Hello,

I'm swapping in a 5.3 L33 from a 2005 Silverado into my '82 S10 truck. I had the PCM reflashed as a first pass at tuning for my combination (T56 Magnum, Cam Motion spec'd cam, disable rear O2, disable security).

I'm using the stock throttle pedal assembly and TAC module from the donor 2005 Silverado (the engine came with the PCM, harness, TAC module, pedal assembly).

The intake and throttle body are from a 2007 TBSS (87mm TB, gold blade, factory GM part). I'm using a TorqueRush X-link to connect the TB to the TAC module.

I tried to start it for the first time today. The engine will fire, run for a second or so, and die. It originally threw codes P0120 and P2135. After doing some diagnostics, it now throws P1125 and P2125 instead.

I have verified that the 5V and low reference at the throttle pedal are present (5V to low reference is 5V, 5V to ground is 5V). Using my DMM the pedal seems to respond properly when I measure resistance across each of the two sensors (APP1 and APP2) from high reference to the signal pins, but it's hard to tell with a digital multimeter.

I have not yet tried to test the rest of the wiring from the TAC module to the pedal, so that's next.

TorqueRush states some resistance readings for the throttle body itself with the throttle blade in different positions, and mine seems to be in-line with what they say.

I checked the harness between the TAC module and the connector that plugs into the X-link with my multimeter, and all wires showed that they were good.

With the key on, engine off, if I manually close or open the throttle body, the throttle position on my Bluetooth scan tool (Torque Pro app on my phone) changes like I would expect.

The Torque Pro phone app doesn't seem to show pedal position for me, just throttle blade position, so I'm not sure what pedal position the TAC module/PCM sees.

I'm trying to narrow it down to the APP sensor, the TAC module, the X-Link, or the throttle body itself. I'll check the harness from the pedal to the TAC module again, but how do I rule out the other parts?

I am leaning towards the APP sensor or the harness to it, since before I did a bunch of tests it threw P0120/P2145, and now it's throwing P1125 and P2125.

About a month ago, I finally had it wired enough to try out (but had not yet had the PCM reflashed, so I couldn't try to start it yet). I recorded a video of the throttle body blade opening and closing when I operated the throttle. It doesn't do that now (no throttle blade motion when I push on the pedal), but it does quickly close the throttle blade, then let it go back to the spring-loaded position when the key is turned on. It makes me think (hope?) I've finished breaking whatever what intermittent.

Any suggestions are greatly appreciated.

Thanks,

 

Hello,

I *think* I figured it out. tl;dr -- I found a wiring fault between the TAC module and the pedal. A pin on the pedal side of the TAC harness was loose and not making good contact with the sensor.

I decided that the easiest way to test the harness between the TAC module and the pedal was to leave it plugged into the pedal, unplug it from the TAC module, and take resistance measurements from the center (signal) pin to the 5V and low reference wires for each APP1 and APP2 potentiometers. For APP2 I saw single-digit K ohm readings among all three wires, so I knew all three of those wires were good. For APP1, though, I only saw an open circuit on pin D (5V reference) between it and the other two wires for APP1 (pins B and C)

I unplugged the pedal sensor, and I realized my meter leads were long enough that I was able to probe between the TAC module harness side and the pedal side. I checked pin D from one connector to the other, and it was good -- 0 ohms. Hrm, must be a bad pedal sensor. I checked the resistance at the pedal sensor itself, and it was good.

After some wiggling of wires to no avail, I gave the pedal connector a close inspection. Pin D didn't look great, so I removed it and found it was a loose fit on the pedal sensor's pin. I re-tensioned it but that didn't help. In this mix I also lost contact on the white/black wire (the other 5V reference). Re-tensioning that pin fixed it. For Pin D, I ended up finding a suitable replacement pin from a spare harness plug I had left over from my factory harness reworking, and that seems to have fixed it.

Now when I press the pedal the throttle blade moves, and the PCM no longer throws any codes for the throttle.

It still doesn't start -- it fires but immediately dies. I'm going to make another thread for that.

 

Starts then dies = VATS still enabled

 

Generally true , VATS disables the injectors [ on the ground side ] , they will pulse 3 or 4 times at startup and then stop , If it starts and runs with someone spraying starting fluid in the intake , VATS is even more suspect .

 

Hello,

I visited my tuner today, and he disabled security and confirmed several other settings to make sure it was configured properly. It worked -- I was able to start it tonight