losing pedal imput

[lytemup454]

I’m hoping you can help me out. I have an 04 LQ4 out of a Yukon. It has the stock wiring harness, TAC, Pedal, and Throttle body all from the original donor vehicle. I had Wait4ME performance mod my stock harness and do my tune. It wasn’t much of a tune just deleting vats, rear o2 sensors Ect. I am also putting a manual trans behind this motor, so I asked Wait4me to delete the automatic stuff in the computer.
I can start it and drive but if I put more than about 20% Throttle then I lose all input to the motor and it just idles. I can turn it off and wait the 6 seconds and start all over again. I’ve changed out the throttle body, TAC, and the Pedal one at a time. All with the same result. I called Jess at Wit4Me he said he wasn’t sure because you can’t turn the pedal function off in the computer so it had to be somewhere in the TAC , Pedal, Throttle Body loop. I checked the TAC to the pedal harness lastnight and it didnt show and damage to the wires, but it just carries the signal from the APP to the TAC. which it does. I also asked Jess about the Automatic sensors, and if the computer is expecting some input that it wasn’t getting so it shut down as a safety feature. He said there wasn’t anything that would do that. I have hooked a Tech2 up and it isn’t throwing any codes, I’m not sure what else to check or change out. Does anyone have any ideas on what to check next? Thanks for your help.
Ian

[OldCreek]

Ian,

I've had the same issue with my LQ9 and it's been a bit of a pain.

What error codes are you throwing? I've gotten codes that list the pedal sensor failure but I've, also, replaced those and checked the wiring.

One thing I've tried with only one failure initially, is putting a small sticky pad at the base of the pedal lever arm. i.e. the pedal cannot fully return to its base. Apparently, the sensor resets every time the car is turned off and it doesn't matter if the lever arm doesn't return to its base.

We'll see if this helps but it seemed like the failure was occuring less than before, anyways.

Also, I noticed that my TCC brake line wasn't wired correctly so I switched that over yesterday. Maybe that was part of the issue?...maybe you should check yours.

Wil

Also, check to see if any of your TAC cruise control wiring ends are exposed and shorting out. I'm not sure if this would be an issue...(That is to say if your wiring is not hooked up to a cruise control stalk/pad.)

[BR3W CITY]

this might not solve anything, but fwiw.... on auto truck if there is a problem with the tcc switch or the misfire count is too high (big cam or actual problem), it will pull the truck out of lockup. Is there any similar provision for the manual? (i.e. limiting throttle or input response as a safety measure because of percieved mechanical fault)

[lytemup454]

I'm not throwing any codes which is strange to me but it's all new to me as well. I dont know about what the provisions are for a manual trans but it will do it hot, cold, just fired.... doesnt matter. So I dont think it is the TCC switch or misfire it runs smooth until you give it too much pedal

[BR3W CITY]

Originally Posted by ls1tech

I checked the plug with a multi meter,
Got 5v on purple wire and white/blk wire but
Light blue wire got 1.7 volts on sweeping the pedal
Drk blue wire only gotm3.8 volts

Swapped the sensor on the pedal and got 4.8 on the dark blue wire
And unfortunately I don't remember about the light blue.

For the sensor to work you need 5v on the purple and white/blk

The light blue and dark blue wires sweep. One sweeps from 0-5 volts and the other is 5-0 voltage.

Replaced the sensor and worked perfect, I did notice the internals of the stock app sensor was loose feeling and didn't have tension where the slot of the pedal goes in.

I tested the new switch by plugging it in and turning it with a screw driver. Nothing happened, upon installing it on the pedal it lined up on the slot and had to turn slightly for the screw holes to line up. That was the key for the sensor to reading.

I read another thread where someone had a stock sensor that wouldn't work unless he slightly moved the pedal down then it would read while running, he had to make a sort of bump stop so the pedal wouldn't move so far.

Anyways replace the switch if your not getting the voltage you need at the plug :-) have a nice day

Found this in a post over @ ls1tech. Thats how this guy solved his problem.

[lytemup454]

I did grab another pedal out of the junkyard last weekend and it did the same thing. I think I might have to just buy a new app sensor and try it again. Do you have the original link to that post?

[BR3W CITY]

I was on a different computer yesterday so I don't have the history.

I searched something like "dbw losing input lq4" and then looked through "view more results from ls1tech.com" happen to come across it.

[smoky02]

Did this fix the problem?

[lytemup454]

I haven't bought a new App sensor yet, I did buy a new Wiring harness and nothing has changed. I think I'm going to send the computer off to get looked at, and make sure everything is correct. Not sure what else to do. I don't think a new app sensor is going to help, I tried the one from the junk yard and it didn't change anything.

[BR3W CITY]

I didn't read back through, but if your using an HP tuners type product for the tune, the tuner should be able to actively monitor the input levels, which would be able to at least tell you if thats NOT the problem.

[lytemup454]

i'm in Colorado and he is in IL. I'm hoping he can figure out something I need my truck back.