DBW problem

[low82c10]

5.3/4l603
what would cause my throttle to not respond while the engine is running?
switched 12v i press throttle and it responds, when it starts i get not throttle

i talked to the guy who did my harness also and i have a hard start issue it wont start till after a few tries. he asked if the check engine light is on or off when i try cranking it over and i told him it turns off. what would cause the computer to loose power?

as far as the throttle i know its the right pedal tac module b/c the guy ran my engine with all my parts and it did indeed start.

i tested to make sure my switched 12v is getting 12v while cranking with a test light and it is, im kinda lost at this point? what would cause this a bad ground maybe i dunno?

[BR3W CITY]

are there any codes?
I assume that you have a relay for the starter, and not just running a hot wire from the ignition assembly, otherwise the ignition switch isn't really meant for that load and you can get a huge voltage drop or metl the ignition switch.

You can start the engine just fine even with the wrong tac gear, it just won't respond to the pedal , or the pedal will only partially respond and throw a code.

There more, but thats a start off the top of my head.

[low82c10]

i got three wires to make the engine run, a switched 12v, a consistent 12v,and a wire to the fuel pump. the switched and consistent 12v i got the wires going to my fuse box, what i did was find a switched 12v and consistent 12v and thats were i landed those wires. and as far as the throttle deal, ive seen this motor run out of the truck it came from and everything worked fine i just dont see why its giving me problems now?

[BR3W CITY]

I'll ask again, since what you posted really doesn't help me help you.

Are there any dtc codes?
Are you running a relay for the start (and for the fuel pump)? Those things should NOT be directly wired off ignition or switched +12v

I know you saw it run, but was it DRIVING or just sitting idle or on an engine stand? The wrong TAC/DBW pieces WILL allow it to run, but will not allow normal throttle function.

The three wires you reference are probably the 3 main wires coming from your swapped harness I assume?

Heck a lack of ground can cause weird flickering issues with the CEL.
Please make sure you do NOT have anything like the starter direct wired off the pcm, otherwise your pcm is on a borrowed life span.

[68GMCCustom]

My truck had a dbw problem where the pedal didn't work.
Got another pedal...worked fine.

[low82c10]

I don't know if I have any dtc codes as to I don't have anything to check them with. I know my harness has two relays for fans and another I think is for the fuel pump. I saw this complete engine get pulled and told them what I wanted off of there so chances of me getting the wrong tac or pedal are really slim. Yes the three wires are coming off my main re worked harness. The guy who did my harness ran a wire from starter to alternator so I'm not sure where the PCM is getting power from if its the three wires that come off the main harness or not, I would call the dude up but never has time and won't respond to email so I gave up on him
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[BR3W CITY]

Keep trying, he might be the only one who knows, since he actually wired it.

Starter to alternator.....maybe im too buzzed but that doesn't sound right.
alt to battery, battery to starter power lug (large gauge), and then there is a switched signal wire (to starter solenoid), which IIRC is off a relay, and the unit is self grounded.

Alternator should just have the charging cable, and then the molex plug in connector, which I believe contains the computer power...I just can't remember if the computer gets power direct off the alternator plug (through a fuse) or if it came off the battery. I'd have to grab my wiring harness manual to see.

[68GMCCustom]

my harness had 4 wires along with a small fuse panel and two relays. One wire was a red +12v ign. feed to the fuel pump relay. one wire was orange +12v to battery...and one was red +12v ign. feed for ecm.....plus one very important shorter black wire w/lug coming from roughly the middle of the harness....providing ground for all the circuits.

[low82c10]

found the problem just in case someone has this same issue, my orange wire from my re-worked harness requires consistent 12v...well where i had it landed on my fuse box was not a true consistent 12v so the computer would loose power while cranking over.....got it started drove it around the block...what a bad ass feeling!!!

[68GMCCustom]

Oooops.....