350 small block tbi crank no start

I recently bought an 89 k20 with a small block tbi in it and replaced the alt and battery, everything seemed to be working mint. Took it out a few times in the mud and no problems! Until yesterday I went through some mud and it bogged down and stalled. I thought I may have got some water in it so I waited a few minutes like I did last time it happened. Tried starting it and it would not stay running, I had to tap the throttle half way down for it to stay running and even then it would still stall out. Now it won't start at all. Pulled the spark plugs, they were black but doesn't look like its from oil. Turned it over with out the plugs in to maybe get some of the water out of the cylinders. Put them back in, still nothing. What to do now?

I had an 89 Camaro that did that. Disconnect the battery an wait 5 minutes before connecting it back up (resets the ECM). If it starts after the reset, then repeats the same problem after 100 miles or so (sometimes less), look for a bad ground going to the ECM.

I had it disconnected for an hour when I thought it was just out of fuel and it still didn't start. Just replaced plugs still nothing

Welcome to the forum. How much mud got thrown around under the hood? Is it possible that you blinded your TPS (throttle position sensor) with mud?

Just for future reference, if you ever think that there's any chance that you've sucked water into your engine letting it sit will not help you. Pull the plugs, spin it over to expel any liquid, then replace the plugs and start. If you crank the engine with liquid in one or more cylinders you'll bend rods big time. Many of the newer vehicles have a start circuit where the starter engages, and remains engaged until start, or some programmed number of revolutions. If you hydraulic lock one of those (like a Jeep JK) the starter hits, bends rods, then smokes the wiring harness trying to get the rev count. I witnessed that when a guy behind me thought it would be cool to blast into the creek that was about 3' deep....

Troubleshooting in person is MUCH easier than troubleshooting on the internet.

Troubleshooting 101
1. Does it have spark? IF so, then 2, else 3
2. Does it have fuel? IF so, then 4, else 5
3. Wipe water out of distributor
3A. Did it start? IF so, then OK, else 5
4. Does it have timing correct? Check crank sensor, loose distributor, timing chain
4A was timing correct? IF so, then 6
5 No fuel, check fuel pump, oil pressure interlock, injector pulse, etc.
5A was there fuel and fuel pressure? IF so, then 6
6. Ask someone to help in person

To add to #2, check the fuel pressure. Those TBI's were known to have regulator failures. I think they need 11psi but you can shim the regulator to 12-13 and they lose their hesitation and gain throttle response.

Should I start by pulling fuel filter/fuel lines? How do I check to see if the regulator is junk?

spray some starting fluid into intake-see if it fires off-if it does its definitely fuel system related---
On a vehicle that old you could have serious blockage in the filter sock, any lines could be deterioated, debrios in regulator etc
Also I think u may have to set timing by disconnecting some wire connector and set to 10 degrees then reconnect and ecm then sets timing electronicly
When u turn on the ignition can u hear the fuel pump momentarily come on????

Check the stupid little jumper wire on coil to distributor. Coil should have two modeled plugs on top one comes out of the harness the second goes around to the back of the dist. The tabs break off on them and the get loose. Won't hit a lick if either is loose.