p1221 and tps issues

[InsaneOctane]

So now the first 10% of my pedal is a dead spot. This is a new APP sensor, along with the new TPS.

 

[gmcman]

Is this a GM pedal from the dealer?

Here's a good article, I don't know if it's wired the same as ours. Is the dead spot measured at the pedal or at the TB?

Part 1 -How to Test the GM Accelerator Pedal Position (APP) Sensor 1
http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/app-sensor-tests-1

 

[gmcman]

There's a chance you may just need a PCM reprogram, but it's a likely $50 gamble at the dealer if you can negotiate.

 

[InsaneOctane]

It was a Dorman pedal. I ended up putting the stock pedal back on it and there's no dead spot. Just the same general symptoms as before. I checked the tests on that website and both pedals read differently from the voltage readings on the page, but the two pedals had identical voltages. Chevrolet wants 115 bucks for a PCM flash so if I do that I want to know it's the PCM and not another issue. The thing that makes me think it's the PCM is the fact that both pedals had a 2.1-2.5 voltage difference between closed and wide open, but the wires going to the throttle from the PCM hardly changed. Or there could be a short somewhere maybe?

 

[InsaneOctane]

Figured out the issue. There was a broken wire (the purple wire from the TB). It was broken just enough to keep a weak intermittent connection at the PCM so I went to the junkyard and got the wire with the pin from the PCM and spliced it in. It gets a much better connection now but at this point I think the PCM needs to get flashed. If the pedal is on the floor when you turn on the switch the butterfly opens completely them resets to 35% open. So I'll probably get it flashed this week sometime and hopefully I'll be good to go.

 

[Mooseman]

Try just resetting the PCM by disconnecting the battery for 30 min. Maybe it needs to relearn the TPS.

 

[InsaneOctane]

I tried that and the reset gmcman said to do.

 

[Tiggerr]

That could be the built in torque management kicking in too possibly. A tune would take care of that.

 

[Mooseman]

I tried that and the reset gmcman said to do.

Before or after fixing the wire? If it hasn't been done since the fix, I would redo it.

 

[gmcman]

Long story short. ....my TB harness was cut, took awhile to get them all spliced back together with only about 1" of wire to work with.

Took many tries to get the TB working, had to crimp, recrimp, recrimp, many times to get the connections right, would have been best to solder.

Just make sure every wire is connected and without any glitches. If one wire is broken, there may be others. Check the pins at the PCM, pedal, TB, as well as inside the harness. ANY disruption in voltage will trigger a REP, it's the PCM erring on the side of caution.

 

[Mooseman]

Definitely soldering and shrink tubing is the best.

 

[InsaneOctane]

We checked every wire to the PCM TB and APP. New wire was soldered and heat shrunk tubed. Battery and fuse reset were both done after the wire was fixed.

 

[InsaneOctane]

Ok so the throttle body is working as it should now with the PCM flash. However I still am having issues with it being slow to start, bogging when the pedal is pressed, and idling rough occasionally. I'm thinking maybe fuel pressure or spark plugs? The spark plugs have been on there for 100k miles so I'm gonna pull them and see how they look.

 

[Mooseman]

They would be due to be replaced regardless so plan on it. Might as well do the fuel filter too.

 

[InsaneOctane]

I did the fuel filter a couple weeks ago and ran some seafoam through it. I've also heard about injector clogging being an issue on these cars.

 

[dmyers4321]

Double check the TB harness, use some electronics cleaner on the terminals, make sure all the pins are in their proper position.

Pull fuses 10 & 28 for about 10 min.

Turn key to ON with all the dash lights on. DO NOT START AND DO NOT TOUCH GAS PEDAL. TB will perform series of noises during this time.

Leave key ON for about 5 minutes. DO NOT turn key off. DO NOT turn key off for the duration of the relearn

Start engine, DO NOT TOUCH GAS PEDAL, let idle for about 8-10 min.

Once engine has fully warmed, idle should settle around 600-625RPM. Generally under 650 RPM.

Is this the pcm reset sequence?

 

[Mounce]

Pull fuse 10 and 28 for 10-30 minutes and replace them. That resets the pcm. The rest of his post is what to do IF you clean your throttle body which if you reset the pcm you have to clean it or you'll have a bad time. Will idle bad and randomly stall when AC is on.