmissions shifting, both, neither?
I ask because someone on another forum was asking about tuners and when I put up that mine corrected for tire size and seemed pretty accurate I assumed it was correcting the speedo and am getting some grief about it and I'd like to have my facts straight. BTW mine came with the truck and no instructions-I'd have checked them if I had them.

Second question: I found in a search that the SCT wil make the truck have a high idle if the DPF is deleted and no sensors are hooked up. My DPF is off but there are 4 probes that are hooked up in my exhaust. My truck will switch to a high idle of ~1100-1200rpm when it's cold out but everything I've read says that if the probes are hooked up it won't high idle. So this has me curious as to if my SCT is making it high idle or if it's had something else done....not an issue just curious.

 

[jdgleason]

Question 1: The change is for the speedometer.

Question 2: The hi idle referred to with no sensors is different than cold hi idle. It will always idle around 900 rpm with no sensors. Cold, warm, driving etc. Cold high idle will shut off when you touch the pedals.

 

[O2ShootTheJ]

this first part im not going to address as i'm not too familiar with the SCT yet, but for the second part it's normal for the truck to do that in cold weather. It does that stock.

 

[chromehound]

Ok - yeah the truck drops to 750ish rpm when I hit the brake but the way I had read the other post had me thinking that the cold weather hi idle was the same as the one with no sensors. Curiosity satisfied.

 

[WoodBoy]

The tire size is for shift points

 

[Derek@Vision Diesel]

So 900 RPM idle is normal once youve deleted the DPF and tuned it with an SCT? It seems like its fairly hi to me, truck really wants to pull through the brakes haha

 

[WoodBoy]

No that is not normal. It is how it idles if you do NOT install the dpf sensors back in the new exhaust. SCT needs the sensors in the exhaust. You may can just hook them up and tie them to the frame IIRC

 

[6.4psd916]

Ya, you can tie them to the frame, that's what I did, and with 37s I have to put at 34.5 to get the right speedo mph

 

[Jmoore1225]

If the speedo ia off, it's safe to say that the mileage would be off to correct?

 

[chromehound]

So 900 RPM idle is normal once youve deleted the DPF and tuned it with an SCT? It seems like its fairly hi to me, truck really wants to pull through the brakes haha

Mine with the SCT and sensor in the pipe idles normal @ 750, high idle @1100ish.

Ya, you can tie them to the frame, that's what I did, and with 37s I have to put at 34.5 to get the right speedo mph

I put in 37 for my 37s and my speedo is 2mph over what the GPS and radar speed things say I'm doing - so 35 on the gauge is 33 by everything else. Gonna have to try and remember to try the 34.5 size next time I mess with the adjustments and see if it gets closer to a 0 variance.

 

[Derek@Vision Diesel]

Yeah must be a sensor issue.

I had to cut the very back one out of the old exhaust, so its just dangling, but plugged in. I think cutting the probe sent a signal that it failed, only thing i can think of

 

[3brorce]

Dont want to steal thread but how do you monitor using the Livewire? I hit start to monitor and it gives me an error. Does it need to de in gear to start to monitor?

 

[6.4psd916]

You have set up what you want it to monitor first, then follow the directions, but it doesn't shut off when the truck shuts off, you have to unplug it I believe

 

[Derek@Vision Diesel]

Dont want to steal thread but how do you monitor using the Livewire? I hit start to monitor and it gives me an error. Does it need to de in gear to start to monitor?

Shouldnt have to be in gear, ive monitored sitting in my garage

 

[tbsimmons]

Key just has to be on.

 

[3brorce]

Key just has to be on.

Does it go off on key off? So you have to go into set up monitor then just follow directions from there. got it. Thanks

 

[Jmoore1225]

Mine with the SCT and sensor in the pipe idles normal @ 750, high idle @1100ish.



I put in 37 for my 37s and my speedo is 2mph over what the GPS and radar speed things say I'm doing - so 35 on the gauge is 33 by everything else. Gonna have to try and remember to try the 34.5 size next time I mess with the adjustments and see if it gets closer to a 0 variance.

So for 35's on the tire change I should put 33 or maybe even 32.5? Speeds a Lil off. & like I said in a previous post, Wouldn't that make your odometer off a Lil as well?

 

[chromehound]

On the odometer being off because the speedo is off I'm going to say no being that one is a measure of velocity and the other is a measure of distance - think of it like this if you go to a drag strip and go 100mph (on the gauge) in 1/4 mile you still only went the 1/4 mile you just did it faster and if your gauge is like mine then you actually go 98mph (gauge still reads 100mph) in a 1/4 mile but it's the same 1/4 mile - at least that's my understanding but I really have no clue and the only thing I'd say with the tire size/speedo issue is try it-that's my plan next time I change things.

How far off is your speedo? I really don't mind mine being off that little bit because then I know I'm under the speed limit a little, I just figure if I can get it to a zero variance I'll do it.

Anybody feel free to correct me since I'm not 100% on this.

 

[strokin20]

When I had 35's on mine I set my tire size in the sct to 33.1 and it was dead nuts on at 70 with my gps. So the theory of taking two inches off the actual tire size has worked for me so far.

 

[bigrpowr]

anyone actually ever measure tires once inflated and installed? subtract an inch almost always. sometimes more. i cant say i have ever seen a true 33, 35, 37 ..etc.