8.1 swap and throttle too sensitive

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04-14-2022
ratnfested

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8.1 swap and throttle too sensitive

Hi

I swapped an 8.1 from a 02 2500hd into a 78 squarebody, I used the original PCM and TAC module, I bought a Tac harness and pedal from PSI conversion. No throttle mapping has been touched because the warnings make me nervous I will brick the PCM.

So my issue is that I get 0-178% pedal position in VCM scanner as I depress the pedal to the floor, I get 0-100% TPS by the time the pedal position hits 68%, So basically I get full throttle by the time the pedal is 1/3 of the way to the floor. If needed I am going to go get a 02 pedal but I would like to fix this if I can with remapping.

I will attach the tune and if someone has an idea I would really love to hear your feedback.

Thanks
05-12-2023
Bqueasy

Bump.
Working on a similar issue with 5.3 swapped jeep. I believe it is related to throttle mapping but cant seem to find a way to alter it.

BQ
05-12-2023
blindsquirrel

https://www.google.com/search?tbs=li...ustable-pedals
05-12-2023
blindsquirrel

more: https://www.google.com/search?tbs=li...rs.com+dbw+150
05-13-2023
blindsquirrel

What causes this is when you take a donor that had adjustable pedals and put it in a swap vehicle with a different pedal assembly. Nobody uses the adjustable pedal garbage in swaps so this shows up pretty often. And it's really hard to find out afterwards whether a PCM/OS came from a truck built with adj or non-adj pedals after the fact.

If anybody knows what's different between the adjustable & nonadjustable PCMs/calibrations, please post it. I have looked and can't find anything - compared stock files for both types between trucks that were confirmed by the owners to be adj or non-adj and there's no difference. The TACs are the same p/n, and those are not programmable modules not even with SPS. It's either the pedal mechanism/sensor itself, or something in the tune that's not shown in the Editor (if it's this last one, then the only solution would be to flash with a calibration from a truck built with non-adj pedals, but at least it would be fixable).

This is all guesswork based on what's left over after eliminating everything else I can think to check.
06-07-2023
RootBreaker

I am slowly getting my square running again and have the same issue. I used a pedal from partsgeek and a drive by wire harness from amazon. worked great but 1/4 throttle is like full throttle.. cant stop the tires from spinning!!
06-12-2023
horsepowerguru427

Quote:

Originally Posted by blindsquirrel

What causes this is when you take a donor that had adjustable pedals and put it in a swap vehicle with a different pedal assembly. Nobody uses the adjustable pedal garbage in swaps so this shows up pretty often. And it's really hard to find out afterwards whether a PCM/OS came from a truck built with adj or non-adj pedals after the fact.

If anybody knows what's different between the adjustable & nonadjustable PCMs/calibrations, please post it. I have looked and can't find anything - compared stock files for both types between trucks that were confirmed by the owners to be adj or non-adj and there's no difference. The TACs are the same p/n, and those are not programmable modules not even with SPS. It's either the pedal mechanism/sensor itself, or something in the tune that's not shown in the Editor (if it's this last one, then the only solution would be to flash with a calibration from a truck built with non-adj pedals, but at least it would be fixable).

This is all guesswork based on what's left over after eliminating everything else I can think to check.

Interesting, my friend who i tune for just started a squarebody swap with an 8.1 of unknown origins. something I'll have to look out for i suppose, but all his shit is slow AF, so he'll be happy if he can spin the tires :D
06-12-2023
blindsquirrel

It's not specifically an 8.1 thing, it happens on all of these Gen 3 trucks.
06-12-2023
horsepowerguru427

well, i kinda assumed that. anything that had adjustable pedals is what i figured. I just havent ran into it yet and his swap is similar to what this thread was about so it made me wonder.
06-12-2023
blindsquirrel

https://www.google.com/search?tbs=li...edal+150+-ford
06-13-2023
Alvin

Quote:

Originally Posted by ratnfested

Hi

I swapped an 8.1 from a 02 2500hd into a 78 squarebody, I used the original PCM and TAC module, I bought a Tac harness and pedal from PSI conversion. No throttle mapping has been touched because the warnings make me nervous I will brick the PCM.

So my issue is that I get 0-178% pedal position in VCM scanner as I depress the pedal to the floor, I get 0-100% TPS by the time the pedal position hits 68%, So basically I get full throttle by the time the pedal is 1/3 of the way to the floor. If needed I am going to go get a 02 pedal but I would like to fix this if I can with remapping.

I will attach the tune and if someone has an idea I would really love to hear your feedback.

Thanks

This sounds like...

When you log DBW GEN 3 trucks the ACCEL pedal will show like it's going to 200% but it isn't actually. You can take the intake tubing off and watch the throttle body to verify.

Otherwise if it seems too sensitive.. Have you modified the pedal in anyway? Is the gas pedal mounted lower than the brake? This is normal for every car. If the gas pedal is a higher position than the brake the car will feel really sensitive and hard to drive. I'm not sure why.. but it makes a huge difference.
06-13-2023
blindsquirrel

I believe people with the issue have confirmed that the TB really does hit WOT with the pedal at around half travel (actual travel, not the indicated % in the scanner). The rest of the pedal past that just does nothing.