2002 8.1L Tac Module issues

[gametech]

With regards to your other problem, all of the ride command nav systems are junk. I use android as a phone and got a used iphone solely to use carplay on my '21 challenger because of reading how bad the bike nav was before I bought it. I did not realize I needed a bluetooth headset for it to work, so I tried the bike's nav on my way home from the dealership. It was showing a turn 100' ahead when the road was actually over 1/2 mile away. Also, the traffic and weather never worked at all on mine. I suppose the rest of this forum will be confused by this post.

[loosegravel]

I was surprised to see your post here!

[twenglish1]

Im still curious though, did you figure out what the true solution is to this problem? Is it an issue with the APP Sensor itself? Did you determine if something was missing from the pedal assembly?

[loosegravel]

Wow! I?m just going over this thread. I must look like a complete fool! I use my phone many times to reply to quotes. Those quotes from other members seem to keep piling up in my posts and they do not go away! And, things like apostrophes, commas, parentheses?many of them show up as question marks on my replies. Very strange. Please tell me that I?m not the only person with this problem!

[loosegravel]

Im still curious though, did you figure out what the true solution is to this problem? Is it an issue with the APP Sensor itself? Did you determine if something was missing from the pedal assembly?

I decided to go back to my lap top so I can reply without looking like a fool.

This was a mystery for me. I looked very closely at the metal pedal assembly, and I couldn't find or see where anything was missing. I can tell you that when I initially replaced the APP sensor, I simply unplugged the original pedal assembly and then connected the 10-pin harness directly to the new APP without installing it onto the pedal assembly. (The APP sensor has its own internal return spring.) When I initialized the PCM and the TAC module they behaved the same way. The PCM went into the continual re-boot mode where the FP relay was fibrillating, the FP would not shut off and there was no com with the PCM. In my head, I eliminated the APP as the cause of this problem, and I moved on. Yesterday I decided to try a paper "shim" about .150" thick under that part of the throttle pedal arm where it meets the base when it's fully retracted and that was when things started to behave normally. I was simply preventing the APP from returning fully. My fix so far is to use a piece of rubber under that part of the throttle pedal arm where it meets the base when it's fully retracted. It has worked now every time that I have initialized the PCM and the TAC. The engine starts and I have throttle. I'm going to call it a day for now.

[loosegravel]

With regards to your other problem, all of the ride command nav systems are junk. I use android as a phone and got a used iphone solely to use carplay on my '21 challenger because of reading how bad the bike nav was before I bought it. I did not realize I needed a bluetooth headset for it to work, so I tried the bike's nav on my way home from the dealership. It was showing a turn 100' ahead when the road was actually over 1/2 mile away. Also, the traffic and weather never worked at all on mine. I suppose the rest of this forum will be confused by this post.

What's your name on the Indian forum?

[gametech]

What's your name on the Indian forum?

Same username on almost all forums.

[loosegravel]

I just wanted to post a follow-up on the TAC module issues I was having last January. I didn't take any pictures of what I'm about to disclose here, so please forgive me. I'll do my best to describe what I found in detail.

At that time in January, I was solely focused on the chassis for this project. For those who don't know, I have a 2001 Suburban 2500HD 4x4 chassis with an 8.1L, 4L80E that I shortened 2'. I mounted a 1977 K5 Blazer to this chassis. The throttle on this 8.1L is an early fly-by-wire. I had to modify the throttle pedal assembly where the APP is also mounted.

Last January I was attempting to run the 8.1L engine in this chassis while the K5 body was still off. After modifying the all-metal throttle pedal assembly to be the correct length for the K5 floorboard, I was having problems when powering up the TAC and the PCM. The FP relay was "fibrillating", and the fuel pump would not turn off at that time. The engine would start and run, but only for a second or two. After several hours of trouble-shooting this problem, posting my findings here (thank you @twenglish1 for your help and anyone else who was attempting to help me with this problem) I stumbled onto a "band aid" solution. This problem was occurring with a couple of different APP sensors and TAC modules. (yes, I attempted to throw parts at this problem because I didn't know what else to do) This problem was also active while the APPs that I had were simply plugged in but not mounted to the throttle pedal assembly. The APP has its own internal spring, so it naturally returned to a preset point. I used a piece of tape to prevent the APP from returning all the way to that set point. Then, I initialized the TAC and the PCM. The FB relay problem was not happening, and the engine would start and run. I also had throttle activation. At that point (last January) I mounted the APP to the throttle pedal assemble and made a .180" shim to prevent the throttle pedal from returning all the way. Again, the FP relay issue was gone, I could start and run the engine, and I had throttle activation.

Fast forward to now. Lately I have made some progress with this body-swap project. After many hours of cutting out all of the rust and welding new panels/pieces into place, body work etc. the body is now permanently mounted to the chassis. I'm in the process of reassembling the dash, getting the steering column in place so I can "steer" this thing around in and out of the shop while pushing it. The brake pedal assemble is now modified to work with the hydro boost system. The throttle pedal assembly is now mounted to the floor. The front clip is still off of this thing, so I have good access to the firewall etc. Well, yesterday I attempted to start the engine to check the hydro boost system for leaks and the FP relay issue reared its ugly head again. I removed the throttle pedal assembly from the floor so I could take a closer look to it. For the life of me, at first, I couldn't see anything that had changed. My .180" shim that I installed last January was still in place. I removed the APP sensor and installed a piece of tape to prevent it from returning all the way. I initialized power to the TAC module and PCM. The FP relay acted normal, the engine would start and run. So, WTF! Then, I used a small crescent wrench on the slotted shaft that engages with the APP and rotated it. That shaft would rotate without the throttle pedal moving! I thought "this isn't right!"

I was bound and determined to see what the hell was going on with this throttle pedal. To disassemble the throttle pedal assembly, I had to grind off (3) rivets that held part of it together. The APP shaft should be one with the throttle pedal arm I believed. I was correct! The APP shaft is splined where it connects to the throttle pedal arm. The splines were stripped and that's why the shaft was turning independently from the throttle pedal arm. This was throwing the APP out of tolerance and causing problems with the TAC module and PCM. The TAC needs to see a specific value from the APP when the system is initialized. The APP cannot send the correct value if it is retuned all the way. It has to be set ever so slightly off of the fully retuned position. That value was changing ever so slightly. I determined where the shaft needed to be to hold the APP sensor just off of the full returned position at idle. Then, I welded the shaft to the throttle pedal arm. I reassembled the throttle pedal assembly using 10-32 screws and locknuts in place of the rivets. I plugged it in, and it seems to work now!

I must have damaged the splines on the APP shaft while I was modifying the throttle pedal assembly. What a trip!

[twenglish1]

Awesome, glad you figured it out! I have never seen that happen before but it makes sense! At power up it is looking for both sensors to be at the resting position, i believe they are inverse of each other so one close to 0v and one close to 5v, id be curious what happens if you push the pedal a quarter of the way down or so and turn the key on, would think it would do the same thing. Weird too that the PCM was just boot looping as a symptom