03 5.3 ignition schematic?

[LSXmyford]

we still have a no start condition

anyone have a 03 5.3 engine wiring schematic, specifically ignition related? coil packs area?

engine cranks
fuel injectors/fuel pump work fine, has pressure
still getting no fire and this is pcm number two (VATS supposed to be removed)
crank and cam sensor are new
getting no codes

guess we should start at the coils and work backwards until things operate correctly.

Only test performed at this time was to remove the four wire pigtail from the coil packs, turn key to "run" position. one wire shown 12v, one shown to be a good ground, other two received no positive voltage nor were they grounds.

we understand one or two have to be signal wires so this is expected, my question, how do we test those two wires, or should I say, what should be seen at each of those four wires and when? Im guessing an intermittent signal should be receive to either or both, so a simple test light should flash if the starter is engaged, no?

thanks, this is getting a wee bit frustrating.

[KySilverado]

I have the schematic saved and everything on my pc for you. Photobucket isn't cooperating. I'll keep trying.

Mine did something similar on an engine swap. Broke a wire on the crank sensor. No codes.

[468Blazer]

would really appreciate it. This was my worse fear in doing the swap. If it wasn't for bad luck I wouldn't have any at all. lol.

[LSXmyford]

anyone know the specifics on testing the cam and crank sensor? ohms to look for?


got a manual but all it tells is how to replace the damn thing.

[NITROUS]

What DTC codes are you getting? For the engine not to start there has to be something when you scan it. You have to get signal from the CMP and CKP for it to start. If the engine cranks and turns I would look at these 2 sensors first becasue the PCM triggers the coil by grounding the appropriate IC circuit using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.

• Low reference
• Chassis ground
• Ignition 1 voltage
• The appropriate IC circuit

[NITROUS]

Turn ON the ignition, with the engine OFF.
Disconnect the CKP sensor.
Measure the voltage from the CKP sensor 12 volt reference circuit and a good ground.
Compare the measured voltage with the system voltage.
Is the difference more than 0.5V?
If not replace the CKP.
If yes, test for a short to ground in the CKP 12 volt reference circuit or the CMP sensor 12 volt reference circuit.
Test for poor connections at the coils.
If problem isn't solved there has to be a ground issue somewhere or check fuses again.
Check and clear all DTC's and scan again.

I'd start here and rule out the CKP and CMP.

[LSXmyford]

Turn ON the ignition, with the engine OFF.
Disconnect the CKP sensor.
Measure the voltage from the CKP sensor 12 volt reference circuit and a good ground.
Compare the measured voltage with the system voltage.
Is the difference more than 0.5V?
If not replace the CKP.
If yes, test for a short to ground in the CKP 12 volt reference circuit or the CMP sensor 12 volt reference circuit.
Test for poor connections at the coils.
If problem isn't solved there has to be a ground issue somewhere or check fuses again.
Check and clear all DTC's and scan again.

I'd start here and rule out the CKP and CMP.

Voltage from cam sensor = 11.49
voltage at crank = 11.48
voltage at pcm 12v constant (system voltage?) = 12.4

something of note, when he put the meter probe to the crank sensor reference circuit, it shown 11.48, when he removed his probe from ground, it would show 6 volts...WTH?

another puzzler. he tested the ckp wires from pigtail to pcm, and resistance was correct, nothing out of the ordinary.


all coil connections have been removed and reconnected. he even tested resistance from the coil to the pcm, all checked out good.

no codes.

any suggestions.

Low reference
Chassis ground
Ignition 1 voltage
The appropriate IC circuit

what should be seen voltage wise at each of these? he has 11.4, I would assume at the ignition voltage, and he has one proven ground, what about the IC circuit, while cranking and low reference?

[468Blazer]

another note on the grounds. there are only 2 grounds in harness. Here is how I have my grounds.

2 Ground wires in 03 harness to back of engine.
Back of engine to chassis.
Battery to chassis.
Battery to engine on head.
Any grounds that were in old harness grounded to plate beside altnator.

[LSXmyford]

yep, first post.

new cam and crank sensor.



ok fellas, ease up a little.

Lets knock things out one at a time.

to make things easier for me to process, could you quote my messages, and break them down, responding to each section individually? Id appreciate it.

When you says system voltage, it would be correct for me to think that would be voltage from battery + to ground, correct?

if yes, then the cam and crank ground wires are off alot, which would mean ground correct? Im 30mi away and hes taking care of things, so he wont be able to double check the two harness grounds until later this evening.


this engine came out of a wrecked vehicle, so it ran for sure up until it ran off the road. allegedly, it was driven around the shop that my bro purchased it from.

engine is bone stock.


throttle pedal sensor is new, remember it was throwing a code for this, so it was replaced, now no codes.




id like to throw this out there again.
when he tested the four wires at the coil, one was 11.4 volts roughly, one was a ground, two were dead as a hammer with or without key on, did not test with cranking engine, should he? again, resistance from coil packs to pcm were tested and confirmed ok.


is there another way to read rpm, he just has a basic scanner tool. could he connect the multimeter, set on ohms to the rpm wire? I have no idea, just speculating?



know off the top of your head which pin signals the coils, what voltage should he see, should it be intermitant, Im guessing 5v and yes? he has the pin sheet with what is what, just wanna double check.

[LSXmyford]

should add. he purchased a new coil pack, checked for spark. nada.
he is using the newly programmed pcm.