5.7li tbi no start. need help

[crazydriverz]

This engine will not start unless we dump gas into carburetor. Changed the fuel pump, fuel filter and fuel regulator. At the shraeder valve we are getting 20psi. I hear that it only needs to be at 10-12psi to run. Please help what else is controlling fuel to being dumped into the engine!

[Blue Bowtie]

What year TBI?

There is at least one and probably two fuses for the injectors. Those need to be intact and supplying 12V to the injectors.

Typically, for the system to work the ECM has to receive reference pulses from the distributor to indicate the engine is turning and at what rate. Based upon the timing of this the ECM will operate the injectors in the throttle body. Since the engine apparently fires when fuel is pored into the throttle body we can presume the distributor is turning and creating pulses, otherwise there would also be no spark.

The voltage from the throttle position sensor and the indication of the manifold pressure sensor will determine the length of the injector firing time to vary the amount of fuel delivered. One feature of the system is the "clear flood" mode. If the throttle plates are held fully open the TPS reports that to the ECM and the ECM will not deliver pulses to the injectors. Therefore, it is important to have a voltage from the TPS in a reasonable range to allow the injectors to operate.

A quick way to determine if the injectors are getting any operating pulses from the ECM is to measure the voltage at the injector connector using an analog meter. A 12V test light also works well for this. Digital meters may not be able to react quickly enough to display any meaningful reading.

There are also very fine screens in the base of the injector pod which are intended to keep debris out of the injectors. If these are clogged no fuel will flow. Before disassembling the TB to inspect those it would be good to eliminate the other possibilities first.

[crazydriverz]

I think I is spoke. Its a 1998 Sierra truck with a 5.7 engine it has the spider type injector. See we put the fuel pressure gauge in the rail and after it pressure up to 20psi I open the valve to the pressure tester and dump the fuel into the carburetor and BOOM THAT ENGINE STARTS TO PURR. until the gas if burned up that I just dumped in. Lol. So I know there is fuel up into line that goes into the top of the spider. But from there what else can prevent the fuel going into the injectors.

[crazydriverz]

Sorry didn't read all of the post. But ok I'll check that.