I’m completely stuck trying to diagnose a no-start issue on my 3rd gen Camaro TPI and could really use some insight. The car was running perfectly with no drivability issues, smooth idle, and no stalling, and then out of nowhere it just wouldn’t start the next time I went to turn the key, with nothing changed in between. Since then I’ve tried nearly everything and am now leaning toward an ECM-related issue because I’ve tested multiple ECMs and they all behave differently. The original ECM that came with the car does not prime the fuel pump with the key on and the engine only tries to fire off what seems like leftover fuel in the rail, but with that same ECM I do hear the IAC clicking for a few seconds after turning the key off, which makes it seem like it’s at least partially functioning. The other ECM I have is from a 1987 IROC, and with that one the fuel pump primes immediately, the cooling fan turns on right away, injectors fire, and I have spark, but the engine doesn’t seem to try to fire nearly as much as it does with the original ECM, and I don’t hear the IAC move or click at key-off. That ECM did allow the car to start once, but only if I held the throttle open, and the engine died as soon as I let off and has not started again since. Each ECM has its own MEMCAL and they are not interchangeable. I’ve replaced or verified the cap, rotor, ignition control module, spark plugs, plug wires, O2 sensor, MAF sensor, coolant temperature sensor, and the sensor under the plenum, all of which are new or known good and were only used for start attempts, and I have spark with both ECMs. The timing isn’t perfect but should be close enough for the engine to at least start and try to run. Spraying starting fluid and closing the throttle and going to start it appeared to make no change. The battery has been charged and drained multiple times during testing, so I’m also wondering if low voltage during cranking could be causing ECM issues. At this point the main things I’m suspecting are the ECM itself, the IAC, the ignition coil, or possibly a voltage or reference signal problem, but I’m struggling to understand what could have changed so suddenly when the car had been running so well right before this happened. Any ideas or diagnostic direction would be greatly appreciated.

Have you verified that you actually have around 40 psi fuel pressure? The pump is supposed to run for a few seconds when the key is turned on but that does not mean the engine is receiving fuel. You could be out of gas, have a clogged fuel filter, hose came off pump in tank, some injectors stuck open, etc.

It has 42 psi of pressure and return and feed line are new as well as tank and sending unit.

Hmm, this is a weird one, so you have fuel pressure. Did you check for spark?

Yes it has spark and it's bright blue so I'm assuming the spark is good.

Fixed it for you.

You might want to try squirting a few ounces of gasoline, instead of starting fluid. Check the ignition timing, it might be way off.

What is the voltage at the battery when cranking? I had a crank / no start Ford 5.0 that cranked over fine, but the voltage was too low, for the ECU. Good luck.

Timing should be pretty close, since it’s only been moved slightly from where it was when the car last ran well, so it should at least be in the right ballpark. I’ve checked the battery some, but the testing was finicky because I had to clamp the multimeter leads onto the battery terminals. The voltage would jump around from about 9.8 volts down to 8.7 volts while cranking and dropped down to even 8.25 but im unsure of quality of numbers since it would display numbers far to low from loose connection. Sometimes it would fire and climb to around 10.5 volts, but eventually the leads would vibrate loose and the meter would show unrealistically low numbers once the connection slipped. I'll plan on taking the battery somewhere to get it checked though then to see if that is the issue.

The battery tested good so it's not the battery either but i guess I'll pull distributor again even though it should be right since its ran great where it's at but maybe somehow it switched up

With the injectors unplugged with the ECM that primed fuel it will sound like it's going to start and fires some and turns fast enough the starter can't keep up but obviously when I stop using the starter it dies bc its not getting fuel. When i then plug in the injectors it will barely fire and then stop firing all together basically.

Try using jumper cables and a running car or a battery Jump Box, that should get the cranking voltage close to 12 volts. IF it starts your battery is bad.

I've got that battery tested and it's good. I have pulled the distributor and put it back in and it sounded the same. I replaced the ignition coil and nothing changed. I'm getting a iac Wednesday but I'm doubting that's the issue since it doesn't run with throttle.

I got a noid light and checked injectors and at first 1,2,3,4 didn't light and 5,6,7,8 did light. I wiggled on the harness a little bit and then all of them lit so I plugged them into the injectors and let the battery charge for a little bit. I came out after a few hours and cranked it and it was just doing the same thing so I unplugged them again and put the void light on them and none of them lit and won't even shaking the harness again?