I have a 1990 chevy c1500 4.3 tbi with a flooding problem. When I start the truck most of the time I have to hold the pedal down.Also when I let off the gas pedal there is a small backfire.I did notice there is a small hose connection on the 4-speed manual transmission that looks like its missing a hose where does this go. Could there be a vacuum leak.I changed the speedometer because the temp gage did not work but there is no difference.I changed the distributor cap ,rotor ,spark plugs,wires,battery,tbi and temp sensor. The truck runs really smoothe at idol and while driving just the flooding problem Thanks Frank

First check to see if they are getting the proper signal from the ECM. Use a noid light to see the signal. Could be bad injectors or wiring .

https://www.gmtruckclub.com/threads/1990-chevy-5-7l-tbi-fuel-problem.1472109/

didnt specify year model or engine --generic answer --if the tbi is flooding ---check the fuel pressure regulator --and the tbi itself

Check the TPS Sensor for open spots

The fuel pump may be going also & binds up
thus no fuel

I'm having the same trouble with the flooding after warm start...if it's the temp sensor, would the temp gauge be working? It's in a 1991 Chevy van with an injected 350 carb.

You have a bad injector or a defective throttle control switch. You can test the throttle switch if you have a ohm meter, if you do get back to me and I will tell you how to test it.

check temp sensor is reading low if -35 it is the sensor most likely also look 4 vac leek...

That eliminates the crankshaft and camshaft position sensors. Have you checked the fuel injector itself for an open winding or stuck valve plunger? There should not be a steady 12 volts to the injector--if good injector, it would be spraying fuel steadily into the throttle body. But at least the engine should try to run if poorly. Take the injector out, dry it off with air, and intermittently apply 12 volts to one terminal while grounding the other. You should hear a click from inside every time you touch 12 volts. If not, replace it. If it does, it may be plugged with debris. Try blowing through it in reverse with compressed air.

fuel pressure isnt right.. need to get a fuel pressure regulator so you can regulate the gas flow..

Is it flooded? Have you tried holding the accelerator to the floor? You have gas spraying out of the injectors when cranking? Does it even try?

91 is 8valve TBI injection.
it is flooding.
the starting fluid is more combustible and starts a flooded motor.
kinda like adding dynamite to bbq lighter fluid.
hahah
ok,
try a tune up.
then try holding gas pedal to floor, this is super secret unflood mode and cuts fuel injection.

the issues why its flooding, not starting is normal for that condition.
so its:
1: bad need of tune up
and or
2: leaking injector.

the former you can figure out.
cap/wires/plugs /rotor, filters, there i said it.

or
this car has a viewable fuel injector
one an do 2 things with it.
key on five times , or 5 seconds on, not cranking
and other person looks down throttle body neck
yes, off comes the tube on top.
and makes sure the injectors dont dribble full time, key on.

or
the ECT is bad.

or dash pot is not opening at key on crank.

or
cold start, IAC is clogged.

complex it is,
it will take hard work to check everything.

http://carfix.stufftoread.com/
see flooding here.