81 c30.....5.3
 

Long story short, I had the 5.3 In a c10 pickup and it ran perfect (stand alone harness 3 wire hook up). I got a C30 truck and put the engine in that, I went to fire it up and it wouldn't start. I grounded the wire but power steering pump and it fired up like a champ.



After about 6 start ups, it was running and all of a sudden it died, now on switched 12V it doesn't kick the fuel pump on for a few seconds nor do I have throttle response on switched 12V. I used to be able to push the gas on switched 12V and the throttle would respond, now I got my response or no fuel pump.


I directly hook up the fuel pump and it works. I've checked all my grounds and they are to Bare metal. With switched 12V both number 1 pins are grounded.

Harness is drive by wire, I tried unplugging the throttle body and the pedal and no luck. Also I swapped the fuel pump relay with a fan relay, still no luck,


Any idea where I should look next ? Thanks you.

Re: 81 c30.....5.3
 

Sounds to me like you have lost power to the pcm, coils, or injectors. Most likely power to the pcm.

You can check PCM Connector Blue 19 for switched ignition power. Then Blue 20 and 57 for constant battery power.

Was the harness a new harness or a rewire?

Bill

Re: 81 c30.....5.3
 

I will check that today, so with a test light and everything connected, poke the wires you mentioned correct?

This was a re worked harness, it ran perfect in the other truck and fired right up in this one I'm just stumped.

Re: 81 c30.....5.3
 

Just checked pin 19 for switched that works as it should.

Check 20 and 57 for constant and that's there.

Re: 81 c30.....5.3
 

Now check the pink wire at the White color coil connector on each bank. Also check the pink wire on all of the injectors,

Then check the dark green/white wire in PCM Red connector Cavity 9 for the fuel pump relay signal. The PCM outputs a + signal on this wire.

You should use a Digital Multi Meter when testing circuits on a fuel injection harness. You could damage the PCM if you are not careful.


Bill

Re: 81 c30.....5.3
 

Checked both pink wires a coil connector both have 12V, on switched 12V should I be getting 12v at each injector?

I don't have a red connector to my PCM only a blue and green. I think green connector pin 9 is for the fuel pump correct?

Re: 81 c30.....5.3
 

I thought you were DBC. Yes, since you are DBW you will check the Green Connector. Each injector should have 12v at the pink wire.

Re: 81 c30.....5.3
 

Green connector on switched 12v has nothing, right as the turn the key the my meter jumps a few and goes to zero. And the pink wire on each injector does not have 12v on switched ign.

Re: 81 c30.....5.3
 

Sorry each injector does have 12v

Re: 81 c30.....5.3
 

Ok, now you will want to check for Ground at the PCM, and power and ground at the tac module connector.

On the PCM Connectors cavities 1 and 40 should have a good ground on BOTH connectors.

On the TAC Module Connector Cavity 7 should be Switched Ignition, and Cavity 15 should be Ground.

Also, Have someone crank the engine while you check for power at Green 9

Re: 81 c30.....5.3
 

PCM pin 1 and 40 show good ground with my test light.

TAC. Module 7 is good with switched 12V and 15 shows ground with test light.

Re: 81 c30.....5.3
 

Just noticed with the fuel relay disconnected I get 12V to pin 9 on PCM.

Re: 81 c30.....5.3
 

Any idea what could be causing it to loose power with the relay connected? I've swapped relays and still the same problem.

I've also tested the relay with 12v and a meter and it give the readings it should.