What if you bring the RPM up right away,,,, will it still cut out?

Was messing with it this morning and it fired up and ran for about 20 secs then shut off. Checked fuel pressure and spark and all was good. Now it won't fire off at all unless you sit on the switch and let it turn over 50 times..... and then it will fire off and shut right down. It will rev up but then shut down.

Plus probably soaked with fuel now after so many cold starts. Hopefully water didn't revert in from all the starts + dying.

Pull the plugs anyway and check.

Did you try to give it any extra throttle before your turn the key?

I've tried just about eeverything. It's getting fuel and fire so i don'tuunderstand why it won't stay running. It has to be a sensor.

Is there an oil pressure switch on the motor that will kill the power to the fuel pump? If so, maybe that is getting funky and causing it to cut power to the pump?

Worth looking into, that should be cheap.

I'm not sure what year or model we are working on, but I have seen very strange problems when the ignition module in the distributor went haywire. You still get spark but not at the right time, and a bad ground can cause stupid problems like this. If it's newer then maybe crank or cam Position sensor, but if it's older, then I would run jumpers to the fuel pump to verify that isn't the problem and check fuel pressure.

Hold on, I just looked at your first post and 30 psi is to low for fuel pressure with the key on. You need to look closer at your year / model and see what it's supposed to be. More details!

Dumb question, but has anybody hooked the fuel pump overflow line to a vacuum port? It's a very tempting thing to do, but as soon as the engine runs long enough to develop vacuum it holds the diaphragm open.

Just found a problem on my boat causing a similar issue. It would act up occasionally-motor would shut off for a split second, then come back on, finally acted up enough to diagnose. After trying many different avenues, I cut the tach wire at the coil. Problem disappeared! I need a new tach, or replace the wire. I'll probably do both. I know it's not a common cause of problems, but it might be worth a try on your boat.

Steve

It's a 1996 502 efi. I got it to fire off yesterday and it quit in 5 seconds.... I got it to fire off again and it ran like normal. Turned it off and tried to fire it back up and I'm back to the same thing..... a 5 sec. shut down. Tried to crank it again and it never fired off..... just turned over and over..... very, very irritating