no start problem

[sylvester]

I need help.. my 79 SC won't start and its making some engine noise. when the engine is turning over. also it backfires. but what's weird is when I take the fuel pump relay out. then back in (prime) it starts and run good without any engine noise. my battery is also low. I also change the fuel pump two weeks ago. any ideas is very appreciated I'm lost thank you very much.

[T77911S]

i don't know what you mean by (prime).
are you running the FP before you start it?

depending on how low the battery is it may not be operating the CSV.
battery needs to be good,
CSV should fire when cranking. it gets its power from the starter and its ground from the thermo time switch (TTS).
If you are (priming) the system and it starts it could be the check valve at the FP or the FP is not running when cranking.
the FP should run when cranking.

you can try 2 other things.
1 with the key on, lift the sensor plate for 2-3 seconds then start
2 remove the connector on the top rear of the AFM. this will run the FP with the key on and engine off. let the FP run for a few seconds then start.

[Flat6pac]

Moving the relay did something. Look at the point side of the relay, there is letters and numbers representing the different points. Rig a jumper wire between 30 and 87a with key on, this will turn fuel pump on.
With a hot battery, lift the airflow sensor under the air cleaner for a couple seconds. You ll feel resistance as the fuel flows. If your fuel is a problem, this should fire the engine.
Bruce

[sylvester]

Yes., I did run the fuel pump before start. I will try everything you guys suggested and will report back thank you very much.

[patz]

SCs need proper fuel pressure and a good battery. Charge it and get some gauges. Check the fuel pressures.

Could be a wonky relay.