LT1 fuel cutoff/resume

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RustyGee
Posts: 2
Joined: Wed Apr 21, 2021 7:43 am

LT1 fuel cutoff/resume

Post by RustyGee »

Hello,

I tried using the search function first (here and on Google) with no luck.

The car is a '95 Camaro with the LT1 engine and T56 6 speed transmission.

The PCM lists the options to modify Fuel Cutoff RPM 1st Gear and Fuel Cutoff RPM 2nd-6th gear. My question is, how does the PCM know the transmission is in 1st gear if there isn't a sensor on the trans and no input pin on the PCM for the data? I assume it calculates speed based off trans output shaft speed vs rear gear and tire size inputs to determine when the transmission is in first gear. If that's the case, is there a way to modify what mph the PCM thinks 1st gear is?

Essentially, I want the PCM to think that 1st gear is only until 1 or 2 mph. So that the rev limiter will act more as a launch control but as soon as the vehicle is moving, it reverts to the "2nd-6th gear" cutoff table. I have a MSD 6AL2 box that is a 2 step but I'm trying to solve this for future use or to help others who need/want a cheap launch control system on the LT1 cars.

Thanks!
-Rusty
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dex
The Ford Guy
Posts: 579
Joined: Thu Oct 07, 2004 6:38 am

Re: LT1 fuel cutoff/resume

Post by dex »

The ECU probably infers the current gear from the vehicle speed and the engine speed.
chevyguy1978
Posts: 1
Joined: Wed Apr 21, 2021 2:55 pm

Re: LT1 fuel cutoff/resume

Post by chevyguy1978 »

ok so chevy has shift servo's to change gears. now this is done my using a couple of sensors. first sensor safety neutral switch, when put in d or l, or 1, or m it defaults to first gear. next it uses the input and output sensors, along with speed sensor, and the crank position sensor, and the throttle position sensors simultaneously. doing this the computer decides when to turn on and off certain shift servo's.the transmission on your car has a round plug on passenger side, these wirescome from the computer so if you pull back the snake skin you can see what color wires run to the transmission from your computer. now beings your looking at fuel cutoff you'll most likely want to look at the crank pos. sensor and the throttle pos. sensor, and speed sensor, since these 3 play a major role in when the computer tells the transmission to either upshift and or down shift
RustyGee
Posts: 2
Joined: Wed Apr 21, 2021 7:43 am

Re: LT1 fuel cutoff/resume

Post by RustyGee »

Dex, it seems we have the same thoughts on how it works. Just need to know how to tell the PCM what "1st gear" is.

Chevyguy, my post is about a 6 speed car, manual transmission.
InvisibleFrisbee
Posts: 1
Joined: Sun Oct 17, 2021 4:24 pm

Re: LT1 fuel cutoff/resume

Post by InvisibleFrisbee »

Did you ever figure this out? I'm interested as well for my LT1
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