1997 F355 Won't Start. Fuel Relay? Immobilizer?

Re Immobiliser:
Does the immobiliser LED extinguish? Does your car have a start relay bolted onto the footwell relay panel?
If yes to the above, then your Immo is probably ok. The Immo on my car (with a relay), controls cranking.

Re fuel control:
With ignition on, do the CEL & SD lights illuminate?
When cranking, do you have power at the fuel pump fuse?
If so, your crank sensor and ECU control circuits are probably ok.
If you jump the pump relay pins 30 and 87, can you hear your fuel pump running?

Re spark
Do you have power at pin 2 of the coilpack with the key on? Or maybe you have a cheap spark detector to see if you have spark (without having to pull plugs).

Up to this point, you don’t have to start pulling the engine to pieces or lifting the car in the air.

Please let us know how you go.

 

I meant to say at either coilpack

 

Souns lke an electrical issue based on the fact the the engine stopped very suddenly. Ignition sytem and fuel system are the areas to start the investigation. Since you recently removed the fuel pump, check to see if anything is broken with the plug.

 

If it were me, and it's not, this is what I would do.

Open up the battery location. Check to make sure your battery posts are clean and tight against the battery cable. Measure the voltage to make sure it is healthy. Charge it if it is not.
Check the battery cut off switch, make sure it is clean.
Your relays and fuses are now pushing 30 years old. Replace ALL of them.

Once that is done and you have eliminated all the fuses and relays as potential issues.

Jump the fuel pump relay. Check fuel pressure at the fuel filter. Did you get 55psi? Try to start the car properly, did you get 55 psi there?

Remove the cover over the ECU behind the right seat. Inspect all those connectors, especially the Non-ECU ones. Pull them out, inspect all pins, are they mis aligned, bent, corrodes, with broken wires?

Go back to the engine bay, left hand side, inspect the connectors at the left side up-right post. Are they intact? Check the pins. Inspect the 12V connections at the right hand side up-right. Do you have 12V?

You should have found the problem somewhere along those checks.

 

The only time my car wouldn't start (cranked but wouldn't fire) was when the connector for the crank sensor was slightly loose.

So I would just make sure that connector is well seated.

 

Did the cranking sound strong?

Yelcab and my suggestions have a lot of commonalities. I suggested looking at the power going to the coilpack/s because the power goes through these additional connectors (near the ECU). Checking the CEL & SD lights checks injector relay operation.

What you do really depends on what you have around your house and your skill levels. It's very difficult to investigate electrical issues without a volt/ohmmeter. Also, to jump a fuel pump relay, you'll need a fairly thick piece of wire and something to strip the insulation with. Maybe some household fusewire would do. Just don't burn your fingers on the naked wire. The power going to the main contacts of the fuel pump relay is always live, so be careful when you jump the relay. To check fuel pressure on a 5.2 car, you'll need spanners, perhaps a new fuel-resistant o-ring and a fuel pressure gauge.

Did the car eventually restart when the engine cooled down? Intermittent problems are a pain to diagnose.