Throttle position percentage?

GetMore · July 2, 2006

I've got a question: I tried doing the crank position learn today and the scanner just kept saying it was waiting for full throttle. I was standing on the gas pedal for about 10 seconds and it didn't change.

I then tried checking the signal from the throttle position sensor and it did start at 0%, but only went to 99%, no matter how hard I pressed the pedal to the floor.

So, do I have a TPS problem, or do I just need to keep the engine bouncing off the rev limiter for a longer time? If I need to do it longer how long does it take?

TIA

Haulin' 8.1 · July 2, 2006

I use an OTC Genesis for that. Mine doesn't use throttle position as far as I know. It only needs to have reached a prescribed RPM to preform the procedure. You start the test and hold heavy throttle just long enough to reach 4000 on a truck V8 (gas engine). I wouldn't recommend going any higher or holding a high nuetral rev for so long. A freewheeling high RPM is the most stressful thing you can do to connecting rods. They will break just from the inertia. 4000 is the limit.

Your engine has to be at operating temperature and all accessorys like A/C turned off.

In any case which engine are you working on? And what type of throttle system is it? Cable or electronic?

Vernon

Ape0r · July 2, 2006

I use an OTC Genesis for that. Mine doesn't use throttle position as far as I know. It only needs to have reached a prescribed RPM to preform the procedure. You start the test and hold heavy throttle just long enough to reach 4000 on a truck V8 (gas engine). I wouldn't recommend going any higher or holding a high nuetral rev for so long. A freewheeling high RPM is the most stressful thing you can do to connecting rods. They will break just from the inertia. 4000 is the limit.

Your engine has to be at operating temperature and all accessorys like A/C turned off.

In any case which engine are you working on? And what type of throttle system is it? Cable or electronic?

Vernon

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IIRC if its an '01 its got a cable. Assuming thats the case, have you tried actuating the throttle valve manually at the TB?

Haulin' 8.1 · July 2, 2006

If he's got an '01 with the Allison he's got drive by wire. They all do. 6.0 or manual has cable.

Vernon

GetMore · July 2, 2006

It's an '01, 6.0, 4 speed auto and has a throttle cable.

The scanner said the coolant temp had to be over 158F, with A/C off. Those criteria were met.

I have not tried actuating the TB directly.

The scanner said to hold full throttle and let the fuel cutoff limit the engine speed, which should happen at 4000-5000 rpm. I've got a tune on my PCM, so my redline is a little higher.

I didn't like holding it there, but I though I had read that that's the way it's supposed to be done.

Haulin' 8.1 · July 2, 2006

Hook the scanner up and try what ApeOr suggested to see if there's still some slack in the cable that could be the reason you can achieve 100%. If so see if you can make adjustments to the cable and or brackets to pull it more taughnt and get 100 with the pedal. You don't have a thick floor mat do you? LOL

Alternatively it may take grinding or fileing down the throttle stop a bit, but go slowly and check the scanner often because if you go past 100% it could set a code and limp. The LS1 car guys do this to acheive max throttle opening.

I don't know how the raised RPM limit would effect the test but I don't think it's the reason you're having a problem. 4000 is all that's required. Heck I sneak up on it carefully to avoid going much past it.

Vernon