Is the fuel pump powered while key is in "Start" position?

 

 

If it's not powered in the Start position, it will not start. Many things are cut out in the Start position. Make sure the fuel pump is not one of them.

 

Keep in mine you need power to the ECM on start and run. As I recall from my 67 Nova LS swap the starter and coil wire needs to be "combined" so you have 12 volt on cranking and then releasing the key to the run position. It's been awhile on that swap. Also no resistor wire you need a full 12 volts.

 

See if you get anything with a code reader hooked up to the OBD II port. You need full time power to the PCM "keep alive" wire and the PCM ignition hot wire that actually boots up the PCM.

Rick

 

 

Check ignition relay and make sure its getting fire while ign is on and starting. This is almost always the issue with a new swap.

Fuel pump is usually on its own power source for ign.

If u want take the ign relay apart and touch the tab together while cranking and see if it runs. This will for certain let u know.

A good ign source on the c10s is the original hei power wire to the coil at the distributer. This is what i always use. Its pink wire. Use it for ign and starting hot!!

 

I'm currently building a 68 C10 with a LS1 but my stock wiring was junk so I replaced it with a Painless kit. I do have a "stock" 68 C10 wiring diagram. Let me take a look at it and see what should be used for crank and run. Can you check to see if you are getting power to the fuel pump while cranking? Also 12 volts to the ECM while cranking?

 

I'm putting a 5.3 into a 70 C-10 right now and was wondering the same thing about how to make the coils & injectors HOT while cranking. I have the relays set up to power the fuses that feed the circuit for the coils & injectors, but I'm not sure they will be HOT while cranking. If you guys come up with a good solution, please let me know. My fear is that if I try and tie a power wire for the coils & injectors to the starting circuit, then the starting circuit will also be getting power as soon as the key is placed in the RUN position which could be disastrous. I guess a diode could be used to prevent that from happening though.. Has to be a better way though.

Also, should I run my START/HOT wire from the ignition through the trans. mounted neutral safety switch, and then through the PCM? If I run the START wire straight to the starter from the ignition switch, how will the PCM know I'm starting the engine? Or, does it not matter as the PCM is just waiting on a CKP signal to fire the fuel pump, and the coils & injectors?

 

On my harnesses I've purchased the PCM only needs a 12 volt constant and 12 volt in start and run. Two separate wires. I wouldn't run the PCM 12 volt switched thru the neutral safety switch. I'd run the start wire to starter, typically a purple wire thru the neutral safety switch and then to the starter.

 

 

Again no electrical expert but the purple wire is to and thru to the starter. Again I think the purple wire will give you 12 volt on start only. Not run.

 

Do you have 12 volt power at the OBD II code reader port? Does a code reader operate there? That will tell you if you have everything powered correctly - PCM keep alive power and PCM ignition 12 volt power.

Rick

 

 

Purple wire is only used for the starter to signal to crank. Do not jump off this wire! That isnt the right way to do it.

If anything install a push button start so youll have hot while cranking for the ign relay.

Like i said above. Use the original hei ign wire. Its PINK! Works on every ls swap ive done, and ive done alot of them! OR break out the tester and check fuses and wires at the ign switch for a constant hot with key on and while cranking.

Run this to your new harness ign red wire for the ign relay.

For a TEST:
You can also take the new standalone harness red ign wire and run it to the battery. Relays should power up and click on. Crank engine and it will/should run if vats etc. are removed.

 

Thank you all for the insight and replies.
Trouble Shooting Update
I disconnected the main lug at the starter so it wouldn't crank the engine over every time I checked ign voltage.

• Confirmed that the Fuel Pump has 12+ in run and crank
• Confirmed All Injectors have 12+ in run and good ground (Couldn't check for 12+ ign at plug end, working alone tonight) did confirm that their fuses are recieving 12+ while cranking
• Confirmed Both Coils have 12+ in run and good ground (Couldn't check for 12+ ign at plug end , working alone tonight) did confirm that their fuses are recieving 12+ while cranking
• Confirmed that my Pink Wire for my ign has 12+ in run and crank
• Confirmed that the relay is receiving 12+ from the ign hot wire
• Confirmed that PCM pins Blue 1 & 40 have good grounds
• Confirmed that Blue pin 19 has 12+ in run, will have to wait until tomorrow to check for 12+ while cranking
• Blue Pin 20 and Pin 57 the 12+ constant wires DID NOT have 12+ until the key was in the run position? its my understanding that these should be 12+ hot at all times regardless of the positions?
• Bluw Pin 74 is a pink wire and is labeled PCM Ign Source? I do not remember why i switched out the yellow temp senor wire? could this be messing with the PCM causing it not to fire?

Thank you all for all the help.

 

yes 12v + to Blue 20 and 57 at all times.

Blue 74 should be for your ECT signal

Blue 75 is 12v+ in run and crank <<< this is probably the problem

and get your serial port wired to record actual data instead of guessing and hoping!