Wont start

[Christian ojeda]

My buddy has a 1990 suburban with the 350tbi, I know its a squarebody but the engine and fuel system is set up the same way as the 88 to 94 trucks. has fuel from the pump and all the way to the throttle body with good pressure, has spark because it fires up when you pour fuel down it, has injector pulse because we tested it but fuel won't come out of the injectors, desperately need help. Here is a list of things that are new. New fuel pump, rebuilt throttlebody, new fuel filter, new injectors, new fuel pump relay, all fuses are good and new ignition control module, (for those that don't know, that controls your injector pulse)

 

[PlayingWithTBI]

has injector pulse because we tested it but fuel won't come out of the injectors

I'm curious, how did you verify that it has injector pulse?

 

[Christian ojeda]

I'm curious, how did you verify that it has injector pulse?

Voltage meter and probed power on injectors then cranked and watched the voltage raise and lower

 

[HotWheelsBurban]

Is the coil good? And the wiring to it and the module? Pickup coil in distributor good? Cap and rotor good?
When my truck like this quit, it was the fuel pump. I don't remember if these have a relay for the fuel pump, but if you're getting fuel to the TBI, that should be working.

 

[PlayingWithTBI]

Voltage meter and probed power on injectors then cranked and watched the voltage raise and lower

The ECM grounds the injectors, they're always fed 12V with key on. You should use a Noid light to test that.

 

[Schurkey]

has fuel from the pump and all the way to the throttle body with good pressure,

Define "good pressure".

has spark because it fires up when you pour fuel down it,

That verifies pickup coil, ignition coil, cap, rotor, plugs and plug wires. It verifies about half of the ignition module.

has injector pulse because we tested it but fuel won't come out of the injectors,

I swapped a Treasure Yard throttle body onto my '88 K1500. Ran like crap. Figured out that one injector wasn't spraying, so four cylinders weren't running. I shut down the truck, swapped injector connectors. Re-started truck--same injector didn't fire. I was puzzling my options while the truck loped at idle.

About the time I figured I'd swap the top piece that held the regulator and the injectors...it starts running properly. The stuck injector freed itself. Has been running fine for maybe ten years since then.

Yet another good reason to use Top Tier (high detergent) fuel.

Here is a list of things that are new. New fuel pump, rebuilt throttlebody, new fuel filter, new injectors, new fuel pump relay, all fuses are good

"New" injectors? Did those injectors ever work properly?

Do you still have the "old" injectors to swap in?

A 'noid light, or a low-amps current probe and oscilloscope (maybe a multimeter could work) is the proper way to verify the injector power/ground.

and new ignition control module, (for those that don't know, that controls your injector pulse)

No. At least, the ignition module doesn't control the injectors directly.

The ignition module sends a reference signal to the ECM, the ECM controls the injector pulse. If the ECM doesn't get that signal from the ignition module, it may not fire the injectors, and it may not turn on the fuel pump relay.

 

[Christian ojeda]

Define "good pressure".


That verifies pickup coil, ignition coil, cap, rotor, plugs and plug wires. It verifies about half of the ignition module.


I swapped a Treasure Yard throttle body onto my '88 K1500. Ran like crap. Figured out that one injector wasn't spraying, so four cylinders weren't running. I shut down the truck, swapped injector connectors. Re-started truck--same injector didn't fire. I was puzzling my options while the truck loped at idle.

About the time I figured I'd swap the top piece that held the regulator and the injectors...it starts running properly. The stuck injector freed itself. Has been running fine for maybe ten years since then.

Yet another good reason to use Top Tier (high detergent) fuel.



"New" injectors? Did those injectors ever work properly?

Do you still have the "old" injectors to swap in?

A 'noid light, or a low-amps current probe and oscilloscope (maybe a multimeter could work) is the proper way to verify the injector power/ground.


No. At least, the ignition module doesn't control the injectors directly.

The ignition module sends a reference signal to the ECM, the ECM controls the injector pulse. If the ECM doesn't get that signal from the ignition module, it may not fire the injectors, and it may not turn on the fuel pump relay.

Well its what I thought was good pressure because the guys at the shop he works at said that it's supposed to have over 40 pounds! The "master" tech had him buy a new pump because he was getting 12 pounds of pressure and now he's getting around that for fuel pressure. Thought that was nuts so I looked it up and turns out he's only supposed to have 9 to 15 pounds of fuel pressure.

The injectors did work properly when I installed them in his truck last year.

Thanks for the info about the ICM I actually didn't know that.

So if you Crack the fuel line AFTER the filter and let a little bit of gas out it tries to start so given the new knowledge about his fuel pressure I'm thinking maybe he has way too much and it's having the same effect as if you turn a bottle upside down and the water won't fall out because there's no space. Either way it was still having this issue before the fuel pump was even changed so I'm still stuck at square one

 

[Schurkey]

12 psi is fine. I've heard--but never verified--that the TBI injectors can stick closed if the fuel pressure goes too high. I think it'd take 30+ psi to do that, though.

WHERE are you testing the fuel pressure?

 

[Christian ojeda]

12 psi is fine. I've heard--but never verified--that the TBI injectors can stick closed if the fuel pressure goes too high. I think it'd take 30+ psi to do that, though.

WHERE are you testing the fuel pressure?

He's got over 40 lbs

Tested from the back of the throttle body by the shop he works at, I'm currently driving and need a few minutes but I'll explain in a second. His shop totally screwed him with this one and I'm just trying to figure it out for him.

 

[Christian ojeda]

The tech at the shop he's working at originally tested fuel pressure at the throttle body, it came back to 12 pounds, they told him it wasn't enough and that's why it wasn't getting fuel, so they had him buy a new pump and they tested pressure again and got over 40 pounds. They were trying to tell him he needs 60 pounds of pressure which I thought was absolutely nuts so I looked it up and it's supposed to be between 9 and 15 with the early tbi design. So I'm thinking he's getting way too much pressure, another thing is if you Crack the fuel line at the output of the filter and let a little bit of the gas drain out it fires up for a few seconds and then stalls again. He was having this no start issue before the pump was even changed though, the injectors are pulsing, I probed them with a multimeter and while in the run position they were getting power and while cranking they would raise and lower also once it starts running it will run for a little bit before it dies proving the injectors are getting power